Soil moisture affects disease severity and colonisation of wheat roots by Rhizoctonia solani AG-8

Experiments were conducted to study how the soil moisture affects rhizoctonia root rot of wheat, colonisation of root by Rhizoctonia solani AG-8, spread of fungus in the soil and microbial activity of soil. Four soil moisture levels ranging from 15 to 75% water-holding capacity of a sandy soil at saturation, which equated to a soil water potential range of −10 to −3 kPa, were tested. It was found that the disease severity decreased up to 69%, as the soil became wetter. The soil moisture status at and above 20% WHC however, did not significantly affect the spread of the fungus in soil. Colonisation of roots by young unpigmented hyphae of the fungus diminished with increasing soil moisture, from 80% of root length colonised under relatively dry conditions (15% WHC) to 20–25% under wet conditions (75% WHC). Soil microbial activity increased with increasing soil moisture and may be associated with suppression of pathogen activity through competition.