ALLELE DISTRIBUTION OF SOD-S SUPEROXIDE-D ISMUTASE LOCUS IN SPRING BARLEY IN THE FORMER USSR

Mechanisms of allele frequency distribution of the Sod S locus, which controls isozymes of root superoxide dismutase, were studied in spring barley varieties grown in the former USSR. Uneven distribution of Sod S1 and Sod S2 alleles in different agroclimatic zones covering the en tire territory of the former USSR was discovered. On the whole, the So d S1 allele occurs more frequently. The frequency of the Sod S2 allele decreases from north to south; at its extremes, it is 31.8 and 10.7%, respectively. From west to east, the Sod S2 frequency increases from 12.1% (Western Ukraine) to 50.0% (Eastern Siberia - the Far East). The variation in frequencies, discovered in this work, is consistent with physiological experiments and estimates of allele frequencies in wint er barleys obtained earlier. Allele frequency distribution probably is determined by two main factors: (1) temperature conditions in the zon e of roots and (2) soil quality characteristics. In old spring barley varieties, Sod S2 occurs more frequently than in new varieties. Until the middle of the 1900s, the frequency of this allele exceeded one-thi rd among cultivated varieties. Beginning in the 1950s and continuing t o the present time, the frequency of this allele has decreased two-fol d in newly zoned varieties. Taking into account the importance of this enzyme for a plant species, the mechanisms of zonal distribution of t he revealed alleles, and physiological experiments conducted in the Br eeding and Genetics Institute, we assume that the Sod S2 allele contro ls barley tolerance to acid and saline soils.