(1) Plant Breed. Lab., Faculty of Agriculture, kyoto University, Sakyo-ku, Kyoto, 606
An earliness gene, Ef-1, which is located on Nishimura's 7th chromosome (Sato
and Shinjyo 1983), was first detected by Tsai and Oka (1965). From the
recurrent backcrosses of Taichung 65 with two varieties, Tatong-tsailai and
Bozu 5, six different isogenic lines were developed in the genetic background
of Taichung 65; ef-1m+ (=Taichung 65), Ef-1am, Ef-1bm, Ef-1am+, Ef-
1bm+ and ef-1m, where Ef-1a and Ef-1b are the alleles at the Ef-1
locus, each of which accelerates floral differentiation by approximately one
week, and m is a modifier which promotes the action of Ef-1 by more than 10
days (Tsai and Oka 1970).
All isogenic lines, with the exception of the line having Ef-1am, were sown on every 15th day from April 10 to June 24 in Kyoto, Japan, and days to heading from sowing (DH), number of leaves emerging on the main stem (NL), culm length (CL), lengths of upper four internodes (In1-In4) and number of elongated internodes (NI) on the main stem were investigated, to clarify the effect of Ef-1 on internode elongation and final culm length.
DH ranged from 67.6 to 132.1, and NL from 12.4 to 19.2 over all lines and sowing times. DH was highly correlated with NL for each line and sowing time. Thus between both the characters, a high positive correlation coefficient, 0.84, was obtained even when all lines and all sowing times were pooled. When NL was more than 15, four characters, CL, In3, In4 and NI were all positively and highly correlated with DH and NL for each line and for each sowing time, and their regression coefficients on DH and NL were little different from each other between lines and sowing times. When sowing times and lines were pooled, however, the correlation coefficients of the four characters with NL, 0.87- 0.94, were much higher than those with DH, 0.53-0.77. When NL was 15 or less, on the other hand, those characters were almost constant, irrespective of NL, as was observed in the relationship between NI and NL (Takeda 1977).
These results clearly indicate that when NL exceeds 15, CL and some other characters closely related to internode elongation are determined by NL. This suggests that Ef-1 does not act directly on internode elongation and culm length, but indirectly, through the decrease in the NL caused by its primary action, i.e., the acceleration of floral differentiation. This is also supported by the finding of Tsai and Oka (1968) that the pleiotropic effect of Ef-1 on number and size of organs is the secondary effect of the gene.
References
Sato, S. and C. Shinjyo, 1983. An experiment of genetic study on heading time in rice, Oryza sativa L. Bull. Col. Agr., Univ. Ryukyus 30: 145-153 (in Japanese with English summary).
Takeda, K., 1977. Internode elongation and dwarfism in some gramineous plants. Gamma Field Symp. 16: 1-20.
Tsai, K.H. and H.I. Oka, 1965. Genetic studies of yielding capacity and adaptability in crop plants. 1. Characters of isogenic lines in rice. Bot. Bull. Acad. Sinica 6: 19-31.
Tsai, K.H. and H.I. Oka, 1968. Ibid. 3. Futher observations on the effect of earliness gene E, in the genetic background of a rice variety, Taichung 65. Bot. Bull. Acad. Sinica 9: 75-88.
Tsai, K.H. and H.I. Oka, 1970. Ibid. 4. Effects of an earliness gene, mb, in the genetic background of a rice variety, Taichung 65. Bot. Bull. Acad. Sinica 11: 16-25.