Reciprocal Translocation in Rice (A Preliminary Note)

Abstract

Structural change of the chromosomes seems to be little known in the rice plant, though it has been discovered early by Ramiah et al 1935. The writers investigated several semi-sterile strains induced by X-ray irradiation, and recognized their sterility was due to ”reciprocal translocations”. Some genetical and cytological observations of those strains will be reported in this paper. Two varieties, Taichung no. 65 (a representative Horai or Japanese variety in Formosa) and Pei-ku-fua-lo (a native variety of first-crop-nature, were used. Germinating seeds were X-rayed by one of the writers, Chang, in the Agricultural College of National Taiwan University, on Feb. 14, 1948, and field tests were made in the Taiwan Agricultural Research Institnte. Dose of X-ray: 4 m. a., 80 k. v., 30 cm, 80 minutes. A number of semi-sterile plants, different in fertility even within a plant with the ear, were obtained from the X-rayed seeds. In the second generation, there were found several strains which gave fertile plants and semi-sterile plants 50-30 in fertility) in approximately 1:1 ratio. In the third generation and afterwards, the fertile plants were found to breed true, but the semi-sterile plants continued segreation in the same manner ac in the second generation. Such a behavior of sterility seems to be of the same type as found by Ishikawa (1927 and other workers (2, etc). Four strains of this type, taken arbitrarily from those, were observed in the Taiwan Provincial College of Agriculture by Oka and Hong. From each of these four strains, seed of one sterile plant was taken as the materials. Two of them, named XA-1 and XA-2, are the fourth generation seed of Taichung no. 65, and the other two, named XB-1 and XB-2, are the third generation seed of Pei-ku-fua-lo. All of the plants obtained from these seeds showed normal growth and were in appearance same to ordinal Taichung no. 65 or Pei-ku-fua-lo. Variations of the percentage of fertile grain in these strains are given in Table 1. Three strains, XA-2, XB-1 and XB-2, showed clearcut segeregation of fertile and semi-sterile plants, but XA-1 showed a seemingly continuous variation of fertility. Secondly, several plants of each strain were back-crossed to original Taichung' no. 65 or Pei-ku-fua-lo, using the former as the pollen parent. Fertility of paternal plants and the variation of fertility among the plants produced from the back-crosses are given in Table 2. In XA-1, the back-cross produced no sterile plant. In other three strains however, the following facts were found as a general rule: Original variety x fertile plants produced either fertile or sterile plants and the segregation of fertile and sterile plants was never seen within the same cross. In contrast, original variety x semi-sterile plants produced both fertile and semi-sterile plants in the same manner as the selfing of semisterile plants.