Future Cotton Lines Could Resist Two Major Diseases

Future cotton breeding lines may naturally resist two fungal wilt diseases that cost U.S. cotton producers yield losses of $114 million in 1996. That’s because scientists with USDA’s Agricultural Research Service, working with Texas A&M University researchers, partially purified a key enzyme that inhibits the cotton plant’s ability to defend itself against Verticillium and Fusarium wilt.

The finding gives researchers a strategy for developing bioengineered genes to disarm the enzyme, thus strengthening the plant’s natural defense system against diseases. Chemist Robert D. Stipanovic at ARS’ Southern Crops Research Laboratory in College Station, Texas, will report on the work Wednesday at the American Chemical Society meeting in Las Vegas, Nev.

The diseases produce a wilt that reduces yield and can kill the entire plant. Chemical controls are generally too costly. The new finding comes at a time when traditional breeding methods have obtained the most resistance that they are likely to achieve.

All cotton plants produce natural antibiotics to fight off fungal invaders. The scientists found that one antibiotic, desoxyhemigossypol, is the most toxic to fungi. The problem is that some genes in susceptible cotton plants convert this antibiotic into another, less toxic compound. To overcome this, researchers hope to block the formation of the enzyme responsible for this conversion. The enzyme is known as desoxyhemigossypol-O-methyl-transferase.

To construct a gene to block the enzyme, the researchers will use a complex biotech approach called antisense. First they will isolate a gene responsible for key chemical steps to forming the enzyme. Then they will produce an antisense gene--a gene whose specific makeup is akin to a mirror image of the enzyme-forming gene.

The antisense gene, inserted into a cotton plant, should block formation of the enzyme that weakens the antibiotic. The researchers estimate that this accomplishment may occur within two to three years.

Scientific contact: Robert D. Stipanovic, ARS Southern Crops Research Laboratory, College Station, Texas, phone (409) 260-9232, fax (409) 260-9470, rds846a@acs.tamu.edu.