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Ecology and Epidemiology

Integrated Control of Rhizoctonia solani Damping-Off of Radish: Effect of Successive Plantings, PCNB, and Trichoderma harzianum on Pathogen and Disease. Y. Henis, Professor, Department of Plant Pathology and Microbiology, Hebrew University of Jerusalem, Israel; A. Ghaffar(2), and R. Baker(3). (2)Associate Professor and Fulbright-Hays Scholar, Department of Botany, University of Karachi, Pakistan; (3)Professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins, CO 80523, USA. Phytopathology 68:900-907. Accepted for publication 28 November 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-900.

When applied to soil at rates of 0.04-0.15 g/kg (dry weight basis), wheat-bran cultures of Trichoderma harzianum protected radish seedlings from damping-off induced by Rhizoctonia solani and also increased radish germination in noninfested soils. Protection lasted for five successive weekly plantings. Pentachloronitrobenzene (PCNB) at 4 μg/g soil (active) added with T. harzianum inoculum had an additive effect on disease control and a synergistic effect on the decrease in inoculum density of R. solani propagules. In the absence of T. harzianum PCNB alone delayed the decrease of viable R. solani propagules. At a relatively low initial inoculum density (five propagules/g soil) when radishes were replanted every week, inoculum concentration rose during the first 3 wk. Cultures of T. harzianum added to this soil permitted no increase in inoculum density. With high inoculum levels (80 propagules/g soil) T. harzianum accelerated reduction in population of R. solani in comparison with nontreated controls. After four or five successive plantings of radish in infested, nonamended soil, however, incidence of Rhizoctonia damping-off decreased substantially. A conduciveness test was developed and used for quantitative evaluation of the ease with which disease increased in a given soil. Soil conduciveness declined to a minimum in the nonamended, infested treatment after five successive plantings. The concept of incorporating soil conduciveness (along with inoculum quality and inoculum concentration) into the capacity portion of the inoculum potential is suggested.