Studies on the spread of Verticicladiella procera by soil-borne and insect-borne propagules

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Virginia Polytechnic Institute and State University

Studies were undertaken to determine the dispersal mechanisms of Verticicladiella procera Kendrick, the causal agent of Procera Root Disease (PRD).

Propagule germinability in artificially infested soil decrease rapidly under natural and controlled conditions. Colonization of seedlings in artificially infested soil was rare and symptoms were not displayed by colonized seedlings.

Natural populations of V. procera were closely associated with colonized root tissue. Colonization of field planted seedlings was related to proximity to root collars of diseased trees and insect activity on the seedlings.

Insects (Coleoptera) contaminated with V. procera were found in plantations both with and without PRD. The percent of weevils and bark beetles contaminated with V. procera was 64 and 0.76 respectively. Verticicladiella procera was transmitted to white pine bolts in the field and under controlled conditions following visitation by contaminated insects. Verticicladiella procera was associated with larval galleries and frass in trap bolts and was observed fruiting in insect galleries in root systems of diseased trees.

This evidence suggests that transmission by insects, especially weevils, is the more important mechanism for dispersal and that soil-borne propagules have a minor role in pathogen spread.