Heterosis in Japonica/Indica F1 Rice Hybrids with Special Reference to Nodal Root Function.

Abstract

Although root system of japonica/indica F1 hybrids of rice (Oryza sativa L.) must play an important role for expression of heterosis, few studies have been conducted. This study was carried out to evaluate how the function of root system in japonica/indica F1 rice hybrids is related to heterosis for shoot growth. Two F1 hybrids grown in culture solution for 45 days after sowing and F1 hybrid cultured in soil-filled pots till full ripening were compared with parents. Shoot dry weight of F1 hybrids was greater than that of parents when their stem and nodal root numbers were similar to those of parents. Heterobeltiosis for shoot dry weight reached the maximum 180 when the F1 hybrid surpassed parents in the stem and nodal root numbers. F1 hybrids were the same as one or both parents in S/R ratio, but dry weight of a single nodal root of F1 hybrids exceeded that of parents in most cases. Moreover, nitrogen uptake rate of a single nodal root (Nno) as well as leaf area and shoot dry weight of a single nodal root in F1 hybrids was greater than those in parents during vegetative growth. Nitrogen uptake rate per root system dry weight (Ndw), however, was much the same. These results strongly suggest that in japonica/indica F1 hybrids, more photosynthate is partitioned to each nodal root, so that this enhances its function and consequently, the entire root system.