Alfalfa mosaic virus: occurrence and variation among isolates from forage legumes in Ethiopia

Field samples and seedlings of 51 leguminous forage species were tested for alfalfa mosaic virus (AMV) in routine monitoring of seed multiplication fields of the International Livestock Research Institute (ILRI), Ethiopia. The virus was detected in 24 species and a solanaceous weed Solanum nigrum. Of these, the following 17 species are being reported for the first time as hosts of the virus in world literature: Aeschynomene falcata, Centrosema pascuorum, Chamaecrista rotundifolia, Desmanthus virgatus, Desmodium intortum, Leucaena leucocephala, Macroptilium atropurpureum, Macroptilium lathyroides, Macrotyloma axillare, Medicago truncatula, Neonotoniaa wightii, Sesbania sesban, Stylosanthes scabra, Trifolium calocephala, T. steudneri, T. tembense and Vigna parkeri. The solanaceous weed S. nigrum was suspected to play a role in the virus epidemiology. The level of seed infection varied from 0.00% to about 13.00%. Infectivity studies on 5 isolates of the virus revealed heterogeneity in prevalent AMV isolates. Two major strains were identified, based on the development of necrotic local lesions on Vigna unguiculata accessions. One of the isolates which failed to incite local necrotic lesions on V. unguiculata infected Phaseolus vulgaris cv. Top Crop systemically. Differences among isolates were also noticed in their concentration in different hosts as indicated by ELISA absorbance values.