Mesocotyl elongates in the dark and appears in between the seminal root and coleoptile, and is related to emergence of rice seeds. The degree of mesocotyl elongation is one of the traits which affect stand establishment in direct-seeded rice.

Variation in mesocotyl length of rice cultivars was investgated. Dao Ren Qiao, a Chinese indica (hsien) rice cultivar, lacked the ability for mesocotyl elongation. To analyze the trait, Dao Ren Qiao was crossed to Surjumkhi, an Assam cultivar, having an average length of mesocotyl of 39.2mm. F1 plants were backcrossed to both cultivars. Frequency distributions for mesocotyl length in the F2 and the backcrossed F1 populations were so complex that loci for the trait have not been detected based on the segregation data. QTL analysis was undertaken to detect loci conferring mesocotyl elongation in rice using RFLP markers mapped on rice chromosomes (Saito et al. 1991; Kurata et al. 1994).

F3 progeny lines from 96 F2 plants of the cross between Surjumkhi and Dao Ren Qiao were used for QTL analysis. Forty F3 seeds from each F2 plant were germinated in glass tubes (3cm in diameter) containing 2ml of distilled water and were grown at 30°C in the dark for 10 days. Mesocotyl length of each F3) seedling was measured and the mean value was used for statistical analysis. DNA was extracted from bulked F3 seedlings. 71 polymorphic RFLP markers were used to determine the genotype of individual F3 lines. Linkage analysis and interval mapping of QTLs were performed using MAPMAKER (Lander et al.1987).

The mean value of mesocotyl length in F3 lines varied from 0.5 to 27.8mm. Three QTLs at a LOD threshold of 2.0 were detected on chromosomes 3, 6 and 11 (Table 1). One of QTLs was linked to a RFLP marker, G175, near the end of chromosome 3 and held 32.3% of the phenotypic variance for mesocotyl length.

Research Notes 127

Table 1. Markers linked to QTLs conferring mesocotyl elongation in rice

*LOD and % variation explained were calculated at the putative

QTLs by MAPMAKER.

References