Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2002
Publication Date: March 20, 2002
Citation: Bell, A.A. 2002. Bronze Wilt as a cause of yield stagnation. Proceedings Proceedings of the National Cotton Council Beltwide Cotton Conference. Interpretive Summary: Bronze wilt is a newly recognized disease of cotton in the USA. Modern cultivars and breeding lines were evaluated for susceptibility to bronze wilt. Most of the cultivars (109 out of 128) contained symptoms that are diagnostic for bronze wilt. The nature and extent of plant damage caused by the disease was determined and it was found that the bacteria causing bronze wilt may either disrupt root development and function or secrete toxins that are transported to and damage leaves of some cultivars. Bronze wilt may be a major cause of yield stagnation in cotton, since the causal bacteria are present in all seed lots being sold for planting.
Technical Abstract: Cultivars and breeding lines submitted for the 2000 Uniform Variety Trials were inoculated with Agrobacterium tumefaciens isolate 25A, grown in the greenhouse, and observed for plant development, yield, seed quality, bronze wilt, root necrosis, and bacterial concentration in roots. Losses from bronze wilt were entirely due to reductions in seed weight, which were accompanied by large increases in the percentage of light seed. In contrast, losses from root necrosis were entirely due to reduction of seed number per plant with no change in seed weight or percentage of light seed. Decreased root weight occurred with both symptoms. However, the greatest reduction in root weight occurred before flowering with root necrosis, and after fruit set with bronze wilt. Cultivars and individual plants with root necrosis consistently had greater concentrations of A. tumefaciens in roots than those without symptoms, whereas bacterial concentrations in roots of cultivars with bronze wilt were not different or slightly less than those in cultivars with no symptoms. The results are consistent with the hypothesis that root necrosis is truly a susceptible reaction to A. tumefaciens, whereas bronze wilt results from toxins produced in roots and transported to leaves during fruit development. Losses from root necrosis may be a major, unrecognized cause of yield stagnation in cotton, since A. tumefaciens strains similar to 25A now occur in all cotton seed lots.