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Adaptation of Cotton Genotypes to an Acid, Aluminum Toxic Soil¹

Aluminum toxicity, associated with subsoil acidity, limits rooting depth of cotton (Gossypium hirsutum L.) in certain soils of the southern U.S. Shallow rooting means greater susceptibility to drought and less effective use of subsoil nutrients. Liming subsoil to detoxify A1 is difficult and often not economically feasible. An alternative or supplemental approach is to select or breed cotton genotypes with greater A1 tolerance.

Fifty-four cotton genotypes were screened for A1 tolerance in greenhouse pots of an acid, Al-toxic Tatum subsoil (clayey, mixed, thermic, typic Hapludult) treated with 375 µg/g CaCO₃ (pH 4.7 to 4.9) or 3,000 µg/g CaCO₃ (pH 5.3 to 5.4). Aluminum tolerance was measured by relative growth, which is defined as the dry weight of tops or roots at low pH (4.7 or 4.9) expressed as a percentage of that at the higher pH (5.3 to 5.4). In one experiment, relative yields of genotypes (pH 4.7 compared with 5.3) varied from 50 to 25% for tops and from 78 to 35% for roots. In a second experiment, relative yields (pH 4.9 compared with pH 5.4) ranged from 29 to 10% for tops, and from 51 to 12% for roots. Genotypes showing greatest tolerance to the acid subsoil included Pima S-2, Acala 4-42, LaDASS 5194, LaDASS 5187, Stoneville 213, Delcot 277, McNair 612, and Dixie King 3. Three Coker genotypes had tolerance approaching that of Stoneville 213; these were C-Misc,73-110, C-Misc,73-113 and C-Sgs,71-704. More sensitive genotypes were Auburn 56, Coker 201, Deltapine 16 and several experimental lines, including LaDSI 19979, C-Misc,73-114, C-8103, 71-106, and C-7105-73-319.

Acid soil tolerant and sensitive genotypes did not generally differ significantly in concentrations of Al, Mn, Ca, or P in whole plant tops. However, A1 and Ca concentrations tended to be higher in chlorotic and/or cupped leaves than in normal leaves of selected genotypes.

Results indicated that cotton genotypes vary significantly in A1 tolerance and that further improvement may be made through plant selection and breeding. This approach has the potential to alleviate the shallow rooting problem of cotton in strongly acid subsoils. Very high correlation (0.001 level) between top and root yields (r = 0.968 and r = 0.979) in two experiments on the acid Tatum subsoil (pH 4.7 to 4.9) indicated that measurement of either component may be adequate in screening populations for A1 tolerance.

Key Words: Al Toxicity • Subsoil acidity • Mn toxicity • Rooting depth • Drought tolerance • Breeding Al tolerant plant varieties • Gossypium hirsutum L. • Gossypium barbadense L.

² Soil scientist, Plant Stress Laboratory, SEA, AR, USDA, Beltsville, MD; professor of agronomy, Louisiana State Univ., Baton Rouge; and director of cotton breeding, Coker's Pedigreed Seed Company, Hartsville, S.C.

Received for publication October 26, 1979.