ORIGINAL PAPER Genetic diversity for aluminum tolerance in sorghum

Abstract Genetic variation for aluminum (Al) toler-ance in plants has allowed the development of cultivars that are high yielding on acidic, Al toxic soils. How-ever, knowledge of intraspecific variation for Al tol-erance control is needed in order to assess the potential for further Al tolerance improvement. Here we fo-cused on the major sorghum Al tolerance gene, AltSB, from the highly Al tolerant standard SC283 to inves-tigate the range of genetic diversity for Al tolerance control in sorghum accessions from diverse origins. Two tightly linked STS markers flanking AltSB were used to study the role of this locus in the segregation for Al tolerance in mapping populations derived from different sources of Al tolerance crossed with a com-mon Al sensitive tester, BR012, as well as to isolate the allelic effects of AltSB in near-isogenic lines. The results indicated the existence not only of multiple alleles at the AltSB locus, which conditioned a wide range of tolerance levels, but also of novel sorghum Al toler-ance genes. Transgressive segregation was observed in a highly Al tolerant breeding line, indicating that po-tential exists to exploit the additive or codominant effects of distinct Al tolerance loci. A global, SSR-based, genetic diversity analysis using a broader sor-ghum set revealed the presence of both multiple AltSB alleles and different Al tolerance genes within highly related accessions. This suggests that efforts toward broadening the genetic basis for Al tolerance in sor-ghum may benefit from a detailed analysis of Al tol-erance gene diversity within subgroups across a target population