Even Pima varieties of cotton grown in Arizona and California showed yield losses that year. High temperatures during this stage of cotton development caused excessive abortion of bolls and seed embryos. Bell found two species of bacteria in seed from 24 farms in the upper coastal area of Texas. Greenhouse studies confirmed that heat stress and the bacterial species contributed to reduced yields of between 20 and 50 percent and led to poor fiber and seed quality. Wilted leaves of affected plants turn reddish to copper just before the plants collapse.
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.