Susceptibility of Historically Dominant Runner-Type Peanut Cultivars of the Southeastern United States to Early and Late Leaf Spot

A greenhouse experiment was conducted to test the hypothesis that cultivar use contributed to historical shifts in disease predominance patterns in the southeastern United States over the past 50 years. Passalora arachidicola, the causal agent of early leaf spot (ELS), and Nothopassalora personata, the causal agent of late leaf spot (LLS), were inoculated separately or together on three historically dominant cultivars, Florunner (1970 to 1996), Georgia Green (1996 to 2008), and Georgia-06G (2008 to present), and on one susceptible cultivar, Georgia Valencia. These results suggest that the transition from Florunner to Georgia Green could have contributed to the historical shift from LLS to ELS predominance observed in the 1990s, with sporulation potential as a possible mechanistic explanation. There was no evidence that Georgia-06G contributed to the resurgence of LLS in recent years. A negative association between ELS and LLS, where LLS is more suppressed in the presence of ELS, demonstrates that the dynamics of the ELS-LLS disease patterns are complex. Understanding factors that contribute to disease predominance will improve predictive abilities and support the development of cultural practices and fungicide programs specific to the pathogen that is expected to dominate.