VIEW ARTICLE

Effectiveness of Specific Genes and Gene Combinations in Conferring Resistance to Races of Xanthomonas malvacearum in Upland Cotton. K. M. El-Zik, Postdoctoral Fellow (currently Plant Breeder and Geneticist, Lockett Seed Company, P.O. Box 1579, Vernon, Texas 76384) Department of Plant Sciences, The Texas Agricultural Experiment Station of Texas A&M University, College Station 77843; L. S. Bird, Professor, Department of Plant Sciences, The Texas Agricultural Experiment Station of Texas A&M University, College Station 77843. Phytopathology 60:441-447. Accepted for publication 1 October 1969. DOI: 10.1094/Phyto-60-441.

Eight strains of Gossypium hirsutum were intercrossed to produce a complete diallel set. Plants in the field were inoculated with separate suspensions of Xanthomonas malvacearum, races 1 and 12, and a 1:1 mixture of the two. Each plant was assigned a disease grade (1-10) representing the extent of leaf infection. Race 12 was more virulent than race 1. Virulence of the mixture was intermediate between races 1 and 12. The parental lines having the major gene B₄ and the gene combination B₂B₃ were the most resistant to both races, followed by the B₂B₆ and B₂B₃B₇ combinations. Austin (B₇) was highly resistant to race 1 and less resistant to the mixture and race 12. Empire WR (B_Sm), Deltapine TPSA (B_Dm), and Texacala (B_Tm) were susceptible to both races. The B₇ gene negatively influenced the gene combination B₂B₃ in the presence of race 12. The major genes showed isodirectional dominance towards resistance. Transgressive segregation for the minor genes was indicated. Symptom expression with race 12 was influenced by environment more than with race 1. The B₄ and B₂B₃ genes were less influenced by environmental fluctuations than others. The genetic background was important in the expression of the major genes.