Potential Reasons for Prevalence of Fusarium Wilt in Oriental Melon in Korea

This study aims to examine the potential reasons for the current prevalence of the fusarium wilt in the oriental melon. Twenty-seven isolates obtained from oriental melon greenhouses in 2010-2011 were identified morphologically and by analysis of gene () and internal transcribed spacer (ITS) rDNA sequences as 6 species (8 isolates of , 8 , 5 , 3 , 2 , and 1 ), which were classified as same into 6 sequence-based phylogenetic clades. Pathogenicity of the isolates on the oriental melon was highest in , next in and , and lowest in the other species tested, suggesting and were major pathogens of the oriental melon, inducing stem rots and vascular wilts, respectively. Oriental melon and watermelon were more susceptible to than shintosa and cucumber; and cucumber was most, oriental melon and watermelon, medially, and shintosa was least susceptible to , whose virulence varied among and within their phylogenetic subclades. Severe root-knot galls were formed on all the crops infected with ; however, little indication of vascular wilts or stem and/or root rots was shown by the nematode infection. These results suggest the current fungal disease in the oriental melon may be rarely due to virulence changes of the fusarium wilt pathogen and the direct cause of the severe root-knot nematode infection, but may be potentially from other pathogen infection that produces seemingly wilting caused by severe stem rotting.