Testing of blast resistance in F2 rice seedlings in different doses of nitrogen and seasons.

Abstract

Blast resistance in parental rice varieties Zenith, Tetep, Tadukan, Ratna, Karuna and Co. 13 and F2 seedling derived from them were tested during kharif (October, 1981) and rabi (February-March, 1982) seasons applying high and low doses of nitrogen against C1, virulent and C3, less virulent isolates of Pyricularia oryzae. Zenith, Tetep and Tadukan were found resistant and Ratna, Karuna and Co. 13 were found susceptible to either isolates. Genetic constituent for blast resistance in Zenith and Tetep to C1 and C3 isolates was found to be digenic and monogenic, respectively. But in Tadukan two and three genes operate against both the isolates respectively for resistance. Resistant×resistant crosses produced some susceptible plants in F2 generation during both the seasons due to application of low and high doses of nitrogen to C1 isolate only. Susceptible×susceptible crosses could not produce a single resistant plant against C1 and C3 isolates. Variation in nitrogen doses and seasons did not affect the genetic status of the plants. Only we observed some shifting of ratios, i.e., from 13:3 to 9:7, 57:7 to 54:10, and so on due to high dose of nitrogn.