Inheritance of resistance to southwestern cotton rust within upland cotton (Gossypium hirsutum L.)

Abstract

An investigation was conducted to elucidate the manner of resistance expression in the cotyledons, petioles, and stems of Gossypium hirsutum L. to the pathogen Puccinia cacabata Arth. and Holw. Confirmation of previous reports was obtained for the single gene inheritance of leaf and cotyledon resistance. Expression of resistance in petioles and stems was found to be independent of cotyledon resistance. Some association of petiole with stem resistance was noted. Parental populations were not homozygous for petiole or stem resistance and, therefore, the number of genes conditioning expression in these plant parts could not be determined. However, a model for the mode of expression of resistance in the various plant parts was postulated. The possibility of linkage or association of resistance in the various plant parts with the expression of the glandless and nectariless traits was explored. There was no evidence of an association of cotyledon or stem resistance with either morphological trait. Rust susceptibility in the petiole was associated with both glandlessness and nectarilessness. An investigation of possible phenotypic associations between cold tolerance and seedling disease resistance related traits with rust resistance was mainly negative. Two traits, the velocity of seedling emergence and seedling root lengths were weakly associated with rust susceptibility. These relationships require further investigation.