Genetic Analysis of Seedling Traits Regulated by Light in Weedy Rice

The Korean weedy rice, PBR (photoblastic rice) was reported to have light-inducible seed germination (photoblastism) and long mesocotyl. In previous studies, we mapped two QTL each for photoblastism and mesocotyl length using progeny from a cross between Ilpumbyeo and PBR. One F8 line CR7124 having photoblastism and long mesocotyl, was chosen and crossed to Ilpumbyeo to produce 95 F3 lines for QTL mapping. Germination percentage of CR7124 and Ilpumbyeo was 3.3 ± 2.4% and 91.7 ± 7.1%, respectively in the dark condition. 95 F3 lines ranged from 28.6% to 100% in germination. For mesocotyl, Ilpumbyeo and PBR elongated up to 1.5 mm and 18.5 mm, respectively whereas 95 F3 lines ranged from 0.9 mm to 16.3 mm. The mesocotyl length showed highly negative significant correlation with germination rate in dark condition (r = 0.70, P ＜ 0.0001). QTL mapping using 95 F3 lines confirmed the linkage of two QTL for photoblastism and mesocotyl length on chromosome 1. Eight F4 lines with different PBR chromosome segments in the target region were used for substitution mapping of pbr1 and qMel-1. It appears that qMel-1 was located in the interval RM11252 - RM7419, a region of approximately 4.7 Mb. pbr1 was located in the interval between RM7202 and RM11729. Although further fine mapping of two QTL is necessary to know the relationship of these two traits, these results together with the highly significant correlation between two traits indicate that two QTL are linked. DNA markers linked to these QTLs would be useful in facilitating the selection of lines with enhanced mesocotyl elongation.