SURVIVAL OF RHIZOCTONIA-SOLANI AG-4 IN RESIDUAL PEANUT SHELLS IN SOIL

The survival of Rhizoctonia solani AG-4 in residual peanut (Arachis hy pogaea) shells was studied for 2 yr. Surface sterilized mature peanut pods colonized by R. solani AG-4 and untreated pods were placed separa tely in fiberglass-mesh bags and buried at 0, 7.6, and 25.4 cm depths in Tifton loamy sand in field microplots. Shells of pods were sampled at 6-mo intervals and assayed on tannic acid-benomyl agar for the reco very of R. solani AG-4 and other soilborne fungi. Recovery of R. solan i AG-4 after 6 mo was greater (P less-than-or-equal-to 0.05) from shel ls of treated pods placed on the soil surface than on those buried in the soil. Survival of R. solani AG-4 from shells at 12 mo was not diff erent (P less-than-or-equal-to 0.05) from those at 6 mo. R. solani AG- 4 was isolated from less than 1% of the total shells after 18 and 24 m o. The fungi most commonly associated with untreated shells were speci es of Fusarium, Gliocladium, Pythium, Trichoderma, and binucleate Rhiz octonia (CAG-3 and CAG-5). Fusarium spp. were recovered at a higher (P less-than-or-equal-to 0.05) level than other fungi during the last tw o sampling dates. Fusarium was the most abundant genus recovered at th e conclusion of the study. Throughout the investigation, Trichoderma s pp. were commonly isolated at a greater (P less-than-or-equal-to 0.05) frequency from treated than from untreated shells and at increased bu rial depth. The increase of these fungi after 12 mo indicated that the inoculum potential of R. solani AG-4 remaining in the shells was dimi nishing. Burial of peanut pods 20-25 cm deep with a moldboard plow cou ld effectively reduce the inoculum from the root zone of the following crop.