Variability and genetics of tolerance for aluminum toxicity in rice (Oryza sativa L.).

A study was undertaken to investigate the variability among lowland rice cultivars and the mode of gene action of aluminum (Al) toxicity tolerance in rice. Pregerminated seeds were grown in a nutrient solution containing 30 ppm Al and in normal nutrient solution, and relative root length (RRL) was determined at the 14-day-old stage to characterize genotypes for tolerance. Sixty-two traditional rice cultivars grown on lowland acid sulfate soil areas of Asia and West Africa were tested. Tolerant varieties 'Azucena', 'IRAT104', and 'Moroberekan', moderately sensitive 'IR29' and 'IR43', and sensitive 'IR45' and 'IR1552' were used to investigate the genetics of tolerance by diallel analysis. Of the 62 cultivars tested, only 3 were found to be sensitive to A l toxicity. Among the tolerant cultivars identified, 11 ('Siyam Kuning', 'Gudabang Putih', 'Siyam', 'Lemo', 'Khao Daeng', 'Siyamhalus', 'Bjm-12', 'Ketan', 'Seribu Gantang', 'Bayer Raden Rati', and 'Padi Kanji') were found to possess higher levels of tolerance than the improved tolerant upland cultivar 'IRAT104'. Diallel analysis revealed that high RRL is governed by both additive and dominance effects with a preponderance of additive effects. The trait exhibited partial dominance, and one group of genes was detected. Heritability was high, and environmenal effects were low. Findings suggest that when breeding for A1 toxicity tolerance, selection can be made in early generations. The pedigree method of breeding would be suitable. Combining ability analysis revealed the importance of both general combining ability (GCA) and specific combining ability (SCA) in the genetics of A1 toxicity tolerance in rice. GCA was more prevalent than SCA. Tolerant parens 'Azucena', 'IRAT104', and 'Moroberekan' were the best general combiners. The presence of reciprocal effects among crosses suggested the proper choice of parents in hybridization programs. Results indicated that 'Azucena', 'IRAT 104', and 'Moroberekan' should be used as the female in crosses for A1 toxicity tolerance.