STUDIES ON THE METHODS FOR EVALUATION OF MODERATE RESISTANCE TO THE BROWN PLANTHOPPER, NILAPARVATA LUGENS (HOMOPTERA:DELPHACIDAE) IN RICES,ORYZA SPP.

The modified seedling bulk screening test was used to evaluate the resistance to the browns planthopper in cultivated and wild rice,where five second or third-instar nymphs were used to infest each seedling at the 3.5 to 4 leaf stage.The results indicated that this screening technique could be used efficiently to identify resistance not only in the resistant rices,but also in the moderately resistant ones.But if the insect population was changed to 14 nymphs per seedling at the same leaf stage,the plants with moderate resistance would be rated as susceptible.Tolerance was evaluated as functional plant loss index (FPLI) based on plant dry weight using the formula described by Panda and Heinrichs (1983 ).On the other hand,a similar mathemetical formula based on plant growth rate used was as follows:The FPLI that was calculated on the basis of plant growth rate was demonatrated to exhibit the same trend as that based on plant dry weight.Therefore using the former parameter in determining the FPLI will save time and labor,and is not detrimental to the seedlings,since it only involves measurement of plant height.