AGROECOLOGICAL EVALUATION OF ROMAINE LETTUCE VARIETIES IN THE CONDITIONS OF THE VOLGA DELTA
The article presents the results of research on the extension of varietal diversity of lettuce ( Lactuca sativa L. ) in the natural and climatic conditions of the Volga delta. Among the various varieties of lettuce, the most popular representative is Romaine lettuce (Cos lettuce). The soil and climatic conditions as well as traditional experience of growing vegetables favor a significant increase in lettuce production in the region. The cultivation of Romaine lettuce varieties adapted to specific conditions allows to increase the period of consumption of vitamin green products from early spring to late autumn. Evaluation of the main economically valuable traits of Romaine lettuce varieties contributes to the realization of the potential productivity of each variety at different growing times. The article provides the experimental data on the main parameters of lettuce plants of promising Romaine varieties (Maximus, Batsio, Amadeus, Quintus) when growing by seedlings in open ground in the early spring and summer period. It was established that in case of planting seedlings in the summer period (III decade of August), the temperature factor accelerated the passage of phenological phases of lettuce plants development, and produced products were characterized by high marketability and quality. The best indicators of the parameters of lettuce head for different periods of cultivation were recorded on the Batsio variety, which ensured the formation of the highest yield. Its average yield of lettuce heads during the spring growing period was 32,1 t/ha, exceeding other varieties by 4,2-7,2 t/ha. For the summer planting of seedlings the yield of the Batsio variety was 34,3 t/ha, and its exceedance in yield was 7,2-8,1 t/ha. According to the results of biochemical analysis, it was found that the head of the Batsio variety contained a higher amount of sugars (2,97%) and vitamin C (31,7 mg%), while the Amadeus variety had a higher dry matter content (5,96%). The accumulation of nitrates in the products of all varieties of Romaine lettuce was not recorded above the maximum permissible concentration (MPC).