Abstract

Three black Sigatoka assessment protocols, (i) assessing disease severity 6 months after planting, (ii) estimating disease development over time in the different accessions, and (iii) assessing the youngest leaf spotted (YLS) at flowering were appraised. The assessment was implemented on 18 diploid accessions together with susceptible and resistant checks, planted in a 4 × 5 rectangular lattice design with two replicates at Kawanda Agricultural Research Institute in Uganda during 2005 to 2007. Natural disease inoculum was used with experimental plots planted in locations between the rows of a susceptible local cultivar that acted as a spreader. All the three assessment techniques were able to classify the Musa accessions into resistant and susceptible classes. However, the rankings of the clones according to their resistance were not consistent. The rankings of YLS correlated positively with those of area under disease progress curve (AUDPC) (P<0.05). The AUDPC rankings correlated strongly with the rankings of disease development time (P<0.001). The AUDPC and YLS significantly predicted bunch weight although the coefficient of determination was low. Overall AUDPC resulted in the highest coefficient of determination (R²=0.84) in detecting black Sigatoka response among the diploid Musa clones. Considering the time taken for the banana plants from planting to flowering, it is recommended that the disease resistance be assessed six months after planting and the disease severity data be converted into AUDPC data.

Key words: Youngest leaf spotted, disease development, severity.