Diseased plant stems turn deep red to maroon. During the day, I've placed my hands on the leaves of affected plants and found them warmer than comparable leaves of healthy plants. Bell discovered that a new strain of the bacterium Agrobacterium tumefaciens is associated with bronze wilt and is present in the seed of all U.S. cotton varieties. He was the first scientist to isolate the newly discovered strain, called biovar 1, from both seeds and roots of affected cotton, peanuts, soybeans, and dry beans. Though this doesn't prove that the bacterium causes bronze wilt, there is a high correlation between the presence of the bacterium and disease symptoms.
More research is needed to pin down the precise relationships between the organism and bronze wilt.
In several areas of the Cotton Belt, popular cotton varieties are bred with specific genes that convey bacterial blight resistance and early fruiting, explains Bell. This variety provides the desired early fruiting, which permits farmers to save on insecticides. Breeders who used Tamcot SP37 as a parent for earliness could have inadvertently separated the B genes from each other. Greenhouse studies showed that varieties with B7 alone are very susceptible to bronze wilt and develop high Agrobacterium populations in roots. Plants with one dominant and one recessive gene remain healthy, but when they have two recessive genes they develop bronze wilt.