Identification, occurrence and pathogenicity of Rhizopycnis vagum on muskmelon in Spain

Abstract

Rhizopycnis vagum is a recently described coelomycetous fungus that contributes to vine decline of muskmelons in Honduras, Guatemala, Texas and California. This fungus has been associated with roots of muskmelon plants affected by vine decline in most Spanish muskmelon production areas. Isolates were collected from 1996 to 2000 and identified from their cultural and morphological characteristics and by sequencing the ITS region of the ribosomal coding nuclear DNA (rDNA) and phylogenetic analysis. A few isolates from muskmelon with growth characteristics similar to R. vagum were identified as Phoma terrestris. Watermelon, Cucurbita hybrids used as rootstocks for watermelon production, Amaranthus sp. and grapevine were also hosts for R. vagum. Based on disease reaction in muskmelon roots, the pathogenicity of 10 isolates of R. vagum from different hosts and geographical origins was verified. The fungus caused root discoloration, corky lesions, and eventually the presence of pink coloration on the roots. Rhizopycnis vagum appears to be a minor pathogen that contributes to muskmelon vine decline complex in Spain through infection of roots.