| The introduction of genomic fragments of close related species provides an effective way to enrich genetic diversity and create new germplasm in crops.In such perspective,African rice(O.glaberrima,AA),one of the cultivated rice varieties,offers new genetic sources for the improvement of Common rice or Asian rice(O.sativa,AA).The identification of compatible accessions derived from O.glaberrima and O.sativa interspecific hybridization would facilitate broader access to the African rice gene pool and would lead to the development of large backcross population increasing the likelihood of obtaining fertile progenies.However,in such,to be really efficient for breeding programs,one first needs a comprehensive picture of the genetic diversity among the individuals and the genetic characteristics of heterosis within the derived hybrids.The objectives of this study were to detect and analyze Heterotic Loci(HL)for agronomic traits in a population of partial interspecific hybrids(PIH)and characterize the PIH genetic basis of heterosis.In addition,the molecular profiling of the PIH pollen parents,consisted of a set of 79 rice introgression lines(ILs)carrying variant introgressed segments of O.glaberrima,was performed to determine the genomic proportion extent and location of introgressions along the chromosomes.Moreover,analysis of Quantitative Trait Loci(QTL),Trait-Marker Associations,Population structure,and Genetic Diversity were performed using the ILs.Field experiments were carried out in two successive years to evaluate seven agronomic traits of the parental lines(GZ63S and ILs)and their 79 corresponding F1 PIH.A total of 23 interspecific HLs on 10 chromosomes were detected in two years.Among them,14 were found to be associated with yield-related traits,and we found six HLs to be consistent with detected QTLs.And,four stable HLs were identified in all 2 years,in which,RM3763 associated with plant height was detected in two years both for HL and QTL.Additionally,the phenomenon of pleiotropism was also found in all the interspecific HLs for the seven agronomic traits investigated.The testcross F1 PIH population showed superiority in most yield-related traits and was characterized by a high frequency of overdominant interspecific HLs.Spikelets number per panicle,filled grains number per panicle and plant height had positive mean of heterobeltiosis in both two years;while,seed setting rate,panicles number per plant,and 1000 grains weight had negative mean of heterobeltiosis.For days to heading,its negative mean values of heterobeltiosis(?-10.09%in both years)could be beneficial to crop production for enhancing early maturation,as early matured plant is beneficial to the rice producers and consumers because whether the growing period was short the plant could be protected from insects attacks or any harmful agents susceptible to affect the quantity and quality of rice grain yield.The positive heterobeltiosis for filled grains number per panicle(18.49%and 18.22%)might be attributed to the interaction of favorable genes of both parents and a good fertility restoration ability of the pollen parents(ILs).Mean of positive heterobeltiosis for spikelets per panicle were 15.12%and 22.90%,ranging from-42.19%to 70.22%and from-14.81%to 89.37%,in the two years,respectively.This could indicate that the PIHs have a promising potential in yield related traits and for application in rice production.Further,we used graphical representation of molecular data to assess the average proportion of PGG in the ILs,which varied from 12%to 29.1%.The relative informativeness of each marker was evaluated on the basis of its PIC value.PIC values of the SSR markers used averaged 0.27 and ranged from 0.04 for RM144 to 0.55 for RM231.The genetic distance between ILs ranged from 0.02 to 0.62 with an average value of 0.31.Using STRUCTURE software,the maximum of ad hoc measure ?K was found to be K =2 which indicates that the entire population can be grouped into two subpopulations.A total of 24 QTLs were identified for the seven agronomic traits of ILs in the two years.Among them,four QTLs were identified in all 2 years.The Trait-marker association analysis showed 44 SSR marker alleles(50.6%)with significant marker-trait associations identified between the markers and 7 agronomic traits including panicle number per plant,spikelet number per panicle,grain number per panicle,1000 grains weight,plant height,seed setting rate and days to heading at a significance level of P=0.05 and each association explained 5%to 28%(cumulatively)of phenotypic variation.Among the 123 significant trait-marker associations detected,7 were in the same or similar genomic regions where QTLs were detected in previous studies.This study is the first attempt for the identification of interspecific Heterotic Loci between the two cultivated rice species,African rice and Asian rice.Therefore,our results may help to lay the foundation for exploring the genetic mechanism of interspecific heterosis in rice.The exploitation and utilization of interspecific heterosis is a promising new way to develop next generation of super high yielding hybrid rice and significant progress was made on breeding partial interspecific hybrid(PIH)rice.The above results confirmed that construction of IL population carrying O.glaberrima genomic fragments could be an effective approach to increase the genetic diversity of O.sativa genome and genetic diversity is known to be the foundation for heterosis utilization for high yield hybrid rice breeding.An appropriate level of the proportion of glaberrima genome(PGG)could facilitate pyramiding more favorable genes for developing more adaptive and productive rice.The detected loci associated with agronomic traits may provide opportunities for rice breeders to control these traits via marker-assisted selection(MAS)and pyramiding.The present study has demonstrated the utility of SSR analysis for the study of genetic diversity,population structure and trait-marker associations' analysis in interspecific ILs from the two cultivated rice varieties.These data could help in optimizing the selection of ILs for breeding inbred varieties as well as parental lines of interspecific hybrid rice. |
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