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Poster: Diseases of Plants: Disease Detection & Diagnosis


Using Color Spectrophotometry to Evaluate Disease Severity of Macrophomina phaseolina in Soybean
J. JORDAN (1), A. Mengistu (2), H. Kelly (1) (1) University of Tennessee, U.S.A.; (2) USDA, U.S.A.

Charcoal rot is a soilborne disease of soybean caused by the fungus Macrophomina phaseolina (Tassi) Goid. The fungus is associated with hot dry weather and can dramatically reduce yields. Two current methods are used to evaluate disease severity in root tissues: colony forming units (CFU) and visual severity ratings. These methods are time consuming and expensive. Therefore, a more efficient methodology is needed to improve the screening process. We evaluated the use of color spectrophotometry as an alternative method for screening disease severity in 2006-2010 using 340 conventional and 893 roundup ready cultivars. Field plants were sampled at the R7 growth stage and evaluated using CFU, visual ratings (1-5 scale), and a color spectrophotometer. As previously reported, CFU values and visual ratings were predictive of each other across all years (F=7.66, p<0.05). Color data was not predictive of severity ratings (F = 2.70, p = 0.10), however they were negatively correlated across all years (r = -0.62, p<0.001). This association suggests that this method may be used as alternative in disease severity quantification of charcoal rot.