USDA, ARS, Griffin, GA 30223
University of Kentucky, Lexington 40546
Plant species in the genus Desmodium (Fabaceae) are used as forage and cover crops and include a number of common weeds such as beggarweed (D. tortuosum) and beggarlice (D. intortum). Accessions of the genus are part of the plant genetic resources collection maintained at Griffin, GA. Peanut stunt cucumovirus (PSV) was detected in naturally infected plants of Desmodium sp. PI 322505 (from Brazil) in a germ plasm regeneration plot by a direct antigen coating-enzyme-linked immunosorbent assay (DAC-ELISA) with an antiserum against PSV strain ER (subgroup I) originally isolated from cowpea in Georgia. The infected plants showed mild mosaic symptoms. Indicator host studies in the greenhouse revealed symptoms characteristic of PSV on Nicotiana tabacum cv. Burley 21 (ringspots and oak leaf pattern), Chenopodium album subsp. amaranticolor (chlorotic local lesions), and Vigna unguiculata (chlorotic spots followed by systemic mild mosaic). These symptomatic indicator plants tested positive for PSV by DAC-ELISA. Greenhousegrown plants of D. incanum (kaimi-clover) and D. uncinatum (Spanish tick-clover) were inoculated with the field isolate and the plants were tested for PSV by DAC-ELISA (10 infected of 10 tested and 3 infected of 9 tested, respectively). The PSV isolate infecting Desmodium spp. was found to contain satellite RNA and it generated the predicted products in reverse transcription-polymerase chain reactions (RT-PCRs) with primers based on specific PSV-ER sequences. The RT-PCR products were confirmed by restriction-enzyme digestion (1). This is the first report of PSV naturally infecting a member of the genus Desmodium. Because some members of this genus may grow as perennial weeds near peanut, cowpea, or other host crops, this genus may serve as an alternate/overwintering host for the virus.
Reference: (1) R. A. Naidu et al. Phytopathology 85:502, 1995.