Diallel analysis of callus growth and plant regeneration in rice seed-callus

Genetic characteristics of callus growth and plant regeneration in rice with seed-derived calli were studied in 6 × 6 diallel crosses using Japonica cultivars. Genetic parameters estimated by Hayman's method showed the high additive gene effects and involvement of two groups of genes for callus growth, which were identified as incomplete dominance. On the other hand, both dominance and additive effects were important for plant regeneration, and further epistatic effects were observed in this character, while the analysis of 5 × 5 subdiallel for plant regeneration showed non-epistatic relation and involvement of 2 groups of genes. Graphical analysis using Vr and Wr for the callus growth showed that Norin 1, Somewake and Daikoku 1 possessed dominant genes which suppress callus growth, while Kuju, Sasanishiki and Murasaki-ine whose callus growth was more vigorous had recessive genes. The frequency distribution of callus growth in F2 generation between Kuju and Somewake showed a segregation which agreed with the expected ratio for a single factor control (3:1). On the other hand, relationship between Vr and Wr in the 5 × 5 subdiallel for plant regeneration showed that Daikoku 1, which had a relatively high capacity for plant regeneration, possessed more dominant genes, while Norin 1 and Kuju, which had lower capacities, possessed recessive genes. The reciprocal F1s between Norin 1 and Somewake showed excellent capacities for plant regeneration (average of reciprocal crosses: 62%). Strategies for genetical improvement of plant regeneration are discussed.