Effects of Root Decay on the Relationship between Meloidogyne spp. Gall Index and Egg Mass Number in Cucumber and Horned Cucumber.

A greenhouse study was conducted to determine if root necrosis had an effect on the relationship between root-knot nematode gall index and egg mass number. Thirty-four cultigens of Cucumis (14 accessions, 12 cultivars, and six breeding lines of C. sativus, and two accessions of C. metuliferus) were evaluated against four root-knot species (Meloidogyne arenaria race 2, M. incognita race 1, M. incognita race 3, and M. javanica) measuring gall index, root necrosis, and egg mass number. Root necrosis affected the gall index-egg mass relationship. At lower root necrosis values, a stronger relationship existed between gall index and egg mass number than at higher root necrosis values. Root tissue was destroyed by root necrosis, and normal root-knot nematode reproduction would not occur, even though root galling was still observed. The races of M. incognita tested had a greater effect in predisposing C. sativus and C. metuliferus to root necrosis than did M. arenaria race 2 or M. javanica. This study showed that root necrosis had an adverse affect on the relationship between gall index and egg mass number in cucumber.