Effect of immunomodulators on potato resistance and susceptibility to Phytophthora infestans

The mechanisms of induced resistance and susceptibility of potato (Solanum tuberosum L.) tubers to late blight agent (Phytophthora infestans Mont de Bary) were studied using an elicitor chitosan and an immunosuppressor laminarin. It was elucidated that treatment of disks from potato tubers with chitosan resulted in salicylic acid (SA) accumulation due to activation of benzoate-2-hydroxylase and hydrolysis of SA conjugates. Such SA accumulation in potato tissues inhibited one of the antioxidant enzymes, catalase, inducing an oxidative burst and resistance development. The mechanisms of induced susceptibility to the late blight causal agent were studied using an unspecific immunosuppressor, laminarin, an analogue of natural specific suppressor of potato immune responses, beta-1,3,beta-1,6-glucan. It was established that the development of immunosuppression in tissues treated with laminarin did not affect the SA level in tissues. However, catalase sensitivity to SA reduced in laminarin-treated tissues, and the enzyme activity increased. In its turn, this might result in the reduced level of hydrogen peroxide in the cells and, as a sequence, in the increased potato susceptibility to late blight.