Analysis Of QTL Epistasis On Heading Date And Developmental Traits Based On SSSLs In Rice

Both heading date and developmental traits are important agronomic traits. Appropriate length of heading date is not only the precondition for rice varieties to adapt various ecological environments, but also the foundation for human to get ideal grain yield. Development traits are mostly the important components of ideotype, directly relating to the biological and the economical productions of rice. Epistasis is one of main genetic components on complex quantitative traits, which plays an important role on such as heading date and developmental traits. In this study, 9 single segment substitution lines were used as experimental materials to culture multi- segment pyramiding lines and then to structure half diallel crossing populations for analysis of epistasis on heading date and developmental traits among QTL. The main results are as follows:1) 5 SSSLs were confirmed truly carrying with significant additive and/or dominant effects of QTL on heading date, which increased heading days-8~20d. Of them, S1 was the only line with early-maturing QTL and its additive was environment-stable, while others were late-maturing and environment-sensitive. Dual QTL epistases on heading date were prevalent and with 30.00% of significant effects, which increased heading days-18~7d with most negative and environment-sensitive effects. Triple QTL epistases were with 29.55% of significant effects, to enhance heading days 6~21d which were mostly with positive and environment-sensitive effects especially in the condition of short day during late season.2) For various traits measured, dual QTL epistases showed effects with the different directions, but triple QTL were mainly with negative epistases. Various epistatic components of one QTL combination were always with the same of effect directions and influenced multi-traits simultaneously.3)The pyramiding lines of S3/S1 and S3/S1/S5 were with the shortest heading days, which could be expected to be developed as early maturing varieties. S3/S5 and S4/S1/S5, S2/S5 and S3/S2/S5 could be expected as medium maturing and late maturing varieties, respectively.4) The developmental traits as plant height, tiller number and leaf number appeared sigmoid growth curves derived from the dynamic changes of their QTL effects in the whole development process. The cumulative effects of additives, dominances and epistases exhibited growth or decline along with the growth and development of plant. During the various developmental stages, QTL had different net expressing on magnitudes and directions, and common features to express repeatedly reversely.5) For three developmental traits, dual QTL epistases exhibited mostly negative effects. Of them, the epistases appeared mainly in various stages for plant height, in the early stages for tiller number and in various stages for leaf number. For the three traits epistatic effects varied from-22 cm to 15 cm, from-7 to 5 and from-29 to 39, respectively. The patterns of growth and development were the different for plant height, first descending and then ascending for tiller number, and the same as tiller number or continual declining for leaf number.6) Phenotypic correlations among traits derived mostly from genotypic correlations, and then from the correlations of QTL components. The positive phenotypic and genetic correlation depended on both QTL additive and dominant correlations between heading date and plant height, while the negative correlations rested on QTL epistatic correlations between heading date and panicle number. At various stages, all correlation coefficients were positive among the three traits, and derived mainly from three effect components of QTL between tiller number and leaf number and QTL epistases between plant height and tiller number, and between plant height and leaf number, respectively.Analysis of epistases among QTL on heading data and developmental traits had revealed their genetic basis and developmental patterns, contributed to predict the pyramiding effects on these QTL, and provided the basis and materials for the molecular pyramiding breeding for these traits. In addition, the methodology used in this thesis can be also applied to the epistatic analysis for other traits.