Cross Resistance to Stemborers in Rice Varieties12

Abstract

Sixteen rice varieties were tested in the field under the natural insect infestations and 8 varieties were tested in the greenhouse under artificial infestations against Chilo suppressalis (Walker). Tryporyza incertulas (Walker). T. innotata Walker, and Sesamia inferens (Walker). The varieties significantly differed among themselves in their degree of susceptibility to the borers. There was a highly significant correlation between any 2 species, suggesting a general similarity in their susceptibility or resistance to all 4 species. Rexoro, Milfor (6)2, Binolayangun, Muey Nawng 62M, Pankhari 203, and Paimat were consistently susceptible, while TKM 6, PTB 10, Su Yai 20, Mudgo, DV 139, and Taitung 16 were consistently resistant. The field populations of borers differed significantly among the varieties and were closely related to the varietal susceptibility. In general, susceptible varieties had high larval survival and growth and suffered more damage. The larvae on the resistant varieties TKM 6, Chianan 2, and Taitung 16 had very poor growth. Mudgo and DV 139 had high larval survival and growth as well as high field borer populations but suffered less damage because of their tolerance. The actual number of deadhearts in an infested hill or unit area of the field was independent of the total number of tillers. Differences in the borer susceptibility existed even when the varieties were cultivated at identical tiller density.