Abstract:

Heterosis of F₁ hybrid is correlative to genetic distance between its parents, the sterile and the restorer lines, at certain extent. Study on genetic diversity dynamics of widely used sterile and restorer lines of hybrid rice (Oryza sativa spp. indica L.) at different stages will help to choose parents efficiently and to improve hybrid yield. In present research, 31 pairs of AFLP (amplified fragment length polymorphism) primers were used to detect genetic distances of 19 restorers and 13 sterile lines of WA-type hybrid rice that were widely used at different stages. All polymorphic bands were recorded by 0/1 method. Genetic distances (GD) of Nei & Li between all possible pairs of parents were calculated using AFLP data. Chi-square genetic distances between parents were calculated based on the standardized values of 15 agronomic traits of 32 parents. 32 rice parents were clustered based on GD values and on Chi-square distances by UPGMA respectively. The results were as follows: (1) A total of 535 clear polymorphic bands were detected among 32 parents, and on average 17.3 distinguishable bands were observed after amplification with each primer pair. (2) The result of dendrogram based on AFLP markers was similar to that on agronomic traits analyses in grouping of 32 parents of sterile and restorer lines, but a few differences between two dendrograms were detected in diversity among sterile or restorer lines. (3) There were relatively larger genetic differences among 32 parents, and the GDs between sterile and restorer lines were larger than those among restorers as well as among sterile lines. (4) The GDs among early-stage restorers were lower than those among middle-stage and late-stage restorers. Similar trend was observed on the GDs between sterile lines and restorers in 3 stages. These trends were positively correlated with the yield trend of hybrid rice, i.e. the yield of hybrid rice was largely improved in the middle-to-late 1980s and was stunted after 1990s. (5) The GDs among late-stage sterile lines were larger than those among early-stage sterile lines, but the GDs between early-stage sterile lines and restorers showed no significant difference from those between the late-stage sterile lines and restorers. (6) The trend of GDs based on AFLP markers of restorers in 3 stages was similar to yield trend of hybrid rice cultivars. GDs based on molecular makers can be used as one reference in choosing restorers in hybrid crossing.

Key words: Hybrid rice (Oryza sativa spp. indica L.), Genetic difference, AFLP (amplified fragment length polymorphism), Agronomic traits