Comparison of stem borer damage and resistance in semidwarf Indica rice varieties and prototype lines of a new plant type

Abstract

The rice ( Oryza sativa L.) “new plant type” (NPT), currently under development at the International Rice Research Institute, Philippines, differs in genetic background and plant architecture from the semidwarf Indica varieties that now predominate in tropical lowland areas. The NPT is derived from tropical Japonica germplasm and has fewer and larger stems and panicles than do semidwarf Indica varieties. We compared stem borer damage and resistance in NPT lines and semidwarf Indica varieties under field and greenhouse conditions. Stem borer damage in field plots of the NPT lines IR65564 and IR68011 was higher than in plots of the Indica varieties IR64 and IR72 during the 1999 dry season but not the wet season. In both seasons, IR68011 had higher densities of egg masses of the striped stem borer (SSB, Chilo suppressalis) than did the other three entries. There were no consistent differences among entries in density of egg masses of the yellow stem borer (YSB, Scirpophaga incertulas). In the 2000 wet season, stem borer populations were low, but SSB egg masses were found only on IR68552-100, the only NPT line in the experiment. In all three seasons, NPT lines had higher proportions of SSB larvae and pupae in stems after harvest, and lower proportions of YSB, than did Indica varieties. In artificially infested field cages, SSB larval survival was highest on reproductive stage plants of IR68011 in the 1999 dry season and there was a trend of higher YSB adult weight on IR68011 in the 1999 dry and wet seasons. Three NPT lines and three Indica varieties evaluated under greenhouse conditions showed no consistent differences in resistance to either stem borer species, as measured by percent survival from egg to adult and female development time and weight. The lack of consistent differences in stem borer survival and development between the NPT lines and Indica varieties was contrary to the expectation that the morphology of the NPT would render it more susceptible to stem borers. Our results indicate that NPT lines are not consistently or strongly more susceptible to stem borers than are improved Indica varieties and suggest that ovipositional attractiveness to SSB is a factor contributing to higher stem borer damage to some NPT lines.