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
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+-.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.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.
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 0. 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.