In order to evaluate the effect of different Trichoderma isolates on reducing the effects of drought stress on Polianthes tuberose flower, two factorial experiments were carried out based on a completely randomized design with three replications. In the first and second experiments, the first factors were Bi and 65 isolates of Trichoderma harzianum at three levels -0, 10, 20% v/v- and the second factor in both experiments was three levels of drought stress -25, 50, 100% field capacity-. The results showed that both isolates increased fresh and dry weights of the biomass and root dry weight of Polianthes tuberosa plant under stress conditions. The fresh weight of the biomass increased by 4 -g- in 25 % stress level by Bi isolate and 14 -g- by isolate 65, indicating the growth of this flower in the presence of Trichoderma fungus. The amount of proline in the treatment of isolate 65 at the 20% level increased compared to other levels of the fungus in 25 and 50% stress levels. Relative water content and leaf green area increased as a result of using two fungal isolates under increasing stress levels. In general, it seems that the isolates Bi and 65 of Trichoderma harzianum have different effects under drought stress conditions.

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