Secondary infection and fertilizer response of wheat initially infected with Rhizoctonia solani

Abstract

Wheat plants which had been inoculated with a primary Rhizoctonia solani infection which was short-lived, continued to suffer damage throughout the growing season from a range of common root-rot and minor pathogens, including Fusarium equiseti, F. avenaceum, Cochliobolus sativus, Microdochium bolleyi, Alternaria alternata and a white basidiomycete, presumably a Coprinus . The seedling Rhizoctonia-Alternaria association was replaced at tillering by a Fusarium-Cochliobolus association, culminating in a climax association dominated by the Microdochium-Coprinus -like basidiomycete at heading. Wheat produced twice as much dry matter in sterilized soil than in natural soil; root weights were 50% higher and shoot:root ratios correspondingly higher. The better growth in sterilized soil is attributed to the lack of pathogens that affected root growth. Response to N:P:K fertilizer applied after tillering was greater in natural soil except for two inoculation treatments in which root damage was sufficiently extensive to prevent efficient nutrient uptake. The implications of these findings upon the course of Rhizoctonia attack upon cereal crops in the field is discussed. The primary Rhizoctonia infection is supplanted early by a complex of secondary invading fungi. These are capable of sufficient damage to be the causes of loss of yield as crops mature. The more severe the primary Rhizoctonia attack, the more severe is the secondary common root-rot which follows. The Rhizoctonia disease complex comprises a diverse group of fungi with varying capacities to cause damage throughout the growth of the cereal crop. The disease syndrome might be more accurately described as the ‘ Rhizoctonia -induced common root-rot’ of cereals.