Factors affecting the invasion of tomato roots by Verticillium albo-atrum

Abstract

Anatomical studies have been made of the process of invasion of seedling tomato roots in sterile nutrient solutions and in non-sterile John Innes compost 2 weeks after inoculation with Verticillium albo-atrum. Three levels of sucrose, 200, 2000 and 20,000 p.p.m., were supplied in the sterile solutions. With 200 p.p.m. the fungus was confined to the piliferous layer and lignitubers projected into the outer layer of cortical cells. With 2000 p.p.m. sucrose, invasion of the outer layers of the cortex and lateral root tips occurred and large numbers of lignitubers were found in this region. Invasion of all root tissues, including the xylem, occurred with 20,000 p.p.m. sucrose and few and small lignitubers were evident. Nitrogen was supplied as nitrate at 1·58, 15·8 and 158 p.p.m. in sterile solutions but did not affect the degree of penetration by hyphae or ligni-tuber production. In non-sterile compost or sand the degree of invasion and lignituber production were comparable with those found with 200 p.p.m. sucrose in sterile nutrient solution.