Seedling Tolerance to Aluminum Toxicity in Hard Red Winter Wheat Germplasm

Abstract

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.

Aluminum Partitioning in Intact Roots of Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars

“…There were stain intensity differences between the sensitive and tolerant root tips, which is in agreement with previous reports (5,16,27). Al, at concentrations (50 Mm) that inhibited root growth and changed protein synthesis patterns (19), accumulated mainly in the cell walls, intercellular spaces, and nuclei of the cortical and epidermal root tip cells (Fig.…”

“…The hematoxylin staining technique has been used to screen Al-tolerant cultivars of wheat (5,16,27 1 and 2). There were stain intensity differences between the sensitive and tolerant root tips, which is in agreement with previous reports (5,16,27).…”

“…At low pH, Al bound to clay minerals dissolves in the soil solution and becomes available to roots. Al toxicity is manifested primarily by inhibition of root growth, and varieties of the same species often show different degrees of sensitivity to Al (1,2,5,9,24). Tolerance to Al is genetically controlled (3,5,8) and regulated by several genes (3,22).…”

“…Al toxicity is manifested primarily by inhibition of root growth, and varieties of the same species often show different degrees of sensitivity to Al (1,2,5,9,24). Tolerance to Al is genetically controlled (3,5,8) and regulated by several genes (3,22). The toxic effects of Al on plants are well documented (2,8,10,17,24); however, very little is known about the mechanisms of Al toxicity and much less is known about the mechanisms that control Al tolerance.…”

Genetic analysis of aluminum tolerance in Brazilian barleys

“…The hematoxylin staining method of Polle et al (1978) was chosen because it has given results consistent with root measurements (Takagi et al, 1981;Carver et al, 1988), and has been used in genetic studies and in wheat breeding programs (Carver et al, 1988).…”