Studies on tolerance of rice cultures against brown planthopper, Nilaparvata lugens

Studies to investigate the tolerance mechanism of resistance in some selected rice cultures, which were found to be highly resistant to moderately resistant in glasshouse and field screening against brown planthopper, Nilaparvata lugens were carried out in the glasshouse conditions on the basis of plant dry weight loss caused due to its feeding. The tolerance and antibiosis index of each test culture was also calculated by comparing dry weight of insect developed and produced on test culture with the susceptible check TN1. The studies were carried out on 30 and 60 days old plants. The mean functional plant loss index (FPLI) was the lowest in MTU IJ 206-7-4-1 (14.7%), NLR 20131 (18.0%), and MTU 1075 (20.6%) compared to resistant check PTB 33 (24.9%) and susceptible check TN1 (31.8%). The mean tolerance index was highest in rice culture RGL 7001 (0.74) and lowest in MTU IJ 206-7-4-1 (0.12). MTU IJ 206-7-4-1 (0.88) and RGL 7002 (0.74) recorded highest mean antibiosis index which were more or equal to resistant check PTB 33 (0.74). The overall results indicated that the rice culture MTU IJ 206-7-4-1 recorded lowest FPLI, tolerance index and highest antibiosis index among the cultures tested and was superior to resistant check PTB 33 in tolerance parameters. MTU IJ 206-7-4-1 also took longer days to wilt at two population levels of BPH nymphs.