Foliar spraying of elicitors in pear trees induced resistance to Cacopsylla bidens

The pear psylla, Cacopsylla bidens (?ulc, 1907) (Psylloidea, Psyllidae, Psyllinae) is a serious pest of pear worldwide. In this research, the effects of salicylic acid (SA), chitosan, γ-aminobutyric acid (GABA), and Serenade Aso (Bacillus subtilis QST713) were studied on the induced resistance of pear trees to C. bidens. The treatments showed a significant difference in terms of population growth of C. bidens after 7 and 14 days during two years. In 2019, the mean population growth of total life stages of C. bidens in the studied treatments was significantly lower than control after 7 and 14 days of spraying. In 2020 (7 and 14 days after spraying), the percent decline in the mean population of pear psylla (total life stages) was highest on chitosan treatment (75 and 85 %, respectively) and the lowest on control (30 and 48 %, respectively). GC–MS analysis revealed the range of chemicals in the pear leaves under different treatments. Based on the results, 23 compounds were identified, including 9 alkaloids, 6 flavonoids, 4 polyphenols, 3 terpenoids, and one glycoside. In all treatments except Serenade, the amounts of alkaloids increased compared to the control. Furthermore, the activity of catalase and glutathione S- transferase enzymes in C. bidens under chitosan treatment was significantly higher than others; but the activity of peroxidase significantly decreased on chitosan compared to SA and GABA. The lower levels of peroxidase in C. bidens reared on trees treated with chitosan indicate this insect has not been able to detoxify plant secondary metabolites effectually. In addition, our findings suggested that chitosan on pear trees could act effectively in reducing the C. bidens population and can be considered in integrated management programs of this pest.