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Greenbugs: More Than Little Green Bandits! November, 1998 |
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The greenbug is a serious pest of wheat in the Southern Plains. Every year producers lose up to $60 million because of reduced yields and increased pesticide application costs. At present, insecticides are the primary control measure, but genetic resistance to greenbugs is finally becoming available in wheat. About the size of a sesame seed, this light-green aphid is truly a marvel of evolution and adaptation. The greenbug is a prolific reproducer with a voracious appetite. Under ideal environmental conditions, a female greenbug can start reproducing when she is about seven days old. She gives birth to nymphs (tiny look-alike versions of herself that are all females) at the rate of up to five per day. At that rate, she can produce from 30 to 90 nymphs in her short lifetime of about a month. Each of her nymphs can start reproducing when they are one week old, and so on, and so on. Thus, greenbugs that crawl, or land, on a wheat leaf can quickly become established through explosive population growth and can wreak havoc on wheat fields, not only by their feeding, but also by transmitting barley yellow dwarf virus. Work on developing greenbug resistance in wheat began in the 1950s. Today, six different genes that confer resistance to greenbugs are available in wheat. However, the insect has proved to be a worthy enemy. For every resistance gene found in wheat, greenbugs have been found that are able to overcome this resistance. These new forms of greenbugs are called biotypes. An example of this phenomenon is TAM 107 wheat and biotype E. Even before biotype C-resistant TAM 107 was released to growers in 1984, biotype E (a new deadly greenbug able to damage TAM 107) was found in the field. Biotype E is now the predominant greenbug biotype in wheat-producing areas of the Southern Plains. TAM 110, a new hard red winter wheat released by the Texas A&M Agricultural Experiment Station, is currently the only cultivar available with resistance to biotype E. We have recently developed an excellent source of resistance to biotype E in the form of the wheat germplasm line GRS 1201. GRS 1201 also is resistant to greenbug biotypes B, C, G, I, and K. The resistance gene is located on a short piece of a rye chromosome that was transferred to wheat, similar to the resistance gene in TAM 107. This type of wheat-rye chromosome transfer has been known to impart undesirable flour quality traits (e.g., shorter mix times, weaker dough, etc.). However, individual breeding lines selected from crosses involving GRS 1201 have quality traits that fall within acceptable limits for U.S. hard wheat breeding programs.
The Wheat Improvement Team has its work cut out.
We have an excellent source of greenbug resistance in GRS 1201 that has been
crossed with locally adapted varieties such as Custer and Jagger to develop
multibiotype-resistant, high-performance wheat. Superior greenbug-resistant
breeding lines will be identified over the next two to three years for
subsequent statewide testing . We now have a greenbug-resistant wheat
(OK95616-14C) undergoing evaluation in this year's regional performance
testing program that was developed using biotype E resistance similar to that
found in TAM 110. We will keep you posted on our progress.
Submitted by David Porter of the USDA-ARS, on behalf of OSU’s Wheat Improvement Team.
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