DETERMINATION OF SEROLOGICAL DIFFERENTIATION INDEX VALUES OF TURNIP YELLOW MOSAIC-VIRUS (TYMV) STRAINS BY SINGLE RADIAL IMMUNODIFFUSION

An attempt was made to test the applicability of the single radial immunodiffusion method for determination of serological differentiation index (SDI) in plant viruses, based on a comparison of the terminal size of the ring-shaped immune precipitates. Rabbit polyclonal antisera against British isolates/strains ''Edinburgh'' (E), ''Northumberland'' (N) and S of turnip yellow mosaic virus (TYMV) and the virus strain E were used. The experiments were conducted with antisera placed in 3 mm basins in 1% agar gel (on 5 x 5 cm glass slides) containing the crude virus sap centrifuged at low speed. Following reactions with homologous antiserum in four consecutive two-fold dilutions, a calibration curve was drawn showing linear proportionality between steps of two-fold dilutions of antiserum and the logarithm of the respective precipitates diameter. From reactions of heterologous antisera SDIs between strains E and S and between E and N could be read from the graph directly They were determined in decimal fractions (0.9 and 3.3, respectively), which is more precise than in commonly performed SDI determinations (SDI expressed m whole numbers) by precipitin tests m free liquid or double radial immunodiffusion.