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Effects of Meloidogyne hapla and Macroposthonia ornata on Cylindrocladium Black Rot of Peanut. Mamadou Diomande, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650, Present address of senior author: Laboratory of Nematologie, ORSTOM, Adropodoume, Abidjan, Ivory Coast, West Africa; M. K. Beute, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 71:491-496. Accepted for publication 29 September 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-491.

Two peanut cultivars, four microsclerotial (ms) inoculum densities of Cylindrocladium crotalariae (0, 0.5, 5, and 50 ms per cubic centimeter of soil for Cylindrocladium black rot (CBR)-resistant NC 3033 or 0, 0.025, 0.25, and 2.5 ms per cubic centimeter of soil for CBR-susceptible Florigiant) and three inoculum densities of Meloidogyne hapla eggs or Macroposthonia ornata larvae and adult mixtures (0, 103, and 104 per 15-cm-diameter clay pot) were tested in all possible combinations in greenhouse factorial experiments. CBR severity on both NC 3033 and Florigiant plants increased in the presence of 103 and 104 M. hapla eggs. M. ornata increased disease severity at 104 nematodes per pot with 0.25 and 2.5 ms per cm3 soil on Florigiant, but failed to affect the disease syndrome on NC 3033 in all combinations tested. Positions, but not the slopes of inoculum density-disease curves were changed by M. hapla on both peanut cultivars and by M. ornata on Florigiant only. ED50 values for C. crotalariae inocula decreased as nematode density increased with all combinations except those of M. ornata on NC 3033. Artificial injuries in the apical meristem region before inoculation with two ms led to more infections than when roots were either uninjured or injured further from the growth zone, suggesting that wounding may be an important factor in these interactions.