22. Multiple alleles detected at locus sd-1

Kuo-Hai TSAI

Agronomy Department, National Chun- Hsing University, Taichung, Taiwan 40227, ROC

Taichung 65 (T65) is a representative Ponlai (Japonica) rice variety of Taiwan, known to have a wide adaptability. There are two strains of this variety, one preserved at Taichung (T65-T) and the other at the University of Ryukyus (T65-R). T65-R is six days earlier heading and somewhat taller than T65-T when tested at Taichung in the winter crop season (Tsai 1986). Hybrids of T65-R with T65-T and its early-heading isoline, T65(20)Ea were investigated to look into their genic differences.

The F2 population between T65-R and T65(20)Ea Segregated into 120 early: 47 T65 types (including R- and T-types) showing fitness to a 3:1 ratio. Among T65-type segregants, one dwarf offtype was found, and its progeny was fixed and named T65d. The characters of this line were compared with those of T65-T and its two semidwarf isolines, 32-68 with sd-1 introduced from TN1 (Taichung native 1) and D65-313 with sd-7(t) induced by X-ray irradiation (Tsai 1989); suffixes 8 and 3 indicate the number of backcrosses. Line T65d was about 12 cm shorter than T65-T, and about 12 cm taller that 32-68. Its height was similar to that of D65-313 with sd-7 (Table 1).

Table 1. Plant height of T65 and its semidwarf lines
==============================================================================
Line (Author's code)                           Height (cm)
                                            Winter     Summer
==============================================================================
T65-T                                        102        99
T65sd-1 (32-68)                               75        73
T65sd-7 (D65-313)                             87        85
T65sd-1a (T65d)                               90        86
F1, T65xsd-1a                                           97
F1, T65sd-1 X sd-1a                                     84
F1, T65sd-7 x sd-1a                                    100
==============================================================================

Crosses were made for testing allelism of dwarfing genes carried by the three semidwarf lines. The F1 plants between T65 and T65d were similar to T65, and the F2 segregated into 3 tall (T65): 1 short (T65d), suggesting that T65d has a recessive allele for its dwarfism. The F1 plants from T65d X 32-68 with sd-1 showed the same stature as of T65d, and the F2 segregated into 3 T65d type: 1 sd-1 type (Table 2). This suggests that T65d has a dwarfing allele at the sd-1 locus which is dominant over sd-1. This allele is named sd-1a. T65 has allele +sd-1 at this locus, which is known to be incompletely dominant to sd-1 (Tsai 1986). Accordingly, there is a multiple allelic series consisting of +sd-1, sd-1a , and sd-1, which is located on chromosome 1.

On the other hand, the F1 plants between lines with sd-1a and sd-7(t) showed the same stature as of T65, and the F2 segregated into 9 T65: 6 semidwarf (similar to parents): 1 double recessive type (Table 2). This shows that sd-1a and sd-7(t) are independent.

Table 2. F2 segregation patterns between T65 and its semidwarf lines
=============================================================================
Cross             Plants showing type        Double   No. of   X2 (ratio)
            ==============================   dwarf    plants
             T65  sd-1a    sd-7    sd-1
=============================================================================
T65xsd-1a     78    22                                 100     0.48(3:1)
sd-1xsd-1a          62              26                  88     0.97(3:1)
                    ______
sd-7xsd-1a    81      66                      12       160     2.40(9:6:1)
=============================================================================
All chi-squares are non-significant.

 

References

Tsai, K. H., 1986. Possible genic differences between two Taichung 65 strains, one preserved at Taichung and the other from Ryukyus. RGN 3: 75.

____, 1989. An induced dwarfing gene, sd-7(t), obtained in Taichung 65. RGN 6: 99-101.