Season and plant age effect evaluation of plantain for response to black sigatoka disease.
The response of 110 Musa spp. cultivars to black sigatoka caused by Mycosphaerella fijiensis was studied in 1990-91 at IITA-Onne, in southeastern Nigeria, under natural infection conditions. The plant crop cycle was divided into 3 periods according to different combinations of climate and growth stages of the plant: rainy season before flowering, dry season before flowering and rainy season after flowering. All Musa cultivars were rated susceptible because the final symptom stage developed within 18-25 d. Before flowering, black sigatoka development was faster in the rainy season than in the dry season. Significant correlations were found between rainfall and incubation time (r=-0.62, n=12). Symptom evolution time and youngest leaf spotted were correlated both in the rainy season (r=-0.98, n=110) and the dry season (r=0.66, n=110) suggesting that data recording is more effective in the rainy season than in the dry season. The higher correlation in the rainy season appeared related to favourable conditions for host plant and fungus development. Both symptom evolution time and youngest leaf spotted were useful variables for determining host plant response to black sigatoka. In the rainy season after flowering, Musa cultivars developed symptoms of black sigatoka more slowly than in the rainy season before flowering, suggesting a change in the host susceptibility with age.