Seedling Tolerance to Aluminum Toxicity in Hard Red Winter Wheat Germplasm

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Critically acid soils (pH < 5.0) now exist in the major wheat (Triticum aestivum L.) production areas of the Southern Great Plains. This condition has encouraged the identification and development of hard red winter (HRW) wheat genotypes that can tolerate higher amounts of soluble soil AI. The objectives of this research were to identify Al‐tolerant HRW genotypes better adapted to soils high in soluble Al and to determine alternative gene sources. Seedlings were grown in nutrient solutions containing 0.18, 0.36, and 0.72 mM AI. As a measure of tolerance, the degree of staining on root tips of 5‐d‐old seedlings was visually scored after exposure to hematoxylin. A total of 156 HRW pureline cultivars, ancestors, and parental lines used in HRW breeding programs was classified into four tolerance levels, i.e., very susceptible (54%), moderately susceptible (15%), intermediate (14%), and tolerant (17%). Several ancestors from other wheat classes showed intermediate or tolerant responses including ‘Kenya 58’, ‘Mediterranean’, ‘Purplestraw’, and ‘Red Fife’; yet, the predominant ancestor of HRW wheat, ‘Turkey’, was very susceptible. Eight of the 16 tolerant USA cultivars shared similar pedigrees, and thus probably shared the same source(s) of Ai tolerance (i.e., ‘Sonora 64’ and ‘Trapper’). Confirmed sources of tolerance in remaining cultivars included ‘Centurk’ and ‘Prelude’, although several were derived from parents classified as very susceptible. Nine of the 15 intermediate USA cultivars were separated into two groups based on their distantly related Al‐tolerant parents (Kenya 58 and Prelude vs. Mediterranean). In summary, AI tolerance in HRW wheat could not be traced in a single lineage to any single ancestor or to a set of closely related lines. These results provide an information base to test for different genes among sources and to help develop recommendations of more tolerant cultivars for acid soils high in soluble AI.