Effect of solarization and Gliocladium virens on sclerotia of Sclerotium rolfsii, soil microbiota, and the incidence of southern blight of tomato

Soil solarization in combination with the introduction of the fungal antagonist Gliocladium virens was evaluated as a potential disease management strategy for control of southern blight caused by Sclerotium rolfsii on tomatoes in North Carolina. Highest soil temperatures measured during the solarization period in 1988 and 1990 were 41 and 49 C, respectively, whereas maximum differences in soil temperature between plots that were solarized and plots that were not solarized were 9 C in 1988 and 14 C in 1990. G. virens significantly reduced numbers of sclerotia of S. rolfsii by 100, 96, and 56% to depths of 30 cm in 1988, 1989, and 1990, respectively, whereas solarization alone reduced numbers of sclerotia by 62% in 1990. When disease pressure was high in 1988, disease incidence in plots planted immediately after treatment was reduced by 49% in solarized soils amended with G. virens before solarization as compared to untreated controls. When disease pressure was low in 1990, disease incidence was reduced by either 77% in solarized soils or 53% in soils amended with G. virens alone, but the combined treatment did not significantly reduce disease the season after treatment. At shallow depths, introduced (G. virens) and indigenous fungi (Trichoderma spp.) did not survive solarization, but recovery of Trichoderma spp. increased when alginate bran pellets containing G. virens were added at depths of 20 and 30 cm in soil. Populations of thermotolerant fungi increased in solarized soils at 10-cm depths, whereas populations of fluorescent pseudomonads decreased immediately after solarization. Plant dry weights were doubled 4 wk after solarization as compared to untreated controls, but fruit yield of tomato planted the season after solarization was not affected by either solarization or the presence of G. virens. Solarization for a 6-wk period during the warmest months of the summer between a spring and fall-grown vegetable crop and treatment of solarized soils with G. virens could provide an additional management alternative for southern blight in the coastal plains of North Carolina.