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404 FLORIDA STATE HORTICULTURAL SOCIETY, 1972
attractancy of bacteria cultures to Anoetus was
consistent with previous tests.
Discussion
The soil-inhabiting, saprophytic mites Anoetus
feroniarum and Rhizoglyphus robini can survive
and reproduce on several fungi and bacteria com
monly associated with Gladiolus hortulansus. Anoe
tus is strongly attracted to bacterial cultures of
Pseudomonas marginata and Pseudomonas mar-
ginalis. Rhizoglyphus prefers Fusarium oxy-
sporum.
The fact that mites are attracted to selected
phytopathogens may be important in elucidating
possible disease-vector relationships of gladiolus
in Florida. The demonstrated affinity by Anoetus
for bacterial cultures, in particular the pathogenic
isolate P. marginata Br-1, suggest that the vector
capabilities of this mite should be investigated.
Conversely, the demonstrated affinity by Rhizo
glyphus for Fusarium cultures, and not bacterial
cultures, does not readily relate to published re
ports implicating Rhizoglyphus mites as vectors of
the causal organism of bacterial scab, P. margin
ata. It should be pointed out that the species of
Rhizoglyphus used in these experiments is not
the same as reported by Forsberg (3, 4) to be a
vector of P. marginata. Species, or even clonal,
variation in preferences for certain disease-causing
organisms should be investigated.
As noted in Experiments 3, 4, 5, hypopal
populations of Anoetus were the most migratory
and best stage by which to test attractancy of
cultures. The hypopus is a non-feeding migratory
form resistant to, and apparently formed as a re
sult of environmental stress. They are transported,
or will migrate, to areas of higher nutritional
levels and lower environmental stress before com
pletion of life cycle (6, 8). Since both Rhizogly
phus and Anoetus have a hypopal state in their
life cycle, the importance of this stage relative
to their suggested vector roles demands further
study.
Literature Cited
1. Bald, J. G. and R. N. Jefferson. 1952. Injury to gladioli associated with the root mite, Rhizoglyphus rhizo-phagus. Plant Dis. Reptr. 36: 435-437.
2. Englehard, A. W. 1969. Bulb mites associated with diseases of gladioli and other crops in Florida. Phytopath ology 59: 1025 (Abstr.).
3. Forsberg, J. L. 1959. Relationship of the bulb mite Rhizoglyphus echinopus to bacterial scab of gladiolus. Phy topathology 49: 539 (Abstr.).
4. . 1965. The relationship of Pseu domonas marginata, Stromatinia gladioli, bulb mites, and chemical soil treatments to the occurrence and control of scab and Stromatinia rot of gladiolus. Phytopathology 55: 1058 (Abstr.).
5. Lelliott, R. A., Eve Billing, and A. C. Hayward. 1966. A determinative scheme for the flouorescent plant patho
genic pseudomonads. J. Appl. Bacteriol. 29: 470-489. 6. Poe, S. L. 1966. A study of certain factors influencing
hypopial transformation in Caloglyphus boharti (Acarina: Tyroglyphidae) M. Sc. Thesis, Northwestern State College, Natchitoches, Louisiana.
7. 1971. Microfaunal populations on gladiolus corms. The Florida Entomologist 54: 127-133.
8. Woodring, J. P. 1963. The nutrition and biology of saprophytic sarcoptiforms. In Advances in Acarology. J. A. Naegele (ed). 1: 89-111.
9. Yoshizawa, T., I. Yamamoto, and R. Yamamoto. 1971. Synergistic attractancy of cheese components for cheese mites, Tyrophagus putrescentiae. Botyu-Kagaku. 36: 1-7.
SEED PROPAGATION OF CALADIUM AND DIEFFENBACHIA
R. D. Hartman and F. W. Zettler
I FAS Plant Pathology Department
Gainesville
and
J. F. Knauss and Eleanor M. Hawkins
IF AS Agricultural Research Center,
Apopka
Abstract. Aroids do not ordinarily set seed
under natural conditions in Florida and hence are
commercially propagated by vegetative means.
However, producing seed provides a means of ob-
Florida Agricultural Experiment Stations Journal Series
No. 4615.
taining pathogen-free plants as well as new hy
brids. Through cross pollination, viable seed of
caladium (Caladium hortulanum Birdsey) and
dieffenbachia (Dieffenbachia picta Schott) were
obtained. Each fertilized caladium ovary con
tained < 14 seeds whereas dieffenbachia ovaries
were single-seeded. Caladium fruits ripened 5-6
weeks after pollination and abscissed from the
spadix. Dieffenbachia fruits became red upon
ripening 10-12 weeks after pollination, but re
mained loosely attached to the spadix. Seed of
both species germinated readily when removed
from the fruit and planted in moist peat.
Plants of the family Araceae comprise a sub
stantial proportion of the ornamentals produced
HARTMAN ET AL.: CALADIUM AND DIFFENBACHIA FROM SEED 405
commercially in Florida. Approximately 96% of
the world's commercially produced caladiums are
grown in Florida (7), and aroids such as aglao-
nema, dieffenbachia, philodendron, pothos and syn-
gonium account for nearly half of the State's
foliage industry (9). In addition, Ci*yptocoryne
spp. are aroids of considerable significance to Flor
ida's unique aquarium plant industry. Aroids are
propagated commercially almost exclusively by
vegetative means rather than by seed.
Various nematodes, bacteria and fungi infest
avoid nursery plantings in Florida and cause
serious economic losses. In addition, a virus of
aroids called dasheen mosaic virus has been
shown to be widespread in Florida and elsewhere
(1, 3, 11). Hartman and Zettler (5) surveyed
foliage nurseries and caladium plantings in Florida
and provided evidence that certain mainstay dief
fenbachia and caladium cultivars are uniformly in
fected with dasheen mosaic virus and hence virus-
free plants are no longer available. Such wide
spread incidence of disease among aroids is abetted
by propagating these plants vegetatively. As
pointed out by Baker (2), relatively few plant
pathogens are seed-bome, and thus, seed propa
gation provides a useful means of eliminating phy-
topathogens that have proliferated in vegetative
material. Calla lily, for example, is an aroid that
can be grown free of soft-rot bacteria, water molds
and Rhizoctonia infections by planting seed rather
than corms (2).
Despite the considerable potential of seed propa
gation as a method to rid aroids of phytopathogens
and to create new horticultural varieties, most
Florida growers are not aware of the techniques
involved in producing aroid seed. A notable excep
tion is the hybridization of philodendrons as de
scribed by McColley and Miller (8) and by West
and Miller (10). Caladium growers once were
supplied with new caladium hybrids by Mr. Frank
M. Joyner, a caladium hobbyist from Tampa, but
he has become inactive in recent years and this
work has since received no attention. Dieffenbachia
species were once hybridized at the turn of the
century, but are no longer grown from seed; thus
growers must rely upon chance somatic mutations
for new cultivars. As indicated by McColley and
Miller (8), special techniques must be employed
to obtain seed of many aroids. Unfortunately the
paucity of published reports on the specific hy
bridization techniques for aroids deters growers
from using seed propagation as a useful and im
portant tool. Accordingly, this study with dief
fenbachia and caladium was conducted.
Materials and Methods
The crosses were made between plants of
Dieffenbachia picta (Schott) 'Exotica' or Calad
ium hortulanum (Birdsey) 'Candidum.' The pa
rental stock used in these crosses was provided
by Mr. Lamont Marchman of Evergreen Gardens
of Apopka, Inc. and Mr. Norman Hickerson of
Hickerson Flowers, Inc., of Apopka, Florida. Dief
fenbachia plants were grown in a stock bed in a
fiberglass house at Apopka and pollinated May-
June, 1971, whereas caladiums were grown in
Gainesville either in a greenhouse or outdoors and
pollinated May-June, 1972. The pollination pro
cedures were similar to those described by McCol
ley and Miller (8) for philodendron. All crosses
were made between 6-10 a.m. or 5-8 p.m. Caladium
and dieffenbachia like philodendron are dicho-
gamous. Pollen was collected daily with a camel-
hair brush and transferred within 48 hours after
shedding to neighboring receptive blooms of differ
ent plants. Bloom receptivity was indicated 1)
when the spathe began to unfurl revealing the dis
tal portion of the spadix and 2) by the increased
stickiness of the stigmatic surfaces of the spadix.
Prior to pollination, the spathe was cut away from
the spadix, discarded, and the pollen was gently
applied to the proximal ovulate portion of the
spadix with a brush.
Results
Dieffenbachia fruits, although cream colored
during most of their development, became red when
ripe approximately 10-12 weeks after pollination.
Dieffenbachia fruits did not abscise but remained
loosely attached to the spadix (Fig. 1). A spadix
bore 15-30 ovaries, each containing a single round
seed 5-6 mm in diameter which was green when
mature. Seeds germinated within 20 days after
they were removed from the fruit and planted in
moist peat.
Unlike dieffenbachia, caladium fruits ripened
5-6 weeks after pollination and abscissed from the
spadix (Fig. 2). The exposed fruit surfaces re
mained green throughout their development with
out apparent color change at the time of abscission.
The unexposed surfaces of the ovary walls were
cream-colored at maturity. Ovulate portions of the
spadix contained approximately 200 seed-bearing
ovaries, each containing 1-14 oval seeds which
were 1-1.5 mm in length and light tan in color.
As many as 1500 seeds were obtained from a
single spadix. Seeds germinated readily 8-10
days after removal from the fruit and planting
406 FLORIDA STATE HORTICULTURAL SOCIETY, 1972
Fig. 1. Dieffenbachia spadix. A) during pollen shed. B) developing fruit 5-6 weeks after pollination. C) mature fruit 10-12 weeks after pollination.
Fig. 2 Caladium spadix. A) at time of pollination. B) distal portion during pollen shed. C) proximal portion just prior to fruit abscission. D) shed fruit at abscission 5-6 weeks after pollination.
HARTMAN ET AL.: CALADIUM AND DIFFENBACHIA FROM SEED 407
B Fig. 3. Dieffenbachia seedlings 12 months after germination. Note differences in foliar variegation patterns (A) and
in degree of shoot proliferation (B).
408 FLORIDA STATE HORTICULTURAL SOCIETY, 1972
them in moist peat. Seed germination rate de
creased markedly, however, when seeds were
dried and stored 2 weeks at 23 C and 53% rela
tive humidity.
Seedlings were maintained in a greenhouse at
about 60% shade in isolation from commercial
aroid stock. Plants were transferred from peat to
a steam-sterilized soil/perlite mix contained in
clay pots and treated routinely with a liquid formu
lation of 20-20-20 fertilizer.
Although parental 'Exotica' dieffenbachia and
'Candidum' caladium plants used in this study were
virus infected as evidenced by symptoms observed
at the time of pollination, none of the more than
500 resulting dieffenbachia and 1000 caladium
progeny displayed virus symptoms, indicating that
the seedlings were virus free.
A small percentage of the dieffenbachia seed
lings exhibited albinistic tendencies and died
shortly after germination. The juvenile foliage of
the surviving dieffenbachia progeny was nonvarie-
gated and variegated leaves did not develop until
4-8 months after germination. Similarly, juvenile
leaves of caladium were homogeneously green and
variegated leaves did not develop until about 3
months after germination.
A year after germination a marked variation
was noted among the 207 randomly selected dief
fenbachia seedlings which had grown to 30-34 cm
in height. Fifty-three of the progeny exhibited
none of the white variegation typical of the 'Exoti
ca' parents. The foliar patterns of the remaining
progeny varied from those having relatively local
ized areas of white to those having white patterns
exceeding in area that of the original parents
(Fig. 3a). A few plants exhibited a degree of
yellow foliar coloration unlike the 'Exotica' parents.
Marked differences in leaf shape and apical dom
inance were also noted among the progeny. Where
as some of the leaves had dimensions similar to
those of the parents, others were somewhat more
lanceolate. Apical dominance was expressed when
axillary buds of some progeny grew only after the
apical meristem was removed, whereas the axillary
buds of other progeny proliferated regardless of
the presence or absence of the apical shoot (Fig.
3b).
Discussion
Our results indicate that seed of dieffenbachia
and caladium can be readily obtained and that the
progeny, unlike the parents, appeared free of virus
and other phytopathogens. Our results with dief
fenbachia further suggest a rich but ignored
genetic potential for deriving improved horticul
tural varieties. A need exists for "color" among
foliage plants such as that provided by the golden-
green variegated pothos. A concerted breeding pro-
grad with species of Dieffenbachia could enrich the
industry by infusing it with such color, as this
study suggests.
The genetic potential of caladiums has been
amply demonstrated in the 2000 or more named
varieties developed by earlier workers such as
Nehrling, Mead, Leitze and others (6). Neverthe
less, most of these evaluations have been based
upon foliage characters. Incorporation of other
factors such as bulb size and cold-hardiness could
be considered in a selective breeding program as
well.
In a competitive market the value of develop
ing new hybrids is self-evident. What may be more
significant, but less obvious, is the means that
seed propagation provides to rid planting stock
of serious plant pathogens. However, when a patho
gen-free plant is placed in a nursery environment,
it will eventually become infected with the phyto
pathogens which plague the parental plants. There
fore, once a desirable hybrid is obtained, a certifi
cation program should be enacted to maintain and
propagate pathogen-free plants. These plants could
act as a mother block from which propagating ma
terial would be obtained for nursery production.
The technique of meristem-tip culture provides a
means of rapid propagation and maintainence
of plants in a sterile environment and would be an
important facet of a certification program. Meri
stem-tip culturing procedures have been estab
lished for caladiums and have proved useful as a
means of rapid propagation and maintenance of
disease-free plants as well as a means of obtaining
pathogen-free plants of established cultivars (4).
Literature Cited
1. Alconero, R. and F. W. Zettler. 1971. Virus infections
of Colocasia and Xanthosoma in Puerto Rico. Plant Dis. Reptr. 55:506-508.
2. Baker K. F. 1957. The U. C. system for producing healthy container grown plants. California Agrr. Exp. Sta.
& Ext. Service Manual 23. 332 pp.
3. Gollifer, D. E. and J. F. Brown. 1972. Virus diseases of Colocasia esculenta in the British Solomon Islands. Plant Dis. Reptr. 56:597-599.
4. Hartman, R. D. and F. W. Zettler. 1972. Mericloning as a potential means of obtaining virus free plants from
aroids commercially produced in Florida. Proc. Fourth Org.
Soil Vegetable Crops Workshop 60-62. 5. and F. W. Zettler. 1972. Dasheen
mosaic virus infections in commercial plantings of aroids in Florida. Phytopathology 62:804. (Abstr.).
6. Hayward, W. 1950. Fancy-leaved caladiums. Plant Life 6:131-142.
7. Holms, L. L., J. Hendry, L. Tubbs. A. L. Hall, and D. Dittmar. 1965-75. Caladium Bulbs, Highlands County DARE Rep. 11 pp.
8. McColley, R. H. and H. N. Miller. 1965. Philodendron
NEEL: WEED CONTROL IN CONTAINERS 409
improvement through hybridization. Florida State Hort. Soc. Proc. 78:409-415.
9. Waters, W. E. 1969. The ornamental horticulture in dustry of Florida and its implication to production in tropical Americas. Trop. Regional Proc. Amer. Soc. Hort.
Sci. 13:1-8.
10. West, E. and H. N. Miller. 1956. Some notes on philo-dendron hybrids. Florida State Hort. Soc. Proc. 69:343-347.
11. Zettler, F. W., M. J. Foxe, R. D. Hartman, J. R. Edwardson, and R. G. Christie. 1970. Filamentous viruses infecting dasheen and other araceous plants. Phytopathology
60:983-987.
WEED CONTROL IN CONTAINERS WITH HERBICIDE-
IMPREGNATED MULCH MATERIALS
P. L. Neel
IF AS, Agricultural Research Center
Fort Laudardale
Abstract. Four herbicides (Dacthal, simazine,
Treflan, Lasso) incorporated into two types of
mulch materials (potting soil or pine bark chips)
at rates of 0, 1, 2, 4, and 8 times (x) those recom
mended on soils high in organic matter were ap
plied in a % inch deep surface layer to "gallon"
(6*4") containers of newly rooted cuttings of
Gold Dust Croton (Codiaeum variegatum L.).
Tests were conducted from October 2, 1971 to
May 2, 1972, at the ARC, Ft. Lauderdale, Florida.
Visual evaluations were made at 2, 4, 8 and
28 weeks. No phytotoxicity was observed from
any treatment. Weed control initially (2-4 weeks)
was good with each herbicide except Dacthal when
soil incorporated. After 8 weeks weeds were
noted in the 1 and 2x rates of both simazine and
Treflan soil incorporation treatments. After 28
weeks excessive weed growth was found in every
soil-incorporation treatment except the 2, 4, and
8x rates of Lasso and the 8x rate of Treflan.
Pine bark chips alone reduced weed growth
up to 8 weeks, with higher rates of bark-incorpo
rated Lasso and Treflan providing control at 28
weeks.
Controlling weed growth in container grown
nursery stock is a major expense, with up to 30%
of the cost of production attributable to weed con
trol with hand labor. There are a number of good
herbicides on the market for use in field crops,
but they have been used to a limited extent in
container operations. Many are not even labeled
for use on container grown ornamental plants.
This is due to several factors including difficulties
in controlling rates of application, plant sensi
tivity and the limited root volume of plants in
Florida Agricultural Experiment Station.
containers. Tolerances of plants in containers and
methods and rates of application should be in
vestigated to determine the best approach to the
problem (1, 3).
Herbicide activity and movement in the soil
is greatly influenced by organic matter in the
mix, with high organic matter soils usually re
quiring more chemical for a given amount of
activity than a mix low in organic matter. Thus
work done with one soil mix may not be applicable
on another, although it may serve as an indicator
of what to expect. (3).
Perhaps the simplest way to apply herbicide
is through a sprinkler system. Because the herbi
cide must cover surface of the soil for full effect,
its application through a Chapin system is not
feasible since the rate of water application through
such a system is insufficient to cover the soil sur
face. Uniformity and irrigation rate of sprink
lers are quite variable. Also, the plant itself may
shield a portion of the soil from direct contact
with the herbicide in the water. These factors
either reduce the margin of safety or reduce
(the potential for) weed control. A variation of
sprinkler irrigation application would be applying
herbicide by spraying, or watering with a hose,
but again rate of application would be subject to
considerable variation depending on methods used
and the technique of the applicator.
Herbicides may be applied as granular formu
lations, which gives more control of rate, but com
plete coverage of the soil surface is still a limiting
factor. Of added concern is the possibility that
granules might be washed down the sides of the
container if soil shrinkage occurs between
waterings.
Use of an herbicide-impregnated mulch should
eliminate these problems. Good coverage of the soil
surface at a fairly uniform rate of application
could be obtained. In addition, the mulch material
can materially reduce weed growth and loss of
water, and keep the soil cooler than exposed soil.
Fiber disks placed on top of the soil employ the