The resistance of twenty one rice germplasms of the guilan province were evaluated in the field under the natural insect infestations against steiped stem borer (SSB) chilo suppressalis WLK. Number of dead hearts, White heads and average number of larvae per hill were recorded during 1995-97. The rice germplasms were significantly different in their degree of resistance to the pest. In all of these tests , the susceptible germplasms had about 10 times more ?dead hearts? and number of larvae per hill than the resistant germplasms. Observations showed that some germplasms which were highly resistant at one stage become susceptible at another stage, while several others maintained their resistance or susceptibility throughort the growth season. This indicates that the factors responsible for"dead hearts" and "white heads" (r=0.27) . cultivars Nemat, 305(IRON-13) abd 338 had consistently moderate resistance, It was Conchided that sone rice germplasms of the Guilan province have moderate resistance to SSB,In general , each one of the three methods used in this evaluation, number of white heads at harvesting season proved to be effective , but using them in combination is more reliable.
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