evaluation of trichoderma stability in different soils and its effects on the growth performance of cucumber

trichoderma spp. are known as efficient plant growth promoting agents. hence, enrichment of soil by appropriate population of trichoderma is useful and important for effective plant growth promote. present study aimed to investigate the plant growth promoting effects of five strains of the genus trichoderma species include: trichoderma harzianum tr6, t. harzianum t22, t. asperellum t34, t. atroviride p1 and t. harzianum on cucumber and select the most efficient candidate under greenhouse conditions. then this superior strain was applied in various soils including normal, phosphorus-defective soil, potassium-defective soil, alkaline soil, soil with two levels of salinity and acidic soil to evaluate the detailed effects on cucumber growth parameters under greenhouse conditions. the results showed that trichoderma strain tr6 led to statistically significant improvement in examined growth indices in soils suffering from salinity and potassium- and phosphorus deficiency. in view of stability of trichoderma population in different soils, comparison of means showed that the highest population was achieved in acidic and normal soil and the lowest population occurred in the soils with high level of salinity and alkaline soils. generally, we concluded that low trichoderma population under some soil conditions is likely due to the lack of optimum condition for its growth and it can improve plant growth under these stressed soils by restoring its population by adding successful strains of trichoderma to the soils.