Assessment of Lineages of Cercospora kikuchii in Louisiana for Aggressiveness and Screening Soybean Cultivars for Resistance to Cercospora Leaf Blight.

Cercospora leaf blight (CLB) became much more prevalent in Louisiana beginning in 1999. A previous study showed that the Louisiana population of Cercospora kikuchii, the causal agent, was dominated by a new lineage that differed from those collected in other locations at earlier times. In this study, we tested whether the dominance of the new lineage was caused by higher aggressiveness and screened soybean cultivars for resistance to CLB. Representative isolates from both lineages were used individually to inoculate six soybean cultivars in the greenhouse. Contrary to expectations, the new lineage was less aggressive. Three virulence groups were defined in this pathogen based on correlation of the aggressiveness of individual isolates on soybean cultivars. Other possible causes that led to the dominance of the new lineage in Louisiana are discussed. Eleven soybean cultivars were tested for disease reaction at two locations over 3 years in the field. Two cultivars, AG5701 (Asgrow) and TV59R85 (Terral), were among the more resistant cultivars to CLB both in the greenhouse and in the field.