14. 
Effects of genes controlling plant height in near-isogenic lines of Indica and
Japonica cultivars
K.H. TsM
Department of Agronomy, National Chung Hsing University, Taichung, Taiwan 40227

 
We have two famous rice varieties in Taiwan. Taichung-Native 1 (abbr. TN-i) is the first Indica variety carrying the well known Dee-geo-woo-gene semidwarfing gene, sdi (previous symbol was sd-i; Suh and Heu 1978 ; Kikuchi and Ikehashi 1984 : Tsai 1991 Linkage group 1). This semidwarf variety was selected from a cross of Dee-geo-woogene x Tsai-yuan-chung in 1949 (Huang et a!. 1972), which contributed to the “Green Revolution” in rice (Oka 1974). Taichung 65 (T65) is a Japonica rice variety selected from a cross between two Japanese varieties, Kameji and Shinriki, around 1923 (Iso 1957). T65 is well known for its wide adaptability (Matsuo et a!. 1972), and has tall stature (Tsai 1989).
The sdi gene derived from TN-i was first introduced into T65 and a dwarf nearisogenic line of T65, T65(8)sd1, was produced after eight backcrosses, where (8) indicates the number of backcrosses. It was observed that in the genetic background of T65, +sdl, seemed to be incompletely dominant over sd1. The allele, sdi, shortened the elongated internodes moderately, therefor it reduced the plant height strongly (Tsai 1989; Murai et a!. 1995).
On the other hand, a tall near-isogenic line of TN-i derived form T65, was obtained after six backcrosses using TN-i as the recurrent parent, which was coded as TN1(6)T. TN-1(6)T headed four days earlier than TN-i, but headed almost at the same time as T65. TN-1(6)T was 28-34cm taller than that of TN-i, and 7-13 cm taller than that of T65.
TN-i and TN-1(6)T had the Indica background, and T65 and T65(8)sdl had the Japonica background, and they were intercrossed. The degree of dominance for plant height observed in their reciprocal F1 plants is shown in Table 1. The allele for tall stature appeared incompletely dominant over sdi, in the backgrounds of the two varieties, although it showed somewhat a larger degree of dominance in the background of the Japonica variety (T65) than that shown in the Indica one (TN-i). The F2 populations of these cross combinations showed 1 tall : 2 intermediate : 1 short (or 3 tall : 1 short) segregation ratio. The successive observed results proved that both T65 and TN- 1(6)T had the dominant allele +sdl, and both TN-i and T65(8)sd1 had the recessive allele sdi. For the other

 


 

crosses, their F1’s tended to show the overdominance for tallness, and the F2 populations showed the transgressive type of segregation (Table 1).
The agronomic characters expressed by the two alleles, +sdl and sdl, were compared in the different backgrounds of Indica and Japonica cultivars. Regarding the effects of the allele +sdl, the Indica variety, when compared to the Japonica, had longer panicle and internodes, except for a shorter first internode. With the allele +sdl, the plant height of the Indica variety was 5 to 10 cm greater than that of the Japonica variety. The Indica variety with +sdl seemed to have favorable yield characters, but it proved to be lodging susceptible due to its longer lower internodes. In general, the variety with dwarfing gene shows shorter internodes and plant height than those of the tall variety. The gene sdl almost equally reduced the plant height, panicle length and upper intemodes in the both varietal backgrounds. But, it seems the sdl tended to reduce the lower internodes more in the Indica variety than those in the Japonica variety. Moreover, it did not affect spikelet number per panicle (Table 2). This gene may be useful in breeding Indica variety.
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