Influence of bean seedling root exudates on the rhizosphere colonization by Trichoderma lignorum for the control of Rhizoctonia solani

Application of Trichoderma lignorum as a seed coating (8 x 10(6) conidia/seed) or wheat bran preparation (1 x 10(6) cfu/g) at a rate of 20 g/kg soil, greatly reduced the number of bean seeds infested by Rhizoctonia solani, and the percentage of healthy seeds reached 92\%. Germination of conidia of Rhizoctonia solani in bean rhizosphere soil was inhibited after soil or seed application with Trichoderma lignorum. Bean seedling exudate increased the mycelial growth rate of Rhizoctonia solani and Trichoderma lignorum in vitro. Under greenhouse conditions, the addition of germinating bean seed exudate to soil infested with Rhizoctonia solani and planted with bean, reduced the disease control capability of the antagonist. Plants grown from seeds treated with Trichoderma lignorum had roots with lower levels of Rhizoctonia solani in their rhizosphere than the roots of untreated seeds. Trichoderma had little effect on the survival of Rhizoctonia solani in non-rhizosphere soil. However, application of Trichoderma lignorum as a wheat-bran preparation, conidial suspension or seed coating reduced the pathogen counts in the rhizosphere soil of beans.