Relationship between natural occurrence of banana streak badnavirus and symptom expression, relative concentration of viral antigen, and yield characteristics of some micropropagated Musa spp.

Micropropagated plants of 36 Musa genotypes with diverse genetic background s, including 14 tetraploid plantain (TMPx) and banana (TMBx) hybrids, were evaluated for their response to banana streak badnavirus (BSV) infection un der three environments from 1995 to 1997 in Nigeria. The characteristics ev aluated were the natural incidence of BSV based on symptoms and virus index ing, relative concentration of BSV antigens in leaf tissues determined by E LISA, and some growth and yield descriptors. Virus occurrence and symptom e xpression, as well as the relative concentration of BSV antigens, fluctuate d greatly between seasons during the cropping cycle, being high during the rainy season and low or negligible during the hot dry season. The natural i ncidence of plants with symptoms and BSV-infected plants varied between gen otypes. Incidence of BSV on most International Institute of Tropical Agricu lture (IITA) TMPx hybrids and three Fundacion Hondureoa de Investigacion Ag ricola (FHIA) hybrids was high in the three environments, with some variati on. Most landraces and some FHIA or Empresa Brasileira de Pesquisa Agropecu aria (EMBRAPA) hybrids were not BSV-infected under either environment at On ne. However, a few expressed some foliar symptoms at Ibadan and indexed BSV positive. The relative concentration of BSV antigens in leaf samples was a lso high in most TMPx and some FHIA hybrids, but low in most landraces. Whi le BSV infection had no significant effect on most growth characteristics, it had a highly variable effect on bunch weight loss among the genotypes. T here was no relationship between the natural incidence of BSV, concentratio n of viral antigen and bunch weight loss among the 11 TMPx hybrids, three F HIA hybrids and three plantain landraces. Despite the high natural BSV inci dence and the high relative antigen concentration in their leaf tissue, TMP x 548-9, TMPx 2637-49, TMPx 7002-1 and FHIA 21 suffered less than 15% bunch weight loss, and TMPx 548-4 and FHIA 22 suffered no loss. These results su ggest that under the conditions specified in this study, these hybrids coul d be tentatively classified as 'field tolerant' to BSV.