Blackeye Cowpea Mosaic Potyvirus Research Articles

Characterization of a Severe Strain of Cucumber Mosaic Cucumovirus Seedborne in Cowpea.

A new seedborne strain of cucumber mosaic cucumovirus (CMV) that induces severe symptoms on many cowpea genotypes was detected in Georgia in 1994. This strain, designated CMV-Csb, is asymptomatic on tobacco, but it produces more severe cowpea stunt symptoms when present in combination with blackeye cowpea mosaic potyvirus than do the more prevalent CMV isolates. The new strain is seedborne in cowpea (1.5 to 37%), has no associated satellite RNA, and is classified as a member of subgroup I of CMV strains based on nucleic acid hybridization assays.

First Report of Cowpea Aphid-Borne Mosaic Potyvirus from Cowpeas Grown Commercially in the U.S.

Cowpea aphid-borne mosaic potyvirus (CABMV) is one of several seed-borne viruses known to limit cowpea (Vigna unguiculata (L.) Walp. subsp. unguiculata) production in Africa, Europe, and Asia, but CABMV has not been reported on commercially grown cowpeas in the United States (1). However, a sesame (Sesamum indicum L.)-infecting isolate of CABMV was recently characterized from plants growing near cowpea introduction plots in Georgia (2). In February 1997, we received samples of three seed lots of cowpea cv. Chinese Red that had been harvested in southern Texas during 1996. Approximately 28% of the plants grown from these seed lots expressed strong mosaic symptoms on primary and trifoliate leaves. Viruslike symptoms were reproduced following mechanical transmission to plants of Chinese Red cowpea, Nicotiana benthamiana, and soybean (Glycine max L.) cv. Lee. When Coronet and Pinkeye Purple Hull-BVR cowpeas were inoculated with sap extracts from symptomatic Chinese Red plants, chlorotic lesions developed on inoculated leaves, but only Coronet plants supported symptomless systemic infections. Similarly inoculated plants of Chenopodium quinoa (L.) and common bean (Phaseolus vulgaris L.) cvs. Pinto and Black Valentine developed localized chlorotic lesions. In Ouchterlony gel diffusion assays, extracts from symptomatic cowpea plants did not react with antisera to blackeye cowpea mosaic potyvirus (BlCMV), cucumber mosaic cucu-movirus (CMV), southern bean mosaic sobemovirus, cowpea mosaic comovirus, cowpea severe mosaic comovirus, or cowpea chlorotic mottle bromovirus. In the indirect enzyme-linked immunosorbent assay, sap extracts from symptomatic plants reacted with antiserum to CABMV, giving OD values at A405 of 0.10 to 0.25, and reacted weakly with antiserum to BlCMV, with OD values at A405 less than 0.035. Extracts from healthy control plants gave OD values at A405 less than 0.010. No positive reactions were obtained with antisera to bean yellow mosaic potyvirus, peanut mottle potyvirus, soybean mosaic potyvirus, or CMV. To our knowledge, this is the first report of CABMV in commercially grown cowpea from the U.S.

Occurrence of Cowpea Stunt Disease Causing Viruses on Wild Bean in Arkansas.

Cucumber mosaic cucumovirus (CMV) and blackeye cowpea mosaic potyvirus (BlCMV) interact synergistically in dually infected plants to cause cowpea stunt disease (1,2). During a July 1996 survey of cowpea stunt-affected fields in the Arkansas River valley, several wild bean (Strophostyles helvola L. Elliott) plants expressing mosaic symptoms were observed and collected. Sap was extracted from symptomatic leaves and used as inoculum to conduct a host range study. Virus symptoms diagnostic for BlCMV, CMV, or cowpea stunt were observed 6 to 8 days post-inoculation on Vigna unguiculata (L.) Walp. subsp. unguiculata cv. Coronet, while chlorotic lesions and mild systemic mosaic symptoms developed on Nicotiana benthamiana. Enzyme-linked immunosorbent assays (ELISAs) conducted on extracts from symptomatic cowpea and N. benthamiana 14 days after inoculation verified the presence of CMV and BlCMV in single and mixed infections. Additional symptomatic wild bean plants were collected from the same site in October 1996. ELISAs and Ouchterlony gel diffusion assays confirmed the presence of CMV and BlCMV, as well as soybean mosaic potyvirus (SMV), cowpea chlorotic mottle bromovirus, and alfalfa mosaic virus (AlMV) in symptomatic wild bean plants. While some of the collected plants were infected with only one virus, others had combined infections of CMV and BlCMV or these two viruses with AlMV. Interestingly, AlMV isolated from wild bean caused symptoms on greenhouse-grown cowpeas that were as severe or more severe than those caused by the cowpea stunt synergy, often resulting in plant death within 8 to 10 days after inoculation. The SMV from wild bean did not induce symptoms on cowpea and was not detected in extracts from inoculated cowpea plants by Ouchterlony gel diffusion assays, but was able to systemically infect soybean (Glycine max L.) cvs. Bragg and Lee. Another virus known to infect cowpea, southern bean mosaic sobemovirus, was not detected in any of the samples tested. To our knowledge, this is the first report that wild bean can serve as an alternate host for cowpea stunt-causing viruses in single and mixed infections. In addition, these data suggest that AlMV may pose a threat to Arkansas-grown cowpeas.

Survey on cowpea virus incidence and distribution in Nigeria

Enzyme-linked immunosorbent assay (ELISA) was used to detectviruses in649 cowpea leafsamples collectedfrom115 fields during a 3-year survey carried out from 1991 to 1993 throughout all agroecological zones in Nigeria. Six viruses, cowpea aphid-borne mosaic potyvirus (CAMV), blackeye cowpea mosaic potyvirus (BICMV), southern bean mosaic sobemovirus (SBMV), cowpea mottle carmovirus (CMoV), cowpea (yellow) mosaic comovirus (CpMV) and the cowpea strain of cucumbermosaic cucumovirus (CMV-CS)were detectedin 390 outofthe 649 samples assayed. There was considerable variation in both disease incidence and virus distribution in the different crop habitats within and between seasons. Thus, while SBMV had the highest incidence (27.4%) and was the most prevalent (66.7% in 1991, CAMV had the highest incidences (11.3% and 28.8%, respectively) and was the most prevalent 33% and 68%, respectively) in 1992 and 1993. CpMV and CMoV remained consistently moderate both in incidence and prevalence throughout the duration of the survey. The detection of the three beetletransmitted sphericalviruses (SBMV, CpMV and CMoV)in the Sudanand Sahel Savanna indicates that there is no ecological restriction to the distributionofanyoftheviruses.Incidence ofmultipleinfectionofuptofour and five viruses in individual samples was observed, but mixed infection with two viruses was more prevalent (13%). The potential for horizontal resistance breeding based on common vector transmission is discussed.

Identification and characterization of viruses infecting bambara groundnut (Vigna subterranea) in Nigeria

Eight viruses were identified infecting bambara goundnut in farmer's fields in Nigeria: cowpea aphid-borne mosaic potyvirus, blackeye cowpea mosaic potyvirus, peanut mottle potyvirus, cowpea mottle carmovirus, cowpea mosaic comovirus (cowpea yellow mosaic virus), cowpea mild mottle carlavirus, cucumber mosaic cucumovirus and southern bean mosaic sobemovirus. The importance of these viruses to the crop is discussed and details on their ecology and geographical distribution are given.

Identification of cowpea (Vigna unguiculata) cultivars and lines immune to variants of blackeye cowpea mosaic potyvirus

Fifty‐one cowpea (Vigna unguiculata) cultivars and lines were tested by mechanical inoculation against seven geographically and pathogenically diverse isolates of blackeye cowpea mosaic potyvirus (BICMV), to identify genetic resources with comprehensive BICMV resistance. Five genotypes, IT 80S 2049, Big Boy, Corona, Serido, and Tennessee Cream #8 were immune from all seven isolates, and an additional three genotypes, TVu‐2657, TVu‐2740, and TVu‐3433, were immune from all isolates except PU‐7B, an aberrant B1CMV isolate. The diversity among BICMV isolates was illustrated by the range of responses to inoculation among cowpea genotypes, many of which were either immune from or tolerant of individual B1CMV isolates.

Tolerance to Blackeye Cowpea Mosaic Potyvirus Not Correlatedwith Decreased Virus Accumulation or Protection from Cowpea Stunt Disease

Progeny from a near-isogenic cowpea line responded heterogeneously when infected with a cowpea stunt-derived isolate of blackeye cowpea mosaic potyvirus (BICMV). One group of plants developed a delayed, mild reaction to BICMV while sister plants rapidly exhibited strong systemic mosaic symptoms. Conversely, enzyme-linked immunosorbent assay (ELISA) results indicated that BICMV generally accumulated to the same levels and at the same rates in these two plant groups. Similar results were obtained for two commercial varieties that expressed different BICMV symptoms. Symptom analyses and ELISA were used to demonstrate that one of these commercial varieties was highly resistant to this virus isolate. All genotypes responded with similar, mild reactions when inoculated with cowpea stunt-derived cucumber mosaic cucumovirus (CMV). Both symptoms and ELISA-detectable levels of CMV decreased as plants aged. Mixed infections with BICMV and CMV resulted in severe cowpea stunt disease symptoms and high concentrations of CMV coat protein 20 days after inoculation in all plants that did not express extreme resistance to BICMV. Interestingly, at early time points after inoculation, differences in symptom severity between singly and dually infected plants were not consistently correlated with significant differences in relative CMV concentrations. The results indicate that (i) resistance to BICMV, as determined through visual observation, is not adequate when evaluating germ plasm for cowpea stunt disease resistance, and (ii) rapid development of severe symptoms on dually infected plants may not be due solely to increased CMV concentrations.

Seedborne Viruses in Preintroduction Cowpea Seed Lots and Establishment of Virus-Free Accessions

Seeds from 60 cowpea preintroductions from Botswana, India, and Kenya were increased at the University of California Riverside. Second generation seed were planted in insect-free greenhouses at two locations and resulting seedlings were assayed by direct antigen coated enzyme-linked immunosorbent assay (DAC-ELISA) for the presence of eight seedborne viruses. By visual selection and DAC-ELISA, 10 virus-free mother plants for each of the 60 accessions were established. The seedlots from these mother plants were subsquently planted in isolation plots at St. Croix, Virgin Islands. Seedlings from the St. Croix seed increase were observed and tested by DAC-ELISA and were found to have remained free from viruses during this field exposure. One or more of the following viruses were detected in 40 of the 60 preintroductions: 32 containing cowpea aphid-borne mosaic potyvirus (possibly blackeye cowpea mosaic potyvirus in some cases); 23 with cowpea severe mosaic comovirus; 22 with southern bean mosaic sobemovirus; seven with cucumber mosaic cucumovirus; and seven with cowpea mottle carmovirus. None were found to contain ELISA-detectable cowpea mosaic comovirus or cowpea mild mottle carlavirus. Twenty preintroductions were free of ELISA-detectable seedborne viruses. Virusfree experimental seed lots were produced for limited use by interested cowpea breeders

Inheritance of resistance to potyviruses in Phaseolus vulgaris L. III. Cosegregation of phenotypically similar dominant responses to nine potyviruses

We have identified monogenic dominant resistance to azuki bean mosaic poty virus (AzMV), passionfruit woodiness potyvirus-K (PWV-K), zucchini yellow mosaic potyvirus (ZYMV), and a dominant factor that conditioned lethal necrosis to Thailand Passiflora potyvirus (ThPV), in Phaseolus vulgaris 'Black Turtle Soup 1'. Resistance to AzMV, PWV-K, ZYMV, watermelon mosaic potyvirus, cowpea aphid-borne mosaic potyvirus, blackeye cowpea mosaic potyvirus, and lethal necrosis to soybean mosaic potyvirus and ThPV cosegregated as a unit with the I gene for resistance to bean common mosaic potyvirus.

SEED-BORNE VIRUSES IN U.S. COWPEA CROPS: A STATUS REPORT AND STRATEGY FOR VIRAL DISEASE CONTROL

Blackeye cowpea mosaic potyvirus is the most easily observable seed-borne virus in cowpeas, but is typically seed-transmitted at lower rates (i.e., 0.1 to 2%) than the less conspicuous cowpea severe mosaic comovirus or cucumber mosaic cucumovirus. All three viruses are readily vector transmissible after seed-borne inoculum reaches the field, perpetuating and spreading the viruses. Individually and particularly in mixtures, these viruses are capable of decreasing both seed quality and yield. Disease-tolerant cultivars are available, but fail to control viral diseases. Development of superior new cowpea cultivars with multiple viral-disease resistance is clearly within reach and has become essential to long-term, sustainable, profitable cowpea production. This breeding objective requires public-research supported efforts by the combined cowpea seed and processing industries. Southern bean mosaic sobemovirus is also recognized as an important cowpea pathogen, but was encountered at a much lower frequency than the above three viruses in both plant and seed samples, in 1992 and 1993.

Relationship of Cowpea Seed-Part Infection and Seed Transmission of Blackeye Cowpea Mosaic Potyvirus in Cowpea

Blackeye cowpea mosaic potyvirus (BICMV) was seedborne in four cowpea seed lots (two genotypes) at incidences of 0.4-50%. Fully mature seeds were hydrated and separated into testae and embryos. Each embryo was separated further into two cotyledons and the embryo axis. These were tested separately for BICMV by DAS-ELISA and by bioassay on Chenopodium amaranticolor. Viruses occurred in cotyledons and/or embryo axes in Coronet 1985cs, Coronet 1986cs, and PI 517912 but only in the cotyledons in Coronet 1987. Viral antigen was found in or on the testae, but very little infectious virus was present. The germinability of cowpea seeds of five accessions that were hydrated, decorticated, and stored 12 wk ranged from 60 to 100%

Peanut stripe virus disease of groundnut—a review

Abstract A virus, first reported from China in 1983 as producing a mild mottle in peanut (Arachis hypogaea) was further characterized and named peanut stripe virus (PStV) in the USA. It has since been reported from major groundnut‐growing areas in South‐east Asia including India, and has been found to cause economically significant crop losses. Besides groundnut, it infects soybean (Glycine max) cowpea (Vigna unguiculata), Indigofera amoena, Pueraria phaseoloides, Stylosanthes capitata and S. craba naturally. It is seedborne and transmissible mechanically by sap as well as by the aphid Aphis craccivora. The movement of infected seed has resulted in its wide dissemination. The virus is serologically closely related to blackeye cowpea mosaic potyvirus (BICMV), Azuki bean mosaic potyvirus (AzMV) and the serogroup B strains of bean common mosaic potyvirus (BCMV), and distantly to clover yellow vein and soybean mosaic potyviruses. PStV was initially described as a new virus, but recent molecular studies have s...