22. Genetic control of apiculus hair length

Yo-Ichiro Sato

National Insitutue of Genetics, Mishima, 411 Japan

The length of apiculus hair is known to serve an an Indica-Japonica discriminating character as it is longer in Japonica than in Indica. No major genes have yet been reported for this character except for gl-1 and gl-2 for the absence of hair or glabrousness. The mode of inheritance of this character was studied in randomly selected F3 plants and their derivative lines from an Indica x Japonica cross. The parents used were f.145 (Indica, black hull, apiculus hair 0.32mm) and T65 (Japonica, nonblack hull, apiculus hair 0.90 mm).

Fifteen F4 plants derived from F3 lines with apiculus hairs shorter than 0.7mm showed an apiculus hair length ranging from 0.1 to 0.7mm (Table 1). Almost all of 14 F4 plants dreived from F3 plants with apiculus hair longer than 0.7 mm had the same range of hair length as of the parental F3 plants. The F4 plants derived from other 7 F3 plants with similarly long apiculus hair segregated into 2 classes of hair length, shorter and longer than 0.7 mm. The number of plants with short and long apiculus hair were 37:96, which fitted the 1 : 3 ratio expected when monogenic segregation was assumed (x2=0.56, non-significant). The numbers of F4 lines with all long, all short and segregating apiculus hair were 14,15 and 7 respectively, which appeared to fit a 3 : 3 : 2 ratio (x2=0.63, non-significant). These data suggested that the apiculus hair length was controlled by a major gene, although there are other modofier genes. Tentatively this gene is symbolized as Aph/aph.

Of 21 F3 plants with long (longer than 0.7 mm) apiculus hair, only one had the black hull, whereas 8 out of 15 F3 plants with short (shorther than 0.7 mm) apiculus hair showed black hull. Since the black hull is controlled by 3 genes, Ph, Bh-a and Bh-b (Maekawa et al. 1981), Aph may be linked with one of the three genes. Among 26 F3 plants with yellow hull, 18 had Ph and 9 of them had apiculus hairs longer than 0.7 mm and the other 9 had shorter apiculus hairs. Therefore, the aph gene not seem to be linked with Ph. It may be linked with either Bh-a or Bh-b.

Table 1. Variation in apiculus hair length among F4 lines derived from an Indica x Japonica cross.

==============================================================================
Line Hull  Phenol     Apiculus hair length (10-2mm)  
     color react.  -----------------------------------------------------------
                   5  15  25  35  45  55  65  75  85  95  105  115  125 135 145 155
==============================================================================
1     B     +         4   1    4   6   2
2     B     +             3    2  11   4           1
3     Y     +         1   3    7   6   1
4     B     +         1   1    7   4
5     B     +        10   6
6     B     +            21
7     B     +            13    6   1
8     B     +             5    3   9   2   1
9     Y     +     1            2   2   6   5
10    Y     -                  1   2  12   5  1
11    Y     -             9    2   6   1
12    B     +     2   1  16    2
13    Y     -                  2  12   4   1
14    Y     -                  1       5   6
15    Y     -             2    7   3   5

16    Y     -                                         2    3    7    4   3
17    Y     -                                     3   3    7    3
18    Y     +                                         1    2    6    8   4
19    Y     -                                     1   4    9    2
20    Y     +                                     4   8    6    2    2
21    Y     +                                     1  12    7    1
22    Y     -                                 1   1   3    8    5    1
23    Y     -                                 3   8   6    2
24    Y     -                                         8    9    5
25    Y     -                                                        4   2   2  13
26    B     +                                 4   4   5    1
27    Y     +                                     3   5    3    3
28    Y     -                                         4    6    3    3   1
29    Y     -                                         1    3    5    3   1

30    Y     +                     1   2   3   2   5   4    2
31    Y     -                 5   3   1   7   3   1
32    Y     +                     1   1   2   3   3   6    1    2
33    Y     -                             4   5   2   5    2    1    1
34    B     +                     1   1   2       2   6    5    1    3
35    Y     -                         3   1       5   4    1
36    Y     +                         1   1   2   5   5    1    2         2  1
==============================================================================
Underlines indicate the apiculus hair length of respective F3 plants

Reference

Maekawa, M., T. Kinoshita and M. Takahashi 1981. Geographical distribution of the genes for black hull coloration-Genetical studies on rice plant, LXXVII. Res. Bull. Univ. Farm Hokkaido Univ. 22:20-28. (in Jap. with Eng. summary).