Effect of gamma irradiation on variation in segregating generations of F₂ seeds of rice

The F₂ seeds of two rice crosses, Himalaya 1 x Phul Patas 72 and Himalaya 1 x China 988, were irradiated with 25 kR gamma-rays. The mean values of F₂M₁ generation decreased as compared to F₂ for plant height, spikelet fertility and grain yield in both the crosses, and for panicle length and 100-grain weight only in the cross Himalaya 1 X China 988. On the other hand, mean values in the F₃M₂ generation for spikelet fertility and grain yield increased in both crossesas compared to F₃. However, the variance of F₃M₂ generations did not differ significantly from that of F₃ generation in both the crosses for the characters studied, except for grain yield in the cross Himalaya 1 x China 988. Estimates of heritability and genetic advance in F₃M₂ were lower than in the corresponding F₃ for all the traits in the cross Himalaya 1 x Phul Patas 72, except for plant height and 100-grain weight. However, the estimates of heritability and genetic advance in the F₃M₂ generation were higher than in F₃ generation for all characters, except 100-grain weight and grain yield in the cross Himalaya 1 X China 988. The study also revealed that irradiation has differential effect on the same character depending on the genetic background of the test/segregating material.