21. Photoperiodic responses of the earliness gene, Ef1

K.H. TASAI

Department of Agronomy, National Chung-Hsing University, Taichung, 40227 Taiwan

Genetic analyses for heading behavior have been carried out in the genetic-background of a rice variety, Taichung 65 (abbr. T65), which is a representative Japonica (Ponlai) rice cultivar in Taiwan. The early heading gene, Ef1, (previous symbol was Ef-1) located on chromosome 10 (Sato et al. 1988), is known to be present in various cultivars and wild strains, and T65 has its recessive allele, ef1 (previously called e 1) (Tsai 1985; 1986b, c 1987; 1992; 1995; 1996; Tsai and Oka 1966). The different Ef1 (abbr. E1) alleles were considered to be isoalleles (Tsai 1976; Tsai and Oka 1968). Among E1 alleles, the Efl-a (E 1 a ) was derived from a Northern Chinese variety, Tatung-tsailai (Ttg). A carrier of E a1(20) Ea, moves up floral initiation and heading about 10 days as compared with T65 of the e 1 carrier (Tsai and Oka 1965; 1968). At the m-Efl locus, a recessive allele, m-Efl (m), and a dominant allele, m+carried by T65, were found. The m locus belongs to the 7th chromosome (Tsai 1986a). The m alleles were obtained from two donors, Ttg and Bozu 5 (from Hokkaido), and they were named as ma in line (7) ma and mb in (7)mb, respectively. When combined with e1 the m genes had no effect in the second crop season, but moved up the heading time a few days in the first crop season (Tsai and Oka 1970). The main effect of m to emphasize the heading advancing effects of the E1 alleles which is called the E1-m epistasis (Tsai 1980). The lines with E1 and ma (line Em) were for 20 to 10 days earlier heading than those with E a and m + ((20)Ea ). The E1-m epistasis was intensified under high temperature when planted in May. The two donors, Ttg and Bozu 5 both having E1 and m genes in common, had very short heading days when planted in the second crop season. This suggests that varieties grown in high latitude areas have a high temperature response. The recessive gene, ef2 (e2) retarding the heading time of T65 for about 20 days, was obtained from an induced late-heading mutant of T65, and its dominant allele, Ef2 (E 2 ), was carried by T65 (Tsai 1986b, 1990). The e2 locus is independent of both E1 and m loci. The heading time of plants with e1 e2 (2) e2 was much delayed than that of e1 (T65) when planted in May or June under long-days. When e2 , was combined with e1, m, e2 was semiepistatic to e1, m, it was hypostatic to E1m indicated the nonallelic interaction between the e2 and m genes which differed according to the presence of E1 or e1 (Tsai 1986d).

 

Table 1. Changes in genic effects on heading days according to crop seasons,

           different photoperiods and gene combinations

 

 

Line 1)

 

 

Genotype

  No. of days to headin

Seeded in :

Photoperiodic response 2)

Jan.

(1st crop)

July

(2nd crop)

May

N-plot

S-plot

T65

e1m+E2

120.8

88.7

87.5

79.0

9.7

T65(7)1)ma

e1maE2

118.2

90.3

84.5

87.0

-3.0

T65(2)e2

e1m+e2

138.4

106.6

116.0

105.0

9.5

T65e1me2

e1mae2

129.2

98.3

107.5

85.0

20.9

T65(20)Ea

Ea1m+E2

109.2

78.0

76.0

47.0

38.2

T65E1m

Ea1maE2

94.8

58.0

50.0

51.0

-2.0

T65E1e2

Ea1m+e2

117.7

83.8

94.0

51.0

45.7

T65E1me2

Ea1mae2

101.3

59.0

57.5

46.0

20.0

 

Gene combination

 

Genic effects on heading days compared

With e1 and E1, respectively

e1(T65)

0 (120.8)

0(=88.7)

0(=87.5)

0(=79.0)

ma

(with e1)

-2.6

1.6

-3.0

8.0

e2

(with e1)

17.6

17.9

28.5

26.0

mae2

(with e1)

8.4

9.6

20.0

6.0

E1 (compared with e1)

0 (=-11.6)

0(=-10.7)

0(=-11.5)

0 (=-32.0)

ma

(with e1)

-14.4

-20.0

-26.0

4.0

e2

(with E1)

8.5

5.8

18.0

4.0

mae2

(with E1)

-7.9

-19.0

-18.5

-1.0

 

1. ( ): Figure in parentheses indicates the number of backcrossings.
2. Computed based on data of days to heading from 100 X (N-plot-S-plot)/N-plot (in %).
Notes: Day lengths were 11°49'5"∼14°37'0" and 14°29'0"∼12°44'4" in the first (Jan.15 to June 30) and the second (July 15 to Nov. 10) crop seasons, respectively.
  Temperatures around the floral initiation were ca. 19°∼23°C and ca. 26∼28°C in the first and the second crop seasons, respectively

 

The explanation mentioned above is supported by the experimental results shown in Table 1. For testing the photoperiodic responses on heading genes, T65 and its different near-isogenic lines with established genotypes shown in Table 1, were seeded on May 23 to the natural field (N plot) and short-day (S plot, a 9h photoperiod treated from transplanting to heading) plots, respectively, to observe their heading variations. T65 (e1) showed a 9.7% of shortening rate of heading days for the S-plot compared with the N-plot, which can be regarded as the scale of photoperiodic response. But, the line (7) ma had no such response. A line (2) e 2 with the late heading gene, e2 , showed a shortening rate of heading days similar to that of T65. The line e1 me2 advanced the shortening rate to 20.9% that must have been caused by a nonallelic interaction between m and e2 genes.

As for the E1 gene, it increased the heading advancing effect strongly in the S plot compared with its other experiments. It also showed a high photoperiodic response. A line E1 m had the same heading days in both N and S plots showing no photoperidoic response (Table 1). Genes e2 and E1 compensated each other in the first and the second crop seasons, but e2 was epistatic to E1 in the N plot. In the S plot, E1 e2 line had the heading days similar to that of E1 line indicated that there were an epistatic effect of E1 gene to e2 gene. The behavior of line E1 me2 was also similar to that did in the E1 line on heading days. The three lines, E1m, E1e2 and E1me2 had the similar heading days as that had in E1 -line in the S plot. These results showed that E1 gene had a strong epistatic effects to cover the actions of m, e2 and me2, respectively, under the short-day conditions. For convenience, in this note there are no descriptions concerned with the interaction between day-lengths and temperatures that affects the heading times.

(Editor's comment: E1, e1 , etc used in the present note are the abbreviations of Ef1, ef1, etc, and not identical to E1, e1, used by Okumoto et al. (1992))

 

References

Sato, S., I. Sakamoto, K. Shirakawa and S. Nakasone, 1988. Chromosomal location of an earliness gene Ef1, of rice. Japan. J. Breed. 38: 385-396.

Tsai, K.H., 1976. Studies on earliness genes in rice, with special reference to analysis ofisoalleles at the E locus. Jpn.J. Genet. 51:115-128.

Tsai, K.H., 1980. Genetic studies on earliness genes of rice by the use of isogenic lines. J. Agr. Assoc. China 110: 1-22. (in Chinese/English)

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

Tsai. K.H., 1986a. Genie analysis of the emphatic gene, m-Ef, of early- flowering in rice. J. Agr. Assoc. China 130:1-15. (in Chinese/English)

Tsai. K.H., 1986b. Genes controlling heading time found in tropical Japonica variety. RGN 3: 71-73.

Tsai. K.H.. 1986c. Genes at the Ef-I locus found in Fujisaka 5 and two Chinese Indica varieties. RGN 3: 73-74.

Tsai, K., H., 1986d. Analysis of genes for late heading in rice. Proc. 5th Intern. Congr. SABRAO (Nov.25-29. 1985, Bangkok, Thailand): 221-236.

Tsai, K.H., 1987. Genes for early heading found in tropical late heading rice varieties. RGN 4: 85-86.

Tsai, K.H., 1990. Unusual mode of inheritance of heading time and occurrence of weak plants observed in rice. Japan. J. Breed. 40: 133-146.

Tsai, K.H., 1992. AT65-like line obtained from Kameji x Shinriki cross. RGN 9: 71-73.

Tsai, K.H., 1995. Genic analysis for heading time in wild rice strains. Jpn. J. Genet. 70: 555-562.

Tsai, K.H., 1996. Genic analysis for heading time in tropical rice strains. Chinese Agron. J. 6: 91-100. (in Chinese/English)

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, 1966. Genetic studies of yielding capacity and adaptability in crop plants. 2. Analysis of genes controlling heading time in Taichung 65 and other rice varieties. Bot. Bull. Acad. Sinica 7: 54-70.

Tsai, K.H. and H. I. Oka, 1968. Genetic studies of yielding capacity and adaptability in crop plants. 3. Further observations on the effects of earlincss 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. Genetic studies of yielding capacity and adaptability in crop plants. 4. Effects of an carliness gene, mb, in the genetic background of a rice variety, Taichung 65. Bot. Bull. Acad. Sinica II: 16-26.