Submitted to: Handbook of Soil Acidity
Publication Type: Book / chapter
Publication Acceptance Date: 8/12/2002
Publication Date: N/A
Citation: Interpretive Summary: Aluminum (Al) toxicity is a serious impediment to crop production on the acidic soils of the earth. Natural variation for tolerance to Al toxicity has been a valuable tool exploited by breeders to improve crop productivity on acidic soils, in conjunction with soil amendment approaches such as lime application. This book chapter reviews our current understanding of the genetics and molecular biology of Al tolerance in the most intensively studied crop with respect to this trait, bread wheat (Triticum aestivum L.). Pedigree relationships support the notion that extreme levels of Al tolerance used in many wheat breeding programs around the world today can trace back to a small set of Brazilian cultivars. Genetic studies indicate that this extreme Al tolerance is associated with one or a few genes. However, when viewed as a whole, the broad and continuous variation for Al tolerance in this species implies that many Al tolerance genes may be present on wheat germplasm. This is important because it suggests that different Al tolerance genes may be combined to enhance the trait in an additive fashion. Efforts to isolate Al tolerance genes from wheat have failed to date, in part due to the fact that they have relied upon the assumption that Al tolerance genes are inducible at the molecular level in response to Al, in contradiction to physiological data supporting constitutive expression of these genes. Synteny between wheat and other cereals may provide a means for isolating these genes through map-based methods.
Technical Abstract: The agronomic challenges associated with acid soils have brought plant breeders into a research arena often considered a principal concern of soil fertility and plant nutrition specialists. Their approaches have the same intent: to bring actual crop yields closer to potential yields by modifying the plant genotype or the soil environment. Soil acidification places productivity of currently cultivated lands at risk. As cultivation continues, the likelihood increases that nutrient toxicities associated with low pH will erode yield potential. Nowhere is this more apparent than in the surface-acidified areas of the U.S. southern Great Plains. Natural soil acidification is accelerated by removal of basic cations through the harvesting of vegetation and grain. Even during a period of the most intensive liming application in the U.S. Great Plains, the proportion of wheat fields reporting strongly acidic pH has actually increased. In this chapter, we intend to showcase one of nature's gifts-genetic variability-a one of the many resources available in reducing crop losses with soil acidity. We present our case, not to argue genetic modification as an alternative to lime application or other soil-ameliorative approaches, but as a necessary partner to them. Our discussion will center on aluminum (Al) tolerance as the central component to acid-soil tolerance, without the intention of excluding other legitimate trait systems that might be targeted in plant breeding programs, such as P-utilization efficiency and Mn tolerance. Plant breeders have traditionally emphasized Al tolerance, because it often evolves in plant materials common to acid-soil environments.