Proc. Fla. State Hort. Soc. 108:51-53. 1995.

SUSCEPTIBILITY OF PURPLE BELL VINE TO CUCUMBER MOSAIC AND IMPATIENS

NECROTIC SPOT VIRUSES

V.Jones and GaryW. Simone

Florida Extension Plant Disease Clinic

Plant Pathology Department

University of Florida, IFAS

Gainesville, FL 32611-0830

Additional index words. Ornamental.

Abstract. The susceptibility of the tropical perennial, purple bell vine (Rhodochiton atro-sanguineum (Zucc.) Rothm.) to a range

of plant viruses was determined. Stock plants were obtained

commercially, indexed by direct or indirect enzyme-linked im-

munosorbent assay (ELISA) for tomato spotted wilt virus

(TSWV) and Impatiens necrotic spot virus (INSV) and main

tained in the greenhouse. Vegetatively propagated liners were

mechanically inoculated at the six to eight leaf stage with one

isolate each of nine viruses: cucumber mosaic (CMV), INSV,

pepper mottle, potato X, potato Y, tobacco etch, tobacco mo

saic, tomato mottle, and TSWV. Inoculated plants were exam

ined for symptoms on a weekly basis beginning 5 days after

inoculation. Plants were destructively sampled 6 weeks after

inoculation and assayed by direct ELISA, indirect ELISA, or nu

cleic acid hybridization using complementary DNA probes.

Purple bell vine was determined to be susceptible to both CMV

and INSV. CMV produced chlorotic local lesions and devel

oped systemically, causing leaf deformity, mosaic, exaggerat

ed leaf dentations, and marginal leaf chlorosis. INSV produced

chlorotic and necrotic local lesions and developed systemical

ly producing leaf deformity and flower symptoms consisting of

spotting, deformity, and reduction in size. TSWV did produce

local lesions in inoculated leaves but typically never went sys

temic within the plant. The other viruses tested did not infect

purple bell vine.

The purple bell vine (Rhodochiton atrosanguineum = R. vol-

ubile Otto & Dietr.) is one of many introduced species that

contribute to the attractiveness of Florida's landscapes. As

these species gain in popularity, they pose risks for the occur

rence of new plant diseases to Florida. A landscape sample of

this plant received in 1991 at the Florida Extension Plant Dis

ease Clinic reflected viral symptomatology. This was subse

quently determined to be infected by the Impatiens necrotic

spot virus (INSV=TSWV-I strain), a new host for this virus.

Plant disease literature on this host was non-existent at the

time (Alfieri et al., 1984; Farr et al., 1989; Thornberry. 1966).

We evaluated the susceptibility of this flowering ornamental

to a range of endemic Florida viral pathogens to anticipate

other viral diseases that might occur in nursery production or

landscapes with this species.

The genus Rhodochiton'^ a member of the Scrophulariace-

ae and represents an obscure genus of three species endemic

to Mexico. The purple bell vine is presently the only cultivat

ed species (Huxley et al., 1992). It is grown as a greenhouse

ornamental or a warm-season annual in the temperate areas

while being used as a perennial vine in south central and

south Florida. This vine is cold sensitive below 5°C (40°F).

The appeal of this flowering vine is in the purple-black flow-

Florida Agricultural Experiment Station Journal Series No. N-01209.

ers that consist of a lobed, rose-pink calyx and a blood-red to

maroon-colored corolla.

Materials and Methods

Purple bell vine liners were obtained from Logie's Green

houses (Davidson, CT 06329) in the fall of 1992. Liners were

grown in Metro-Mix 300™ (Scotts-Sierra Hort. Products Co.,

Marysville, OH 43041) in 5-inch pots as stock plants. Plants

were indexed serologically for both INSV and tomato spotted

wilt virus (TSWV) by commercially available direct enzyme

linked immunosorbent assays (ELISA) from Agdia, Inc.

(Elkhart, IN 46514). Plants were then vegetatively propagat

ed. Plant production and inoculation studies were performed

in a glass greenhouse under 3000-3500 foot candles and a

temperature range of 18°C (65°F) to 28°C (82°F).

Plants received overhead irrigation every 2 days and were

fertilized with a hose proportioner using Peters Peat-Lite Spe

cial (20-10-20) (Scotts-Sierra Hort. Products Co., Marysville,

OH 43041). The plants received weekly application of insec

ticides rotated among the tank-mix combination of acephate

(Orthene®) + dienochlor (Pentac®) + bifenthrin (Talstar®) or

kinoprene (Einstar II®) or diazinon (Knox-out®).

Nine viruses were chosen for a virulence evaluation by me

chanical transmission in Rhodochiton. Viruses used included

cucumber mosaic virus (CMV), pepper mottle virus (Pep-

MoV), potato virus Y (PVY), tobacco etch virus (TEV), potato

virus X (PVX), tobacco mosaic virus (TMV), tomato mottle vi

rus (TMoV), INSV, and TSWV. All viral isolates were endemic

to Florida, and were part of the Florida Extension Plant Dis

ease Clinic virus collection. All viruses were maintained in

desiccated host tissue over DrieriteR (W. A. Hammond Drier-

ite Co. Xenia, OH 45385) at -24°C (-6°F) except for TMoV,

INSV and TSWV. These viruses were maintained in living res

ervoir hosts: TMoV in Lycopersicon esculentumh., INSV in Impa

tiens balsamina L., and TSWV in Nicotiana tabacum L. cv. Burley

21.

Inoculum preparation for all viruses except TMoV in

volved mechanical transmission to one of two reservoir hosts.

Both TSWV and INSV were inoculated into Nicotiana

benthamiana. Mechanical transmission was achieved by dust

ing three leaves of each reservoir host with 320 grit carborun

dum. Virus-infected tissue (either dried or fresh tissue) was

ground in a mortar and pestle over ice at a 1:10 ratio of tissue

weight to volume of buffer. The buffer used was 0.5M potassi

um phosphate (pH 7.2), with 0.005% mercaptoethanol as a

reducing agent. The virus inoculum was rubbed onto the car

borundum-coated leaves with sterile fabric interfacing. Reser

voir hosts were allowed to become systemically infected and

then were checked by light microscopy for appropriate plant

virus inclusions as a test of identity and purity.

Inoculations of Rhodochiton were conducted in the spring

of 1993. Four to eight plants were inoculated across six to

eight leaves per plant by the procedure described previously.

A known susceptible host was inoculated with each virus as a

positive control. Plants rubbed with buffer alone served as a

negative control. Plants were observed daily for local lesion

development and the onset of systemic infection. Plants were

destructively sampled 6 weeks after inoculation. Plants were

Proc. Fla. State Hort. Soc. 108: 1995. 51

subsampled to include roots, lower stem, inoculated leaves, new leaves, flowers (if present) and the shoot meristem to de termine virus location.

The presence of the virus was verified by one of three

methods. TMoV samples (20ul) were extracted in 40ul of

TRIS(10mM)/EDTA(lmM) buffer (standardized to pH=8.0). Plant sap was spotted onto a nitrocellulose mem

brane and probed with a P32 labelled complementary DNA

probe for TMoV (courtesy of E. Hiebert, Plant Pathology

Dept, Univ. of Fla., Gainesville). Both TSWV and INSV were

assayed by direct ELISA. The remainder of the viruses were as

sayed by indirect ELISA, using virus-specific antisera and alka

line phosphatase conjugated goat anti-rabbit antisera (Sigma

Chemical Corp., St. Louis, MO 63178-9916). Both direct and

indirect ELISA were conducted in 96-well microtitre plates and results were read with a Molecular Devices Emax Reader

(Molecular Devices Corp. Menlo Park, CA 94025).

Results and Discussion

The following viruses were unable to infect Rhodochiton at

rosanguineum: PepMoV, PVX, PVY, TEV, TMoV and TMV. Se-

rological assays yielded no evidence of virus replication and

movement into this host (data not presented).

Plants inoculated with INSV developed chlorotic local le

sions on inoculated leaves within 7 to 10 days. These lesions

enlarged into necrotic ringspots within 2 weeks. The virus

moved rapidly in the plant. Symptoms of necrotic flecking,

leaf malformation, and ringspots developed in systemically in fected tissues 3 to 7 days after local lesions (Fig. 1). Flowers

produced on infected plants were reduced in size, with dis

torted, necrotic corollas (Fig. 1). Systemic symptoms were not

consistent on all branches from an infected plant. After 6

weeks, plants were rinsed free of soil and sequentially sam

pled from the roots to the shoot meristem to determine the

virus distribution within the plant. A sample stratification of

two plants using ELISA is presented in Table 1. Shaded data

squares represent positive absorbance values that indicate the

presence of this virus in specific plant samples. The virus had

proceeded from the inoculated leaf throughout the plant.

Note the absence of virus in the lower stem node (below inoc

ulation point) and the absence from Vine A leaves 2 and 3.

This erratic distribution is characteristic for both INSV and

TSWV in their respective hosts.

The inoculation of TSWV typically failed to proceed sys

temically in any experimental unit. Inoculated leaves did de

velop small, necrotic local lesions within 2 weeks. A plant

stratification is presented in Table 1. TSWV could be detected

in the inoculated leaf and in this atypical instance, one leaf

immediately above this point at the time of destructive sam

pling. In all other TSWV-challenged plants, this virus was se-

rologically detected in only the inoculated leaf. Repeated

tests failed to show any TSWV movement after inoculation,

therefore Rhodochiton is considered a non-host for TSWV.

Rhodochiton plants challenged with CMV were systemically

infected. Local lesions developed as chlorotic spots within 7

days of inoculation. Inoculated leaves abscised within 2 weeks.

Systemic infection was evident within 14 days. Typical symp

toms of systemic CMV infection in Rhodochiton included leaf

distortion, exaggerated leaf dentation, mosaic and broad ar

eas of marginal chlorosis (Fig. 2). Systemically infected plants

bore no flowers during the experimental period. Two strati

fied, CMV-infected plants are presented in Table 2 in contrast

Figure 1. Symptoms induced by Impatiens necrotic spot virus (INSV) in

purple bell vine. (A) Chlorotic concentric ring spotting in leaves. (B) Flower

distortion induced by INSV compared to healthy flowers (far right and left).

Table 1. Distribution of tomato spotted wilt virus (TSWV) and Impatiens

necrotic spot virus (INSV) in Rhodochiton atrosanguineum 6 weeks after inoculation.

Plant tissue

Crown roots

Lower stem

Inoculated leaf

Vine A-leaf 1

-leaf 2

-leaf 3

Vine B-leaf 1

-leaf 2

-leaf 3

-flower

INSV

2.049*

0.087

1.684

0.164

0.089

0.079

2.027

L922

2.172

1,242

Direct ELISA stratification

TSWV

0.064

0.059

2,010

1.556

0.086

0.057

0.061

0.065

0.062

0.064

HEALTHY

0.068

0.085

0.065

0.078

0.069

0.077

0.067

0.067

0.074

0.085

'Shaded data squares represent positive ELISA absorbance values that indi cate the presence of virus.

to a healthy control plant. CMV did not proceed uniformly

throughout the plant and thus some leaf positions were with out detectable virus.

Rhodochiton atrosanguineum has been determined to be a

new host for INSV and for CMV in Florida. This plant must be

recognized as a potential reservoir host for these viruses in

nurseries producing both floral and bedding plant species.

The perennial nature of this vine in south Florida provides an

52 Proc. Fla. State Hort. Soc. 108: 1995.

Figure 2. Leaf deformity, marginal chlorosis and mosaic caused by cucum

ber mosaic virus in purple bell vine.

opportunity for this species to act as a reservoir host for both

these viruses in the landscape as well.

Literature Cited

Alfieri, S. A. Jr., K. R. Langdon, C. Wehlburg and J. W. Kimbrough. 1984. In

dex of plant diseases in Florida. Bulletin 11. Fla. Dept. of Agr. Consumer

Services, Div. Plant Industry. Gainesville, FL.

Table 2. Distribution of cucumber mosaic virus (CMV) in Rhodochiton atro-

sanguineum 6 weeks after inoculation.

Indirect ELISA stratification

CMV

Plant tissue Plant 1 Plant 2 HEALTHY

Roots

Roots

Lower stem

Inoculated leaf

Vine A-leaf 1

-leaf 2

-leaf 3

Vine B-leaf 1

-leaf 2

-leaf 3

Shoot apex

1.228*

0.735

1:124

0.576

0.156

L661

0.548

1.128

2.158

1.799

L952

1.493

1.048

0.214

0.420

0.160

2.081

0.114

0.142

0.175

0.273

—

0.136

0.137

0.106

0.156

0.151

0.126

0.120

0.136

0.112

0.112

0.127

'Shaded data squares represent positive ELISA absorbance values that indi

cate the presence of virus.

Farr, D. F., G. F. Bills, G. P. Chamures and A. Y. Rossman. 1989. Fungi on

plants and plant products in the United States. APS Press. St. Paul, MN.

Huxley, A., M. Griffiths and M. Levy (eds.). 1992. The new Royal Horticultur

al Society dictionary of gardening. Vol. 4. Macmillan Press Ltd. London,

England.

Thornberry, H. H. 1966. Plant pests of importance to North American agri

culture. Index of Plant Virus Diseases. HndBk. 307. U.S. Dept. of Agr.,

Washington, D.C.

Proc. Fla. State Hort. Soc. 108:53-57. 1995.

PREEMERGENCE WEED CONTROL IN TUBEROSE1

James P. Gilreath

Gulf Coast Research and Education Center

University of Florida, IFAS

Bradenton, FL 34203

Additional index words. Herbicide, tuber, Polianthes tuberosa.

Abstract. Thirteen preemergence herbicides were evaluated for

crop response and weed control in tuberose (Polianthes tube

rosa L.) grown in flatwoods soil. Each herbicide was applied

twice during 1986 and four times in 1987. Plots were hand-weeded weekly during 1986 to evaluate herbicide effects,

whereas herbicide treated plots were handweeded only prior to

each application in 1987 to evaluate weed control as well as

herbicide effects. Oxyfluorfen and thiobencarb were injurious

to tuberose when applied pre- or postemergence in 1986,

whereas methazole and clomazone only damaged plants when

applied postemergence. Tuberose plant vigor was not affected by herbicide treatment until after three applications of herbi

cide in 1987 at which time only those plants treated with prodi-

amine or oryzalin were as vigorous as plants in handweeded

Florida Agricultural Experiment Station Journal Series No. N-01108.

Mention of a specific proprietary product does not constitute an endorse

ment by the author or the University of Florida. Growers should consult the

label before application of any herbicide.

plots. Crabgrass (Digitaria ciliaris (Retz.) Koel.) control was

generally excellent with all treatments, except methazole, oxy

fluorfen, and thiobencarb. Control of eclipta {Eclipta alba L.)

was good with all herbicides until after the third application

when only napropamide, methazole, clomazone, and oryzalin

controlled eclipta as well as handweeding. After four applica

tions of herbicide treatments, napropamide no longer con

trolled eclipta as well as handweeding; whereas, methazole,

clomazone, and oryzalin continued to control eclipta as well as

handweeding.

Plots treated with cinmethylin, prodiamine, and oryzalin pro

duced as many flowers and equivalent flower weight as hand-

weeded plots. Foliage production was similar to spike

production with the exception that less biomass was produced

with cinmethylin than with handweeding. More tubers were

produced in plots treated with cinmethylin, DCPA, clomazone,

and oryzalin than with napropamide in 1986. Prodiamine, di-

ethatyl, and oryzalin were the only herbicides which produced

more tubers than the nontreated control plots (weedy) in 1987.

Oryzalin, prodiamine, clomazone, and alachlor produced as

many medium to large size tubers as handweeding.

Tuberose, grown for both flowers and tubers, has never

been a large acreage cut flower crop in Florida, in part due to

production problems. Historically, weed control has been

one of the predominant production problems. Although

some weed control research has been conducted (W. Skroch,

personal communication), no published reports have been

Proc. Fla. State Hort. Soc. 108: 1995. 53