Immunomodulating effect of elicitors and suppressors upon infection of potato with Globodera rostochiensis (Wollenweber, 1923) Beherens, 1975

Abstract

Potato cyst nematode (PCN) Globodera rostochiensis is classified with the most dangerous and economically significant pathogens of the family Solanaceae. This nematode decreases the yield of potato (to 60%), worsens the quality and marketable condition of tubers, as well as enables potato infection with other diseases. Potato cyst nematode is a sedentary endoparasite of potato roots, fighting with which is hampered due to the good adaptation of the parasite to environmental conditions, long (10 to 15 years) lifespan of cysts in the absence of the host plant, and the threat of occurrence of aggressive pathotypes in the case of introduction of nematode-resistant potato cultivars in a monoculture. With regard for these facts, the method of resistance induction using elicitors is of special interest in terms of protecting potato from G. rostochiensis [1]. The first works indicating the possibility of application of elicitors for stimulation of plant resistance to phytohelminths were performed at the Institute of Parasitology, Russian Academy of Sciences, and the Bach Institute of Biochemistry, Russian Academy of Sciences. Those studies were performed with tomatoes infected with the cotton root-knot nematode Meloidogyne incognita [2, 3]. An increase in immune potential, induced by treatment with elicitors, resulted in a pronounced stimulation of growth and development of tomatoes, suppression of the severity of damage of roots by the nematodes, and caused changes in the morphophysiological and populational parameters of the parasite. The goal of this study was to investigate the effect of immunomodulators in the potato‐ G. rostochiensis system. A low-molecular-weight soluble chitosan with an average molecular weight of 5 kDa and acetylation degree of 15% [4] was used as an elicitor. Laminarin (Sigma, United States), a β -1,3-glucan with single side β -1,6 -bonds, was used as an immunosuppressant. Chitosan was used at a concentration of 100 µ g/ml; laminarin, 300 µ g/ml (this concentration was used in our previous studies). This study was performed with four potato cultivars: Krinitsa (PCN-resistant), Istrinskii (resistance to PCN is not determined), Superior (PCN-sensitive), as well as the transgenic potato carrying the ∆ -endotoxin gene from Bacillus thuringiensis var. tenebrionsis (Bt). The latter cultivar, resistant to the Colorado beetle, was obtained from cultivar Superior (Monsanto, United States). Before planting, potato tubers were treated with aqueous solutions of the immunomodulators at the specified concentrations. The control tubers were treated with water. Tubers were planted in 500-ml containers. On the fourth day after planting, soil was infested with a suspension of nematode larvae (10000 parasites per plant) as described earlier [5]. The experiment was performed in ten replicates. The degree of potato infection and the effect of immunosuppressants were assessed three months after planting. For this purpose, the number of cysts in soil, their size, and the number of eggs contained in them, as well as the weight of tubers of the new harvest were determined.