Investigating the effect of various biotic and abiotic inducers on wheat resistance to brown rust disease (Puccinia triticina)

Introduction
Wheat is one of the most important crop plants that provides food for more than 80% of the world’s population. Wheat leaf or brown rust caused by Puccinia triticina is the most prevalent rust disease in wheat. One of the method of managing plant diseases such as wheat leaf rust is chemical control using fungicides, but this method has environmental risks. Therefore, utilizing beneficial microorganisms and environmentally-friendly chemical compounds is a sustainable strategy in the management of plant diseases. This method enhances plant resistance through induced resistance and reduces the damage caused by diseases. The objective of this study was to compare the effect of several biotic and abiotic inducers on the increase of induced resistance in wheat against leaf rust disease.
Materials and methods
The sensitive wheat variety, Karim, was used to perform this experiment. The seeds were disinfected with 1% sodium hypochloride and germinated on wet sterile filter paper. Germinated seeds were transferred to plastic pots containing sterile soil and the pots were placed in the greenhouse. The experiment was conducted in a completely randomized design with six treatments and three replications. The treatments were including Trichoderma harzianum (5×10⁵ spores per ml), Pseudomonas fluorescence (with a concentration of 0.7), salicylic acid (with a concentration of 3 mM), potassium phosphite (with a concentration of 1 g/liter), chitosan (with a concentration of 400 ppm) and a positive control as check treatment. The studied treatment were sprayed on wheat seedlings at two-leaf stage. After 24 hours, the seedlings were infected with the disease-causing fungus with a concentration of 10⁶ spores per ml using a fogger. The treated and control plants were sampled to measure the activity of superoxide dismutase, catalase, and peroxidase enzymes at 0, 24, 48 and 72 hours after infection, and to evaluate the disease severity after 15 days. SAS software was used for analysis of variance and comparison of means by Duncan’s test at 5% probability level and Excel software was used to draw two-dimensional graphs.
Research findings
The results indicated that there was a significant difference in enzymes activity levels between the studied treatments and the control treatment. Potassium phosphite and Pseudomonas fluorescens treatments showed the highest increase in the activity level of superoxide dismutase, catalase and peroxidase enzymes immediately after the inoculation of P. triticina compared to control treatment. Furthermore, the three treatments of P. fluorescens, chitosan and potassium phosphite at 24 and 48 hours and the three treatments of P. fluorescens and T. harzianum and chitosan at 72 hours after the inoculation of P. triticina had the highest increase in activity of superoxide dismutase, catalase and peroxidase enzymes compared to the control treatment. The results showed that there was a significant difference in disease spread in 15 days after the inoculation of P. triticina between the control treatment and other treatments. The disease symptoms in potassium phosphite, P. fluorescens, chitosan, T. harzianum and salicylic acid treatments decreased by 22.38%, 40.29%, 44.77%, 52.23% and 58.20% compared to the control treatment, respectively.
Conclusion
The results of this study showed that biotic inducers such as T. harzianum fungus and P. fluorescens bacteria and abiotic inducers such as salicylic acid, chitosan and potassium phosphite had a significant effect on the control of wheat leaf rust disease in greenhouse conditions. It seems that a part of the pathogenic process of P. triticina fungus in wheat plants is due to decrease in the levels of catalase, peroxidase, and superoxide dismutase enzymes, which leads to the breaking of inherent resistance in the plant and the appearance of disease symptoms. It can be concluded that biotic and abiotic inducers can increase the level of catalase, peroxidase and superoxide dismutase enzymes in diseased plants, and reduce the number of brown rust leaf spots. Therefore, these inducers may be a suitable alternative for chemical compounds in the future.