Evaluation of compatibility and effect of Trichoderma harzianum and Pseudomonas fluorescens against disease complex of tomato

The antagonistic fungal species Trichoderma harzianum (teleomorph: Hypocrea lixii) is a versatile bio-control agent and is used for the management of pathogenic fungi infecting various crops. Some strains are also effective against nematodes. For the effective management of disease complex of crops caused by nematode + fungus/bacterium, it is often necessary to use a combination of two or more bio-agents. This necessitates studies on the compatibility of the strains of bio-agents to be applied together. Hence, five strains of T. harzianum (Th1-Th5) were evaluated for their compatibility with two strains of Pseudomonas fluorescens Migula (Pf1 and Pf2) in vitro by direct confrontation assays and in vivo in tomato by means of root colonization/rhizospheric competency. The results indicated that different isolates of T. harzianum are compatible with P. fluorescens both in vitro and in vivo. Each of the strains showed different levels of compatibility. The strains with higher compatibility of 89.1% have shown a better performance in the field in reducing the nematode induced disease complex caused by Meloidogyne incognita and Fusarium oxysporum f.sp. lycopersici. A reduction in soil nematode population by 52.7% and reduction in percent disease incidence by 61.4% was observed. The results suggest that the combined application of the highly compatible strains of T. harzianum and P. fluorescens, as seed and substrate treatment, appears promising for the control of nematode induced disease complex under field conditions with a 23.8% increase in yield in tomato.