Changes in defense genes expression in cucumber root after inoculation with Trichoderma, Pseudomonas and their combination*

In nature, plants are exploited by a plethora of microbes species that can cause severe diseases or establish beneficial relationships with them and improve plant growth or help the plant to overcome biotic or abiotic stresses. Trichoderma and fluorescent pseudomonads are the most useful beneficial microbes. In this study, the effects of Trichoderma harzianum Tr6, Pseudomonas sp. Ps14 and their combination, which isolated from cucumber rhizosphere and were able to induce resistance on cucumber, were evaluated on cucumber immune system by evaluation of defense gene expression. The results showed that expression of β-1,3-glucanase and chitinase transiently increased after inoculation with both microbes. The transient increase of expression of PR1 and LOX1 was observed after inoculation with Tr6 and its combination with Ps14, whereas only LOX1 was increased after inoculation with Ps14. These findings indicate that the plant defense system was activated against beneficial microbes but later these microbes actively suppress the immune system of plants to establish a mutualistic interaction.