THE EFFECT OF AMARANTHINE ON THE STRESS-RESISTANCE OF TOMATOES (<i>Lycopersicon esculentum</i> Mill.) INVADED BY THE ROOT-KNOT NEMATODE (<i>Meloidogyne incognita</i>)
Root-knot nematodes of the genus Meloidogyne are sedentary parasites that infect the root system of plants, the annual damage from which in the world exceeds 80 billion EUR per year. Infection of plants with these nematodes causes biogenic stress, which is associated with changes in the respiratory processes of plants, a decrease in photosynthesis, the appearance of highly reactive oxygen radicals in the tissues with the formation of toxic intermediate products that cause oxidative stress. The high biological activity of amaranthine isolated from Amarathus tricolor L. combined with antioxidant properties, show the promise of its study as a factor resistance to stress of plant during invasion by parasitic nematodes. In this work, we first showed the adaptogenic properties of amaranthine towards tomato plants infected with root-knot nematode. We investigated the effect of the amaranthine beta-cyanine pigment extracted from A. tricolor on the parasite-host system of the tomato Lycopersicon esculentum Mill. and root-knot nematode Meloidogyne incognita (Kofoid & White, 1919) Chitwood 1949. Aqueous solutions of the amaranthine in concentrations from 0.1 to 2.0 mg/ml were tested. When studying the effect of amaranthine on nematodes in vitro, it was found that the analyzed compound has a nematostatic effect in the range of concentrations from 1.0 mg/ml and lower. The 2.0 mg/ml concentration was lethal for M. incognita . The effect of amaranthine on biometric and photosynthetic characteristics of tomato plants infected with the root-knot nematode M. incognita , and morphological and physiological parameters of nematodes from plants treated with amaranthine were evaluated in a lab greenhouse. Before planting, the seeds were soaked in amaranthine solutions (0.5 and 1.0 mg/ml) for 3 hours, and then seedlings reached the phase of 3-4 true leaves were sprayed with solutions at the same concentrations and infected with nematodes (three thousand larvae per plant). This experiment revealed stimulating effect of the amaranthine in the tested concentrations on plant development. The treated seeds sprouted 2-3 days earlier than the control seeds, the average root length of the seedlings treated with the 1.0 mg/ml preparation on day 7 significantly differed from the control (18 %, p ≤ 0.05). The effect of amaranthine on nematodes was evaluated on day 40 after invasion. A comparative analysis of nematodes from the test and control plants showed that the plant treatment with 0.5 and 1.0 mg/ml aqueous amaranthine solutions led to a decrease in the number of nematodes on the roots. The number of sexually mature females per gram of roots under the treatment with 0.5 and 1.0 mg/ml solutions was 2.1 and 1.3 times less compared to the control. Female nematodes from such plants were 1.2 times smaller in both variants; the number of eggs was also 15-20 % less (p ≤ 00.05) as compared to control. The complex of protective mechanisms in infected tomato plants induced by the action of exogenous amaranthine includes stabilization of photosynthetic processes disturbed by the nematode, accumulation of carotenoid antioxidants, switching of non-cyclic electron transport from water in the Photosystem I to pseudocyclic, stimulation of tomato plant growth. Out findings indicate that amaranthine exhibits adaptogenic properties associated with the weakening of negative biochemical and functional changes in plants during nematode invasion. Amaranthine can be proposed as a novel biogenic inducer which provides protective effect due to activation of non-specific plant response to biotic stress under pathogen invasion in greenhouse conditions, and also possesses growth-promoting properties.