Adaptation of Cotton Genotypes to an Acid, Manganese Toxic Soil¹

Abstract Certain soils of the Eastern Cotton Belt are potentially Mn‐toxic. The problem is not always economically prevented or corrected by conventional soil management practices. An alternative or supplemental procedure is to develop plant genotypes having superior resistance to Mn toxicity. Sixty‐five cotton ( Gossypium species) genotypes (cultivars, strains, and breeding lines) were screened in greenhouse pots of an acid (pH 5.1), Mn‐toxic Grenada (fine silty, mixed, thermic, typic, Fragiudalffs) silt loam. Nine of these genotypes, plus two from Brazil, were compared on the same soil at pH 5.1 versus pH 6.9. The cotton germplasm evaluated differed widely in resistance to Mn toxicity as indicated by “crinkle leaf” symptoms and vegetative top dry weight. Genotypes showing greatest resistance included C310,73‐307, LaDSIS 12513; and LaDASB 12609. Manganese sensitive genotypes included C‐Sgl,70‐517; C‐417‐2912; and Coker 201. Top dry weights of cotton genotypes on the unlimed, Mn‐toxic Grenada soil at pH 5.1 were negatively and highly significantly correlated with crinkle leaf rating. However, top dry weights were not significantly correlated with Mn concentrations in either the two youngest leaves (fourth or fifth) or in samples composed of the three youngest leaves plus petioles. Hence, different internal Mn concentrations are required to induce crinkle leaf symptoms and reduce top dry weights in the different genotypes studied. Crinkle leaf symptoms were significantly and positively correlated with Mn concentrations in the two youngest leaves but not with those in leaf plus petiole samples. Results indicate that cotton genotypes differ significantly in tolerance to excess Mn. The development and use of Mn tolerant cultivars would be helpful in situations where the control of Mn toxicity by soil management may not be economically feasible.