INITIAL SCREENING OF CHILI AND SWEET-PEPPER GERMPLASM FOR RESISTANCE TO CHILI THRIPS, SCIRTOTHRIPS DORSALIS HOOD

A preliminary evaluation for resistance to chili thrips, Scirtothrips dorsalis Hood of 41 and 194 pepper (Capsicum annuum L.) germplasms dur ing 1987 and 1988, respectively, indicated chili accessions may be a p romising source of resistance, In contrast, all sweet pepper accession s tested were highly susceptible. A number of chili accessions produce d a moderate yield, in spite of a high thrips infestation indicating t olerance to S. dorsalis. Rating for thrips damage was more reliable an d efficient than estimating thrips numbers in screening pepper accessi ons for resistance to thrips. Highly significant, positive correlation between ratings at the seedling stage and final rating for thrips dam age indicated the feasibility of screening pepper accessions at the se edling stage. Comparing the similarities in rating among accessions re sulted in 40 distinct groups. The variance-covariance matrix of the da ta from these 40 groups was subjected to principal component analysis. This accounted for 56 and 18 per cent of the variation across the two principal axes, respectively. Projection of chili and sweet pepper ac cessions along these two axes revealed three distinct clusters. About 80 per cent of chili accessions formed the first cluster, 58 per cent of the sweet pepper accessions formed the second cluster and a third c luster exhibited intermediate ratings for thrips damage. The significa nce of these findings in relation to geographical divergence and resis tance to thrips among pepper accessions is discussed.