STUDIES ON THE RESISTANT MECHANISMS OF RICE VARIETIES HAVING MODERATE RESISTANCE TO THE BROWN PLANTHOPPER, NILAPARV ATA LUGENS (STAL)

Rice varieties having a moderate level of resistance (MR) to the brown planthopper (BPH), Nilaparvala lugens, were studied to determine the mechanisms of resistance. The resistance in MR rice varieties was due to a combination of strong tolerance and a certain degree of antibiosis, but the resistant varieties generally had a high level of antibiosis and nonpreference. The number of feeding marks produced by the proboscis of BPH on the MR rice varieties was significantly less than that on the resistant varieties, indicating that the feeding frequency of BPH on the MR varieties was lower. The results showed that the BPH caged on the resistant variety ingested less food consequently the plants suffered slight injury from BPH. The resistant variety Mutlgo had the lowest functional plant loss index (FPLI) and percentage of yield loss compared to the MR and susceptible varieties. The MR varieties such as Zhong shanhong and Baoxuan 2 had a stronger compensatory ability in comparison with the susceptible variety TN,when they were injured by BPH with the same level of population, as demonstrated by the fact that the MR varieties had lower FPLI, higher level of photosynthetic activity and yield. The BPH fed on the MR varieties had lower value of food metabolic utilization than those on the susceptible variety TN1, although among them there were no distinct differences in quantity of food ingested and honeydew excreted. In all varieties tested, the respiratory intensity of the injured plants was significantly lower than that of the healthy ones. But the injured plants of the Mudgo variety had a greater decrease of respiratory intensity than those of other varieties.