Blackeye Cowpea Mosaic Virus (BICMV) in Yard-Long Bean in the Mariana Islands

Micronesica

dpe i te ain Ilns n i ieygon o lcl ua consump human local for grown widely is and Islands Mariana the in adapted to og en smr pplr eas i rw bte a lwr elevations. lower at better grows it because popular more is bean long in Atog cmo sa bean snap common Although tion.

et al. 1990, al.Wall et ee h ms peaet ies polm o adln ba o Ga. n early In Guam. on bean yard-long of problems disease prevalent most the were

aphids; therefore a virus was suspected. Identification was essential for its control.its for essential was Identification suspected. was virus a therefore aphids; h proe fti suy a t ietf te asl gn o h msi disease, mosaic the of agent causal the identify by to was and study this of mechanically purpose The transmitted was mosaic of agent causal the 1988 in tests n t sre yr-og en aite fr eitne o it. to resistance for varieties bean yard-long screen to and

92.Tdy rp o adln ba hv ihicdne fmsi (Kimmons mosaic of incidence high a have bean yard-long of crops 1922). Today

Vigna unguiculata

Abstract-A

aprgs en ryr-og en wsdtrie vahs rne stud range host via determined was bean) yard-long or bean (asparagus e,rn itrae n PSEIA et o ecnitn wt te black the with consistent be to tests PAS-ELISA and interface ring ies, y opa oac iu (lM) Sp ncltos f 9lgms re legumes 39 of inoculations Sap (BlCMV). virus mosaic cowpea eye a tasitd y apterous by transmitted was Seed species. non-legume 24 of 9 did as infected, becoming 31 in sulted

rnmsin curd n3%o adln ba sestse. h virus The tested. seeds bean yard-long of 37% in occurred transmission motn co pat ifce icue sa bas wne ba, and bean, winged beans, snap included infected plants crop important a bas iaa.Ti i h frt eot f IM o wne bean winged on BICMV of report first the Other is This Gicama). BlCMV. beans with yam consistent are transmission aphid and Seed ion.

ee ug en n sunnhemp and bean mung were Pohcru tetragonolobus. (Psophocarpus

etd ih a-nclto, oe hwd eitne Clia Gen Ar Green Cultivar resistance. showed none sap-inoculation, with tested row (Known-You Seed Co Seed (Known-You row and high yields in field tests over 2 seasons. 2 over tests field in yields high and

adln ad saau ba ae w o te ay omn ae given names common many the of two are bean asparagus and Yard-long

eot o oac ies fba o um ae ak o 1921 to(Anonymous back date Guam on of bean disease a ofmosaic Reports

Blackeye Cowpea Mosaic Virus (BICMV) in Yard-long Bean

rsn drs: ot I Route address: Present

G. C. G.

29(2)

101 111, 1996 111, 101

WALL,

oac ies of disease mosaic

imn 19) na18 uvy oac n odr mildew powdery and 1988 mosaic 1991). a survey, In Kimmons

(L.)

ap subsp Walp.

KIMMONS

AES/CA

o 0,Wiwl,T 37397 304, BoxWhitwell, TN

e-mail: gwall@uog9 e-mail:

the Mariana Islands

Mangi/ao, GU 96923 GU Mangi/ao,

efre wl ih o ies incidence disease low with well performed)

pi craccivora Aphis

S Uiest f Guam of University LS.

Introduction

te ls motn co pat infected plants crop less important Other

Paels vulgaris (Phaseolus

in unguiculata Vigna

sesquipedalis

f lvn adln ba cultivars bean yard-long eleven Of .

ICO AND WIECKO

uog.edu

n nnpritn fash non-persistent a in

(L.)

subsp.

Verde

L.)

RICHARDSON

sas gon yard grown, also is

sesquipedalis The species is specieswell The I

(0.05M

Chenopodium

cv Local Red. Infected Nicotiana benthamiana

hrs. Control plants re

4-6

indirect ELISA (Edwards Coo &

)

sesquipedalis

and lesionwasused a to single inoculate

or by PAS-ELISA.

subsp.

SEROLOGY

HOST RANGE

VIRAL ISOLATION

Micronesica 29(2), 1996

Koch from virus-free cultures were starved for

APHID TRANSMISSION

Materials and Methods and Materials

pH 9.6) for 2 hr at 28 C. Plates were rinsed 4 times

, MECHANICAL TRANSMISSION

amaranticolor, amaranticolor

unguiculata

Reyn., a local lesion host. Three successivesingle-lesion

PBST were then added and incubated overnight at 4 C.

Coste

Aphis craccivora

plus NaNO0.02%

Leaves of yard-long bean plants exhibiting mosaic symptoms collected were

Sap from inoculated symptomatic plants was used to inoculate

Three to eight test plants each of 63 accessions comprising several species

Apterous

Assays of raw sap were carried out by Protein A sandwich ELISA (PAS Polystyrene microtiter plates (Dinatech, McLean, VA) firstwere coated with

102

from the farm of A. Manibusan in Mangilao, Guam, and used to inoculate 7-

leaves were trituratedwereleaves in mortar and pestle with phosphate buffer, pH Leaves 7.9. of test seedlings were dusted with carborundum and mechanically inoculated. day-old seedlings of Plants were then grown in aphid-proof cages in a greenhouse along with control plants, which had not been inoculated.

amaranticolor transfers made were on 7-day-old of seedlingsyard-long bean cv Local Red. The isolate single-lesion was

propagated and maintained in yard-long bean and in Domin.

and varieties were sap-inoculated as above, using young systemically infected leaves of yard-long bean. Plants maintained were in a screenhouse. All tests were repeated at least twice. After 24-30 days, test plants were indexed for infection by back-inoculation to

aphids per plant, for inoculation-feeding periods of hr, then togiven sec30 2 min acquisition on access symptomatic yard-long bean. ceived aphids from asymptomatic plants. Aphids then were transferred to healthy 8 7-day-old yard-long bean five seedlings,

ELISA). This procedure, also known as F(ab per Reddick 1985, et al. was modified. 1991) The procedure was as follows.

protein A (Sigma Chemical Co.) diluted 1:1000 in carbonate buffer saline plus Tween 20 (PBST). Antiserum was added in a 1000 dilution 1: with (all subsequent rinses were done in the same manner), with phosphate buffered Na PBST. Plates were incubated again for 2 hr at 28 C, then rinsed again. Test sam ples extracted in 1 the morning they were again rinsed. Antiserum was again added as before, and

was changed to 1: 1: 10. to changed was

inoculated; initially a 1 :5 sap to buffer ratio was used. In a second trial, the ratio ratio the trial, second a In used. was ratio buffer 1 to a sap :5 initially inoculated;

potting mix, with with mix, potting

Takii & Co., Japan (TR). Seedlings were grown in 5 cm diameter pots, in sterile sterile in pots, diameter cm 5 in grown were Seedlings (TR). Japan Co., & Takii

You Greenpod Kaohsiung Kaohsiung Greenpod You

Guam (MG), Local White, A. Manibusan (MW), and Extra Long Red Seed from from Seed Red Long Extra and (MW), Manibusan A. White, Local (MG), Guam

from from

(BU), Local Red, collected from J. Meno, Malojloj, Guam (LR), Local Black, Black, Local (LR), Guam Malojloj, Meno, J. from collected Red, Local (BU),

tance to the mosaic disease. Varieties tested were: Ferry Morse Asparagus bean bean Asparagus Morse Ferry were: tested Varieties disease. mosaic the to tance

(FA), Surinam (SU), Burpee Asparagus bean (BA), Local Bush or Dwarf bean bean Dwarf or Bush Local (BA), bean Asparagus Burpee (SU), Surinam (FA),

is tu la sae y A-LS. h ts ws eetd ih ed rm field from seed with repeated was test The PAS-ELISA. by stage leaf true first

infected plants. plants. infected

control plants were grown in the screenhouse and tested for virus infection at the the at infection virus for tested and screenhouse the in grown were plants control

cenos wr as collected also were screenhouse

from mechanically inoculated and control plants of yard-long bean grown in the the in grown bean yard-long of plants control and inoculated mechanically from

(Known-You Seed Co., Taiwan) were purchased from a local source. A total of of total A source. local a from purchased were Taiwan) Co., Seed (Known-You

300 300

glycerin in small glass tubes, tubes, glass small in glycerin

layered on top of a a of top on layered

Hampton et al. (1990). Filtered and centrifuged extracts of plant samples were were samples plant of extracts centrifuged and Filtered (1990). al. et Hampton

rest were used in ring interface tests. tests. interface ring in used were rest

from Bos, plus that of BICMV from Kuhn were used in PAS-ELISA tests. The The tests. PAS-ELISA in used were Kuhn from BICMV of that plus Bos, from

gia, Department of Plant Pathology, Athens. The antigens and antisera obtained obtained antisera and antigens The Athens. Pathology, Plant of Department gia,

mosaic virus (PMV) strain n were obtained from C. W. Kuhn, University of Geor of University Kuhn, W. C. from obtained were n strain (PMV) virus mosaic

rotic mottle virus (CCMV), tobacco mosaic virus (TMV) legume strain, and pea pea and strain, legume (TMV) virus mosaic tobacco (CCMV), virus mottle rotic

eeemsi vrs CM) suhr ba msi vrs SM) cwe chlo cowpea (SBMV), virus mosaic bean southern (CSMV), virus mosaic severe

for Plant Protection, Wageningen, The Netherlands. Antisera for BICMV, cowpea cowpea BICMV, for Antisera Netherlands. The Wageningen, Protection, Plant for

(BCMV) and strain W of BICMV were obtained from L. Bos, Research Institute Institute Research Bos, L. from obtained were BICMV of W strain and (BCMV)

were read visually and with an ELISA reader (Uniskan I, Labsystems, Finland) Finland) Labsystems, I, (Uniskan reader ELISA an with and visually read were

at at

ml of 10% Diethanolamine adjusted to pH 9.8) and kept at room temperature for for temperature room at kept and 9.8) pH to adjusted 10% Diethanolamine of ml

PBST, then diluted diluted then PBST,

conjugated protein A (Sigma Chemical Co.) was added added was Co.) Chemical (Sigma A protein conjugated

rinsed. Substrate (Sigma 104 phosphatase substrate tablets) was added added was tablets) substrate 104 phosphatase (Sigma Substrate rinsed.

nuae aan o 2h a 2 .Pae wr te rne. laie phosphatase Alkaline rinsed. then were Plates C. 28 at hr 2 for again incubated

1-2 1-2

seeds in various tests were planted in flats and kept in aphid-proof cages. Seed Seed cages. aphid-proof in kept and flats in planted were tests various in seeds

hr. Reaction was stopped with with stopped was Reaction hr.

lvn aite o yr-og en ee etd n h srehue o resis for screenhouse the in tested were bean yard-long of varieties Eleven

405

Seed of commercially available yard-long bean variety Greenpod Kaohsiung Kaohsiung Greenpod variety bean yard-long available commercially of Seed

Ring interface tests were carried out according to the procedure described by by described procedure the to according out carried were tests interface Ring

Antigen and antisera for the NLS strain of bean common mosaic virus virus mosaic common bean of strain NLS the for antisera and Antigen

J. J.

• •

rz Mlso Ga (B, nw-o Gen ro (Y) Known (KYA), Arrow Green Known-You (LB), Guam Malesso, Cruz,

12 12

Wall et al.: Virus in Legume Crops on Guam and Saipan Saipan and Guam on Crops Legume in Virus al.: et Wall

1: 1: 10

1:1000) 1:1000)

lnspo ad rpiae pr ait. lns ee sap were Plants variety. per replicates 2 and plants/plot

dilution of antisera in phosphate buffered saline plus plus saline buffered phosphate in antisera of dilution

(KYK), (KYK),

SCREENING FOR RESISTANCE RESISTANCE FOR SCREENING

and incubated for for incubated and

SEED SEED

5 5

. .

X X

Equal numbers of seeds from inoculated and and inoculated from seeds of numbers Equal

50 50

Local Green, from A. Manibusan, Mangilao, Mangilao, Manibusan, A. from Green, Local

5 5

TRANSMISSION TRANSMISSION

micro liters of of micro liters

cm. cm.

2 2

hr at at hr

3M 3M

Na OH per well. Reactions Reactions well. per Na OH

(0.1 (0.1

28 28

C. Plates were again again were Plates C.

mg in in mg

250 250

microliters microliters

(1 (1

mg per per mg

10% 10% 103 103

All cul All

I. I. Hintze,

(J. (J.

Walp.). Walp.).

(Trigonellafoenum

(L.) (L.)

amaranticolor. amaranticolor.

C. C.

unguiculata unguiculata

(V. (V.

Results Results

SEROLOGY SEROLOGY

(Pall.) (Pall.) Kuntze), fenugreek

HOST HOST RANGE

APHID APHID TRANSMISSION

Micronesica Micronesica 29(2), 1996

plants plants also reacted positively to these antisera. No

MECHANICAL MECHANICAL TRANSMISSION

Gomez Gomez 1984).

benthamiana benthamiana

& &

N. N.

L), L), and cowpea Silver Mississippi

(Tetragonia (Tetragonia tetragonioides

In In PAS-ELISA, antisera for both strains of BlCMV gave positive reactions

Five Five of aphids plants 8 receiving from (63%) symptomatic plants developed

Thirty-one Thirty-one hosts legume possible developed symptoms of 39 or asymp were

Yard-long Yard-long bean plants inoculated with sap from plants diseased and grown

Statistical analyses were made made Statistical with were analyses software from either NCSS

Field Field tests for to resistance the mosaic were carried disease out at the Man

inoculated inoculated

itive controls. controls. itive No reaction to healthy yard-long bean plants occurred. Sap from

with with sap from inoculated mechanically yard-long bean plants, and with the pos

Control Control plants did not symptoms. develop

characteristic characteristic mosaic symptoms after 7-14 days at all tested acquisition times.

spinach spinach

tivars tivars of yard-long bean developed symptoms. systemic Nine of 24 non-legumes

tomatically by tomatically back-inoculation infected, as verified to were were infected (Table 1). Symptomless infections were detected in New Zealand graecum graecum

in in the screenhouse developed systemic symptoms resembling those observed in mosaic, mosaic, dark green vein-banding, rugosity and epinasty.

growers' fields. Symptoms developed in 75% of the inoculated the inoculated of plants and in 75% included developed Symptoms growers' fields.

iance (Gomez (Gomez iance

were subjected subjected to were square root transformations before performing analysis of var

Kaysville, Kaysville, UT) or SuperAnova (Abacus, Berkeley, CA). Percent incidence data

It It began with planting on April 4, and 1990, ended on July 16, Distance 1990.

between between rows changed was to m. 1.5

A A second experiment with the same varieties carried was out in an adjacent field.

6, 1990. The The number plants 6, of with mosaic 1990. symptoms recorded was for each plot.

planted December 1, 1989 ( end end of planted wet season). The December experiment ( ended 1, 1989 on March

agronomic agronomic practices were done as is customary for local growers. The field was

replications replications were used in a completely randomized design. Fertilizer mended mended rates at 2 and 6 weeks after planting. Irrigation was by dripline. All

(16N:16P:16K) was (16N:16P:16K) applied in a side-dressed band (local practice) at the recom

sisted sisted of single rows of hills. Rows were 5 m long and spaced m 1 apart. Hills

104 104 tests, tests, except for Ferry Morse Asparagus and Surinam, were included. Plots con within within rows cm were 20 apart. Plantings were thinned to plants 2 per hill. Three ibusan ibusan farm under natural disease pressure. All varieties from the screenhouse

Fabaceae Fabaceae

Glycine max max Glycine

Crotalaria juncea juncea Crotalaria

Asteraceae Asteraceae

C11curbitaceae C11curbitaceae

Araliaceae Araliaceae Bignoniaceae Bignoniaceae

Chenopodiaceae Chenopodiaceae

Amaranthaceae Amaranthaceae

Aizoaceae Aizoaceae

Family Family

Phaseolus lunatus lunatus Phaseolus

Pachyrhizus erosus erosus Pachyrhizus

Medicago sativa sativa Medicago

Arachis hypogea hypogea Arachis

Luffa acutangula acutangula Luffa

Cassia alata alata Cassia

Cucubita pepo pepo Cucubita

Synedrella nodifiora nodifiora Synedrella

Chenopodium quinoa quinoa Chenopodium

Chenopodium amaralllicolor amaralllicolor Chenopodium

Spinacea oleracea oleracea Spinacea

Cucumis sativus sativus Cucumis

oyca sp Polyscias

Amaranthus spinosus spinosus Amaranthus

Beta vulgaris vulgaris Beta

Tecoma stans stans Tecoma

Gomphrena globosa globosa Gomphrena

Species Species

Tetragonia tetragonioides tetragonioides Tetragonia

Henderson Bush L Bush Henderson

Du Puis Puis Du

Tropic Sun sunnhemp sunnhemp Sun Tropic

Vinton Vinton

Bragg Bragg

Starr Starr

Spanish Peanut Peanut Spanish

Table I. Reaction of 63 plant species, cultivars, or varieties mechanically mechanically varieties or cultivars, species, plant 63 of Reaction I. Table

Ambassador Ambassador

Chicago Pickling Pickling Chicago Luffa gourd gourd Luffa

Hybrid Sweet Salad Salad Sweet Hybrid

Plant Virus Virus Plant

Mixed Mixed

Bloomsdale Long Standing Standing Long Bloomsdale

Detroit Dark Red Red Dark Detroit

New Zealand spinach spinach Zealand New

Cultivar Cultivar

. .

Wall et al.: Virus in Legume Crops on Guam and Saipan Saipan and Guam on Legume Virus in al.: Crops Wall et

ma ma

inoculated with with inoculated

BICMV. BICMV.

RV, NS RV,

Local Systemic Systemic Local

NL NL

YL YL

± ±

+ +

• •

± ±

+ +

+ + + +

• •

, ,

N N

Reactions Reactions

Mo, LR, LC LC LR, Mo,

, ,

Mo Mo

± ±

Dw, N N Dw, 105 105

M M

± ±

+ +

M M

+ +

± ±

M M

Mo Mo

M, M, YS

M,Mo M,Mo

-(1/6 -(1/6 VB)

M, M, VB,Ru

M, M, VB, Ru M, M, VB, Ru

M, M, VB, Ru

M, M, VB,Ru

M, M, VB, Ru

M, M, VB,Ru

Mo,Dw,N Mo,Dw,N

Reactions Reactions

• •

• • • •

• •

± ±

• •

± ±

+ +

+ + +

+ +

RL RL

Mo Mo Mo,Dw,N

Local Local Systemic

Continued. Continued.

l. l.

Table Table

Micronesica 29(2), 1996 1996 29(2), Micronesica

#5 #5

sesquipedalis sesquipedalis

subsp. subsp.

JI JI

Sweet basil basil Sweet

Surinam Surinam

Mabun Mabun

Maagap Maagap Sumilang Sumilang

Sandigan Sandigan Pole

local local white

local local red

local local green

local local bush

local local black

Green Green Pod Kaohsiung

vulgaris vulgaris

Extra Extra Long Red Seed

DowGauk DowGauk

Burpee Asparagus Burpee Asparagus bean Green Green Arrow

Sete semanas semanas Sete

faba faba minor Serido Serido

Queen Queen Ann

Purple Purple Hull

Mississippi Silver Silver Mississippi

Berken Berken mung bean

California California Blackeye

Fava Fava Bush Long Pod

Wando Wando

Perfected Perfected Wales

Greencrop Greencrop

Black Black Turtle

Cultivar Cultivar

Ocimum Ocimum basilicum

V. V. unguiculata

Vigna. Vigna. radiata

V. V.

Viciafaba Viciafaba

Bell bean bean Bell

Trigonella foenum-graecum foenum-graecum Trigonella

Psophocarpus Psophocarpus tetragonolobus

Pisum Pisum sativum

P. P.

Species Species

V. unguiculata V. unguiculata

Lamiaceae Lamiaceae

Family Family 106 106

the first screenhouse test. All entries were infected. The weaker dilution used for for used dilution weaker The infected. were entries All test. screenhouse first the

seed showed symptoms. symptoms. showed seed

symptoms and tested negative. Sixteen of 50 (32%) seedlings from field-infected field-infected from seedlings (32%) 50 of Sixteen negative. tested and symptoms

and showed mosaic symptoms on the first true leaves. Control plants showed no no showed plants Control leaves. true first the on symptoms mosaic showed and

of infected screenhouse-grown plants tested positive for BICMV in PAS-ELISA PAS-ELISA in BICMV for positive tested plants screenhouse-grown infected of

tionable infection out of 300 plants. Fifteen of 41 plants (37%) grown from seed seed from grown (37%) plants 41 of Fifteen plants. 300 of out infection tionable

positive reactions were observed with the other antisera, except for positive con positive for except antisera, other the with observed were reactions positive

antiserum for BICMV only. Uninoculated controls gave negative results. results. negative gave controls Uninoculated only. BICMV for antiserum

trols. In ring interface tests, yard-long bean samples gave positive results with with results positive gave samples bean yard-long tests, interface ring In trols.

No significant differences in disease incidence were found among varieties in in varieties among found were incidence disease in differences significant No

Tests on plants from nursery-purchased seed were negative except for 1 1 ques for except were negative seed nursery-purchased from plants on Tests

Legend: Legend:

Petunia hybrida hybrida Petunia

N. N.

Nicotiana benthamiana benthamiana Nicotiana

Lycopersicon esculentum esculentum Lycopersicon

Solanaceae Solanaceae

Poacea Poacea

Family Family

. .

Datura stramonium stramonium Datura

Species Species

Triticum aestivum aestivum Triticum

glutinosa glutinosa

tabacum tabacum

Samsun Samsun

Hicks Broadleaf Broadleaf Hicks Plum Pudding Pudding Plum

Marglobe Marglobe

Plant Virus Virus Plant

Minter Winter wheat wheat Winter Minter

Cultivar Cultivar

• no symptoms, no back inoculation or ELISA or inoculation back no symptoms, no •

N-necrosis of plant plant of N-necrosis

Mo-mottle Mo-mottle

M-Mosaic M-Mosaic

C--chlorosis of leaves NL-necrotic local lesions lesions local NL-necrotic leaves of C--chlorosis LC

D-leaf deformity deformity D-leaf

± ±

- no symptoms (negative in back inoculation or ELISA) ELISA) or inoculation back in (negative symptoms no -

+ +

positive, but not in all back inoculations or ELISA ELISA or inoculations back all in not but positive,

symptomless infection (positive in back inoculation or ELISA) ELISA) or inoculation back in (positive infection symptomless

leaves curling downward Ru-rugosity Ru-rugosity downward curling leaves

leaf rolling upward RV-red vein banding banding vein RV-red upward rolling leaf

Dwarfing of leaves RL-red local lesions lesions local RL-red leaves of Dwarfing

Wall et al.: Virus in Legume Crops on Guam and Saipan Saipan and Guam Legume al.: Virus Wall on in et Crops

SCREENING FOR RESISTANCE RESISTANCE FOR SCREENING

SEED TRANSMISSION TRANSMISSION SEED

Table 1. Continued. Continued. 1. Table

YS-yellow spots spots YS-yellow

YL-yellow local lesions lesions local YL-yellow

VB-dark green vein banding banding vein green VB-dark

NS-necrotic spots spots NS-necrotic

Local Systemic Systemic Local

. .

+ +

• •

Reactions Reactions

M, VB, LC LC VB, M, 107 107

indi

MW, MW,

, ,

so, so, the

If If

bentham

. .

in in the second

28ab 28ab

70a 70a

71a 71a

3.72b 3.72b

7.0lab 7.0lab

7.9lab 7.9lab

8.19a 8.19a

10.88a 10.88a

10.33a 10.33a

Mean Mean

KY A A KY

Guam, Guam, planted in

. .

, ,

and and

0. 780) 780) was 0. found between

= =

12b 12b

87ab 87ab 77b 77b

22ab 22ab

86b 86b

20a 20a

96b 96b

3.43b 3.43b

4.70ab 4.70ab

Test Test 2

MG, MG, TR, BA,

Yield Yield T/ha

Discussion Discussion

46a 46a

3.66d 3.66d

8.80cd 8.80cd

Micronesica 29(2), 1996 1996 29(2), Micronesica

ll.44bc ll.44bc

I l.l9bc l.l9bc I

l0.95bc l0.95bc

12.Slabc 12.Slabc

17.13a 17.13a

15.96ab 15.96ab

-0.393); -0.393); although the correlation was low, it was

Test Test 1•

1989 (Test (Test 1989 l) and April (Test 1990 2)

. .

= =

Dec

yet yet significant. The highest yields were obtained by

, ,

Yields Yields of 9 yard-long bean cultivars at Mangilao

followed followed by different letters are different at .05 (Fisher's level Protected

is is important to note, however, that Dijkstra et al. (1987) suggest

. .

0.385)

It It

= =

and and KYK in the first test, and

Means Means

Table Table 2

• •

BU BU

LSD). LSD).

LB LB

BA BA

LR LR

KYK KYK

MG MG

TR TR

KYA KYA

MW MW

Cultivar Cultivar

although although this species did develop green vein-banding. On Serido cowpea, no 0.538), 0.538), but there was a negative correlation between infection scores from

Results Results from all our tests agree with previous descriptions of BICMV

On On California Blackeye Cowpea #5, our test isolate produced mosaic but no

In In the first field test, a positive correlation (r

= =

they they found some cowpea cultivars capable of differentiating between the two vi-

name name BICMV then takes precedence. While Taiwo et al. (1982) considered that

synonymous synonymous until further work can elucidate their separate identities.

that that BICMV and cowpea aphidbome mosaic virus (CAMV) should be considered

strain strain of this potyvirus (Purciful & Gonsalves 1985, Taiwo et al. 1982, Dijkstra

et et al. 1987).

cating cating that the causal agent of the mosaic disease affecting yard-long bean is a

iana, iana,

infection infection developed, while on Sete Semanas cowpea, only 1 of 6 test plants de

veloped veloped vein banding.

downward downward cupping of leaves on all test plants, nor did this occur on

(Tables (Tables 2, 3).

LR, KY A A KY LR,

also also low (r

significant significant at the level. Correlation .05 of visual scores with PAS-ELISA data was

PAS-ELISA PAS-ELISA and yield (r

(r (r

108 108

was was also a positive correlation between visual scores of mosaic incidence and yield

visual visual mosaic scores yielded significantly higher. In the second experiment, there

visual visual scores of mosaic incidence and yield. Varieties with significantly higher

in in disease incidence were found. inoculating inoculating the second test resulted in milder symptoms; however, no differences Wall et al.: Virus in Legume Crops on Guam and Saipan 109

Table 3. Incidence of BICMV in field trials of 9 yard-long bean cultivars at Mangilao, Guam, planted in Dec. 1989 (Test I) and April 1990 (Test 2)

% Incidence-Visual Score % Incidence ELISA Cultivar Test I Test 2 Mean* Cultivar Test 2

BU I.I 5.3 3.2a BA 26a TR 5.6 1.3 3.4a TR 39a BA 6.7 0.6 3.6a KYA 46a LB 7.8 0.3 4.0a LR 56a KYK 10.0 3.6 6.8ab MG 57a KYA 14.4 0 7.2ab LB 65ab LR 15.6 4.6 10.lbc MW 73ab MW 21.1 2.6 l l.9bc BU 88b MG 15.6 9.3 12.4c KYK 88b

Legend: *Fisher's Protected LSD, at .05 significance level. LR: Local Red KYA: Known-You Green Arrow LB: Local Black KYK: Known-You Greenpod Kaohsiung MG: Manibusan Green TR: Takii Extra Long Red MW: Manibusan White BA: Burpee Asparagus BU: Bush ruses in question, Dijskstra et al. point out that this work was based on very few plants being tested, in some cases as few as 3. Furthermore, they argue, when they tried to duplicate these tests using 30-50 plants per cultivar, they got varied results. Because current information in the literature can be confusing in this respect, we chose to follow the suggestion of Dijkstra et al. and call our isolate BlCMV. The fact that BICMV is seed-transmitted is of particular importance. Local growers traditionally save their own seed because their favorite varieties are not commercially available. Incidence rates of mosaic nearing l 00% are not unusual on Guam. Such a high incidence can easily be explained if seed transmission is occurring. None of the other plants in the host range study are ubiquitous enough to be important weed hosts for this virus in our region. Other crop plants of some importance (snap, yam and winged beans) were found to be hosts for BlCMV, and could act as sources of inoculum for yard-long bean. Yam and winged beans can grow year-round on Guam, and they may therefore have a role as intersea sonal sources of inoculum. However, with seed and aphid transmission, yard-long bean is very likely its own primary source of inoculum. If this is the case, then effective control of BlCMV on yard-long bean is dependent on a combination of using clean seed, early rogueing of any seed-infected seedlings, and aphid control, if possible. Additional control steps that can be important are the selection of planting site, and prompt elimination of crop residues. In our region, because of limited land resources, growers may use the same or adjacent fields repeatedly. Planting away from older fields, which are likely to have infected plants, growers are less likely to get aphid-transmitted infections throughout the growing seasons. De- 110 Micronesica 29(2), 1996 struction of older fields as soon as possible would also be advisable to reduce the number of infected plants acting as sources of inoculum. In the two field tests for resistance to BlCMV, visual scoring of incidence and yield data were not consistent. Regarding yield data, this was partly due to the differences in planting seasons. However, there were differences in disease inci dence data that were simply due to the unreliability of visual scoring. Comparing both sets of incidence data for the second season, it is evident that visual scoring failed to detect all virus-infected plants. ELISA assays of virus diseases are more reliable than those based on visual symptoms because the former detect the pres ence of virus in plant samples, even if symptoms are not visible. Symptom ex pression of plant virus diseases is known to be affected by environmental condi tions (Gibbs & Harrison 1976). Unfortunately, ELISA testing was not possible for the first field experiment. Based on the available PAS-ELISA results, BA, TR, KYA, LR, and MG had low infection rates (Table 3). KY A, LR and MG had low incidence and produced good yields in both seasons (Table 2), making them the best overall cultivars tested. BA, although having the lowest incidence levels, has a purple tip and a shorter than standard pod length, which is undesirable for local markets, but would be a good choice for home gardens. MG and TR performed well under the drier climatic conditions of Test 2. MW and LR, on the other hand, did not. These cultivars might be improved through a breeding program in the future. Such a program could also incorporate BlCMV resistance available in cowpea germplasm, such as that seen in cultivars Serido and Sete Semanas. There are reports of at least 2 more resistant cowpea varieties (Kuhn et al. 1984). Visual mosaic symptoms were positively correlated with yield, in spite of the expected negative correlation between yield and PAS-ELISA scores. A grower trying to estimate the extent of damage caused by mosaic and measuring disease by visual symptoms would be misled to believe there is no yield loss caused by this disease. Our PAS-ELISA data being negatively correlated with yield could be explained ifBICMV reduces yield. Subsequently, a separate test was performed to study the effect of mosaic infection on production (Wall & Kimmons 1991), which was found to be reduced considerably. The PAS-ELISA technique developed in the course of this study has become a valuable research tool for working with this disease in our region. The choice of PAS-ELISA over double antibody sandwich (DAS) ELISA was made because it eliminates the need for conjugated antibody. Use of BlCMVantisera and PAS ELISA now provides the ability to rapidly, accurately and cheaply perform virus screening of yard-long beans from Guam, the Commonwealth of the Northern Mariana Islands and other island nations in the West and South Pacific regions. For instance, we have found BlCMV in yard-long bean samples from Saipan, where yard-long bean is also an important vegetable crop. This is the first report of winged bean, Psophocarpus tetragonolobus, as a host of BlCMV. Further testing is needed to clarify the status of yam bean or jicama (Pachyrhizus erosus), Synedrella nodifiora and Polyscias sp. as hosts of this virus. Wall et al.: Virus in Legume Crops on Guam and Saipan Ill

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Received 9 Aug. 1995, revised 12 Mar. 1996