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Interaction of Verticillium albo-atrum and the Root Lesion Nematode, Pratylenchus penetrans, in Tomato Roots at Controlled Inoculum Densities. J. J. Conroy, Graduate Research Assistant, Department of Botany & Plant Pathology, Purdue University, Lafayette, Indiana 47906; R. J. Green, Jr.(2), and J. M. Ferris(3). (2)Professor, Department of Botany & Plant Pathology, Purdue University, Lafayette, Indiana 47906; (3)Associate Professor, Department of Entomology, Purdue University, Lafayette, Indiana 47906. Phytopathology 62:362-366. Accepted for publication 25 October 1971. DOI: 10.1094/Phyto-62-362.

The influence of the root lesion nematode, Pratylenchus penetrans, on infection levels by Verticillium albo-atrum at controlled inoculum densities of both organisms and under controlled environmental conditions was considered. Infection of tomato seedlings, cultivar Bonny Best, by V. albo-atrum was 100% at the inoculum density of 200 microsclerotia/g soil, and infection levels were progressively lower at 100, 75, 50, and 25 microsclerotia/g soil. Consistent increases in infection occurred at all inoculum densities when the nematode was also present. Infection incidence by V. albo-atrum also increased with increases in the nematode population. There was no evidence of a synergistic effect on nematode reproduction, since the number of nematodes extracted from roots of tomato also infected by V. albo-atrum was significantly lower than from roots with the nematode alone. The role of the nematode in increasing susceptibility of the host plant to V. albo-atrum was considered, using a split-root technique. There was no increase in susceptibility of tomato to the fungus pathogen when the nematode was on the same root system but in isolation from the fungus.

Additional keywords: inoculum density, fungus-nematode interaction.