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Read: a full report on bronze wilt in Agricultural Research.

ARS Scientists Are Discovering Why Some Short Season Cotton Varieties Are Susceptible to Bronze Wilt

By Linda McGraw
November 13, 2000

Susceptibility toa bacterium associated with bronze wilt lingers in the genetic background of the most popular short-season cotton varieties grown in the mid-south and southeast. Agricultural Research Service scientists have found the bacterium, Agrobacterium tumefaciens, in the seed of all U.S. cotton varieties.

Short season cotton varieties are bred with specific resistance genes for bacterial blight and early fruiting--characteristics that allow farmers to reduce insecticide use. Commonly used in cotton breeding programs, these resistance genes are generally referred to as “b genes.” Three of the b genes--B2, B3, and B7--are in Tamcot SP37, a Texas cotton variety that has been used in breeding programs worldwide.

Breeders who used Tamcot SP37 as a parent to achieve early fruiting could have inadvertently separated the “b genes” from each other, according to ARS plant pathologist Alois A. Bell in College Station, Texas. Bell is the first scientist to isolate a type of A. tumefaciens, called biovar 1, in both seeds and roots of affected cotton, peanuts, soybeans, and dry beans. Greenhouse studies showed that varieties with B7 alone are very susceptible to bronze wilt.

Bell is looking for genetic markers to develop tests for identifying seed stocks that may carry the genes for susceptibility to bronze wilt. For now, producers should avoid the highly susceptible varieties. Other ARS researchers in College Station are looking for fungal and bacterial biocontrols for bronze wilt to reduce the severity of disease.

A full report on bronze wilt is in the November issue of Agricultural Research magazine.

ARS is the chief scientific research agency for the U.S. Department of Agriculture.

Scientific contact: Alois A. Bell, ARS Cotton Pathology Research Unit, Southern Plains Agricultural Research Center, College Station, TX, phone (409) 260-9518, fax (409) 260-9470, abell@acs.tamu.edu.