Heterosis and Combining Ability For Floral and Yield Characters in Rice Using Cytoplasmic Male Sterility System

Developing high-yielding rice genotypes has become more urgent to ensure global food security with continuing population growth and the threat of environmental pressures. Cytoplasmic male sterility (CMS) system provides a valuable approach for commercial exploitation of heterosis and producing high-yielding and quality hybrid rice. Three CMS lines and ten diverse restorers were crossed using line × tester mating design. The obtained thirty F1 hybrids and their thirteen parents were evaluated. Yield traits as well as certain floral traits characters that influence the efficiency of crossing and hybrid seed production as duration of floret opening (min), stigma exsertion (mm), stigma length (mm), opening floret angle, and anther length (mm) were assessed. Highly significant variations were detected among parents, crosses, and parents vs. crosses for all the studied traits. The CMS line L2 and the restorer T5 were identified as good combiners for stigma exsertion, stigma length, opining floret angle, and duration of floret opening. Moreover, the hybrids L1×T1, L1×T3, L2×T2, L2×T5, L3×T4, L3×T5, and L3×T9 had positive SCA effects for most floral traits. Besides, the CMS lines L1 and L3 as well as the restorers T1, T2, T3, T6, and T9 proved to be the best general combiners for grain yield and certain contributing traits. The hybrids L1×T1, L1×T5, L1×T7, L2×T3, L2×T4, L2×T5, L2×T10, L3×T1, L3×T2, and L3×T6 displayed positive SCA effects for grain yield and one or more of its attributes. Both additive and non-additive gene effects are involved in the governing inheritance of all evaluated traits. The biochemical variations among the certain evaluated genotypes were further studied. The esterase and peroxidase isozymes were applied for verifying the genetic diversity at the protein level among the used CMS lines, restorers, and their crosses. All the applied isozymes displayed polymorphism for the parents and their crosses. The banding pattern and intensity differences provided accurate results on the reliable variability among the tested genotypes.

Mapping of Quantitative Trait Loci for Exserted Stigma Rate By Using (ZS97B/MH63) Ril Population

For increasing pollination and seed set, stigma exsertion has been identified as a major component in hybrid rice. By using a recombinant inbred line (RIL) population derived from an important Indica rice cross between Zhenshan97 and Minghui63, a molecular marker-based analysis of quantitative trait loci (QTL) for stigma exsertion was performed. As a result, six prominent QTL were detected for the exserted stigma rate on chromosome 6, 2, 9, 3, 5 and 1, respectively. qSER-1-1, qSER-2-1, qSER-5-1, qSER-6-1, qSER-15-1, and qSER-18-1 explained 8.1515, 4.6657, 7.2387, 4.8997, 6.925 and 6.9291% of the total phenotypic variance, respectively. In addition, for the qSER-1-1 and qSER-2-1, the ZS97B allele increased exserted stigma rate by about 4.3484 and 3.2836%, respectively; while for qSER-5-1, qSER-6-1, qSER-15-1 and qSER-18-1, the MH63 allele increased exserted stigma rate by approx. 4.1527, 3.4243, 3.9801 and 4.0025%, respectively. Bangladesh J. Bot. 50(3): 551-556, 2021 (September)

Dissection of closely linked QTLs controlling stigma exsertion rate in rice by substitution mapping

Key message Through substitution mapping strategy, two pairs of closely linked QTLs controlling stigma exsertion rate were dissected from chromosomes 2 and 3 and the four QTLs were fine mapped. Abstract Stigma exsertion rate (SER) is an important trait affecting the outcrossing ability of male sterility lines in hybrid rice. This complex trait was controlled by multiple QTLs and affected by environment condition. Here, we dissected, respectively, two pairs of tightly linked QTLs for SER on chromosomes 2 and 3 by substitution mapping. On chromosome 2, two linkage QTLs, qSER-2a and qSER-2b, were located in the region of 1288.0 kb, and were, respectively, delimited to the intervals of 234.9 kb and 214.3 kb. On chromosome 3, two QTLs, qSER-3a and qSER-3b, were detected in the region of 3575.5 kb and were narrowed down to 319.1 kb and 637.3 kb, respectively. The additive effects of four QTLs ranged from 7.9 to 9.0%. The epistatic effect produced by the interaction of qSER-2a and qSER-2b was much greater than that of qSER-3a and qSER-3b. The open reading frames were identified within the maximum intervals of qSER-2a, qSER-2b and qSER-3a, respectively. These results revealed that there are potential QTL clusters for SER in the two regions of chromosome 2 and chromosome 3. Fine mapping of the QTLs laid a foundation for cloning of the genes of SER.

Substitution mapping of the major quantitative trait loci controlling stigma exsertion rate from Oryza glumaepatula

Background: Stigma exsertion rate (SER) is a key determinant for the outcrossing ability of male sterility lines (MSLs) in hybrid rice seed production. In the process of domestication, the outcrossing ability of cultivated rice varieties decreased, while that of wild Oryza species kept strong. Here, we detected the quantitative trait loci (QTLs) controlling SER using a set of single-segment substitution lines (SSSLs) derived from O. glumaepatula , a wild Oryza species. Results: Seven QTLs for SER were located on 5 chromosomes. qSER-1a and qSER-1b were located on chromosome 1. qSER-3a and qSER-3b were mapped on chromosome 3, and qSER-3b was further located at an estimated interval of 898.8kb by secondary substitution mapping. qSER-5 , qSER-9 and qSER-10 were identified on chromosomes 5, 9 and 10, respectively, and qSER-9 was delimited to an estimated region of 551.9kb by secondary substitution mapping. The additive effects of the 7 QTLs ranged from 10.6% to 14.8%, which were higher than those of most loci for SER reported previously. Conclusions: qSER-1a and qSER-1b are novel loci for SER on chromosome 1. All of the 7 QTLs have major effects on SER. The major QTLs of SER will help to develop MSLs with strong outcrossing ability.

Substitution mapping of the major quantitative trait loci controlling stigma exsertion rate from Oryza glumaepatula

Background: Stigma exsertion rate (SER) is a key determinant for outcrossing ability of male sterility lines (MSLs) in hybrid rice seed production. Outcrossing ability in cultivated rice varieties has diminished during the process of domestication, while wild Oryza species keep strong outcrossing ability. Here, we detected the quantitative trait loci (QTLs) controlling SER using a set of single-segment substitution lines (SSSLs) derived from O. glumaepatula, a wild Oryza species.Results: Seven QTLs for SER, qSER-1a, qSER-1b, qSER-3a, qSER-3b, qSER-5, qSER-9 and qSER-10, were located on 5 chromosomes. qSER-1a and qSER-1b were located on chromosome 1. qSER-3a and qSER-3b were mapped on chromosome 3, and qSER-3b was further located at an interval of 931.0kb by secondary substitution mapping. qSER-5, qSER-9 and qSER-10 were identified on chromosomes 5, 9 and 10, respectively, and qSER-9 was delimited to a region of 608.2kb by secondary substitution mapping. The additive effects of the 7 QTLs ranged from 10.6% to 14.8%, and the additive contribution variances explained by each of the QTLs were from 36.3% to 50.6%, which were higher than those of most loci for SER reported previously.Conclusions: qSER-1a and qSER-1b were novel loci for SER on chromosome 1. All of the 7 QTLs had major effects on SER. The major QTLs of SER will help to develop MSLs with strong outcrossing ability.