36. Cytoplasmic diversity among CMS lines of rice

Cytoplasmic diversity among CMS lines is desirable to reduce potential risk of genetic vulnerability in F1 rice hybrids developed by using a single CMS system. A number of cytoplasmic sources have been reported in China, IRRI and elsewhere (Lin and Yuan 1980; Virmani and Edwards 1983; Li and Zhu 1988; Virmani and Wan 1988). Virmani and Shinjyo (1988) reported current status of analysis and symbols for male sterile cytoplasm in rice. This report provides results on cytoplasmic diversity among six CMS lines of rice.

Four indica cytoplasmic male-sterile lines, viz., IR54753A (cms-WA), IR54755A (cms-ARC), Yar Ai Zhao A (cms-GAM) and MS 577A (cms-sp) and two japonica CMS lines, viz., Wu 10A (cms-bo) and Reimei A (cms-KR) were testcrossed with 28 rice cultivars from IRRI, India, Indonesia and Korea. Two cultivars from Korea were Japonica types while others were Indicas or Indica/ Japonica derivatives (Tongil type). CMS line MS 577A was developed in Korea (M. H. Heu, personal comm.) from an unidentified accession of Oryza sativa f. spontanea and its cytoplasm was designated as (cms-sp). Twenty-five to thirty F1 seeds per cross were produced, although some of the crosses did not set seed. The F1 plants of these crosses were grown each cross in one row of ten plants along with the corresponding male parent. The test-cross progenies were classified as fertile (spikelet fertility above 70% and comparable with corresponding male parent), partially fertile (30-70% spikelet fertility), partially sterile (1-30%), and sterile (0-1% spikelet fertility).

Results of test-cross F1s involving four indica CMS lines are presented in Table 1. IR54753A (cms-WA) and IR54755A (cms-ARC) showed differential fertility reaction in 12 out of 28 testcrosses; IR54753A and Yar Ai Zhao (cms- GAM) showed differential fertility reaction in 8 out of 9 testcrosses; IR54755A and Yar Ai Zhao A also showed differential reaction in 8 out of 9 testcrosses. MS 577A (cms-sp?) showed differential reaction from IR54753A (in 13 out of 16 crosses), from IR54755A (in 7 out of 16 crosses) and from Yar Ai Zhao A (in 8 out of 8 crosses). These results indicate that the cytoplasmic factors controlling male sterility in the four CMS lines are different.

Table 1. F1 spikelet fertilities of four indica CMS lines test-crossed with a set of cultivars from IRRI, India, Indonesia and Korea (1988 dry season, at IRRI)

The F1 plants from crosses of two japonica CMS lines, Wu 10A with cms-bo and Reimei A with cms-KR, with 23 cultivars (13 from IRRI, 5 from India, and 5 from Korea) were mostly sterile although three were partially sterile (1-30%). Exceptionally, the crosses of Wu 10A with two Korean Japonicas (Iri 376 and Milyang 84) showed partial fertility (30-70%). Probably, the F1 sterility in these crosses involves ordinary genic sterility in addition to cytoplasmic sterility. In contrast, many crosses of IR54753A (cms-WA) with the same 23 cultivars showed fertility restoration similarly as is seen in Table 1. ln view of quite similar F1- sterility reactions observed between Wu 10A and Reimei A, these two japonica CMS lines may be regarded as having the saine CMS factors which are different from those in cms-WA, although further investigations are needed for conclusion.

From the above results it is evident that CMS lines, IR54753A, IR54755A, Yar Ai Zhao A, MS 577A, possess different cytosterility systems. Young et al. (1983) had also found that CMS lines, V2OA and Zhen Shan 97A (derived from WA cytoplasm), Yar Ai Zhao A (derived from Gambiaca cytoplasm), MS 577A (derived from 0. sativa f. spontanea cytoplasm in Korea) and Wu 10A (derived from Chinsurah Boro II cytoplasm) possessed different cytosterility systems. Therefore, designation of cytoplasm, cms-WA, cms-GAM, cms-ARC and cms-bo as proposed by Virmani and Shinjyo (1989), can be retained. Reimei A (derived from a 0. rufipogon line KR 7 (Cheng and Huang, 1979) appear to have a cytosterility system identical to cms-bo. Therefore both Wu 10A and Reimei A may have the same cytoplasmic designation.

Cheng, Y. K. and C. S. Huang, 1979. Studies on cytoplasmic-genetic male sterility in cultivated rice (Oryza sativa L.). 1. Effect of different cytoplasmic sources on male abnormalities at anthesis. J. Agric. Assoc. China 106: 11-22.

Li, Z. and Y. Zhu, 1988. Rice male sterile cytoplasm and fertility restoration. Pages 85-102. In Hybrid Rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.

Lin, S. C. and L. P. Yuan, 1980. Hybrid rice breeding in China. Pages 35-51. in Innovative Approaches to Rice Breeding. International Rice Research Institute, P.O. Box 933, Manila, Philippines.

Virmani, S. S. and I. B. Edwards, 1983. Current status and future prospects for breeding hybrid rice and wheat. Adv. Agron. 36: 145-214.

____ and C. Shinjyo, 1988. Current status of analysis and symbols for male-sterile cytoplasms and fertility-restoring genes. Rice Genetics Newsletter 5: 9-15.

_____ and B. Wan, 1988. Development of CMS lines in hybrid rice breeding. Pages 103-114. In Hybrid Rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.

Young, J. B., S. S. Virmani and G. S. Khush, 1983. Cytogenic relationship among cytoplasmic genetic male sterile maintainer and restorer lines of rice. Philip. J. Crop Sci. 8(3): 119- 124.