12. A new gamete eliminator from Oryza glaberrima

G. REN¹, P. XU², X. DENG², J. ZHOU², F. HU², J. LI², F. LI¹, Z. ZHANG¹ and D. TAO^2,3

1) Yunnan Agricultural University, Kunming, 650201 China

2) Food Crops Research Institute, Yunnan Academy of Agricultural Sciences, Kunming, 650205 China

3) Corresponding author: taody12@public.km.yn.cn

Rice is the staple food for the world and more than 90 percent of the crop is grown in developing country. In order to provide rice to the world�fs growing population, new varieties with the higher yield potential, wider adaptation, multiple resistance or tolerance for biotic or abiotic factors are essential. However, narrowing of the gene pool by further concentrating favorable alleles already presented in early domesticates, especially in plant domesticates by both farmers and breeders in past years.

Two rice species are cultivated for food production. Oryza sativa originated in Asia and is widely grown. O. glaberrima originated and is cultivated in West Africa, having some advantages such as early maturity, drought tolerance, resistance to rice yellow mottle virus, blast disease and African rice gall midge, and responsiveness to mineral fertilizer. Both species have same genome AA (Chang 1976, Morinaga et al. 1957). The high sterility of interspecific hybrids is a serious reproductive barrier (Jones et al. 1997, Morinaga et al. 1957, Morishima et al. 1962, Morishima et al. 1963, Sano et al. 1979, Sano 1983). They are isolated from each other by strong F₁ sterility barrier although their chromosomes (n=12) normally pair in the hybrid (Chu et al. 1969).

Hybrid sterility and introgression of the quantitative trait loci controlling many important agronomic traits are the key constraints for utilization of the Oryza relatives. In order to shed more light on these issues, sterility of interspecific hybrids controlled by QTLs in preliminary population was used as the study target and the genetics of hybrid sterility in the progenies of O. sativa x O. glaberrima hybrids was studied. Backcross experiments were conducted to introduce alien factors controlling hybrid sterility from O. glaberrima into O. sativa or from O. sativa into O. glaberrima (Sano 1990). We developed a series of O. glaberrima introgression lines in the background of O. sativa for genetic analysis of traits specific to the species. Large variation in pollen sterility was observed during development. One O. glaberrima accession, IRGC102375 introduced from the International Rice Research Institute, was used as female parent, and Danjingyou 1 (a japonica cultivar from Yunnan) was used as male parent to make the cross. Further backcrossing with Danjingyou 1 as a male parent was continued after pollen grain fertility check. Genotyping with 225 SSR markers was done in the BC₆F₁ sterile plants. One sterile plant with one heterozygous marker was selected to make BC₇F₁ secondary mapping population.

Flowering spikelets were collected from each plant and stored in 70% ethanol. Pollen fertility was estimated as the percentage of pollen grains that could be stained with I2-KI solution.

Fig. 1. Distribution of pollen and spikelet fertility in BC₇F₁ of IRGC102375/Dianjingyou 1/8/Dianjingyou 1.

Fig. 2. Sterile gene mapping result in chromosome 1 from BC₇F₁ of IRGC102375/Dianjingyou 1/8/Dianjingyou 1 secondary mapping population.

BC₇F₁ population not fitted the expected 1:1 ratio, with more semi-sterile type (X₂=29.9, p<0.005). Distribution of spikelet fertility was near the same (Fig. 1), which means there was a gamete eliminator caused pollen grain and spikelet semi-sterility, but the role is not full (Sano 1990). This gamete eliminator was mapped on chromosome 1 as a new gene S33 (t) between RM81 and RM294 since no gamete eliminator from O. glaberrima was reported in this region (Fig. 2).

This study was supported in part by the Yunnan Natural Science Foundation (2002C0009Z) and Yunnan Department for Science and Technology (2003RC02, 2004PY01-21).

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