VARIETAL RESISTANCE: FIELD EVALUATION AND SCREENING OF CERTAIN RICE MATERIALS AGAINST THE RICE STEM BORER, CHILO AGAMEMNON BLES., AND ROLE OF SOME FACTORS IN PLANT RELATIVE RESISTANCE

This investigaton was carried out on forty one commercil rice va‌rieties and promising lines to evaluate their relative resistance and select some against rice stem borer, Chilo agamemnon Bles., and role of some factors in this resistance. It proved that :- - Entries; Gz 4255-3-1, Telle Hamsa, Gz 4256-7-4-7 and Gz 4122-23-4-2 were relatively highly susceptible (more prefered) to the rice stem borer infestation showing 10.9-15.2% total damage. On the other hand, entries; Todorokiwase, Gz 4071-16-2-1, Gz4294-10-2, Ka‌gahikari and Gz 4127-2-1-3 were the most resistant (less preferred) showing 2.6-3.5% total damage. - The behaviour of some entries differed as sowing date differed. Most entries were less infested at recommended sowing date than those at the late date. -Rice entries may differ in their susceptibility to the infestation by the rice borer at different stages of the rice plant growth. In general, most of the tested rice entries were more resistant during the tillering stage than flowering stage. - In most entries, the percentage of infestation was affected by the leaf area. There was a positive relationship between them. - Entries of japonice source were less infested with the rice stem borer than indica or commercial varieties. - In general, plant type, sowing date, growth stage, and leaf area play an effective role in the relative resistance of rice plant.