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.