Effect of biocontrol strains of Trichoderma on plant growth, Pythium ultimum populations, soil microbial communities and soil enzyme activities

Five strains of Trichoderma with known biocontrol activities were assessed for their effect upon pea growth and their antagonistic activity against la rge Pythium ultimum inocula. The effect of Trichoderma inocula upon the ind igenous soil microflora and soil enzyme activities in the presence and abse nce of Pythium is assessed. In the absence of Pythium, Trichoderma strain N 47 significantly increased the wet shoot weight by 15% but did not signific antly affect the dry weight, whilst strains T4 and N47 significantly increa sed the root weights by 22% and 8% respectively. Strains TH1 and N47 result ed in significantly greater root lengths. Pythium inoculation significantly reduced the root length and the number of lateral roots and nodules, and s ignificantly increased the root and rhizosphere soil fungal populations. Py thium inoculation significantly reduced the plant wet and dry shoot weights and significantly increased the wet and the dry shoot/root ratio. All the Trichoderma strains reduced the number of lesions caused by Pythium and inc reased the number of lateral roots. The effect of the Pythium on emergence and shoot growth was significantly reduced by all the Trichoderma strains e xcept strain To10. Inoculation with Trichoderma strains TH1 and T4 resulted in significantly greater wet root weights (62% and 57%, respectively) in t he presence of Pythium compared to the Pythium control. Strain N47 signific antly increased the shoot/root ratio compared to the Pythium control. Inocu lation with Trichoderma strains T4, T12 and N47 significantly reduced Pythi um populations. Pythium increased the activity of C, N and P cycle enzymes, whilst four Trichoderma strains reduced this effect, indicating reduced pl ant damage and C leakage. Overall, strains T4 and N47 had the greatest bene ficial characteristics, as both these strains improved plant growth in the absence of Pythium and reduced plant damage in the presence of Pythium. The dual properties of these strains improve the commercial application, givin g them an advantage over single action inocula, especially in the absence o f plant pathogens.