7. Inheritance of stigma exsertion in rice

Yun-Bi XU and Zong-Tan SHEN

Zhejiang Agricultural University, Hangzhou, China

Stigma exsertion rate (SER) in rice is a useful trait to improve seed production in hybrid rice. Earlier studies suggest that stigma exsertion is partially dominant (Virmani et al. 1974) or completely dominant (Li et al. 1979, 1981), and is a qualitative character controlled by a major gene (Hassan et al. 1984). Li et al. (1985) have reported it to be a quantitative character. We studied inheritance of this trait from crosses between a cleistogamous cultivar Dalkoku and three lines, viz., 10674, 15-4, and Xie-ping-zao, possessing SER values 72.9%, 67.2%, and 65.7%, respectively. The SER in all F1 was sligtly lower than better parents in the crosses indicating that it was a dominant trait. F2 plants segregated showing exserted and non-exserted stigma in a ratio of 3: 1 (Table 1). The F3 segregation behavior conformed to 1 : 2: 1 ratio (Table 2). These results indicated that stigma exsertion was controlled by one dominant gene.

Continuous variation for SER in F2 generation indicated that some minor genes may be supplementing the major gene in expression of this trait. Since one of the parents in all crosses studied was cleistogamous, these results should be considered more objective.

SER in Japonica rice was lower than that in Indica rice (Xu et al. 1987). It would, therefore, be important to improve SER in Japonica rice. We made a cross between an Indica cultivar (10674) and a Japonica (Nonghu 16B), and backcrossed to the latter. Selection for Japonica or Indica lines with higher SER was made according to their ratio of spikelet length to width (L/W) and phenol reaction. SERs were 69-82% and L/W ratio 1.83-2.20 in F1-F5. SERs for Japonica-like plants in F2-F5 were 60-74%, but that for Indica-like plants were more than 90%. Stigma exsertion had been introduced from Indica rice to Japonica rice through successive backcrossing and selection. SERs in all improved Japonica lines were more than 70% (Table 3), and much higher than that in widely used Indica CMS Zhen Shan 97A. Their L/W ratios was lower than the Indica parent, and the grains showed negative phenol reaction similar to Japonica cultivars. These results suggested that it is possible to improve outcrossing rate in rice through breeding by using parents possessing a high stigma exsertion rate.

Table 1. F2 segregation for stigma exsertion rate (%)
______________________________________________________________
Cross     Total Mean  0%  5 15 25 35 45 55 65 75 85  X2    P
                 %                                  (3:1)
______________________________________________________________
Daikoku/
10674     235   25.4  69 18 35 46 28 16 12  7  3  1  2.16 >O.10
                        |__________________________|             
                                  186

Daikoku/
15-4      137   30.0  28 12 21 28 25  8  7  5  1  2  1.29 >0.25
                        |__________________________|          
                                 109

Daikoku/
Xie       215   31.3  48 22 26 35 40 27 10  3  4     0.68 >0.25
qing-zao                |__________________________|                                                             
_________________________________167______________________________


Table 2. Segregation of F3 lines  for  stigma  exsertion
_______________________________________________________________
                All plants  Exserted   All plants     X2  
         Total  exserted  non-exserted non-exserted (1:2: 1)  P
                          segregating
_______________________________________________________________
Daikoku/
10674     117      30        61            26       0.49  >O.75
Daikoku/
15-4       78      25        38            15       2.62  >0.25
Daikoku/
Xie-      125      42        60            23       5.98  >O.10
qing-zao
_______________________________________________________________


Table 3.  Characters of selected Japonica lines
_______________________________________________________________
                     Plant   SER (%)                     Phenol
         Generation  number  ___________     L/W       reaction
                             Mean  Range
_______________________________________________________________
Nonghu 26B  P1        31     23.4     0-47.6  1.74±0.12     -
10674       P2        25     88.2  52.4-100   2.70±0.23     +
B40         B2F1      24     71.1  37.7-92.1  1.80±0.21     -
B57         F3        24     74.3  67.0-85.1  1.73±0.19     -
B76         B1F3      24     71.2  46.5-90.3  1.86±0.17     -
C171        B2F6      18     79.3  64.2-93.5  1.96±0.18     -
C262        B1F7      20     84.5  75.3-95.4  2.02±0.25     -
_______________________________________________________________
1 Selected from B40.
2 Selected from B76.

References

Hassan, M. A. and E. A. Siddiq, 1984. Inheritance of anther size and stigma exserion in rice (Oryza sativa L.). Indian J. Genet. Plant Breed. 44: 544-547.

Li, Qin-Xiu, Xu-Xian Peng and Yu-Lan Wang, 1979. Wide-cross between Oryza longistaminata A. Chev. et Rochr. and O. sativa L. Sichuan J. Agr. Sci. Tech. 1: 65-66.

Li, Qin-Xiu, Biao-Xi Liu and Yu-Lan Wang, 1981. Study on wild rice with longer stigma and its use. Sichuan J. Agri. Sci. Tech. 6: 10-20.

Li, Tao and Yi-Wu Chen, 1985. Genetics of stigma exsertion in rice. RGN 2: 84-85.

Virmani, S. S. and D. S. Athwal, 1974. Inheritance of floral characteristics influencing outcrossing in rice. Crop Sci. 14: 350-353.