VIEW ARTICLE

Ecology and Epidemiology

Inoculum Potential of Cylindrocladium crotalariae: Infection Rates and Microsclerotial Density-Root Infection Relationships on Peanut. G. S. Tomimatsu, Graduate student, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061; G. J. Griffin, professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Phytopathology 72:511-517. Accepted for publication 13 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-511.

Numerous infections (1 to >1,000 per plant) caused by Cylindrocladium crotalariae were observed on asymptomatic taproots, lateral, and fine roots of peanut plants grown in naturally infested soils in the field or greenhouse. The majority of observed infections did not appear to be restricted to surface tissues, based on tests involving surface sterilization of roots with 0.1 and 0.25% NaCIO. In a time-course experiment (25 C), the infection rate, I_rº, was 0.120, 0.162, and 0.199 observed infections per meter of root per day per microsclerotium per gram of soil for the first, second, and third 21-day periods, respectively. The infection rate, R_c, for estimated infections (log_e [1/1 – y], in which y is the proportion of plants with necroses) was 0.0017, 0.0038, and 0.0084 infections per plant per day per microsclerotium per gram of soil for the first, second, and third 21-day periods, respectively. Based on the infection-rate curve, each plant had about 300 observed root infections when 50% of the plant population had root necroses. Regression line slopes of 0.98 (R² = 0.94) and 0.99 (R² = 0.94) were obtained for log₁₀–log₁₀ plots of microsclerotial inoculum density vs the number of observed root infections per plant and per unit root length, respectively. Slopes of 21.4 (R² = 0.95) and 2.3 (R² = 0.95), respectively, were obtained for first-order regression lines in arithmetic plots of the same variables. Efficiency of inoculum for observed infection (percent of germinating microsclerotia that infect roots) estimates were high (near 100%), while efficiency of observed infection for necrosis (percent of infections that develop necroses, calculated from log_e [1/1–y]) estimates were low (0.27 to 0.28%).