25. Genes at the Ef-1 locue found in Fujisaka 5 and two Chinese Indica varieties

The gene for early heading, Ef-1 (abbreviated as E), is known to be distributed in various early-maturing Japonicas (Tsai 1973; Tsai and Oka 1966; Sato and Hayashi 1985). Recently, a tropical Japonica variety from the Philippines (Ac. 221) was also found to have an E allele (Tsai 1985). The E locus is linked with pgl (pale green leaf), recombination value being 27% (Tsai 1986), and is located on Nishimura's 7th chromosome (Sato 1976).

An early-heading line of Fujisaka 5 with Se-1^e (or Lm⁶, nonsensitive to photoperiod; Yokoo and Kikuchi 1982) was six days earlier heading than T65(20)E^a with E^a, when tested at Taichung in both the winter and summer seasons. Se-1 is located on Nishimura's 6th chromosome and linked with pi-z for blast-disease resistance. The F\1\ plants of T65(20)E^axLm^e showed the same heading date as of Lm^e, and the F\2\ plants all headed within the parental range showing a segregation pattern fitting a 1:2:1 ratio. This suggests that Fujisaka 5 has an E allel similar to E^a while T65 has an allele similar to Se-1^e. The six-day difference in heading time between the two strains would be due to an allelic difference either at E or at Se-1 locus, or another gene could be involved.

Two early-heading Indica varieties from China, Hsiang-ai-tsao 9 (TK-74) and Chao-yang-tsao (Tk-111), were backcrossed to T65 four times, and semi-isogenic lines showing similar characters as of T65, Tk-74(4) and Tk-111(4), were obtained. Their heading dates were 17 and 11 days earlier than that of T65 in the winter season, respectively, and were both 14 days earlier than that of T65 in the summer season. Their heading dates were therefore similar to that of T65 (20)E^a, Tk-74(4) being 4 days earlier and Tk-111(4) 2 days earlier than the latter. The F\1\ plants of T65(20)E^axTk-74(4) and T65(20)E^axTk-111(4) showed the same heading date as of the earlier parent. The heading dates of the F\2\ plants were distributed within the parental range and had a larger variance than those of the parents. Exceptionally, a late-heading plant of T65 type was found among about 200 F\2\ plants observed in both ocrosses. This may be regarded as an offtype as discussed by the author elsewhere (Tsai 1986). Its frequency is much lower than 1/16 or 6.25%, expected when two independent earliness genes are assumed. Therefore, the experimental results can be taken as indicating that the two Chinese Indica varieties have an E allel at the same locus.

References

Sato, S., 1976. Linkage analysis of rice plant, by the use of reciprocal translocation lines. Bull. Col. Agric., Univ. of Ryukyus 23: 73-104.

Sato, Y.I. and K. Hayashi, 1985. The genetic control of basic vegetative phase in early-maturing native rice varieties. Jpn. J. Breed. 35: 160-166.

Tsai, K.H., 1983. Comparison of intra-allelic structure related to the major earliness genes involved in isogenic and radiation-induced early-maturing lines of a rice variety, Taichung 65. J. Agric. Assoc. China, N.S. 84: 23-47 (in Chinese with English summary).

Tsai, K.H., 1985. Further observations on the Ef-1 gene for early heading. R.G.N. 2: 77-78.

Tsai, K.H., 1986. Analysis of factors suppressing the effects of genes for heading expression in rice. Jpn. J. Breed. 36, Supplem. 2: 262-263. (in Japaneses).

Tsai, K.H. and H.I. Oka, 1966. Analysis of genes controlling heading time in Taichung 65 and other rice varieties. Bot. Bull. Acad. Sinica 7:54-70.

Yokoo, M. and F. Kikuchi, 1982. Monogenic control of basic vegetative phase and photoperiod-sensitive phase in rice. Jpn. J. Breed. 32: 1-8 (in Japanese with English summary).