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Control of Rhizoctonia solani by Pentachloronitrobenzene Accumulated from Soil by Bean Plants. P. R. Bristow, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; J. Katan(2), and J. L. Lockwood(3). (2)(3)Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, (2)Present address: The Hebrew University of Jerusalem, Department of Plant Pathology and Microbiology, Faculty of Agriculture, Rehovot, Israel. Phytopathology 63:808-8138. Accepted for publication 14 December 1972. DOI: 10.1094/Phyto-63-808.

Roots and hypocotyls of 10 plant species tested accumulated pentachloronitrobenzene to levels ca. 0.1 - 2.0 times those in the surrounding soil. The concentration of PCNB in those portions of bean and muskmelon seedlings emerging from soil decreased rapidly after emergence. No translocation of PCNB to upper parts of the plants was evident, and it disappeared rapidly when added directly to cotyledons or filter papers. Bean seedlings grown for 4-7 days in soil treated with PCNB at concentrations up to 30 µg/g were inoculated with Rhizoctonia solani, then placed in moist chambers or transplanted into soil without PCNB. The severity of disease in plants containing PCNB was significantly less than in plants not previously exposed to the fungicide. At the time of inoculation the concentration of PCNB in the outer cells of the susceptible hypocotyl was 3.5-10.0 times higher than in the inner cells. In culture similar concentrations restricted growth of the fungus by 50%. PCNB was concentrated 10-fold above the ambient soil concentration in peat particles recovered from a peat-loam soil mixture treated with PCNB. Increasing the organic matter content of soil or sand reduced the accumulation of the fungicide by bean plants and the level of protection against R. solani.