References
A glutinous variety of tropical Japonica type from the Philippines, Ac. 221
(Inakupa), is non-sensitive to photoperiod and its heading time is 26 days
(winter season) to 12 days (summer season) later than that of T65. It tends to
chlorosis in the seedling stage when temperature is low, and is characterized
by glabrous hulls and a red pericarp. The F\1\ plants of T65x221 showed the
same heading date as of T65 (e-type), and the B\1\F\1\ population (T65xF\1\)
segregated into 7 early (E-type), 7 medium, and 6 late (e-type) plants. From
the selfed progeny of the E-type plants, a homozygous early-heading line, (1)
211-E, was obtained, and its cross with T65(20)Ea carrying Ea (Ef-1a)
proved that variety 221 had an E allele (Tsai 1985a).
From the B\1\F\2\ population, a homozygous late-heading line, (1)221-L, was obtained which headed 14 days (winter season) to 8 days (summer season) later than T65. To assess its late-heading genes, it was crossed with T65 and T65(20)Ea, respectively. The F\1\ plants of T65x(1)221-L were a T65 (e) type, and the F\2\ population segregated into 106 T65 and 42 (1)221-L types, giving a good fit to a 3:1 ratio. This suggests that (1)221-L has recessive late-heading gene lf-2(t), and T65 has its dominant allele, +lf-2. The F\1\ plants of T65(20)Eax(1)221-L showed an early heading time (E-type), and the F\2\ population segregated into 82 early (E-type), 59 T65 (e-type), and 8 late (221- L type) plants. The segregation pattern shows fitness to a 9:6:1 ratio, which may be interpreted as 9 (E+lf-2):6(E lf-2 and e+lf-2):1(e lf-2) assuming that E and 1f-2 are independent and lf-2 homozygote combined with E expresses a phenotype similar to the T65 (e+lf-2) type (Table 1).
Table 1. F\2\ segregation for heading time observed in crosses of a late-
heading line (1)221-L with other lines.
=============================================================================
Cross F\1\ F\2\ heading-time class Very F\2\ X2
heading E-type e-type lf-2 lf-2 late total
type -12 0 +12 +25 +60 no.
=============================================================================
(1)221-l x T65 e (T65) 106 42 148 0.9
(3:1)
" x T65(20)Ea E-type 82 59 8 149 0.8
(9:6:1)
" x T65(0)lf e (T65) 63 39 24 14 140 12.7**
(9:3:3:1)
" x AB60-L-1 " 137 34 34 19 224 5.8
" x AB60-L-2 " 82 33 20 15 150 6.6
" x AB60-L-3 " 95 17 30 7 149 6.5
=============================================================================
** Significant at 1% level
A recessive gene for late heading, symbolized lf-1(t), has been found in an
induced late-heading mutant, T65(0)Lf, as well as in late-heading offtypes
obtained from hybrids between early heading lines, such as AB60 L-1, L-2, and
L-3 (all alleles at the same locus), as reported elsewhere (Tsai 1985b). The
lf-1 gene was also independent of the E locus and when combined with an E
allele, expressed a phenotype similar to an e (T65) type. It resembles lf-2 in
these respects, but the lf-1/lf-1 plants are photoperiod sensitive and about 25
days late-heading as compared with T65 in the summer season. For testing
allelism, (1)221-L with lf-2 was crossed with lines having lf-1. The F\1\
plants were of T65 (e) type, and the F\2\ populations showed a transgressive
range of segregation from the T65 type to a very late one which was about two
months later-heading than T65 (Table 1). This indicates that lf-1(t) and lf-
2(t) are independent. By comparing the heading time of plants sown in May and
June, it was also found that plants with lf-2 were not sensitive to photoperiod
while those with lf-1 were sensitive (Table 2).
Table 2. Test for photoperiodic response of T65 and late-heading lines
References
Oka, H.I., 1958. Photoperiodic adaptation to latitude in rice varieties. Phyton 11: 153-160.
Tsai, K.H., 1985a. Further observations on the Ef-1 gene for early heading. R.G.N. 2: 77-78.
Tsai, K.H., 1985b. Analysis of genes for late heading in rice. New Frontiers of Breeding Research. Proc. 5th Intern. Congr. SABRAO, p. 221-326.