Tomoko IMAOKA and Yuzo FUTSUHARA
Faculty of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-01 Japan
An early maturing mutant was induced from a Japanese variety, Reimei, after gamma-irradiation. The results of gene analysis and short-day treatment proved that this mutant possesses a single recessive gene responsible for photoperiodic insensitivity.
In order to know the variations due to locality, three characters of the mutant and its original variety were evaluated at 3 different locations. As shown in Fig. 1, the heading date of the mutant was 25, 8 and 15 days earlier in Nagoya, Joetsu and Kurashiki, respectively, than the original variety. Although the culm length of the mutant was reduced by 15 and 8 cm in Nagoya and Kurashiki, respectively, it increased by 2.5 cm in Joetsu. On the other hand, the panicle length of the mutant was reduced by 5 and 0.8 cm in Nagoya and Joetsu, respectively, but increased by 3.5 cm in Kurashiki. Of special interest is the adverse response of culm length and panicle length in Kurashiki where the mutant had longer panicles in s ite of shorter culm length, demonstrating that the response of varieties to different environmental conditions considerably varied according to characters.
Oka (1967) reported that the Ponlai varieties of Taiwan obtained after repeated disruptive seasonal selections were insensitive to photoperiod and produced a high yield in both the first and second crop seasons. Matsuo et al. (1972) reported that such Taiwan varieties generally had a high mean yield and showed an average stability among a number of varieties tested in the world. In this study, it was found that the hotoperiodic insensitive mutant had low variability for different local environmental conditions, at least in sofar as heading date is concerned, corroborating the above-mentioned findings.
This early maturing mutant appears promising not only as a breeding material, but also as an experimental material for studying developmental genetics.
Fig 1. Character variations of the early maturing mutant and its original variety in 3 different locations.
Matsuo, T., F. Kikuchi and K. Kumagai, 1972. Studies on the adaptability of rice. I. Comparative studies on the adaptability of rice varieties tested under different conditions in temperate zone. Jpn. J. Breed. 22: 83-91.
Oka, H. I., 1967. Mechanisms of seasonal and regional adaptabilities and yield stability in crop varieties and selection for them. (in Japanese) Advances in Breeding Sciences 8: 42-47. Yokendo, Tokyo.