Distribution of the complementary genes causing F1 weakness in the common rice and its wild relatives. I. L-2-a gene in Asian native cultivars.

The F1 weakness, found in the crosses of a Peruvian rice cultivar, Jamaica, and Japanese lowland cultivars, is known to be controlled by a set of complementary genes, L-2-a and L-2-b, the latter being carried by Jamaica. Geographical distribution of L-2-a gene was surveyed in the Asian native cultivars. Among 130 Japanese lowland cultivars, 122 proved to carry L-2-a gene. In 55 cultivars from various Asian countries other than Japan, all the cultivars classified as the temperate Japonica, 13, carried this gene. None of 26 Indicas and only one of 16 tropical Japonicas were the carriers of this gene. The posession of L-2-a may be considered as a characteristic of the temperate Japonica type of rice.