Quantitative genetics of rice I. Evidence of unexploited genetical variation for yield and other quantitative characters in modern Indica cultivars

Abstract

The question of whether there is insufficient additive genetical variation among modern rice cultivars of Indica type to allow further responses to selection for grain yield and other characters of agronomic importance has been investigated in ten Indica crosses. The parents and their F 1 and F 3 families of each of these crosses were raised in completely randomised blocks in three experiments carried out in different seasons at the Rice Research and Development Institute (RRDI), Batalagoda, Sri Lanka. The results showed that every character scored, including yield and its components, was heritable in every cross. Assessment of the potential of these crosses indicated that it should be possible to obtain useful transgressive segregants for the majority of characters if 100 single-seed descent lines were raised from each, but that for a minority, it would be necessary to produce as many as 460 such lines. Three of these crosses displayed useful transgressive variation as early as the F 3 generation for the majority of characters, including yield and its components. The predicted yields of the best F 3 family of one of the crosses, whose parents were of the 4 1 2 months age class, and that of the top 1% of recombinant inbred lines that could be extracted from this cross were 9.65 t/ha and 11.37 t/ha, respectively. The results from this investigation provided no support, therefore, for the belief that there is a shortage of exploitable genetical variation among modern Indica cultivars and, in particular, are inconsistent with the view that the crop has reached a yield potential barrier of 10 t/ha.