Rapid and mass screening of banana and plantain for resistance to Black sigatoka disease using detached leaf and in vitro plantlets

We describe the use of in vitro plantlets in tubes and detached leaves in screening Musa genotypes against Mycosphaerella fijiensis, the causal agent of Black sigatoka disease. The utility of these two assays was evaluated using eight genotypes with different levels of disease resistance. Differences in disease response were observed when in vitro plantlets in tubes and detached leaves of selected Musa genotypes with different levels of disease resistance were inoculated with M. fijiensis. The response of genotypes depended on their level of disease resistance, with resistant genotypes having longer incubation times and smaller infected leaf areas compared to the susceptible cultivar 'Agbagba' and to relatively less resistant genotypes. A similar pattern in cultivar response was observed for symptom evolution time. Although symptom stages appeared earlier on in in vitro plants compared to detached leaves, genotypes were consistently ranked based on their level of disease resistance. Disease severity data from the two assays were strongly correlated, with higher severity being observed on the susceptible cultivar 'Agbagba' and lowest severity on resistant land race 'Calcutta-4'. The remaining genotypes had disease severity levels corresponding to their levels of resistance to Black sigatoka disease. Based on these results, we conclude that these two rapid assays are reliable for screening banana and plantain for resistance to Black sigatoka disease. (author)