Studies On Partial Interspecific Hybrids Between Indica Male Sterile Lines And Introgression Lines Carrying African Rice Genes

Distant heterosis utilization is a principal key for overcoming the yield frontier in hybrid rice. Comparative studies were made on heterosis of partial interspecific hybrids (PIHs) between indica male sterile lines and introgression lines (ILs) carrying carrying African rice genes (Oryza glaberrima Steud) and that of the indica hybrids. Heterosis and field performance of agronomic traits of64hybrids produced by partial diallel crosses between8indica male sterile lines (6CMS lines and2PTGMS lines) and8pollen parents (4indica restorer lines and4ILs). A total of42partial interspecific hybrids was developed using14introgression lines and3female parents including1CMS line and2PTGMS lines. Genetic diversity (GD) of ILs was evaluated by SSR markers. And the relationship between the GD of ILs and heterosis of their derivative partial interspecific hybrids was analyzed. The main results are summarized as follows:A-Identification of Interspecific Grain Yield Heterosis between Two Cultivated Rice Species Oryza sativa L and Oryza glaberrima SteudField performance for all agronomic traits showed significant differences among the64crosses and their pollen parents at0.05and0.01probability level. Eighteen hybrids have expressed sterility problem due to the lack of fertility restoration ability of their corresponding pollen parents. And12out of these18hybrids were partial interspecific hybrids. Only10partial interspecific hybrids were fertile with grain filling percentage above70%. Among the20crosses expressing positive heterobeltiosis (heterosis over pollen parent) on panicle yield,9scored more than25%heterobeltiosis for panicle yield. Among the agronomic traits evaluated, the highest heterobeltiosis was scored for filled grain number per panicle (101.48%), which is followed by panicle yield (61.70%), spikelet number per panicle (73.33%),1000-grain weight (46.00%), grain filling percentage (33.50%), panicle length (28.80%), plant height (27.74%) and days to flowering (16.00%). Nine promising hybrids were selected in this study following their grain yield performance and heterobeltiosis. The parental lines of the promising hybrids with higher yield potential showed a relatively higher general combining ability. Two hybrids AF-zhong9A/RL1and I1-32A/RL1with highest panicle yield were identified as partial interspecific hybrids. Their common pollen parent RL1was derived from interspecific multiple crosses and contained about12.5%genomic genes from Oryza glaberrima according to its pedigree. This study suggests the existence of interspecific heterosis between the two cultivated rice species in grain yield.B-Relationship between genetic diversity of the introgression lines carrying Oryza glaberrima genomic genes and heterosis of the partial interpecific hybridsField performance of all agronomic traits showed significant differences among the42PIHs produced by crossing14ILs and3male sterile lines. Seventy-five SSR markers revealed polymorphism between the two initial parents (RAM3and Jin23B) of the introgression lines. Sixteen SSR markers designated as informative markers detected the presence of O. glaberrima specific alleles among the parental lines. The proportion of O. glaberrima genomic genes ranged from3.13%to40.69%and GD between the parental lines from1.73%to3.74%. A positively significant correlation was found between O. glaberrima genome proportion of ILs and GD of the parental lines (r=0.79to0.96*). The range of O. glaberrima genome proportion of ILs was positively proportional to heterosis of panicle number and spikelet number per panicle of the PIHs. Twelve promising PIHs were selected from the21heterotic PIHs and14higher yielding hybrids according to their performance and heterosis. In addition, positively significant correlation was observed between heterosis of spikelet number per panicle of the heterotic PIHs and O. glaberrima genome proportion (r=0.59*). The PIHs with the higher grain yield and highest heterobeltiosis were derived from5promising ILs carrying15%to30%of O. glaberrima genes, indicating that an intermediate range of genome proportion of O. glaberrima was more suitable for breeding heterotic PIHs. The PIHs derived from the ILs with O. glaberrima genome proportion less than15%expressed low heterosis for panicle number and spikelet number per panicle while the PIHs involving ILs with more than30%of O. glaberrima genomic genes scored lower grain filling percentage. The results indicate that small genome proportion of O. glaberrima in the ILs minimizes interspecific heterosis expression of PN and SN while very large genome proportion of O. glaberrima decreases GF and FGP of PIHs. Therefore, O. glaberrima genome proportion of the ILs should neither be very small nor very large for developing high yielding PIHs. Consideration of O.glaberrima genome proportion of ILs is important for developing heterotic PIHs and exploiting interspecific heterosis from the two cultivated rice species.