SCREENING OF SWEET CLOVER (Melilotus Adans.) SPECIES DIVER-SITY FOR RESISTANCE TO CHLORIDE SALINIZATION

Saline soils are widespread in the world, including in CIS countries. Species of sweet clover (genus Melilotus Adans.) which are valuable fodder plants, e.g. at insufficient moisture on chestnut saline soils, are also among the best phytomeliorants in the legume family. However, during early stages of growing the sweet clover has poor salinity tolerance. Here, we modified earlier developed test and screened accessions of the VIR World Collection (Vavilov All-Russian Institute of Plant Genetic Resources) for resistance to chloride salinity, and for the first time identified among them the forms with high salinity resistance. In the research we used a laboratory method of assessing salt tolerance. Samples of white and yellow sweet clover were grown under controlled conditions, in water culture, according to the following scheme: control (without salinity); salinity of 3 atm. NaCl; the salinity of 5 atm. NaCl. The length of root and sprout of seedlings were measured after 5-day exposure to the stressor. For each sample we calculated the indices of the root length and the sprout length as the ratio of the relevant medium parameters of plants in the test to that in the control. The higher the index value, the more salt-tolerant the sample is. In our tests, chloride salinity caused growth inhibition of roots and shoots samples of both species. The degree of negative growth response intensifies with an increase in NaCl concentration. It was shown that salt stressor intensifies intraand interpopulation variability of sweet clover growth indicators. It is established that the root length index is more informative diagnostic criterion for laboratory screening for salt tolerance among sweet clover plants. The studied fragment of the collection includes 36.2 % of resistant samples of white sweet clover and 29.6 % of yellow sweet clover, i.e. the adaptive capacity towards excess of sodium chloride in the root zone of the studied species is approximately the same. Salt-resistant varieties of white clover come from Far East (Ryadovoi and Diomid), Kazakhstan (Shedevr 75), Novosibirsk (Lucernovidnyi D-20) and Ivanovo (wild sample k-15650) regions; of yellow sweet clover — from Western Siberia (Omskii 8, Omskii 916, Novosibirskii 1, Severotatarskii, Khorog 2155). Selected salt tolerant forms can serve as initial parental forms for creation of yellow and white sweet clover varieties resistant to chloride salinity during early stages of plant development. This will allow better use of the potential of these species for forage, and for bioremediation goals. According to the obtained data, salt-tolerant sweet clover samples often originate from a region with widespread saline soils that should be considered to determine the strategy of search for forms with edaphic resistance valuable for breeding. Many of the selected salt-tolerant varieties are also characterized by other important breeding traits: high productivity, intensive regrowth after cutting, precocity, biotic and abiotic resistance to viruses, drought, low temperatures, unfavorable overwintering, valuable biochemical properties such as high protein content and low coumarin level.