Genetic analysis for aluminum tolerance in rice (Oryza sativa L.) via molecular markers

A recombinant inbred (RI) population with 150 lines, derived from a cross between an Al-sensitive lowland indica rice variety 1R1552 and an Al-tolerant upland japonica rice variety Azucena, was studied in a solution culture. The roots of seven-day old seedlings were cutoff, leaving 1 cm to uniform the root length before stress. Seedlings were transplanted to plastic culture containers with standard rice culture solution (Yoshida et al. 1976) and Al stress at the concentration of 1 mM Al3+. The pH of solution was adjusted to 4.0 by using I N NaOH or 1 N HCI everyday. The solution was replaced every 3 days. Relative root length (RRL), defined as a ratio of maximum root length under stress to that under normal culture (More et al. 1977), was measured after stress for 2 and 4 weeks at concentration of 30 mg AI3+ and control under pH 4.0, respectively, and conditional variation in RRL at the 4th week stress given the variation at the second week stress was calculated using mixed model approach (Thu 1995). A molecular linkage map with 104 amplified fragment length polymorphism (AFLP) markers (Vos et al. 1995) and 103 restriction fragment length polymorphism (RFLP) markers was constructed to map quantitative trait loci (QTLs) and epistatic loci for Al-tolerance based on the segregation for relative root length (RRL) among the population. Two QTLs were detected at both the second and the 4th week stress on chromosome 1 and 12 from unconditional mapping, while the QTL on chromosome 1 was only detected at the second stress week from conditional mapping. The effect of QTL on chromosome 12 was increased with increase of stress period from 2 weeks to 4 weeks. The QTL on chromosome 1 was expressed only at the earlier stress, but its contribution to the tolerance was prolonged during the growth. At least one different QTL was detected at the different stress periods. Mean comparison between marker genotypic classes indicated that the positive alleles at the QTLs were from Al-tolerant upland rice Azucena. The important heterozygous non-allelic interaction on Al-tolerance was found. The results indicated that the tolerance in younger seedlings was predominantly controlled by additive effect, while epistatic effect was more important to the tolerance in old seedlings (Table 1,2 and Fig. 1).

A recombinant inbred (RI) population with 150 lines, derived from a cross between an Al-sensitive lowland indica rice variety 1R1552 and an Al-tolerant upland japonica rice variety Azucena, was studied in a solution culture. The roots of seven-day old seedlings were cutoff, leaving 1 cm to uniform the root length before stress. Seedlings were transplanted to plastic culture containers with standard rice culture solution (Yoshida et al. 1976) and Al stress at the concentration of 1 mM Al3+. The pH of solution was adjusted to 4.0 by using I N NaOH or 1 N HCI everyday. The solution was replaced every 3 days. Relative root length (RRL), defined as a ratio of maximum root length under stress to that under normal culture (More et al. 1977), was measured after stress for 2 and 4 weeks at concentration of 30 mg AI3+ and control under pH 4.0, respectively, and conditional variation in RRL at the 4th week stress given the variation at the second week stress was calculated using mixed model approach (Thu 1995). A molecular linkage map with 104 amplified fragment length polymorphism (AFLP) markers (Vos et al. 1995) and 103 restriction fragment length polymorphism (RFLP) markers was constructed to map quantitative trait loci (QTLs) and epistatic loci for Al-tolerance based on the segregation for relative root length (RRL) among the population. Two QTLs were detected at both the second and the 4th week stress on chromosome 1 and 12 from unconditional mapping, while the QTL on chromosome 1 was only detected at the second stress week from conditional mapping. The effect of QTL on chromosome 12 was increased with increase of stress period from 2 weeks to 4 weeks. The QTL on chromosome 1 was expressed only at the earlier stress, but its contribution to the tolerance was prolonged during the growth. At least one different QTL was detected at the different stress periods. Mean comparison between marker genotypic classes indicated that the positive alleles at the QTLs were from Al-tolerant upland rice Azucena. The important heterozygous non-allelic interaction on Al-tolerance was found. The results indicated that the tolerance in younger seedlings was predominantly controlled by additive effect, while epistatic effect was more important to the tolerance in old seedlings (Table 1,2 and Fig. 1).