13. Genes for early heading found in tropical late-heading rice varieties

Kuo-Hai TSAI

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

An Indica strain from the IRRI, IR4227-18-3-2 (hereinafter written as IR4227) showed a heading time 26 days later than that of Taichung 65 (T65) in both the winter and summer crop seasons at Taichung. However, its F1 plants with T65 headed 8 days (winter) or 5 days (summer) earlier than T65. The F2 populations segregated into the 5-day early type, T65 type, an about 10 days late- headin type, and the IR4227 type (in summer, Table 1). The B1F1 plants with T65 produced the E-type (about 10 days earlier than T65, like the isogenic line with Ef-1) in addition to the 5-day early type and T65 type. The B1F2 populations from the B1F1 plants of the E type showed a range of heading time from a "very early" type (earlier than the E type, in-between the E and E m types) tp the IR4227 type (Table 1). There were many segregants of the E type and a few of the "very early" type. The selfed progenies (F3) of two E-type plants showed a heading time close to that of the "very early" type. The frequency of plants of the IR4227 type was around 1/16, suggesting that the IR4227 type carries two recessive genes for late heading.

Table 1. Distribution of heading time in F2 Populations 
between T65 and IR4227
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           Earlier E-type Earlier  T65-type Later   IR4227 Total
Population E-type         T65-type         T65-type  type  no.of
          -20 days  -10     -5        0      +10     +26  plants
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T65 X IR4227                 F1
F2                           20       9       8       3      40
B1F1(T65XF1)         8       26       15                     49
B1F2(3-3)     4     80       37       36      2       9     168
(5-2)         2     34       42       91      9      14     192
(7-1)        17     63        3       13                     96
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 (1986, summer season)

IR4227 is a late-heading strain, but it carries genes for early heading and perhaps another gene which suppresses the early-heading genes. The mode of segregation of early- and late-heading plants observed in this cross is similar to that found in the cross between a Philippine late-heading variety, Ac221 and T65 (Tsai 1985, 1986). The early-heading segregants obtained from the Ac221 cross, after being selfed and fixed, were crossed with T65(20)Ea carrying Ef-1a . The result proved that the early-heading gene of Ac221 was allelic to Ef-1.

The Aman varieties of India are highly sensitive to photoperiod. They do not produce panicles in the winter (long day) season at Taichung. The F1 plants of reciprocal crosses between an Aman strain and T65 showed, however, an early heading date in the winter season, being 11 to 14 days earlier than that of T65. The Aman variety would also carry a dominant early-heading gene. Whether or not these early-heading genes found in tropical late-heading varieties are allelic to Ef-1 is now under observation.

References

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

Tsai, K. H., 1986. Genes at the Ef-1 locus found in Fujisaka 5 and two Chinese Indica varieties. RGN 3: 73-74.