PERSISTENCE OF RHIZOCTONIA SOLANI KÜHN IN SOIL

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Abstract
The effect of different living host and nonhost plants 21 days old, soil amendments, and Trichoderma lignorum (Tode) Harz on the persistence of a heavy artificial infestation of Rhizoctonia solani Kühn in a natural virgin Edmonton black loam of optimum moisture content, held at 61° F., was studied under controlled laboratory conditions, A disease rating of host plants was found to be a satisfactory measure of the persistence of R. solani, whereas data from buried glass slides and from root colonization of indicator plants were unreliable for the purpose intended. In natural, unamended soil, a heavy infestation of T. lignorum did not check the growth of R. solani perceptibly, but with the addition of cornmeal it was practically suppressed for several days. In the presence of living potato plants, R. solani persisted as well in natural untreated soil as it did when cornmeal, sodium nitrate, or calcium hydroxide was added. The living or dead roots of potato or wheat plants did not aid or suppress the pathogen. Apparently R. solani disappeared from the soil in 120 days or less when associated with wheat, oat, barley, or corn plants replanted every 21 days, but it was still fairly abundant in soils bearing potato, bean, or pea plants. When potato plants were absent, a heavy soil infestation in the late autumn practically disappeared by the following June. Results indicate that R. solani depends essentially on parasitic nutrition for its persistence in the soil. The hyphae of R. solani commonly inhabited the living roots of host and nonhost plants, but no nutritional relationship with them was detected.