Breeding and extension of indica hybrid rice has been one of the important approaches to increase rice production in China (Yuan, 1998). By contrast, progress in breed ingand utilizing japonica hybrid rice is slow:

1) yield advantage of japonica rice is not so large as indica hybrid rice because of narrow genetic base (Yuan, 1998);
2) there are few restoration lines in japonica for Dian I (cms-D) and BT (cms-bo) types cms lines popularly used at present (Khush et al. 1998, Shinyjo 1984, Virmani 1994, Xiao et al. 1998);
3) the sterility of cms, PGMS, or TGMS lines is sometimes not stable (Yuan, 1998).

Thus, japonica restoration lines are a key prerequisite to promote japonica hybrid rice development in the world.

In 1999, we reported the identification of some japonica restoration lines (WARDA, 1999). We have been searching for japonica restoration lines from present japonica materials for two important and popular cms types, Dian I (cms-D) and BT (cms-bo). These types have similar restoration and maintainer relationships. Some tropical upland varieties and interspecific hybridization progenies of cultivated rices were testcrossed with Dian I type cms line Dianyu 1A. Pollen grain and spikelet fertility of parents and testcross F₁ were investigated in July 2000, Hainan, China. Results indicated that WAB450-11-1-3-P40-HB, WAB450-11-1-2-P61-HB, WAB450-I-B-P-91-HB, IRAT216 and IRAT359 could restore Dianyu 1A, as could famous restoration line C57 and Yunnan japonica restoration line Nan 29. IRAT104 could partially restore Dianyu 1A (Table 1). The restored F₁ had about 50% pollen grain fertility and normal spikelet fertility, indicating that the sterility of Dianyu 1A is gametophytic. This finding might be useful in exploitation of japonica hybrid vigor in China, Korea, Japan, Africa, and Latin America.

In order to know the inheritance of restoration ability, F₁ hybrids of the above lines, and Nan 29, a very important restoration line in Yunnan with Dianyu1A were pollinated with the maintain line Dianyu 1B, distribution of pollen grain fertility stained with 1% I-KI solution of BC₁F₁ indicated that all these lines were controlled by a single dominance major gene (Table 2).

When backcrossed to female parent, Dianyu 1A, backcross prognies were always semi-

fertile, and pollen grain fertility of BC5F2 were obviously classified into fertile and semi-fertile two types with 1:1 segregation ratio, which could be explained again by one gene segregation, too (Table 3).

To determine the allelic relationship with known gene Rf1 located on Chromosome 10, C57, carrying Rf1 (Teng and Shen, 1994), was hybridized with these restoration lines, and Dianyu 1A was pollinated with these F₁ hybrids. The pollen grain fertility score indicated that the restoring gene of WAB450-11-1-3-P40-HB, WAB450-11-1-2-P61-HB, WAB450-I-B-P-91-HB, IRAT216, IRAT359 is the same as Rf1 in C57. Since the restoration of Nan 29 is allelic to that of IRAT216 and IRAT359, it should be allelic to Rf1 locus in C57. Even the restoring gene in IRAT104 is allelic to that in C57, but it is a different allele from Rf1 with partial restoration ability (Table 4).

To promote MAS breeding of japonica restoration lines by PCR markers and utilize the new materials efficiently, 131 SSR markers were used to score 143 BC₁F₁ individuals from Dianyu 1A/WAB450-11-1-2-P61-HB//Dianyu 1B. Rf1 was mapped between RM171 and RM228 on the long arm of chromosome 10. The distance between RM171 and Rf1 is 3.6 cM, and that between Rf1 and RM228 is 10.2 cM (Fig. 1), which confirmed again that restoration gene in WAB450-11-1-2-P61-HB is allelic to Rf1 (Akagi et al. 1996, Ichikawa et al. 1997)

This study was supported in part by Yunnan Natural Science Foundation, Ministry of Science & Technology, P. R. China, and West Africa Rice Development Association (WARDA).

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