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Introduction
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Chapter 1
Introduction
Introduction
2
The existence of human society depends on the ability of plants to harness
light and produce oxygen and organic matter. Domestication of plants for agriculture
resulted in development of many great civilizations in the past, Asian civilization
based on rice, Middle eastern on wheat and barley, and American on maize
(Giovanni, 2008; Michael and Mary, 1999; Michael and Laurence, 2006). Over the
past few thousand years, more than half of the suitable land on Earth has been
converted for agricultural use. Agriculture today is a global business, and a necessity
for the production of food, drinks and other vital commodities such as building
materials, fibers, drugs and medicines (Jason, 2004). New products from plants are
constantly being sought and developed, and plants are crucial for maintaining the
environment, both globally in maintaining our atmosphere, and locally in the form of
recreational facilities. Today, also plants dominate our lives and economy, just as they
have done in all civilizations.
Tuber crops are important group of staple food in the tropical world (Sheafer
and Moncada, 2008). In West Africa, East Africa, the Caribbean, South America,
India and South East Asia, one or more of the tropical tuber crops feature as major
food items in the diet of the people, and in some of these regions, tropical tubers
constitute the major staple food. Meanwhile, tropical tuber crops have received scant
attention from researchers. The main reason for this is that research in tropical
countries has historically been most vigorous in the cash and export crops like tea,
rubber, cocoa, oil-palm, coffee, etc. These crops featured significantly in International
trade, even though many of them were consumed little in the producing countries. The
tuber crops, on the other hand, enjoyed extensive local consumption and importance
but was neglected by the agricultural authorities mainly because they did not earn
foreign exchange (Bradshaw, 2010).
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This situation is now changing, gradually because those parts of the world
where tropical tuber crops are important in the diet are precisely the parts where
population growth is highest, and the threat of large-scale starvation is ever-present. It
has therefore become of great importance, to improve the quantity and quality of
those crops which the people already consume
Recently there have been increases in the volume of tropical tuber crops that
enter into international trade (Wheeling, 2007). Most of these crops or their processed
forms are being sent to developed countries. This increased trade is a stimulus for
further research both in the producing and importing countries. The formation of
International Society of Tropical Root Crops during the last decade is only one
manifestation of this increased importance. The increased importance of tropical tuber
crops has also been expressed in the curricula of various Agricultural Colleges and
Institutions in the tropics.
Root and tuber crops provide a substantial part of the world's food supply, and
are also an important source of animal feed and industrial products. The consumption
of root and tuber crops as food in developed countries is considerably smaller than it
is in developing countries, but their use as animal feeds is relatively higher. On a
global basis, approximately 55% of root and tuber crop production is consumed as
food, while the rest is used as animal feed or for industrial processing for products
such as starch, distilled spirits, and a range of minor products. The relatively high cost
of transportation, processing, and storage, as well as the considerable time needed in
food preparation, frequently makes unprocessed root and tuber crops less attractive to
urban consumers.
There are five major groups of root and tuber crops cultivated across the world
viz. Cassava (Manihot esculenta), Sweet potato (Ipomoea batatas). Potato (Solanum
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tuberosum), Yams (Dioscorea spp.) and edible Aroids (Colocasia esculenta and
Xanthosoma spp.) known variously as Taro (Colocasia) and Tannia (Xanthosoma),
but often referred to as cocoyams. A comparison of the characteristics of major root
and tuber crops is presented in Table 1.1. The annual production of tuber crops
throughout the world over the last decade is summarized in Figure 1.1 and the
average contribution by each of the major root/tuber crops on total world production
in 2009 (latest data available) is presented in Figure 1.2 a and 1.2 b respectively.
Figure 1.1: Tuber crops production across the World during 2000-2009 period
(Data from FAOSTAT; down loaded on 04.04.2011).
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Characteristics
Root/Tube Crop
Cassava
Potatoes
Sweet potatoes
Yam
Taro
Growth period (months)
9-24
3-7
3-8
8-11
6-18
Annual/perennial Perennial Annual Perennial Annual Perennial
Optimal rainfall (cm) 100-150 50-75 75-100 115 250
Optimal temperature (°C) 25-29 15-18 >24 30 21-27
Drought resistance yes no yes yes no
Organic matter requirement low high low high high
Growth in water-logged Soil
Planting material
no
stem
no
tubers cutting
no
vine cutting
no
tubers
yes
corms/cormels
Storage time in ground post
Storage life
long
short
short
long
long
short
Long
long
moderate
variable
Table 1.1: Comparison of the characteristics of major Root/Tuber crops
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Figure 1.2 (a): Contribution of major food crops throughout the world in 2009. Data from FAOSTAT (down loaded on 04.04.2011)
Figure 1.2 (b): Root/tuber crops production throughout the world in 2009. Data from FAOSTAT (down loaded on 04.04.2011)
Introduction
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Cassava (Manihot esculenta Crantz):
Cassava (Manihot esculenta Crantz) is a dicotyledonous perennial plant
(Figure 1.3) originated in North-East Brazil, with an additional centre of origin in
Central America (Rogers, 1963; Hillock et al., 2002). From its places of origin, the
plant has spread to various parts of the world, and it is today cultivated in all tropical
regions of the world. The major cassava producing countries are presented in Figure
1.4. There are 98 species of Manihot recognized (Rogers and Appan, 1973), including
popular cultivating varieties under M. esculenta (eg: Malayan clone-M4 of India) and
wild varieties like M. anomala, M. caerulescence, etc. . The taxonomic position of the
Manihot esculenta Crantz is presented in Table 1.2. It is assumed that cassava
originated by hybridization between two wild Manihot species followed by vegetative
reproduction of the hybrid (Nassar, 2000).
Figure 1.3: Manihot esculenta Crantz
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Figure 1.4: Major cassava cultivating regions in the World
Taxonomic Rank
Nomenclature
Kingdom
Plantae
Order Malpighiales
Family Euphorbiaceae
Subfamily Crotonoideae
Tribe Manihoteae
Genus Manihot
Species M. esculenta
Table 1.2: Scientific classification of cassava
Growth Cycle of Cassava:
Cassava is a propagated almost exclusively from stem cuttings, but in nature and in
the process of plant breeding, propagation by seed is quite common (Hillock et al.,
2002). If the cuttings are planted in moist soil under favourable conditions, they
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produce sprouts and adventitious roots within a week. Flowering of the plant may
commence as early as sixth week after planting, although the exact time that
flowering starts will depend on the cultivar and on the environment. Once begun,
flowering will continue intermittently for the rest of the plants life. Tuber formation
also commence by the eighth week after the planting, as long as the environment
conditions (e.g. photoperiod) are favorable. The tubering process involves essentially
the onset of secondary thickening in some of the adventitious roots which were
previously fibrous in nature. As the thickening progresses, the roots swell and soon
most of the bulk of the root is occupied by fleshy tuber material. Usually, the
secondary thickening commences at the proximal part of the root and progresses
towards the distal portions. Thus, the tuber is fattest at the proximal part in which the
thickening had occurred for a longer time, and it tapers slowly towards the distal
portions.
Cassava Root and Tuber
In cassava grown from cuttings, adventitious roots usually arise from the base of the
cutting. Those roots later develop into fibrous root systems which are the main feeder
roots of the plant. The roots may penetrate to depths of 50-100 cm (Cours, 1951).
Later on, some of these fibrous roots begin to swell and become tuberous. Apparently,
all the fibrous roots are initially active in nutrient absorption; but once any of them
becomes tuberous, its ability to function in nutrient absorption decreases considerably
(Adrian et al., 1969). A mature cassava tuber may range in length from 15-100 cm
and in weight from 0.5-2.0 kg, depending on variety and growing conditions. Popular
high yielding variety (Sree Rekha) and high starch variety (Sree Harsha) in Kerala are
shown in Figure 1.5.
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Figure 1.5: Cassava tuber- (Left) Sree Rekha- a high yielding top cross hybrid
vaeirty, (Right) Sree Harsha, a high starch triploid variety.
The angle and depth of penetration of the tuber, as well as the colour of the
tuber surface, are also varietal characteristics, although brown is the predominant
tuber surface colour. In comparison to the tubers of Yam, sweet potato, or cocoyam,
the cassava tuber is physiologically inactive. No eyes or buds are present on it, and
none will develop on any part of the tuber even when it is stored for long periods, or
planted. As such, the cassava tuber cannot be used as a means of propagation. The
tuber flesh is composed of about 62% water, 35% carbohydrate, 1-2% protein, 0.3%
fat, 1-2% fiber, and 1% mineral matter. Most of the carbohydrate fraction is starch,
which makes up 20-25% of the tuber flesh (Purseglove, 1968). Among the minerals in
the tuber, phosphorus and iron predominate, with minimal amounts of calcium. The
tuber is relatively rich in Vitamin C (35 mg per 100g fresh weight), and contains
traces of Niacin and Vitamins A, B1, and B2, but the amounts of thiamine and
riboflavin are negligible (Chavez et al, 2005). The protein of the cassava tuber is rich
in arginine. The cassava tuber contains small but significant amounts of cyanogenic
glucosides. The two main cyanogenic glucosides are linamarin and lotaustralin. Both
glucosides are highly soluble in water, and tent to decompose when heated to
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temperatures above 150 °C. The enzyme linamarase (linase), which is also present in
the cassava plant hydrolyze both glucosides to produce hydrocyanic acid (Prussic
acid), which is highly poisonous to humans and animals. The rate of this hydrolysis
can be accelerated by soaking the tubers in water, cutting them, or by raising the
temperature up to 75 °C, above 75 °C, the enzyme is destroyed. The concentration of
linamarase is higher in the peel than in the tuber flesh. The concentration of Prussic
acid in cassava tubers ranges from 10 to 490 mg /kg tuber. As the plant gets older, the
prussic acid content of the tuber increases, attains a peak, and then begins to decline
(Sinha and Nair, 1968).
Cassava Stem and Leaves
The cassava plant grows as a shrub with the stem reaching heights of up to 4
m in some varieties, or only attaining heights of 1m or so in some of the dwarf
varieties. The colour of the stem surface is usually greyish or brownish. In older parts
of the stem, prominent node like leaf scars are present, marking the nodal positions
where the leaves are attached. The distance between leaves varies with cultivars and
also with environmental conditions, being shortest when adverse environmental
conditions exists, and longest when growth conditions are favorable (Hillock et al.,
2002). The pattern of branching of the cassava plant varies with different cultivars. In
some, the main stem grows for a while and then produces three branches
simultaneously. Each of these branches then grows and later again produces three
branches simultaneously, and so on (Jones, 1959). In other cultivars, there is less
regularity in the pattern of branching. In any case, the angle of the branches with the
main stem determines whether the plant has an erect or spreading form. Another
important branching characteristic is how close to the ground the initial branches
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arise. The best type of cassava would be one in which the initial branches are a
reasonable distance from the ground, so that, in the field, the crop stand is relatively
open beneath the canopy of leaves. Such branching allows room for cultural
operations between the rows.
The leaves of cassava are spirally arranged on raised nodal portions on the
stem. The leaf of cassava is deciduous, and, even under the best cultural conditions,
each leaf exists for only a few months before it falls off.
Cassava: Reproductive Biology:
The cassava plant is monoecious; bearing separate male and female flowers on the
same plant. The time interval from planting to flowering may vary from 1 to more
than 24 months and depends on the genotype and environmental conditions (Byrne,
1984). Male and female flowers are borne in a single branched panicle, with female
flowers at the base, and male flowers toward the tip. The flowers are small, with the
male flower being about 0.5 cm in diameter, and the female flower slightly larger.
Male and female flowers of cassava plant are presented in Figure 1.6.
Figure 1.6: Male (left) and Female (right) flowers of cassava plant
Introduction
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Flowers usually begin to open around mid-day, and remain open for about one day.
Cassava exhibits protogyny, where female flowers open first and the male flowers
follow 1 or 2 weeks later on a given branch. Therefore, when male flowers open, the
female flowers on the same branch have been fertilized or have aborted. However,
because flowering on a single plant may last for more than two months, both self- and
sib-fertilization may occur, with the proportion of each dependent on the genotype,
the environment, and the presence of pollinating insects (Kawano, 1980, Jennings and
Iglesias, 2002, Ceballos et al., 2004). Flowering in cassava is strongly influenced by
environmental factors. A particular clone may produce no flowers in one
environment, produce only aborted flowers or fail to produce viable seed in another
environment. The pollen grains of cassava are quite large in size and sticky, and wind
pollination appears to be of little consequence. Several species of wasp and
honeybees (Apis cerana, Apis mellifera, etc.) are the main pollinators in different
continents (Kawano, 1980). Cassava pollen shows size dimorphism, the larger grains
being 130 to 150 microns in diameter, whereas the smaller grains range from 90 to
110 microns (Plazas, 1991). In some varieties, the larger grains are more abundant
and have better germination percentages (60%) under in vitro conditions (2 hours at
40°C) than the smaller ones.
Smaller grains typically germinate less efficiently than large ones, and may
have less than 20% viability. Cassava pollen loses viability rapidly after it is shed.
Leyton has reported nearly 97% seed set with newly-collected pollen, 56% seed set
with pollen stored for 24 hours at 25°C, and 0.9% seed set (one seed from 102
pollinations) after 48 hours of storage (Leyton, 1993). In practice, breeders take care
to perform pollinations within one hour after collection of pollen to avoid loss of
viability of the pollen.
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For some clones, induction of flowering appears to depend on long
photoperiods up to 16-hour day length associated with temperatures of around 24 ºC
(Keating, 1982; Alves, 2002). Flowering is also dependent on plant habit. A flower
bud typically forms when the plant branches, so that highly branched genotypes are
more prolific than those with a sparsely branched habit. Flower bud formation is
preceded by apical branching, which is a prominent visual indication of incipient
flowering, and may be used to identify plants in the pre-flowering stage.
After pollination and subsequent fertilization, the Cassava ovary develops into
young fruit. It requires 3-5 months after pollination for the fruit to mature. The mature
fruit is capsule, globular in shape, with a diameter of 1-1.5 cm. The endocarp is
woody, and there are three locules, each containing a single seed. When the fruit is
mature and dry, the woody endocarp splits explosively to release and disperse the
seeds.
The cassava seed is ellipsoidal and 1-1.5 cm long. It has a brittle testa which is
grey, mottled with dark blotches. There is a large caruncle at the micropylar end of the
seed. Germination of the seed requires a long time, and that duration can be shortened
by filing the micropylar end until the white embryo is just visible.
Fertilized seed is viable two months after pollination, and fruit becomes
mature about one month after that, or about three months after pollination (Ceballos et
al., 2004). The fruit is a trilocular schizocarp, and seeds are ovoid-ellipsoidal,
approximately 100 mm long and 4 to 6 mm thick (Alves, 2002). Dehiscence is
explosive; the seed initially falls close to the mother plant, but then may be further
dispersed by ants, which carry an unknown percentage of the seed to their nests in the
soil. Through these two mechanisms of autochory followed by myrmecochory, a seed
may be dispersed up to several meters from its place of origin (Elias et al., 2001).
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15
Seed production and viability are variable, depending largely on the quality of the
female parent (Kawano, 1980). Jennings (1976) reports that one viable seed per fruit
is normally achieved in controlled pollinations, from a maximum of three possible in
the trilocular ovary. Ceballos et al. (2004) indicate that one to two viable seeds are
obtained from each hand-pollination. Newly harvested seeds are dormant, requiring 3
to 6 months of storage before they germinate (Jennings and Iglesias, 2002).
Cassava seeds are adapted to ant-dispersal, with large energy reserves that
allow deep burial and a long dormancy period (Pujol et al., 2002). Seeds can remain
viable for up to 1 year, although germination percentages may decline substantially
after 6 months (Rajendran et al., 2000).
Seed germination is favored by dry heat and complete darkness. Ellis (1982),
working with two-dimensional temperature gradient plates, found that germination
occurred most often when temperatures exceeded 30°C for part of the day, with a
mean temperature of at least 24°C. They have suggest that an alternating temperature
regime of 30°C for 8 hours and 38°C for 16 hours for at least 21 days is the most
appropriate for determination of cassava seed viability under laboratory conditions.
Botanical seed is not typically used for commercial propagation. Genetically, any
particular cassava genotype is extremely heterogeneous, and propagation from sexual
seed results in wide and unpredictable diversity of phenotypes, which is of interest to
breeders but presents difficulties in propagation (Ceballos et al., 2004).
Vegetative propagation
Cassava is normally propagated by means of stem cuttings, which are known
horticulturally as ‘stakes’. Stakes are typically at least 20 cm long, and have 4 to 5
nodes with viable buds.
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Breeding Schemes in Cassava:
As in most crop breeding activities, cassava genetic improvement starts with the
production of new recombinant genotypes derived from selected elite clones.
Scientific cassava breeding began only a few decades ago, and the divergence
between landraces and improved germplasm is not as wide as in other crops.
Therefore, accession in for germplasm bank collected from different research
institutions play a more relavant role in cassava than in other crops that have been
scientifically bred for longer periods of time. Parental lines are selected based mainly
on their performance per se and not much progress has been made to use general
combining ability as a criterion for parental selection. The multiplication rate of
cassava planting material is low as five to ten cuttings can be obtained from one plant.
This implies a lengthy selection process, and in fact it takes about six years from the
time the botanical seed is germinated until enough planting material is available for
multilocation replicated trials.
A typical selection cycle in cassava begins with the crossing of elite clones
and finishes when the few clones surviving the selection process reach the stage of
regional trials across several locations. There is some variation among the cassava-
breeding programmes in the world with respect to the number of genotypes and plants
representing them through the different stages.
Strong emphasis on highly heritable traits (plant type, branching habits and
reaction to diseases, harvest index and dry matter content) is applied during the early
phases of selection, (Hahn et al., 1980, 1990, Hershey, 1984; Kawano, 1998; Ceballos
et al., 2004). As the number of plants representing each genotype increases, the
weight of selection criteria shifts towards low heritability traits such as root yield. The
clones that show outstanding performance in the regional trials are released as new
Introduction
17
varieties and, eventually, incorporated as parents in the crossing nurseries. With that
the selection cycle is finished and a new one begins.
Cassava: Genetics and Cytogenetics:
Studies on the genetics of cassava have been limited and breeders have concentrated
on obtaining the basic information required for effective genetic improvement of the
crop. Cassava and the wild species of Manihot have 2n = 36 chromosomes (Nassar,
1978). Regular bivalent formation has been reported in the pollen mother cells, with
few meiotic abnormalities. The completely paired pachytene bivalents vary in length
from 19.3 to 40.0 microns. The haploid chromosomal complement has three
functional nucleolar chromosomes and six chromosomal types represented in
duplicate. This information has been used to suggest that the present-day cultivated
types are allopolyploids of crosses between two closely related forms. Their two basic
diploid parental taxa while possessing six chromosomal types in common, differ in
three chromosomes of their complement. Hence the present-day cultivars may be
considered as segmental allopolyploids (Magoon et al., 1969). Similar pachytene
studies have been carried out on M. glaziovii and a comparison with the karyotype of
cassava showed many common features, including the same number and a similar
morphology of chromosomes (Krishnan et al., 1970).
Extensive diversity exists for most traits examined to date. This may be due to
introgression of wild species germplasm and to the many environments and uses for
which cassava has been selected over thousands of years. Precise genetic control has
been characterized for relatively few traits in cassava. Single gene control has been
demonstrated for leaf lobe width, root surface colour, albinism, stem collenchyma
colour, stem growth habit, root flesh pigmentation and male sterility (Hershey and
Introduction
18
Ocampo, 1989). A broad range of agronomically important traits have been studied
for their inheritance patterns. Results to date indicate that nearly all these traits are
under multigenic control, with a high proportion of additive genetic effects (Iglesias et
al., 1994). Genetic variability within cassava for some traits, such as resistance to post
harvest deterioration may be limited for breeding objectives. The application of
molecular techniques, such as gene tagging and the identification of gene products,
will complement conventional approaches to genetic studies of agronomically
important traits. A molecular genetic map of cassava was constructed recently by
Fregene et al., (2008).
Diseases and Pests of Cassava:
A number of diseases and pests adversely affect the overall yield and productivity of
cassava in different continents. Cassava is affected by virus, bacteria and fungi.
Cassava is attacked by more than 30 pathogens causing various degrees of losses
(Lozano and Booth, 1974; Calvert and Thresh, 2002; Thottappilly et al., 2003).
Viral Diseases:
Cassava Mosaic Disease (CMD):
Cassava mosaic disease (CMD) is the major viral disease in cassava, caused by
cassava mosaic virus (CMV), which is spread by the vector whitefly (Bemisia tabaci).
The disease is also transmitted when cuttings from infected stem portions are used for
propagation. The disease is prevalent in all cassava producing areas of Africa, India
and Indonesia, but is of relatively rare occurrence in South America. Symptoms of the
disease include a whitish or yellowish chlorosis of the young leaves, accompanied by
leaf distortion and a reduction in size of the leaves. The growth of the entire plant is
Introduction
19
stunted, and the number of axillary branches is increased. Normal increase in tuber
weight is disturbed, so that tuber yield at harvest is considerably reduced.
Several control measures have been suggested for CMD. The most promising
control measure is the use of resistant varieties. Controlling the whitefly, careful
selection of planting material and inactivation of CMV by means of a heat treatment
are also suggested.
Cassava Brown Streak Disease (CBSD):
This is the second major viral disease of cassava caused by cassava brown streak virus
(CBSV). This disease was first reported from Mozambique in 1936. It is most
prevalent in the coastal areas of East Africa, where it sometimes results in serious
yield reductions. The disease is characterized by leaf chlorosis, and brown streaks in
the stem cortex.. The white fly, Bemisia, is probably the vector of the virus, but it can
also be transmitted mechanically. The whiteflies Bemisia afer and Bemisia tabaci are
the leading candidates as the vector of CBSV.
Bacterial Diseases:
Cassava Bacterial Blight:
This disease usually results in heavy yield reductions, and, where infection is severe,
the crop may be lost completely. The symptoms appear on the leaves as angular spots,
blight, and wilting. Cassava bacterial blight is caused by the bacterium Xanthomonas
manihotis. The disease has a wide spectrum of symptoms, including angular leaf
spots, blighting, wilting, vascular necrosis of the stem, dieback, and production of
exudates (Maraite, 1993). Crop losses of 12 to 80% have been reported. The
movement of infected, asymptomatic stems is a major means of pathogen dispersal.
The disease was first reported in South America (Lozano, 1986) and has sub
Introduction
20
sequently been reported in Africa and Asia. The disease can be controlled through
cultural practices, including the use of uninfected planting material and resistant
cultivars (Boher and Verdier, 1994; Lozano, 1986).
Bacterial Stem Rot:
Bacterial stem rot is a relatively new bacterial disease reported from Colombia (CIAT,
1976). The casual organism is Erwinia spp., which penetrates through wounds.
Infection is restricted to the stem. Infected plants show dark necrosis, followed by
wilting, and then die-back. Erwinia carotovora var. carotovora is the causative agent
for stem rot of Cassava.
Fungal Diseases:
Brown Leaf Spot:
Brown leaf spot disease occurs quite commonly in cassava plantations in South
America, Asia, and Africa. The disease is characterized by large, brown, irregular,
necrotic spots which appear on older leaves and infected leaves tend to drop early.
The disease is caused by the fungus Cercospora henningsii. The disease can be
controlled by treating early with cuprous oxide suspended in mineral oil and applied
at the rate of 20 litres hectare-1 (Galato, 1963).
Phyllosticta leaf spot:
This disease is caused by an organism belonging to the species of Phoma. The fungus
grows best at about 20°C, and the disease is therefore most prevalent in cooler regions
or cooler seasons of the year. The disease is characterized by the presence of
concentric rings on the upper surface of infected leaves. Several resistant varieties
have been identified in Colombia and their use is recommended in areas where the
disease is prevalent.
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21
White thread:
This disease is caused by the fungus Fomes lignosus. It causes rotting of the tubers,
and the surface of the tuber is covered by a white network of mycelia. Control
measures include harvesting the tubers early, and burning of the field before cassava
is planted.
Cassava anthracnose:
This disease is characterized by wilting and death of the young stems and leaves after
sunken spots appear on them.
Super-elongation disease:
It is characterized by extreme elongation of the internodes of young stems, and a
distortion of young stems, petioles, and leaf mid-ribs. The disease is caused by a
species of Sphaceloma (CIAT, 1976).
Insects and Mites:
The Variegated grasshopper, Green spider mite, Red spider mite, Web mite, Cassava
hornworm, Cassava scale, White flies and Termites are the various insects and mites
that affect the cassava plant.
Other diseases and pests of Cassava:
The root-knot nematode, a nematode with a wide range of hosts, also attacks cassava.
Infested plants show the characteristic knots on their roots at about five months after
infestation. Control is by the use of resistant varieties.
Mammals, particularly rodents, wild pigs, and monkeys, may also attain local
importance as pests of cassava. They feed on cassava roots and also help to spread
various tuber rots. Control is by setting traps for them.
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22
Economic Importance of Cassava:
The economic importance of cassava is dependent on many factors like heavy calorie
yield, ease of production, ideal planting material, hardy plant characteristics and ease
of breeding. Cassava is used as a basic food staple for human consumption, starch
source, and also for animal feed. It is mainly consumed as boiled tuber or flour
obtained by processing the root. The roots are very rich in carbohydrates, mainly
starch (about 80% dry weigh). They also contain vitamin C, beta-carotene, calcium,
potassium, and food fibers, but are very low in protein (0.5-1.5% fresh weigh) and fat
(about 0.17%). The leaves are consumed less than tubers and have a large amount of
protein (about 7% fresh weight). The high concentration of potentially toxic
cyanogenic glucosides is of great concern that hinders the use of unprocessed cassava.
The use of cassava leaves and tender shoots for human consumption is widespread in
Africa. Cassava leaves are nutritious food. The leaves are much richer than the tuber
in proteins and vitamins. However, the leaves have to be sufficiently detoxified before
being eaten.
The processed forms of the cassava tuber fall into four general categories like
meal, flour, chips and starch (Sreenivasan and Anaatharaman, 2005). The meal and
flour forms account for the bulk of cassava used for human food in the tropics.
Cassava chips and cassava starch are mainly industrial products that are little used for
direct human consumption. There is a high demand for starch in industry, and cassava
starch has been used to fill part of this demand. The production of cassava starch for
industrial use is a highly specialized and highly mechanized process. Grocery tapioca
(Sago) is essentially cassava starch produced by a special process.
In India nearly 60% of cassava is used industrially in the production of sago,
starch and dry chips (Sreenivasan, 2007). Hi-tech starch factories have been
Introduction
23
established in Tamil Nadu for manufacturing several modified starches from cassava.
These include pre-gelatinized starch (for the confectionery and textile industries),
oxidized and cationic starches (for the paper industry), textile grade modified starch
with good tensile and adhesive strength (for the textile industry), and paper grade
starch with ink water resistance, etc. The projected demand of cassava starch in India
is predominantly in the adhesive sector, especially in the corrugation gums, paper and
textile industries. The demand-supply gap in the industrial sector is expected to be 1.5
× 106 t of cassava tubers demanding 750 000 Ha to be brought under cassava
cultivation (Sreenivasan, 2007).
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24
Cassava Statistics:
Harvested area, Yield and Production; Global, Asian and Indian scenario:
Cassava is mainly cultivated in the sub-Saharan Affrica, Asia and Latin
America. According to the latest report Nigeria is the largest producer of Cassava in
the World (FAOSTAT, 2009). The statistics of cassava harvested area, in the world,
total in Asia and especially in India during last decade is presented in Figure 1.7.
Figure 1.7: (Top) Cassava harvested area during 2000-2009 in the World and Asia
(Bottom) Cassava harvested area during the same period in India.
Data Source FAOSTAT (down loaded on 14.03.2011)
Introduction
25
Figure 1.8 and Figure 1.9 shows statistics of Cassava yield (Hg/Ha, Hg = 0.1 kg) and
Production throughout whole world, total in Asia and in India during last 10 years.
Figure 1.8: Cassava Yield during 2000-2009 Period in the World, Asia and in India.
Data Source FAOSTAT (down loaded on 14.03.2011)
Figure 1.9: Cassava production (Tonns) during 2000-2009 Period in the World, Asia
and in India.
Data Source FAOSTAT (down loaded on 14.03.2011)
Introduction
26
A consolidated data on top (in terms of quantity and value) ten cassava producing
country in the World is shown in Figure 1.10. Nigeria is higher producer followed by
Brazil and India ranks 9th in the list.
Figure 1.10: Top (in terms of quantity and value) ten cassava producing countries
Data from FAOSTAT (down loaded on 04.04.2011)
Cassava Research Net Work Across the World:
Throughout the World, the increasing importance worldwide of cassava for human
consumption, animal feed and industrial applications leads to an increasing need for a
wide range of genetic resources to develop better quality cultivars. Therefore, cassava
biodiversity deserves international support and cooperation for its collection,
conservation, study and use. Two major organization involved in cassava research
programmes are described as follows.
Introduction
27
Global Cassava Development Strategy (GCDS) and related organization:
The Global Cassava Development Strategy and implementation plan was initiated by
Food and Agricultural Organization of United Nations (FAO) and International Fund
for Agriculture Development (IFAD) in 1996. GCDS addresses many of the critical
problems associated with cassava. It provides information on strategic research and
development activities undertaken by its partners in areas related to genetic
improvement and biotechnology, improved production systems, post harvest and
processing, environmental considerations, institutional development and policy
research. GCDS also focuses on supporting the development of action plans on global
cassava improvement, global cassava post harvest and global cassava marketing. A
major suggestion of GCDS was that cassava could become the raw material base for
an array of processed products that will effectively increase demand for cassava and
contribute to agricultural transformation and economic growth in developing
countries. GCDS also suggested that genetic improvement of cassava should be
related to the use of cassava.
Important partner organization of GCDS includes Food and Agriculture
Organization of the United Nations (FAO), International Fund for Agricultural
Development (IFAD), International Development Research Centre (IDRC),
International Centre for Tropical Agriculture (CIAT), International Institute for
Tropical Agriculture (IITA), International Cooperation Centre of Agricultural
Research for Development (CIRAD), Natural Resources Institute , International
Laboratory for Tropical Agricultural Biotechnology (ILTAB) and Brazilian
Agricultural Research Corporation.
CIAT, which has been active in cassava research since the 1970s, is one of the
leaders in innovation that has made a large contribution to the crop's success in many
Introduction
28
parts of Asia and Latin America. CIAT maintains a collection of more than 6000
cassava accessions for the FAO including landraces from Asia and Latin America,
clones selected by the CIAT and the IITA, and several wild Manihot species.
Consultative Group on International Agricultural Research (CGIAR):
The Consultative Group on International Agricultural Research (CGIAR), established
in 1971, is a strategic partnership of diverse donors that support 15 international
Centres, working in collaboration with large number of government and civil society
organizations as well as private businesses around the world. Eleven of the CGIAR
Centres maintain international Genebanks. These preserve and make readily available
a wide array of plant genetic resources, which form the basis of global food security.
The objectives of CGIAR are “food for people”, “environment for people” and
“policies for people”.
One of the important outcomes of the research under CGIAR was biological
control of the cassava mealybug and green mite, both devastating pests of a root crop
that is vital for food security, succeed in sub-Saharan Africa. The economic benefits
of this work alone, estimated at more than $4 billion. Moreover, two CGIAR research
centers IITA and CIAT have developed elite varieties of cassava with improved
qualities. IITA has also discovered spontaneous polyploids in cassava, which are
characterized by enormous vigor and variation in form and structure. Selections from
triploids "super cassava" have doubled the yields of existing improved varieties with
normal chromosome numbers. IITA has also introduced to Africa a wider genetic base
for cassava improvement, focusing on materials with resistance to mites, mealy bugs,
cassava bacterial blight, tolerance to drought, low cyanogen potential, and good
cooking quality. Together, IITA and CIAT launched a famous biological control
Introduction
29
campaign of the mealybug and are cooperating with the International Fund for
Agricultural Development in the formulation of a global development strategy for
cassava.
International Crop Research Institute for the Semi Arid-Tropics (ICRISAT),
Hyderabad, Anthrapradesh in India is one of centres under the consortium of CGIAR.
Cassava Research in India:
The average yield of cassava in India is nearly 2.7 times higher that of the World
average (3, 43,678 Hg/Ha and 1, 26,448 Hg/Ha respectively) as per current
FAOSTAT data. The research and development in the area of root and tuber crops in
India has played a major role in improving the status of cassava in terms of
production, yield, quality, disease management, marketing, etc. Research on tuber
crops in India is undertaken mainly at the Central Tuber Crops Research Institute
(CTCRI) Thiruvananthapuram, one of the primier institutions under Indian Council of
Agricultural Research (ICAR). One of the major activities of CTCRI includes genetic
resource management where root and tuber crops germplasm is conserved at field
Gene banks and the genetic diversity and purity of the collections are being assessed
periodically through morphometric as well as molecular marker assisted methods. A
total of twelve improved high yielding cassava varieties have been released since
1971 from CTCRI of which H-165 and H-226 are most popular varieties in Tamil
Nadu and Andhra Pradesh. A number of varieties/cultivars from CTCRI are grown in
different regions of the country. A number of high value products from cassava have
been developed at CTCRI to increase the market potential and to sustain and promote
cassava cultivation to more areas.
Introduction
30
Cassava cultivation in India:
India with an annual tuber crops production of nearly 45 million MT from an area of
2.2 million Ha (Yield = 202213 Hg/Ha), where cassava contributes nearly 21% (~9.5
million tonnes) (FAOSTAT, 2009 data). Although cassava is cultivated in about 13
states of India, major production is from the southern states of Kerala and Tamil
Nadu. Table 1.3 summarizes the area, production and yield of cassava from major
cultivating States in India.
State
Area
(′000 Ha)
Production
(′000 T)
Yield (T/Ha)
Kerala
109.3
2563.5
23.454
Tamil Nadu 97.2 3425.5 35.242
Anthra Pradesh 18.1 111.5 6.16
Meghalaya
Assam
Karnataka
4
2.8
0.8
21.5
13.4
15.8
4.9
4.78
19.5
Table 1.3: Area, Production and Yield of Cassava in different States of India
The time of cultivation of cassava plant in the different states in India is presented in
Table 1.4. As a result of changing life-styles, the influx of money sent home by
Indians working in the Gulf States, and a shift to cultivation of cash crops like rubber
and plantation crops, the area under cassava in Kerala has gradually decreased over
the past 30 years.
Introduction
31
State
Rain fed
Irrigated
Kerala
April-May September-October
December-January
Tamil Nadu June March
Anthra Pradesh June March
Madhya Pradesh June September (higher yield)
Table 1.4: The time of cultivation of cassava plant in the different states in India Ref: Edison
There are a number of biological constraints to cassava yield improvement.
These include a low multiplication rate, bulky planting material required for
cultivation, rapid drying out of stakes and incidence of cassava mosaic disease (CMD)
and root rot. One of the most fascinating strategies to overcome the low multiplication
rate ant bulkiness of planting material is the true cassava seed program (TCSP). Work
on TCSP was initiated in India almost two decade ago, and has advantages such as a
150 times increase in propagation rate, longer viability of seed, and non-transmission
of mosaic virus through seed.
The shift in focus of cassava from a food to an industrial crop has led to a
change in the breeding strategy for cassava as well. For the industrial zones of
TamilNadu and Andhra Pradesh, importance is being given to develop high starch
varieties with CMD tolerance, early harvestability and better post-harvest storage life.
Management strategies to improve cassava production include agronomic
interventions, such as the development of low input and mycorrhizal technologies,
natural resource utilization and water management. As a management strategy for
Introduction
32
CMD, branching types are also preferred due to better canopy spread with
consequently lower yield reduction from the disease. Testing and popularization of
cassava varieties through outreach programs like the Lab to land Program (LLP),
Institution-Village Linkage Program (IVLP) and on farm trials are another approach
for enhancing cassava production.
Cassava Cultivation in Kerala:
Cassava, which was introduced into India by the Portuguese during the 16th
century as a food crop, is gradually changing its role as an industrial raw material. The
importance of cassava as a food crop was well recognized in Kerala, during the 20th
century, when famine struck India at the time of the Second World War. The crop
integrated well with the traditions and culture of the people of Kerala. Adaptability to
poor soils, an ability to establish in high as well as low rainfall areas, and relative
resistance to pests and diseases are a few of the factors that helped to anchor cassava
in India. Cassava is cultivated in India in about thirteen states with major production
in the south Indian states of Kerala (1, 42,000 Ha) and Tamil Nadu (65,700 Ha). It is
now a major industrial crop in Tamil Nadu and is also gaining importance in Andhra
Pradesh, where it serves mostly as raw material for starch extraction. The phenomenal
growth in the starch and sago trade over the years has also helped in creating rural
employment in Tamil Nadu.
It was reported that cassava is cultivated in all the agro-climatic zones of
Kerala. Farmers utilize all types of cropping systems namely as pure crop, intercrop,
mixed crop and homestead. The study conducted by Sasankan et al., also revealed
high productivity of cassava in low land system (Sasankan et al., 2008). Many cassava
cultivars exist in each locality where the crop is grown. The cultivars have been
Introduction
33
distinguished on the basis of morphology (e.g., leaf shape and size, plant height,
petiole color, etc), tuber shape, earliness of maturity, yield, and the content of
cyanogenic glucoside of the roots. This last-named characteristic has been used to
place cassava cultivars into two major groups; the bitter varieties, in which the
cyanogenic glucoside is distributed throughout the tuber and is at a high level, and the
sweet varieties, in which the glucoside is confined mainly to the peel and is at a low
level.
The flesh of the sweet varieties is therefore relatively free of the glucoside,
although it still contains some (Purseglove, 1968). In general, sweet cassavas tend to
have a short growing season; their tubers mature in 6-9 months, and deteriorate
rapidly if not harvested soon after maturity. The bitter cassava, on the other hand,
require 12-18 months to mature, and will not deteriorate seriously if left unharvested
for several months thereafter. The exact level of glucoside in a particular cultivar will
vary according to the environmental conditions under which the plant is grown. An
introduction from Malaya, called M4 is a popular variety used for culinary purpose in
Southern Kerala.
Need for Cassava Improvement:
The current efforts on cassava improvement mainly focus on varieties resistant to
pests and diseases particularly mosaic and bacterial blight diseases, high yielding,
producing good quality tubers with high starch and protein content, contain low levels
of prussic acid, early maturing varieties, long storage period, minimum of foliage and
adapted to a wide range of environmental conditions, etc.
Introduction
34
The introduction of cultivars from other localities or countries has been one of the
major methods of cassava improvement. Hybridization, followed by selection among
the progeny, is another useful method for improving cassava.
Creation of new genetic diversity:
The first significant large-scale creation of new diversity occurred through controlled
crossing carried out by plant breeders. Hybridization in cassava is relatively easy
(Kawano, 1980) and open pollination schemes are extensively used to increase the
amount of hybrid seed produced. In some regions the principal constraint to crossing
is shy flowering and to date practical methods have not been developed to deal with
non-flowering types. Flowering is controlled by the complex interaction of a range of
genetic and environmental factors. In some areas cassava will flower all year long
while in other locations flowering is seasonal. Cassava is monoecious, with pistillate
flowers opening about two weeks before staminate flowers. Normally, few seeds are
obtained (an average of I to 1.5) and acquiring large numbers of seeds is a labour
intensive and tedious process. Most genotypes appear to suffer drastic inbreeding
depression. Vegetative propagation to preserve superior heterozygotes greatly
simplifies breeding and, whichever breeding method is used, heterozygocity needs
either to be maintained or restored prior to subsequent vegetative propagation. Most
programmes use some form of recurrent selection appropriate for the accumulation of
many genes of minor effect. All existing commercial cultivars of cassava are probably
highly heterozygous.Although difficulties occur at the time of flowering, IITA has
performed extensive intercrossing among wild species and between cassava and wild
species. M. glaziovii has been used as a source of African mosaic-virus resistance in
early East African breeding programmes (Nichols, 1947).
Introduction
35
Mutation has been tried sparingly for cassava. One constraint is the need for
selfing to achieve expression of recessive mutations occurring in the heterozygous
state. This is very difficult for a large number of genotypes due to the asynchronous
opening of staminate and pistillate flowers. Mutation could have more practical
applications when haploid cells, such as microspores, can be regenerated into
plantlets. Haploids and doubled haploids will be a significant research tool for
cassava, with possible applications in genetics, evolution studies, expression of
recessive genes and in a breeding system for true cassava seed.
Polyploid induction, through colchicine-induced tetraploids, has been a subject
of considerable research in India (Graner, 1941; Magoon et al., 1969). The clones
produced generally exhibited the gigas characters associated with polyploidy, such as
increases in leaf breadth and thickness, stomata size, length and girth of petiole and
flower size. Pollen sterility was high, but fertile pollen grains were much larger in size
(180 to 196 microns) compared to diploids (125 to 140 microns). Considerable
genotypic variation was demonstrated in response to polyploidy. Some clones became
weak and could not be maintained, while others were maintained easily for several
generations. Improved yield potential from polyploidy has not been found to be
promising in any of the programmes. In India it was reported that a 42 percent
increase in protein content was achieved by polyploid induction which subsequently
disappeared with continued vegetative propagation.
At IITA work focused on changes in ploidy through inducing production of
unreduced gametes, mainly through interspecific crosses. Four spontaneous
tetraploids and two triploids were isolated from crosses between M. pruinosa or M.
glaziovii and cassava. A majority of the interspecific crosses produced diploid pollen,
Introduction
36
but their frequencies varied with cross-combinations and with genotype within
respective cross combinations (Han et al., 1990). The presence of multivalent in the
polyploids suggests that pairing and crossing over are taking place between cassava
and its related Manihot species. There are no strong incompatibility barriers to
interspecific hybridization, though considerable selection of parent cassava clones is
necessary, which could indicate a highly fluid gene pool within the genus Manihot
and likely widespread introgression among species.
Virtually no somaclonal variation has been detected from extensive studies on
plants propagated from meristem culture or from somatic embryos (Szabados et al.,
1987). Since either of these processes result in considerable variation in many species,
this result suggests that cassava is genetically very stable at these levels of tissue
organization. Regeneration of cassava from individual cells is not possible at present
and it is not known whether genetic stability would be similar for regenerated single
cells.
Genetic markers of cassava:
Genetic markers have become fundamental tools for understanding the inheritance
and diversity of natural selection. They provide Gregor Mendel, the father of modern-
day genetics, the tools for his ground breaking experiment on heredity and more
recently markers have made possible the construction of genetic maps, the cloning of
genes known only by their phenotypes and position on a genetic map, and whole
genome sequencing. The earliest genetic markers in cassava are morphological
(Sumarani et al., 20004), and these markers are governed by alleles with a major
phenotypic effect with little or no environmental effects (Harshey and Ocampo,
1989). The second generations of markers were biochemical, such as Isozymes and
Introduction
37
they provided a useful tool for genetic fingerprinting and the study of genetic diversity
in cassava (Hussain et al., 1987; Ramirez et al., 1987; Ocampo et al., 1992; Lefevre
and Charrier, 1993a, Pillai et al., 2000). Isozymes have been applied to characterizing
relationship among accessions of African cassava germplasm (Lefevre and Charrier,
1993b; Wanyera et al., 1994) and finger printing of the international cassava
collection held at CIAT (Ocampo et al., 1992). The alpha beta esterase system was
found to be most informative, providing 22 alleles, which have complmented
morphological description for the identification of duplicates in the collection at CIAT
(Ocampo et al., 1995).
With the discovery of the molecular basis of natural variation, molecular or
DNA markers have rapidly gained importance in the study of genes, genomes and
genetic diversity. They represented a limitless source of neutral markers for the
quantitative assessment of genetic diversity and “signposts” in gene and genome
mapping. Their abundance in any organism facilitates the resolution of genetic
relationship and genome/gene mapping unknown until the coming of molecular
markers. Cassava genetic improvement could be made more efficient through the use
of easily assayable molecular genetic markers or DNA markers that enable the precise
identification of genotype without the confounding effect of the environment, thereby
increasing heritability. The selection of progenies based on genetic values derived
from molecular marker data substantially increases the rate of genetic gain, especially
if the number of cycles of evaluation or generations can be reduced. Another
application of DNA markers in cassava breeding is reducing the length of time
required for the introgression of traits from wild relatives (Melchinger, 1994),
The prominent molecular marker systems include minisatellites, restriction
fragment length polymorphisms (RFLP) (Botstein et al., 1980) and randomly
Introduction
38
amplified polymorphic DNAs (RAPD) (Williams et al., 1990). Others are
microsatellites, also known as simple sequence repeat markers (SSR) (Litt and Lutty,
1989) amplified fragment length polymorphisms (AFLP) (Vos et al., 1995) and DNA
sequencing of the internal transcribed spacer (ITS) of ribosomal DNA (Baldwin,
1992) and single-copy nuclear genes. More recently DNA chip or oligonucleotide
arrays have been added to an ever growing list of molecular markers (Fodor et al.,
1993). All these marker systems, other than DNA chip have been used in cassava to
assess genetic diversity, genome mapping and gene tagging.
Microsatellites or Simple Sequence Repeat (SSR):
Among the different molecular markers, Microsatellites, or Simple Sequence Repeats
(SSRs) (Tautz and Rentz, 1984: Tautz, 1989), are the most widely applied class in
genetic studies Chavarriaga-Aguirre et al., 1999; Olsen et al. 2001). SSR can be
defined as any one of a series of very short (2-10 bp), middle repetitive, tandemly
arranged, highly variable DNA sequences dispersed throughout fungal, plant, animal
and human genomes. These repeat motifs are flanked by conserved nucleotide
sequences from which forward and reverse primers can be designed to PCR-amplify
the DNA section containing the SSR. The microsatellite alleles, amplified products of
variable length, can be separated through gel electrophoresis and visualized by
Ethidium bromide staining. SSRs are abundant in plants, occurring on average every
6-7 kb (Cardle et al., 2000). They have high level of polymorphism, and are adaptable
to automation (Donini et al., 1998). SSRs are user friendly, highly polymorphic
markers suitable for purity control (Nandakumar et al., 2004), differentiation of plant
cultivars (Bredemeijer et al., 1998: Struss and Plieske 1998), elimination of duplicates
(Lund et al. 2003) and selection of appropriate parents based on genetic distance in
Introduction
39
breeding programmes (Zhou et al., 2006). When first introduced, development of SSR
markers was expensive but now new and efficient methods of repetitive sequence
isolation have been identified which had led to reduced costs and microsatellite-
technique has been increasingly applied in genetic diversity studies.
The present study exclusively uses SSR markers for the DNA analysis and
finger printing for variability and diversity study of Indian cassava cultivars.
A more exhaustive description of molecular marker based genetic studies
particularly in cassava is described in the following chapter-Review of literature.
Introduction
40
Objectives of the present study:
The objectives of the present study are –
1. To study the molecular variability and diversity available in local varieties of
cassava (Manihot esculenta Crantz) and identification of distant varieties for
planning hybridization program.
2. DNA fingerprinting of released varieties of cassava, with a view to protect the
plant breeder’s right. DNA finger printing of popular, local varieties selected
by farmers with a view to protect the Farmer’s Right.
3. DNA analysis of Cassava Mosaic free accessions and also whitefly resistant
accessions to confirm their resistance. Screening apparently resistant of
hybrid populations to confirm actual resistance and escapes.
Introduction
41
Outline of the Thesis:
The present study on “DNA analysis as a tool for Genetic Studies and Molecular
Breeding in Cassava (Manihot esculenta Crantz)” as outlined in this thesis is
presented in seven chapters. The first chapter is a general introduction that give an
over view on Cassava (Manihot esculenta Cranz). The second chapter, Review of
literature gave an elaborate description on genetic markers especially molecular
markers with emphasis on SSR marker studies in Cassava. The third chapter describes
the genetic variability in cassava from a typical cassava growing high land area-
Idukki in Kerala using SSR markers. The fourth chapter presents variability of
cassava among subsamples from old and new collections from CTCRI germplasm
collection using SSR markers. Fifth chapter deals the genetic variability available
among selected cultivars from North Kerala varieties using SSR markers. The sixth
chapter describes genetic variability among CTCRI released varieties and central
Kerala varieties through DNA finger printing by SSR markers. The seventh chapter
deals with application of SSR markers for identifying CMD and whitefly resistant
varieties of cassava. The major observations and a consolidated summary are
provided at the end.
Introduction
42
References Adrian, J., Pyrot, F., Oliveira, J.S and Carvalho, M. F. De (1969) Nutritional study of cassava leaf (Manihot utilissima), Rev. Cienc. Agron. Ser. A, 2: 43-59. Alves, A.A.C (2002) Cassava botany and physiology. In:R.J.Hillocks J. M. Thresh and A.C Bellotti (Eds.) Cassava: Biology,Production and Utilization. CABI Publishing, New York, pp.67–89. Baldwin, B.G (1982) Phylogenetic utility of the internal transcribed spacers of nuclear ribosomal DNA in plants: an example from the compositase, Molecular Phylogenetic Evolution. Botstein, D., White, R.L., Skolnick, M.H & Davis, R.W (1980) Construction of a genetic map in man using restriction fragment length polymorphisms, American Journal of Human Genetics 32: 314-331. Bradshaw (2010) Root and tuber crops (Handbook of Plant Breeding). Springer, 1st Edition.
Bredemeijer, G.M.M., Arens, P., Wouters, D., Visser, D & Vosman, B (1998) The use of semi-automated fluorescent microsatellite analysis for tomato cultivar identification, Theoretical and Applied Genetics 97: 584-590.
Boher, B and Verdier, V (1994) Cassava bacterial blight in Africa. The state of knowledge and implications for designing control strategies. Afr. Crop Sci. 2: 1-5. Byrne, D.H (1984) Breeding cassava, Plant Breeding Reviews Rev 2:73-133. Calvert, L. and Thresh, J.M. (2002) The viruses and virus diseases of cassava. In: Cassava: Biology, Production and Utilization. R.J. Hillocks, J.M. Thresh and A. Bellotti (eds.), pp. 237-260, CAB International, Wallingford, UK. Cardle, L.,Ramsay, L., Milbourne, D., Macaulay, M., Marshall, D., Waugh, R (2000) Computational and experimental characterization of physically clustered simple sequence repeats in plants. Genetics156:847–854 Ceballos, H., Iglesias, C.A., Perez, J.C& Dixon, A.G.O (2004) Cassava breeding: opportunities and challenges. Plant Molecular Biology 56:503– 516. Chavez AL, Sanchez T, Jaramillo G, Bedoya JM, Echeverry J, Bola EA, Ceballos H and Lglesias (2005) Variation of quality traits in cassava roots evaluated in landraces and improved clones. Euphytica, 143: 125–133. Cours, G (1951) (Manioc in Madagascar), Mem. Inst. Sci. Madagascar, Ser. B, 111, Fasc. 2. CIAT (1976) Annual Report, Centro Internacinal de Agricultura Tropical, Cali, Colombia, pp 53-109.
Introduction
43
Chavarriaga-Aguirre, P., Maya, M.M., Tohme, J., Duque, M.C., Iglesias, C., Bonierbale, S., Kresovich, M.W., Kochert, G (1999) Using microsatellites, isozymes and AFLPs to evaluate genetic diversity and redundancy in the cassava core collection and to assess the usefulness of DNA-based markers to maintain germplasm collections. Molecular Breeding 5: 263-273. Donini, P., Stephenson, P., Bryan, G.J & Koebner, R.M.D (1998) The potential of microsatellites for high throughput genetic diversity assessment in wheat and barley, Gen Res Crop Evol 45: 415–421. Ellis, R.H (1982) Investigation of the influence of constant and alternating emperature on the germination of cassava seed using a two dimensional temperature- gradient plate, Annals of Botany 49: 241. Elias, M., Penet,L., Vindry, P., MacKey, D., Panaud, O., Robert, T (2001) Unmanaged sexual reproduction and the dynamics of genetic diversity of a vegetatively propagated crop plant, cassava (Manihotesculenta Crantz), in a traditional farming system.MolEcol 10:1895–1907. Fodor, S.P., Rava, R.P., Huang, X.C., Pease, A.C., Holmes, C.P & Adams, C.L (1993) Multiplexed biochemical assays with biological chips, Nature 364: 555-556. Fregene M, Angel F, Gomez R, Rodrigue F, Chavarraiga P, Roca W, Tohme J and Bonierbale (2008) A molecular genetic map of cassava (Manihot esculenta Crantz). Theor Appl Genet, 95, 431-441. Galato, C (1963) (Cercospora henningsii on cassava in Nigeria) Riv. Agric. Subtrop 57: 60-66. Giovanni F (2008) Feeding the World: an economic history of agriculture, 1800-2000 (Princeton economic history of the western world), Princeton University Press. Graner, E.A (1941) Polyploid cassava induced by colchicine treatment J. Hered., 32: 281-288. Hahn, S.K., Terry, E.R. and Leuschner, K. 1980. Breeding cassava for resistance to cassava mosaic disease. Euphytica 29: 673-683. Hahn, S., Bai, K.V., Asiedu, R.A (1990) Tetraploids, triploids, and 2n pollen from diploid interspecies crosses with Cassava,TheorAppl Genet 79:433-439.
Hershey, C (1984) Breeding cassava for adaptation to stress conditions development of a methodology In: F.S. Shideler and H. Ricon, eds. Proceedings of the Sixth Symposium of the International Society of Tropical Root Crops, Lima, Peru, February 1993, pp 303-314 Lima, Peru, International Potato Center, CIP.
Hershey, C.H and Ocampo, C (1989) New marker genes found in cassava, Cassava Newsletter 13(1): 1-5.
Introduction
44
Hillocks R J., Thresh J M., Bellotti A (2002) Cassava. CABI; First edition. Hussain, A., Ramirez, H., Roca, W.M & Bushuk, W (1987) Identification of cassava (Manihot esculenta Crantz) by electrophoretic patterns of esterase isozymes, Seed Science and Technology 15: 19-22. Iglesias, C., Hershey, C., Calle, F and Bolanos, A (1994) Propagating cassava (Manihot esculenta) by sexual seed, Exp. Agric. 30: 283-290. Iglesias, C., Mayer, J., Chaves, L and Calle, F (1997) Genetic potential and stability of carotene content in cassava roots, Euphytica 94: 367-173. Jason C (2004) World agriculture and the environment: A Commodity-by-commodity guide to impacts and practices. Island Press. Jones, W.O (1959) Manioc in Africa, Stanford University Press, Stanford, 315 C.I.A.T.(Centro International de Agricultura Tropical, Cali, Colombia) (1976) Annual Report 1975. Jennings, D.L (1976) Breeding for resistance to African cassava mosaic, report of an interdisciplinary workshop held at Muguga, Kenya, IDRC 071e, pp, 39-44. Jennings, D.L., Iglesias, C (2002) Breeding for crop improvement In: Hillocks, R.J., Tresh, J.M., Bellotti, A.C. (ed.): Cassava: Biology, Production and Utilization. Pp. 149-166.
Kawano, K (1980) Cassava. In: W.R. Fehr & H.H. Handley, eds. Hybridization of Crop Plants, pp. 225-233. Madison, Wisc., USA, American Society of Agronomy.
Kawano, K., Narintaraporn, K., Narintaraporn P., Srakarn, S., Limsila, A., Limsila, J., Suparhan, D., Sarawat, V and Watananonta, W (1998) Yield improvement in a multistage breeding programme for cassava, Crop Science 38: 325-332. Keating, B.A., Evenson, J.P & Fukai, S (1982) Environmental effects on growth and development of cassava (Manihot esculenta Crantz) I. Crop development. Field Crops Research 5: 271-281.
Krishnan, R., Magoon, M.L & Bai, K.V (1970) The pachytene karyotype of Manihot glaziovii. Genet. Iber., 22: 177-191.
Leyton, M (1993) Crloconservaclon de pollen de yucca B.Sc Thesis, Universidad del valle, Facultad de Ciencian, Dept de Biologia, Cali, Colombia, 113 p.
Lozano, J.C (1986) Cassava bacterial blight:A manageable disease. Plant Dis. 70:1089-1093. Lozano, J.C and Booth, R.H (1974) Diseases of cassava, PANS 20: 30-54.
Introduction
45
Lefevre, F and Charrier, A (1993a) Heredity of seventeen isozyme loci in cassava (Manihot esculenta Crantz), Euphytica 66: 171-178. Lefevre, F and Charrier (1993b) Isozyme diversity within African Manihot germplasm, Euphytica 66: 73-80. Litt, M and Lutty, J.A (1989) A hypervariable microsatellite revealed by in vitro amplification of dinucleotide repeat within the cardiac muscle actin gene, American Journal of Human Genetics 44: 397-401. Maraite, H (1993) Xanthomonas campestris pathovars on cassava: Cause of bacterial blight and bacterial necrosis. Pages 18-24 in: Xanthomonas. J. G. Swings and E. L. Civerolo, eds. Chapman and Hall, London. Magoon, M.L., Krishnan, R and Bai, K.B (1969) Morphology of the pachytene chromosomes and meiosis in Manihot esculenta Crantz, Cytology 34: 612-626. Melchinger, A.E., Graner, A., Singh, M & Messmer (1994) Relationships among European barley germplasm.1. Genetic diversity among winter and spring cultivar revealed by RFLPs, Crop Science 34: 1191-1199. Michael W and Mary BW (1999) Ancient Agriculture: from foraging to farming (ancient technology). Runestone Press Marcel M and Laurence R (2006) A history of world agriculture: from the Neolithic age to the current crisis. Monthly Review Press Nandakumar, N., Singh, A.K., Sharma, R.K., Mohapatra, T., Prabhu, K.V., Zaman, F.U (2004) Molecular fingerprinting of hybrids and assessment of genetic purity of hybrid seeds in rice using microsatellite markers, Euphytica 136: 257-264. Nassar N M A (1978) Genetic resources of cassava: Chromosome behavior in some Manihot species. Indian J. Genet. Plant Breed. 38: 135-137. Nassar N M A (2000) Cytogenetics and evolution of cassava (Manihot esculenta Crantz). Genetics and Molecular Biology, 23, 4, 1003-1014. Nichols, R.F.W (1947) Breeding cassava for virus resistance. East Afr. Agric. J. 15: 154-160. Olsen, K.M., Schaal, B (2001) Microsatellite variation in cassava (Manihot esculenta), Euphorbiaceae and its wild relatives: evidence for a southern Amazonian origin of domestication. American Journal of Botany 88: 131-142. Ocampo, C., Hershey, C., Iglesias, C and Iwanaga, M (1992) Esterase isozyme fingerprinting of the cassava germplasm collection held at CIAT, In: Roca, W. and Thro, A.M, (eds) Proceedings of the 1st international scientific meeting of the cassava biotech network, CIAT, Cali, Colombia, PP, 81-89.
Introduction
46
Ocampo, C., Angel, F., JimCnez, A., Jaramillo, G., Hershey, C., Granados, E and Iglesias, C (1995) DNA fingerprintingto confirm possible genetic duplicates in cassava germplasm. The cassava Biotechnology Network, Proceedings of the Second International Scientific Meeting, Bogor, Indonesia, 22-26 August 1994. Centro Interaclonal de Agricultura Tropical (CIAT), Cali, Colombia, pp, 145-147. Pillai, S.V., Sundaresan, P., Harisankar & Sumarani, G.O (2000) Molecular characterization of germplasm in tropical tuber crops, DAE-BRNS Symposium, Mumbai. Purseglove, J.W (1968) Tropical Crops. Dicotyledons I, Longmans Green and Co, London, 332 pp. Pujol, B., Gigot, G., Laurent, G., Pinheiro-Kluppel, M., Elias, M., Hossaert-Mckey, M & Mckey, D (2002) Germination ecology of cassava (Manihot esculenta) in traditional ecosystems, seed and seedling biology of a vegetatively propagated domestic plant, Economic Botany 56: 366-379. Plazas, J.J (1991) Respresta al cultivo in vitro de microsporas aisladas de variedades de yucca (Manihot esculenta Crantz) Con fertilidad diferencial, B.Sc Thesis, Universi9dad del Valle, Facultad de Ciencias, Dept de Biologia, Cali, Colombia, 75 p. Rajendran, P.G., Ravindran, C.S., Nair, S.G & Nayar, T.V.R (2000) True cassava seeds (TCS) for rapid spread of the crop in non traditional areas, Technical Bulletin series C 28. Ramirez, H., Hussain, A., Roca, W.M & Bushuk, W (1987) Isozyme electrophoregrams of sixteen enzymes in five tissues of cassava (Manihot seculenta Crantz) Varieties, Euphytica 36: 39-48. Rogers, D.J (1963) Studies of Manihot esculenta Crantz (Cassava) and related species, Bull Torrey Bot, 90: 43-54. Rogers, D. and Appan, C. (1973). Manihot, Manihotoides, Euphorbiaceae, Flora Neotropica. Hafner Press, New York, NY, USA Sasankan VR, Anilkumar A, Anantharaman M and Motilal Nehru S (2008) Cassava production system typologies in Kerala state. Journal of Root Crops, 34 No. 1, pp. 61-64. Sinha. S. K and Nair, T.V (1968) Studies on the variability of cynogenic glucoside content in cassava tubers, Indian J. Agric. Sci., 38: 958-963. Sheafer CC and Moncada MM (2008) Introduction to agronomy: food, crops, and environment. Delmar Cengage Learning; 001 edition. Sreenivasan T (2007) Industrial Demand for Cassava Starch in India. Starch/Stärke, 59, 477–481.
Introduction
47
Sreenivasan T and Anaatharaman M (2005) Cassava marketing systems in India. Technical bulletin series, 43, CTCRI, Thiruvananthapuram. Struss, D & Plieske, J (1998) The use of microsatellite markers for detection of genetic diversity in barley populations, Theoretical and Applied Genetics 97: 308-315. Sumarani, G.O., Pillai, S.V., Harisankar, P & Sundaresan, S (2004) Isozyme analysis of indigenous cassava germplasm for identification of duplicates, Genetic Resources and Crop Evolution 51:205-209. Szabados, L., Hoyos, R and Roca, W (1987) In vitro somatic embrogenesis and regeneration of cassava, Plant Cell Reports 6: 248-251. Tautz, D & Renz, M (1984) Simple sequences are ubiquitous repetitive components of eukaryotic genomes, Nucleic Acids Research 23: 249-255. Tautz D (1989) Hypervariability of simple sequences as a general source of polymorphic DNA markers. Nucleic Acid Research 17, 6463-6471. Thottappilly, G., Thresh, J.M., L.A. Calvert and Winter, S. 2003. Cassava. In: Virus and virus-like diseases of major crops in developing countries, G. Loebenstein and G. Thottappilly ( eds), Pages 107-165, Kluwer Academic publishers, 800 pp. Vos, P., Hogers, R., Bleeker, M., Reijans, M., vanderLee, T., Hornes, M., Fritjers, A., Pot, J., Peleman, J., Kulper, M and Zabeau, M (1995) AFLP: a new technique for DNA fingerprinting, Nucleic Acid Research 23: 4407-4414. Wanyera, N.M.W., Hahn, S.K and Aken’Ova, M.E (1994) Introgression of ceara rubber (Manihot glaziovii Muell-Arg) into cassava (M. esculenta Crantz): a morphological and electrophoretic evidence, In: Proceedings of the fifth triennial symposium of the International society for tropical root crops- Africa Branch, Kampala, Uganda, 22-28 November 1992, pp. 125-130. Wheeling BM (2007) Introduction to agricultural accounting. Delmar cengage learning; 001 edition. Williams, J.G.K., Kubelik, A.R., Livak, K.J., Rafalski, J.A and Tingey, S.V (1990) DNA polymorphisms amplified by arbitrary primers are useful as genetic markers, Nucleic Acids Research 18: 6531-6535. Zhou, W.J., Zhang, G.Q., Tuvesson, S., Dayteg, C., Gertsson, B (2006) Genetic survey of Chinese and Swedish oilseed rape (Brassica napus L) by simple sequence repeats (SSRs), Genet Resour Crop Evol 53: 443-447.