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