YIELD LOSS IN PLANTAIN FROM BLACK SIGATOKA LEAF-SPOT AND FIELD PERFORMANCE OF RESISTANT HYBRIDS

Plantain (Musa spp., AAB group) cultivation is threatened by black sigatoka (Mycosphaerella fijiensis Morelet), an airborne fungal leaf spot disease. Several black-sigatoka-resistant tetraploid hybrids have been developed by the International Institute of Tropical Agriculture (IITA). Resistance and yield performance of three hybrids were evaluated and compared with the maternal triploid plantain cultivar Obino l'Ewai with and without fungicide treatment. Plantain yield loss from black sigatoka was 33%, as calculated from the difference in yield between the fungicide-treated and non-treated plantain (23.5 and 15.7 t ha-1, respectively). Yield loss ensued from a reduction in the number of fruits per bunch and lower fruit weight. Black sigatoka also caused delayed flowering and harvest, and premature fruit ripening. Sigatoka evaluation at flowering indicated significantly less leaf spot damage in the three hybrids (TMPx 548-4,548-9 and 597-4) as compared with the susceptible plantain. At harvest, however, hybrid TMPx 597-4 displayed a susceptible response, whereas hybrids TMPx 548-4 and 548-9 still showed field resistance. These two hybrids also had improved agronomic traits, such as high yield, shorter stature, earlier maturity and better suckering. Yield of TMPx 548-9 (33.5 t ha-1) was 43% higher than that of the fungicide-treated and twice that of the nontreated plantain, suggesting that its higher yield was due not only to black sigatoka resistance, but also to heterosis. TMPx 597-4 had poor yield performance (12.7 t ha-1), indicating that tetraploidy per se does not increase yield.