Mapping QTLs for yield and photosynthesis-related traits in three consecutive backcross populations of Oryza sativa cultivar Cottondora Sannalu (MTU1010) and Oryza rufipogon.

MAIN CONCLUSION: Identification of trait enhancing QTLs for yield and photosynthesis-related traits in rice using interspecific mapping population and chromosome segment substitution lines derived from a cross between Oryza sativa and Oryza rufipogon. Wild rice contains novel genes which can help in improving rice yield. Common wild rice Oryza rufipogon is a known source for enhanced photosynthesis and yield-related traits. We developed BC2F2:3:4 mapping populations using O. rufipogon IC309814 with high photosynthetic rate as donor, and elite cultivar MTU1010 as recurrent parent. Evaluation of 238 BC2F2 families for 13 yield-related traits and 208 BC2F2 families for seven photosynthesis-related physiological traits resulted in identification of significantly different lines which performed better than MTU1010 for various yield contributing traits. 49 QTLs were identified for 13 yield traits and 7 QTLs for photosynthesis-related traits in BC2F2. In addition, 34 QTLs in BC2F3 and 26 QTLs in BC2F4 were also detected for yield traits.11 common QTLs were identified in three consecutive generations and their trait-increasing alleles were derived from O. rufipogon. Significantly, one major effect common QTL qTGW3.1 for thousand grain weight with average phenotypic variance 8.1% and one novel QTL qBM7.1 for biomass were identified. Photosynthesis-related QTLs qPN9.1, qPN12.1, qPN12.2 qSPAD1.1 and qSPAD6.1 showed additive effect from O. rufipogon. A set of 145 CSSLs were identified in BC2F2 which together represented 87% of O. rufipogon genome. In addition, 87 of the 145 CSSLs were significantly different than MTU1010 for at least one trait. The major effect QTLs can be fine mapped for gene discovery. CSSLs developed in this study are a good source of novel alleles from O. rufipogon in the background of Cottondora Sannalu for rapid improvement of any trait in rice.

Mapping of QTLs for Yield Traits Using F2:3:4 Populations Derived From Two Alien Introgression Lines Reveals qTGW8.1 as a Consistent QTL for Grain Weight From Oryza nivara.

Wild introgressions play a crucial role in crop improvement by transferring important novel alleles and broadening allelic diversity of cultivated germplasm. In this study, two stable backcross alien introgression lines 166s and 14s derived from Swarn/Oryza nivara IRGC81848 were used as parents to generate populations to map quantitative trait loci (QTLs) for yield-related traits. Field evaluation of yield-related traits in F2, F3, and F4 population was carried out in normal irrigated conditions during the wet season of 2015 and dry seasons of 2016 and 2018, respectively. Plant height, tiller number, productive tiller number, total dry matter, and harvest index showed a highly significant association to single plant yield in F2, F3, and F4. In all, 21, 30, and 17 QTLs were identified in F2, F2:3, and F2:4, respectively, for yield-related traits. QTLs qPH6.1 with 12.54% phenotypic variance (PV) in F2, qPH1.1 with 13.01% PV, qTN6.1 with 10.08% PV in F2:3, and qTGW6.1 with 15.19% PV in F2:4 were identified as major effect QTLs. QTLs qSPY4.1 and qSPY6.1 were detected for grain yield in F2 and F2:3 with PV 8.5 and 6.7%, respectively. The trait enhancing alleles of QTLs qSPY4.1, qSPY6.1, qPH1.1, qTGW6.1, qTGW8.1, qGN4.1, and qTDM5.1 were from O. nivara. QTLs of the yield contributing traits were found clustered in the same chromosomal region. qTGW8.1 was identified in a 2.6 Mb region between RM3480 and RM3452 in all three generations with PV 6.1 to 9.8%. This stable and consistent qTGW8.1 allele from O. nivara can be fine mapped for identification of causal genes. From this population, lines C212, C2124, C2128, and C2143 were identified with significantly higher SPY and C2103, C2116, and C2117 had consistently higher thousand-grain weight values than both the parents and Swarna across the generations and are useful in gene discovery for target traits and further crop improvement.

Detecting CSSLs and yield QTLs with additive, epistatic and QTL×environment interaction effects from Oryza sativa × O. nivara IRGC81832 cross.

Chromosome segment substitution lines (CSSLs) are useful tools for precise mapping of quantitative trait loci (QTLs) and the evaluation of gene action and interaction in inter-specific crosses. In this study, a set of 90 back cross lines at BC2F8 generation derived from Swarna x Oryza nivara IRGC81832 was evaluated for yield traits under irrigated conditions in wet seasons of 3 consecutive years. We identified a set of 70 chromosome segment substitution lines, using genotyping data from 140 SSR markers covering 94.4% of O. nivara genome. Among these, 23 CSSLs were significantly different for 7 traits. 22 QTLs were detected for 11 traits with 6.51 to 46.77% phenotypic variation in 90 BILs. Three pleiotropic genomic regions associated with yield traits were mapped on chromosomes 1, 8 and 11. The marker interval RM206-RM144 at chromosome 11 was recurrently detected for various yield traits. Ten QTLs were identified consistently in the three consecutive years of testing. Seventeen pairs of significant epistatic QTLs (E-QTLs) were detected for days to flowering, days to maturity and plant height. Chromosome segments from O. nivara contributed trait enhancing alleles. The significantly improved lines and the stable QTLs identified in this study are valuable resource for gene discovery and yield improvement.

Genotype × Environment Interactions of Yield Traits in Backcross Introgression Lines Derived from Oryza sativa cv. Swarna/Oryza nivara.

Advanced backcross introgression lines (BILs) developed from crosses of Oryza sativa var. Swarna/O. nivara accessions were grown and evaluated for yield and related traits. Trials were conducted for consecutive three seasons in field conditions in a randomized complete block design with three replications. Data on yield traits under irrigated conditions were analyzed using the Additive Main Effect and Multiplicative Interaction (AMMI), Genotype and Genotype × Environment Interaction (GGE) and modified rank-sum statistic (YSi) for yield stability. BILs viz., G3 (14S) and G6 (166S) showed yield stability across the seasons along with high mean yield performance. G3 is early in flowering with high yield and has good grain quality and medium height, hence could be recommended for most of the irrigated locations. G6 is a late duration genotype, with strong culm strength, high grain number and panicle weight. G6 has higher yield and stability than Swarna but has Swarna grain type. Among the varieties tested DRRDhan 40 and recurrent parent Swarna showed stability for yield traits across the seasons. The component traits thousand grain weight, panicle weight, panicle length, grain number and plant height explained highest genotypic percentage over environment and interaction factors and can be prioritized to dissect stable QTLs/ genes. These lines were genotyped using microsatellite markers covering the entire rice genome and also using a set of markers linked to previously reported yield QTLs. It was observed that wild derived lines with more than 70% of recurrent parent genome were stable and showed enhanced yield levels compared to genotypes with higher donor genome introgressions.