Study On Genetic Structure Of Oryza Rufipogon And O. Nivara Sharma Et Shastry And Their Mating Systems

Oryza rufipogon and Oryza nivara are wild relatives of rice.As important gene pools for rice breeding,they retain many excellent genes that rice has lost.Because they have relatively complex genetic background due to growing in the wild for a long time,their genetic structures and mating systems are still unclear.This study used 12 SSR markers to analyze the genetic structures and mating systems of 12 O.rufipogon populations and 4 O.nivara populations.The results are showed as blow:1.The genetic diversity of O.rufipogon populations was significantly higher than that of O.nivara populations.The mean effective number of alleles(Ae)of O.rufipogon populations was 1.9976,while that of O.nivara populations was 1.5212.The observed heterozygosity(Ho)and expected heterozygosity(He)of O.rufipogon populations were 0.5919 and 0.5049 respectively,but those of O.nivara were only 0.0338 and 0.2638.2.Phylogenetic analysis indicated that,there was significant difference between the two wild rice species.All O.nivara populations clustered together,and O.rufipogon from Wuxuan(WX),Fumian(FM)and Chaling(CL)clustered together,but other O.rufipogon populations had no obvious classification.Further analysis showed that population VT02 from Vietnam and population KHM14 from Cambodia were close to populations from China but population from Nepal(NEP09)had big genetic distance from Chinese populations.3.O.rufipogon and O.nivara are generally belonged to the mixed mating system,but O.rufipogon belongs to a typical mixed mating system and O.nivara is a mainly selfing system.The ranges of the multilocus outcrossing rate(tm)values of O.rufipogon and O.nivara were 0.286-0.660 and 0.128-0.354,and the singlelocus population outcrossing rate(ts)values of them were 0.142-0.567 and 0.102-0.241,respectively.Most populations of O.rufipogon had excess heterozygote and insufficient homozygous;however,O.nivara populations had excess homozygous and insufficient heterozygote.Many populations existed sub-structures in two wild rice species.4.The results of study on the relationship between genetic diversity and mating system parameters showed that the parameters of genetic diversity and mating system are relevant.It was inferred that the populations which had a lower heterozygosity and a higher fixation index,might have a lower outcrossing rate,mainly selfing.On the contrary,the populations with a relatively higher outcrossing rate,might be a mainly mixed mating system.5.Plant mating system could affect the genetic structure of population by gene flow.O.rufipogon had a stronger gene flow within species,with a higer outcrossing rate and a little differentiation within species;whereas O.nivara had a weaker gene flow within species,with a lower outcrossing rate and a relatively large differentiation within species.In this study,we found that there was significant difference between the two wild rice species through a comparative analysis.Genetic factor was important but not the only one that could influence mating system.The results would provide the valuable reference for the protection of wild rice,andbreeding of hybrid rice.