The effect of some chemical elicitors and neem tree extract (Azadirachta indica Jussieu) application on systemic induce resistance of oak trees (Quercus brantii Lindl.) to pathogens

Systemic induce resistance (SIR) is one of the mechanisms for increasing resistance to pests and pathogens in plants. The plant defense system against environmental stress can increase by some chemical elicitors. For this purpose, we used different concentrations of elicitors including salicylic acid, phosphite potassium, leaf extract of neem, two isolates of plant growth-promoting rhizobacteria (PGPR), imidacloprid pesticide. Then, growth inhibition of all treatments were investigated on both fungal (Biscogniauxia mediterranea) and bacterial (Brenneria sp.) pathogens under in vitro conditions. Also, the effect of these elicitors was examined on Quercus brantii trees with declined crown in the forest. After three weeks, some physiological traits of trees such as relative water content and membrane leakage of leaf, chlorophyll and photosystem efficiency were measured. Results of Duncan's mean comparison showed that by increasing elicitors’ concentration, their growth inhibition against fungal and bacterial pathogens was significantly increased. The lowest effect of the growth inhibition was observed for two isolates of plant growth-promoting rhizobacteria. Trees treated with neem extract, phosphite potassium, and imidacloprid pesticides could significantly reduce membrane leakage compared with the control (treated with water), and also the maximum photosystem efficiency of these treatments and salicylic acid were increased. The results indicate that the positive effects of all used natural chemicals in this study in controlling oak decline which can be used against pest and pathogen instead of chemical pesticides such as imidacloprid.