Bacterial leaf streak is a significant disease of wheat (Triticum aestivum) caused by Xanthomonas translucens pv. undulosa. Most wheat cultivars are susceptible, and chemical management is not suitable commercially. Therefore, biological control, induction of plant defense mechanisms or breeding for resistance can be the best ways to reduce the damage caused by this pathogen. The present research investigated the effects of the endophytic fungus Piriformospora indica, of applications of the flavonoid naringenin, and of folic acid applications on wheat resistance against leaf streak disease. Applications of P. indica, naringenin, and folic acid did not affect the growth of the pathogen, rather they reduced the severity of the disease on wheat seedlings by 62, 51.71, 55.16 %, respectively. One millimolar naringenin and folic acid showed the best effect in the induction of plant defense against X. translucens pv. undulosa. The application of P. indica also significantly increased plant growth parameters, such as stem wet weight, while other treatments did not significantly affect plant growth. Enzyme assays indicated that catalase, guaiacol peroxidase, superoxide dismutase activities, and hydrogen peroxide levels in wheat seedlings increased after inoculation of X. translucens pv. undulosa. Accumulation of H2O2 in all treatments was stable from 0 to 6 hours after inoculation (hai) and then increased until 72 hai. In contrast, activation of catalase, guaiacol peroxidase, and superoxide dismutase increased immediately after treatment. These results indicated that these treatments have a synergistic effect on one another. The fungus and chemical inducers used in this study may represent a new approach to control bacterial leaf streak and warrant additional research.

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