GREENHOUSE EVALUATION OF RICE CULTIVARS FOR RESISTANCE TO GALL MIDGE,ORSEOLIA-ORYZAE (WOOD-MASON) AND STUDIES ON MECHANISM OF RESISTANCE

A total of 2256 germplasm accessions, 3000 advanced generation breedin g lines and 150 released varieties of rice were screened under artific ial infestation in the greenhouse. Among these, 15 new germplasm acces sions, 50 breeding lines derived from 16 crosses and 15 released varie ties were resistant. Antibiosis was the predominant resistance mechani sm; antixenosis affecting oviposition was noted in 33 resistant variet ies. Biochemical composition of a set of resistant varieties along wit h susceptible checks, revealed that nitrogen content of seven test var ieties was significantly higher than that of the susceptible checks, w hile in other six varieties it was lower than the checks. Similarly, e ight of the resistant varieties had considerably higher percentage of polyphenolic compounds in basal stem portion, but seven other cultivar s showed significantly lower concentration as compared to susceptible checks. Thus, it was apparent that there was no clear trend among the resistant cultivars as a group in relation to quantitative differences of chemical components analysed.