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 to a
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
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, email@example.com.