Quantitative analysis of resistance in cotton to three new isolates of the bacterial blight pathogen.

Genetic variability for virulence of the bacterial blight pathogen [Xanthomonas campestris pv malvacearum (Smith) Dye] on cotton (Gossypium hirsutum L.) has been shown by the identification of 19 races of the pathogen based on disease reactions of a set of ten host differentials. This study was conducted to determine the inheritance of host resistance to three recently identified isolates of X. campestris pv malvacearum, which are virulent on the entire set of differentials. True leaves of Tamcot CAMD-E, LEBOCAS-3-80, Stoneville 825, and their f1, F2, and backcross progenies were wound-inoculated in the field with separate bacterial suspensions of the virulent HV3, HV7, and Sudan isolates of the pathogen. LEBOCAS-3-80 was replaced with S295, a new immune cultivar, for a greenhouse study in which both cotyledons and true leaves were inoculated. Disease reactions were rated on a scale of 1-10, and genetic models were proposed utilizing generation means analysis. Dominance, when significant, was in the direction of resistance in all but one cross-isolate combination. Digenic interaction components indicated a duplicate type. Narrow-sense heritability for resistance ranged from 0.59 to 0.68; therefore, primarily additive-genetic variability among the selected cutlivars was detected, indicating that breeding for improved resistance to these isolates is a practical goal.