Population dynamics of Myrothecium roridum Tode ex. Fr. and Rhizoctonia solani Kühn in commercial coffee nurseries

Abstract

Sources of inoculum and population dynamics of Myrothecium roridum and Rhizoctonia solani, causal organisms of cankers and root rot in nursery coffee plants, were studied. Six commercial nurseries were selected on the basis of presence of disease, and samples were taken every eight weeks. Correlated with disease incidence were variables such as density of propagules for both pathogens ¡n soil of diseased plants, apparently healthy plants, and chlorotic plants; in fumigated and non fumigated soil; in organic matter used for the mixture; and in sand from the seedbed. Density of propagules of M. roridum was estimated on the basis of the colony-forming units (CFU); that of R. solani, on the basis of percentage of colonized sugarbeet seeds. Neither of the pathogens was detected in the coffee pulp. Higher density of propagules was obtained in the soil at 5-cm depth.The highly correlated density of M. roridum with disease incidence per season and nursery indicated its primary role in coffee stem cankers in the nurseries. The presence of M. roridum in the sand of asymptomatic seedlings and the high correlation with its density in soil of plants in the nursery suggests that seedlings are the primary source of inoculum for canker disease of plants in the nursery.