The effect of Trichoderma harzianum in combination with organicamendment on soil suppressiveness to Rhizoctonia solani

The effect of sheep manure amendment and the biocontrol agent Trichoderma harzianum Rifai on bean (Phaseolus vulgaris L.) damping off and on fungal activity including Rhizoctonia solani in the soil was investigated over a 24-month period. A combination of T. harzianum and sheep manure at all concentrations tested reduced damping off caused by R. solani after manure incubation in the soil for 0–24 months compared to the control at zero time. Disease reduction was 50% after 24 months with the highest concentration of organic amendment (10%). Disease reduction increased with increasing concentration of organic amendment and with the duration of the incubation time. A combination of T. harzianum and sheep manure reduced both the total fungal population and the R. solani population after 12 and 24 months. However, the population of T. harzianum increased with increasing concentration of sheep manure and duration of incubation. The incubation time had a greater effect on the T. harzianum population than did the concentration of the sheep manure. Sheep manure alone was less effective in reducing bean damping off and improving bean growth than a combination of both manure and T. harzianum. In conclusion, the soil suppressiveness to R. solani damping off was enhanced when T. harzianum isolate Jn14 was added to organically amended soil, and this degree of enhancement increased over time.