Pathogenicity of fungi associated with melon vine decline and selection strategies for breeding resistant cultivars

Summary Melone Vine Decline is a severe rot root disease of increasing world‐wide importance. In Eastern Spain it is related to the presence ofAcremonium cucurbitacearumandMonosporascus cannonballus. The strong influence of environmental conditions on the progress of this disease has made its study difficult. A field screening ofCucumis meloaccessions has been conducted over four years. Simultaneously, the pathogenicity of isolates of the two fungi recovered from the screening field was studied. These were more aggressive than other Spanish and American isolates. Percentage of vine decay was scored, togeter with root damage, the latter being evaluated by using four scoring systems based on root characteristics and disease severity. Root inspection alowed the selection of resistance sources, even when aboveground symptoms did not appear, due to the lack of environmental stresses at time of fruit maturity. The root damage scoring if environmental stresses occur during fruit maturity. The accessionC. melovar.agrestisPat 81 consistently exhibited high field resistance level, expressed as a higher percentage of symptomeless plants, together with a significant delay in symptoms appearance. The F1hybrids derived from the cross Pat 81 ×C. melosusceptible varienties showed an intermediate level of resistance between the parents, suggesting a partial dominance gene action. The high resistance level found in Pat 81, and also in its derived hybrids, against the aggressive isolates found in this area, makes it promissing for breeding melon verieties resistant to melon vine decline.