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One of the main focuses of the LSU AgCenter’s soybean breeding program is to develop soybean varieties with resistance to Cercospora leaf blight.
This late-season disease currently is the most damaging disease to soybeans in Louisiana, according to Dr. Blair Buckley, principal investigator on a project funded by the Louisiana Soybean and Grain Research and Promotion Board and a plant breeder with the LSU AgCenter.
The disease is recognized by symptoms of purplish-bronze leaves in the upper plant canopy. Cercospora also contributes to green stem syndrome in which stems remain green after pods and seeds mature.
"This necessitates the use of a harvest aid (desiccant) prior to harvest," Buckley said, adding, "Unfortunately, varieties being grown now are not strongly resistant to Cercospora, and fungicides have not been completely effective against the disease."
Disease-resistant varieties would reduce the need for fungicide applications, Buckley stressed.
In Buckley’s studies, older soybean varieties with some resistance are crossed with good-yielding varieties possessing other desirable traits, he explained.
Crosses are made by removing the anthers (male flower part containing pollen) from flowers of one parent and pollinating those flowers with pollen from the other parent involved in the cross-breeding. Seeds from the "crosses" are then collected and planted to produce the first generation of new plants.
These plants are in turn harvested to produce seed for the second generation of plants. Screening and evaluation for disease resistance and many other traits begin in this second generation, known as F2 plants.
Promising plant lines from screening are advanced to the next generation for continued evaluation, Buckley said.
This season, 140 third-generation lines (known as F3 lines) are being evaluated in the field for reaction to Cercospora and for important agronomic traits. Selection for disease resistance also will be conducted from another 28 F2 populations, Buckley said.
Then evaluation for yield can begin with plants that advance through the studies to the fourth or fifth generation, he said.–Mary Ann Van Osdell
(This article was published in the 2008 edition of the Louisiana Soybean & Grain Research & Promotion Board Report.)