Submitted to: Proceedings on Sustainable Crop Production in the Acid Savannahs
Publication Type: Proceedings
Publication Acceptance Date: October 15, 1999
Publication Date: N/A
Technical Abstract: Natural variation for adaptation to acid soils is well-documented, both within and between crop species. This adaptation is largely related to tolerance to the phytotoxic forms of aluminum (Al) in such soils. Much effort has been expended on trying to elucidate the genetic basis of Al tolerance in crops because such information would enhance the success and efficiency of breeding programs. Results from decades of Al tolerance inheritance studies in crops such as bread wheat provide evidence that differences in Al tolerance between cultivars are frequently under the genetic control of one or a few genes. Frequently, Al tolerance genes are reported to be dominant in nature but it is likely that Al tolerance is gene dosage-dependent. While non-nuclear or cytoplasmic effects have long been known in the plant kingdom, in those cases where cytoplasmic effects on Al tolerance have been examined, no evidence of a cytoplasmic role for Al tolerance variation has been detected. A number of physiological and biochemical mechanisms of plant Al tolerance have been postulated in the literature, but to date Al-induced organic acid exudation at the root apex is the only mechanism for which naturally-occurring intraspecific variation has been detected in a crop and subsequently directly associated with a genetic locus conferring Al tolerance. As our knowledge of the molecular genetics of Al tolerance in related species progresses, we will be in a position to ask if variation within a common set of genetic loci underlies Al tolerance variation in different species. To date, there is some indirect evidence that there may be conservation of Al tolerance gene identity between wheat, barley and rye.