Study On Genetic Bases Of Yield Traits And General Combining Ability For Key Parent "Shuhui527" Of Hybrid Rice

Key parents play an important role in the processing of hybrid breeding. In this study, threeselected advanced backcross populations were constructed using Shuhui527(SH527) as recurrent parent,a key parent of hybrid rice, and three high-yielding cultivars i.e. ZDZ057, Fuhui838(FH838) andTeqing as donors, respectively. Phenotyping and genotyping for these three populations were conductedfor identifying QTL associated with yield and its related traits from donors under different environments.Secondly,228F1combinations were developed by testcrossing57introgression lines (ILs) fromabove-mentioned populations with four types of male sterile lines i.e. XieqingzaoA (XA), II-32A (IIA),Gang46A (GA) and Jin23A (JA), and evaluated for two years in Anhui for detecting on the geneticbases of general combining ability (GCA) and heterosis affecting yield and its related traits. Lastly,tanscriptomic analysis was conducted for two hybrids with high-and low-yielding comparativeheterosis (HC) selected from228testcrossing combinations combing with check combinations (CC)with their parents at three stages for elucidating the mechanism of heterosis. The main resultssummarized as follows:1. A total of94QTL controlling yield and its related traits were identified under two environments,and mainly concentrated on12QTL clusters. For these QTL,60.1%QTL had favorable alleles from thedonors and about40%QTL were detected under two environments.2. The strong and frequent non-random associations between or among QTL affecting filled grainnumber per panicle (GN), spikelets number per panicle (SN) and grain yield per plant (GY) wereobserved in the ILs with high-trait values. Multi-alleles were found in seven QTL and had differenteffects among populations.3. Additive and non-additive gene effects jointly determined the expression of yield and its relatedtraits. Moreover, addictive effects were more important than non-addictive for all traits except GY.4. Thirty-four QTL affecting GCA of yield and its related traits were identified in the twopopulations. Of these,61.8%(21) had favorable alleles from key parent, SH527. Markers RM508andRM587, RM4584and RM224were substituted by ZDZ057alleles in eight ILs with Low-yielding GCAand Teqing alleles in the three ILs with high-yielding GCA, respectively. According to the QTLmapping results, these markers tightly associated with yield and key components, which can be inferredthat these loci probably played a key role in controlling yield GCA of SH527.5. Seventy-nine QTL associated with heterosis of yield and its related traits were identified usingcomparative heterosis (HC) and mid-parent heterosis (HMP) values in the eight testcrossing populations.Of these,49.4%QTL present overdominance, especially for panicle number (PN) and GY, andconversely, additivity for GN and SN.6. The great numbers of differential expression genes (DGEs) were found between XA/WD7withits parents (3589) at three stages by transcriptomic analysis, second is XA/WD34with XA and WD34(3146), and last is XA/SH527and its parents (2912). Except XA/WD7at tillering stage, three hybrids had more additive expression genes than non-additive at three stages, furthermore, the number ofup-regulated genes were always more than down-regulated whether or not additive and non-additiveexpression genes.7. In comparison with parents XA and SH527, a lot of up-regulated genes related to carbonassimilation in photosynthesis and starch and sucrose biosynthesis in carbohydrate metabolism wereobserved in hybrid XA/SH527, which probably resulted in that XA/SH527had strong yield vigor thanits parents.8. Comparing with the check combination, numerous down-regulated genes associated withlight-harvesting in photosynthesis and regulation of transcription exsited in XA/WD7. In addition,expression changes related to circadian rhythm (CCA1, TOC1and GI) and carbohydrate metabolismwere observed in hybrid XA/WD34. These DGEs could play an important role in affecting yieldheterosis in XA/WD7and XA/WD34. Furthermore, Heading dates (HD) of WD34and XA/WD34weredelayed due to the overexpression of OsGI gene.