ASSESSMENT OF THE DEGREE OF DAMAGE OF TOMATO PLANTS BY LATE BLIGHT USING THE METHOD OF INDUCTION OF CHLOROPHYLL FLUORESCENCE

The article is devoted to the study of the issue of diagnosing the damage to the assimilation surface of tomatoes by late blight based on a detailed analysis of the activity of the plant photosystem from the standpoint of the approach to the pathogen as a stress factor in the implementation of photochemical variants of the plant signaling system. The article focuses on the peculiarities of the development of major tomato diseases in view of the specificity of plant growth and physiological processes in closed ground conditions with increasing risks of the intensity of infection and the formation of favorable conditions for the development of the pathogen due to positive gradients of temperature, humidity and ventilation of the agrocenosis. The results of a two-year cycle of research on the use of a portable fluorometer “Floratest” of Ukrainian production to find the relationship between the phenomenon of chlorophyll fluorescence and the degree of damage to the leaf apparatus of tomato plants by measuring the intensity of the process on undisturbed (undetached) leaves after their shadow adaptation for 10 minutes with graphical recording of the results at a second-by-second fixation of the process in a 90-second interval are presented. A graded system of comparison of measurements was used with the selection of leaves of different degrees of damage from 0% damage (baseline control) to 60% damage (the maximum damage of late blight for closed ground conditions). According to the results of the averaged two-year records, a reliable sensitivity of the method for assessing the degree of stress response of the tomato leaf apparatus at the initial stages of infection with the late blight pathogen at the milestone papameter record for 3% level of damage was established in comparison with the obtained chlorophyll fluorescence curves on Kautsky curves, which were used as an absolute reference control in the experiment. Application of the basic parameters of the chlorophyll fluorescence curve (initial fluorescence (F0), plateau zone fluorescence (Fpl), maximum fluorescence Fm and steady-state fluorescence Fst) made it possible to determine the gradient response of the tomato plant photosystem to the intensification of pathogen development in the accounting scale of damage and to obtain index curves of chlorophyll fluorescence for each accounting gradation of damage. Based on the results of the evaluation of derivative indicators of chlorophyll fluorescence analysis in accordance with the provisions of the European protocol for its application, the main trends in the reaction of the assimilation system to the penetration and development of the late blight pathogen were determined. It was noted that the main effective physiological photochemical processes of the tomato leaf apparatus decreased due to an increase in the degree of damage by 1% with an average gradient of 1.35% per 1% of leaf damage with a general increase in the degree of quenching of the plant photosystem by 1.29%.