Suppression of Population Build-up of Brown Planthopper by Resistant Cultivars, with Special Emphasis on Breeding Lines Developed through Repeated Backcrossings

Abstract

To determine the probability and extent of the decrease of brown planthopper (BPH) resistance in japonica type breeding lines, nearly isogenic lines of the two resistance genes, Bph 1 and bph 2, were tested with their recurrent parents in the laboratory and a greenhouse. Difference of antlxenosis in oviposition and feeding by BPH was highly significant between the japonica parent and resistant lines with Bph 1, but less significant or sometimes not significant with bph 2. Difference of antixenosis was not detected between the lines regardless of the number of backcrosses in both sets of Bph 7 and bph 2, except for the fceding tests in Bph 7 Iines. While antibiosis in indica lines was as strong as that of their donor of BPH resistance, the level of antibiosis in japonica lines was usually lower compared to that of their donors of resistance. Decrease in antibiosis in relation to repeated backcrossings was not remarkable in Bph 1. In bph 2, repeated backcrossings seemed to lower the level of antibiosis, though even breeding lines with bph 2 could suppress BPH population build-up so effectively as to prevent hopperburn in the fields.