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Spatiotemporal Separation of Groundnut Rosette Disease Agents

First and sixth author: International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), P.O. Box 1096, Lilongwe, Malawi; second and third authors: Pest Management Department, Natural Resources Institute, Chatham Maritime, Kent ME4 4TB, United Kingdom; fourth author: Virology Department, Scottish Crop Research Institute (SCRI), Invergowrie, Dundee DD2 5DA, United Kingdom; and fifth author: Department of Plant Pathology, University of Georgia, Athens 30602-7274

Analysis by triple-antibody sandwich enzyme-linked immunosorbent assay of groundnut samples from fields in two seasons from different regions of Malawi showed the absence of groundnut rosette assistor virus (GRAV) from some plants showing groundnut rosette disease symptoms and the presence of GRAV in some symptomless plants. Viruliferous Aphis craccivora collected from fields transmitted either GRAV alone, groundnut rosette virus (GRV) with its satellite RNA (sat RNA), or all three agents together, in different proportions. More plants became infected with all three agents when increasing numbers of potentially viruliferous aphids were used per plant, suggesting a dosage response. Electrical pentration graph studies of aphid stylet activities indicated successful transmission of GRV and its sat RNA during both the “stylet pathway phase” and salivation into sieve elements, whereas GRAV was transmitted only during the latter phase. Aphids transmitted all three agents together only during the salivation phase. Reverse-transcriptase polymerase chain reaction testing of viruliferous aphids and of inoculated plants revealed no correlation between the presence of all three agents in prospective aphid vectors and their simultaneous transmission to groundnut plants. These results show that separation of the groundnut rosette disease agents occurs over time and space.