Systemic acquired resistance (SAR) induced by five different phytohormones (plant growth regulators); salicylic acid (SA), abscisic acid (ABA), indole 3-butyric acid (IBA), indoleacetic acid (IAA) and naphthaleneacetic acid (NAA) was investigated against Puccinia striiformis f. sp. tritici (pst) in the Egyptian susceptible wheat genotype Sids-12. Seedlings were sprayed with three different concentrations of each phytohormones and inoculated by uredospore of pst then evaluated against the germination. Results indicated that, all the five chemical inducers were able to inhibit spore germination and showed highly significant differences among treatments, while, ABA and NAA recorded the lowest germination and the highest inhibition percentages at the low concentration (50 mu g/ml). Also, all treatments reduced infection type values and numbers of pustules/leaf compared with control (untreated treatment). ABA treatment at concentration of 50 mu g/ml was capable to induce complete protection for the susceptible wheat cultivar, Sids-12 by significant reduction of infection type (0) compared with control. On the other side, relative gene expression of two pathogenesis-related (PR) protein genes; the antifungal protein (PR-1) and the endochitinase (PR-4) were evaluated for the treated seedlings in all treatments at three different time points comparing with untreated plants and the resistant wheat genotype Misr-3. Results showed upregulation of gene expressions in all treatments for the two tested genes at the three time points (1, 2 and 7 days after inoculation) comparing with control and most of treatments comparing with the resistant genotype Misr-3. This over expression of PR protein genes might be definitive in activation of the host defense mechanism against Pst and playing the important role of resistance induced by chemical inducers as phytohormones in wheat. Also, it was found that ABA treatment was more efficient in inducing the resistance to wheat stripe rust disease than other chemical inducers. The obtained results indicated that phytohormones as inducers can be used to management stripe rust disease in wheat.
