Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/9/2000
Publication Date: N/A
Interpretive Summary: Roots of cotton plants affected by bronze wilt are often infected by various fungi as well as Agrobacterium species. This study was undertaken to determine whether interactions occur between these microorganisms to influence disease severity. The results show significant synergistic interactions between Agrobacterium biovar 1 isolates and the fungal seedling pathogen Rhizoctonia solani. The presence of the fungus greatly increased the incidence of crown galls and root necrosis caused by the bacteria. In turn, certain isolates caused the fungus to be more pathogenic in causing damping-off than did other isolates. The results show that control of the fungal seed pathogen also is important for optimal control of bronze wilt.
Technical Abstract: When cotton seedlings were inoculated sequentially with three cotton isolates of Agrobacterium carrying Ti plasmids (i.e., A. tumefaciens) followed 4-14 days later by R. solani, a high frequency of crown gall tumors developed at the soil line. No tumors developed when plants were inoculated with the A. tumefaciens isolates alone using a variety of wounding techniques. The synergistic interactions were observed with each of the 8 isolates of R. solani from cotton and each of the10 different cotton cultivars. Macrophomina phaseoli, Diplodia gossypii or Phoma exigua used with A. tumefaciens failed to induce galls on cotton. The results indicate that R. solani or its infections may produce unique metabolites that activate virulence genes in infectious plasmids of A. tumefaciens strains obtained from cotton roots.