Wheat breeding for soil acidity and aluminum toxicity

The soils of southern and central-southern Chile where the national wheat production is concentrated are of volcanic origin, with low pH and with high exchangeable aluminum. Soils contain large amounts of phosphorous in organic form, however available phosphorous is low. The high content of free Al negatively affects the root growth of wheat varieties depending on their Al-sensitivity or Al-tolerance. The mechanism of tolerance is exclusion of toxic Al as a consequence of root excretion of queelant organic acids; roots of tolerant varieties are also protected by higher root mycorrhizal colonization. Crosses between sensitive and tolerant material and subsequent selection under low pH and high Al have produced high yielding tolerant cultivars. This paper outlines the development of tolerant wheat varieties, describes the germplasm used and discusses the selection process including including the use of growth chambers, greenhouse assays and field experiments