[Effect of ultraviolet rays on the activity of clover nodule bacteria]

The effect of UV on the survival, morphological variability, and effectiveness was studied with nodule bacteria of clover, strain 374a. The survival of the strain directly depended on the dose of UV rays, being 43.3% at 130 erg/mm2 and 0.000022% at 22,900 erg/mm2. UV irradiation yielded two morphological types of colonies; they differed by the production of slime which was less at higher doses of UV (15,970 to 22,900 erg/mm2). Variants with either positive or negative effectiveness were obtained by the action of UV. The positive variants increased the crop of clover by 21-60%, as compared with the parent strain 347a, while the negative variants decreased it by 18.3-35%.