VIEW ARTICLE

Ecology and Epidemiology

Population Dynamics of Cylindrocladium crotalariae Microsclerotia in Naturally-Infested Soil. P. M. Phipps, Visiting assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607, Present address of senior author: Tidewater Research and Continuing Education Center, Holland Station, Suffolk, VA 23437; M. K. Beute, associate professor, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607. Phytopathology 69:240-243. Accepted for publication 11 September 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-240.

Microplots of soil in 70-cm diameter fiberglass cylinders were used during a 2-yr period to study the dynamics of populations of Cylindrocladium crotalariae microsclerotia (MS) in a naturally-infested field. The effect of fallow, four rotational crops (corn, cotton, tobacco, and soybean), and three peanut cultivars on MS densities in soil was studied over two growing seasons. All three peanut cultivars and soybean were susceptible to infection by C. crotalariae, but corn, cotton, and tobacco were immune. Low rainfall in the first growing season limited disease development, and MS populations did not change significantly in soil planted to host crops. Slight but significant (P = 0.05) reductions in MS densities were detected in fallow soil and soil planted to nonhost crops. After harvest and incorporation of crop residues in soil, MS densities did not change significantly (P = 0.05), according to soil assays in January and April. Florigiant, a susceptible peanut cultivar, developed severe symptoms of Cylindrocladium black rot (CBR) in the second growing season. Soybean and the CBR-resistant peanut cultivars, Argentine and NC3033, showed few or no symptoms. Populations of MS at harvest were 9.6, 5.2, and 1.6 times preplant densities in soils planted to the peanut cultivars, Florigiant, Argentine and NC3033, respectively. MS densities increased 3.7 times in soils planted to soybean. As in the previous growing season, MS densities at harvest were slightly less than preplant densities in fallow soil and soil planted to nonhost crops. After harvest and incorporation of crop residues in soil, MS densities declined sharply between January and April, when soil water in the plow layer froze during several weeks of subnormal temperatures. Field and laboratory tests supported the conclusion that low soil temperatures (≤5 C) caused this sharp decline in MS populations.