Screening of Banana Cultivars to Biotic Stresses

An experiment was conducted at the Horticultural Research Station of Bidhan Chandra KrishiViswasvidyalaya at Mondouri, Nadia, West Bengal, India to evaluate 39 banana cultivars of different genomic groups for tolerance/resistance to pests and diseases during the years 2003-2006. The specific responses of the cultivars to leaf and fruit scarring beetle, pseudostem weevil, nematode (Meloidogyne, Rotylenchulus and Tylenchulus), Sigatoka, Panama wilt and bunchy top were observed. The intensity of infestation was recorded following the code used for evaluation in the IPGRI/INIBAP descriptor (1996). The intensity of infestation was scored by coding 0 = inapplicable, 1 = very low or no visible sign of susceptibility (CR: completely resistant), 3 = low (HR: highly resistant), 5 = intermediate (MR: moderately resistant) and 7 = high (S: susceptible). Multivariate analyses of biotic parameters were made following the nearest neighbourhood method of hierarchical cluster analysis of the squared Euclidean distance matrix and the correlation distance matrix, on the basis of characters measured, which were either cardinal or ordinal in nature. According to the proximity matrix cultivars 'Kanchkela-2' (ABB), 'Kanchkela-3' (ABB), 'Kanchkela-4' (ABB), 'Kanchkela-5' (ABB), 'Kanchkela-6' (ABB), 'Kanchkcla-7' (ABB), 'Manua' (ABB), 'Madhubas' (ABB), 'Bichkela-1' (BB) and 'Bichkela-2' (BB), 'Pantharaj' (ABB), 'Kanthali' (ABB) and Kanthali clone (ABB) were similar or alike in their responses to biotic stresses. Likewise 'Agniswar' (AAA) and 'Amritsagar' (AAA) also were very close to each other. Similarly, 'Giant Governor' (AAA) and 'Robusta' (AAA) were similar. Among the cooking bananas, 'Behula' (ABB) remained separate from the other cooking bananas while 'ChiniChampa' (ABB), 'KanthaliChampa' and 'Martaman' (AAB) formed one group; 'Agniswar' and 'Amritsagar' formed another, and 'Malbhog' (AAB) also remained separate. In the principal component analysis, factors having Eigen values more than unity were considered and then the three factors were extracted that explained 78.5% of total variation accounted for in this study. When comparing factor loading of the first factor, it was found that biotic stresses like Sigatoka, leaf scarring beetle, bunchy top and Tylenchulus had a higher positive loading in contrast to the highest negative loading due to weevil. Similarly to the results from the cluster analysis and the principal components analysis, the cultivars were grouped together as expected in the multidimensional scaling (MDS) group plot.