Physiological Disorders in Citrus, Growth Regulator Studies
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Transcript of Physiological Disorders in Citrus, Growth Regulator Studies
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Physiological disorders in Citrus, Growth
regulator studies in Propagation,Flowering and Fruit setting
Mr. Srikantaprasad, DUHS11PGD27
I PhD
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Mandarin
(Citrus reticulata)
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Physiological disorders
Fruit drop
Mandarins: very high initial flowering and
fruiting, heavy fruit drop
the ultimateyield is often low.
In mandarins three distinct waves.
1 soon after fruit setting,
2 during May- June (June drop)
3 drop of mature fruits before harvesting(pre harvest drop).
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Causes: Fluctuating temperature, low atmospheric humidity,
imbalance of soil moisture, lack of proper nutrition,
hormonal imbalance, incidence of insect pests and diseases
Remedy: maintenance of appropriate soil moisture level
during fruit development and application of growth
regulators2,4-D (10 ppm), NAA (5ppm), 2, 4, 5-T (5ppm)
check fruit drop quite effectively. Further, application or
Aureofungain @ 20ppm helps in better retention of fruits
through control of fungal diseases.
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Granulation
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Granulation
Physiological disorder of juice sacs, they become comparatively
hard, grayish color and enlarged. The concentration of pectic
substances increases, reduction in juice content, TSS and acid
content. Because of low sugar and acid content, the granulated
vesicles become rather tasteless and colorless.
.
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Causes:
Young, vigorous trees are more likely to develop granulated
fruits than older ones. Similarly, large fruits have moregranulation than small ones. In addition, granulation
increases as the picking season advances. The incidence of
granulation is highly specific to the type of the mandarin
being cultivated. It is favoured by high relative humidity
and temperature during spring.
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Remedy:
Spraying of lime.
Regulation of irrigation Applications of 2, 4-D (12ppm), zinc and
copper reduces
correct nutrition should be applied,
fruit should be harvested early.
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Decline
After fruitful production for about 15 years, orchards startbearing little crop and become uneconomical.
They show symptoms of ill health and decline. The affected trees
do not die completely but remain in state of decadence and
unproductiveness for a number of years.
Initially, only a few limbs of the plants are involved but later
whole tree is affected. Plants show sparse foliage, stunted
growth, and sickly appearance and in leaves, mid-rib, lateral veins
and intervenal area show diffused yellow color leading to
ultimate shedding of leaves.
As a result of dieback, twigs become short and bear only a few
narrow leaves at their basal ends. Such plants are also
characterized through excessive flowering and very poor fruit
set.
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Unfavourable soil conditions (presence of hard pan, high pH, poor
drainage and high salts), malnutrition, poor orchard management,
indiscriminate use of fertilizers, intercropping, incidence of insect
pests and diseases are major factors contributing to it.
Good cultural practices, improvement in soil fertility and drainage,
control of insect pests, nematodes and diseases may be useful to
minimize its incidence. Use of resistant and compatible rootstocks
and certified budwood for propagation are strongly recommended
for a healthy and productive mandarin orchard.
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Twig dieback
Along with leaves die and dry up on the
tree, gum appears in the wood. Leaves
drop, dry and there is no gum present.
In navel oranges some of the new shoots
developed during the early warm periods
wilt and die back later and stand out
among the green foliage of the tree.Spring twig dieback is often worse on the
western side of the tree.
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Causes:
Damage to the root system by fungi, nematodes,
salt injury, excessive fertiliser application and
periods of excessive dryness (Low soil temperatures, Low soil
moisture, Dry winds and low humidity, Frost injury)
Melanose fungus
If twig dieback has killed young branches, prune them out to avoid
fruit damage. To control twig dieback, maintain optimum soil watercontent, particularly in late autumn and winter.
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Fruit splitting
Fruit splitting is often seen in navel oranges, lemons and othercitrus fruits when temperatures drop and relative humidity
increases with the approach of winter. Splits occur longitudinally
starting at the navel end, where the rind is thinnest.
Causes: great climatic and soil moisture irregularities.
Internal pressure developed by the pulp causes the rind to split.
Regular application of fertiliser and water to provide smooth,
uninterrupted growth might reduce the problem.
foliar spray of potassium fertilizer (Tucker et al. 1994).
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Albedo breakdown or creasing
A major rind disorder of mature navel oranges in particular, but
other fruits can be affected. It shows up as an irregular patternof grooves and furrows in the rind, and is worse on the shaded
side of the fruit. Creasing is caused by excessive loss of
cohesion between albedo cells (the white layer under the skin)
stressed by expansion of the pulp.
Factors that may contribute are rind mineral levels (e.g. low
calcium or high magnesium), rootstock (higher incidence on
rough lemon), water relations, tree age, nutritional conditions
and tree health.
Creasing can be reduced with pre-harvest
sprays of gibberellic acid as well as
calcium sprays
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Sunburn
Sunburn of fruit is worse in varieties which produce their fruit on the
outside of the trees such as Murcott tangor, Afourer and Satsumamandarins. It can affect citrus trees in various ways, burning the
fruit, leaves and bark. It may be due to direct sunlight or hot drying
winds coupled with inadequate moisture uptake.To minimise sunburn, do not over-prune citrus trees and paint the
stems of young trees or exposed limbs with a white, water-based
paint.
navel orange with sunburn
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Winter yellowsWinter yellows is a disorder of citrus trees which is
common when good growing conditions continue
late into autumn.
Immature foliage goes yellow at the onset of cold weather, but re-
greens and develops normally with the return of warm weather in
spring. In some seasons it affects mature, functional leaves.
Winter yellows usually begins between late March and early April and
develops rapidly as the days shorten.
In severe cases the leaves may fall and there may be some out-of-season blossoming.
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Physiologically, the yellowed leaves have excess starch and the
root system is depleted of starch and parts of it may die.Once warmer temperatures and longer days set in, the tree
gradually recovers but it will be retarded if the root system has
been damaged.
Cause:
Unknown (may be the depleted carbohydrate reserves of the
root system)
Hickson mandarin and Eureka lemon are particularly susceptible
to winter yellows.
Remedy: discouraging late autumn growth of two to five year old trees
(reduce water and fertiliser)
leaving a few fruit on young trees to avoid excess vegetative
growth
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Use of growth regulators
Degreening: application of Ethrel (50ppm) one week before
the actual date of harvesting
Further, fruits dipped in 50 ppm Ethrel after harvesting
develop golden yellow color within 5 days of the treatment.
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New degreening treatments to improve the quality of citrusfruit combining different periods with and without ethylene
exposure Clemenules variety good colour with the lowest incidence
of calyx alteration, the optimum degreening treatment wasbased on 72 h with ethylene and 48 h without ethylenewhen fruit were harvested with a color index of between
9 and 3. Another treatment of 24 h with ethylene plus 48 h without
ethylene is recommended for fruit with an external colorindex higher than 2.
Navelina oranges, highly sensitive to calyx senescence
during degreening, a treatment consisting of 24 h withethylene plus 48 h without ethylene is recommended,which involves harvesting the fruit with a color index ofover 0.
Sdiri, et al., 2011
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Citrus clementine cv.Nules (a seedless mandarin) excellentquality for consumption as fresh fruit
Poor fruit set small-sized fruits.
gibberellic acid (GA3) as a foliar spray environmental
issues A trial with bioregulator containing methyl-xanthine,
Fruit yield was significantly increased in treated trees from17.4 to 25.7% for GA3 and MX treatments, respectively,compared to untreated control trees,
A single foliar application of MX was enough to increasefruit set.
Spray application of MX on clementine mandarins at theend of the flowering period, when all petals have fallen.
Ana Quiones, et al., 2011
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Methyl jasmonate and salicylic acid dips can
enhance the resistance of fruit to chilling
injury probably through an increase in
antioxidant levels.
Siboza et al., 2011
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Cropping system Sweet orange (Citrus sinensis (L) Osbeck Cv. Agege) on alfisol
in Nigeria.
Sweet orange + pineapple no fruits. (pH decreased by 2.17)
There was a build up of nitrogen (N) and organic carbon in the
soil for all the intercrops after the third year of the study. The cropping mixture with legumes highest N value of 0.70 g
N/kg soil as compared to 0.30 g N/kg pre-planting.
Sweet orange leaf analysis for N in all the treatments showed
that leaf N was higher than the 2.5-2.7% optimum level,except for citrus intercropped with cassava, which had a leaf
N concentration of 2.36%.
Olanyan and Fagbayide, 2007
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Sweet orange intercropped with maize/cowpea had thehighest phosphorus (P) level of 0.17%, , while sweet orangeintercropped with cassava or pineapple had the lowest Pvalues.
Potassium (K) was in the adequate range in the sweetorange leaves for all the cropping systems, but the Zncontent was below the satisfactory range of 20-50 ppm.
The nutrient dynamics were results of the interactionamong cropping systems, soil depth, and croppingcycle.
Maize intercropped in the early planting season followed bycowpea in the late season was the most compatible cropwith sweet orange in terms of fruit yield.
Olanyan and Fagbayide, 2007
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The results of 4 year study at coorg
there will be staggered income spread over 10
months in a year when coffee is grown withpepper, cardamom and coorg mandarin.
Mixed cropping also had a higher benefit-cost
ratio of3.10 as against 1.99 in case of mono-
cropping of robusta coffee
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Mites on lemonsshowingfruit bronzing symptom;
mealybugs
iron deficiencyleaf miner
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Scab symptoms on fruit Canker symptoms on leaves and fruit