Pathogenicity of Stagonosporopsis caricae, Stagonosporopsis citrulli, and Stagonosporopsis cucurbitacearum on Five Commonly Cultivated Cucurbit Species

Abstract

Gummy stem blight is a destructive fungal disease that affects all commonly cultivated cucurbit crops. One cultivar each of the five cucurbit species susceptible to gummy stem blight were inoculated with two isolates of Stagonosporopsis caricae, three isolates of Stagonosporopsis citrulli, and one isolate of Stagonosporopsis cucurbitacearum to explore the host range and relative aggressiveness of each isolate. In a series of greenhouse experiments, all isolates were pathogenic to the crops tested, but disease severity differed significantly among isolates and cucurbit cultivars. There also were significant interactions between isolate and cultivar. S. citrulli isolates caused the most severe symptoms across all five cultivars and S. citrulli isolates C-68 and DbHD-10 were consistently among the most aggressive isolates on each cultivar. S. caricae isolates generally caused less severe symptoms, but W-1028 (S. caricae) was among the most aggressive isolates on Tyria cucumber. These results add to the understanding of the relationships of the three Stagonosporopsis species with various cucurbit hosts, reinforcing knowledge about the pathogenicity of the three species across cucurbit crops and the potentially high aggressiveness of S. citrulli.