THE INFLUENCE OF NITRAPYRIN AND SODIUM-AZIDE ON THE GROWTH AND RESPIRATION OF SOME RHIZOBIUM STRAINS

In vitro addition of different concentrations of nitrification inhibit or nitrapyrin and respiratory inhibitor sodium azide to the growth med ia of seven Rhizobium strains representing the four Rhizobium species (R. leguminosarum, R. phaseoli, R. trifolii and R. loti) influenced th e growth of these strains within 48 h at 28 degrees C incubation on a rotary shaker. All doses of nitrapyrin inhibited growth. In contrast, 0.1 mg l(-1) enhanced the respiration rate of the strains using Warbur g's respirometer. The doses 10 and 100 mg l(-1) were highly toxic and depressed the respiration rates of Rhizobium within 180 minutes. Appli cation of 10 mM NaN3 enhanced the growth and respiration rates of all the strains. The growth of R. leguminosarum (Lobab Z and Bukkony 75/4 strains) was stimulated by 20 mM and also R. phaseoli (Bab 5/3 strain) by 30 mM NaN3. The growth and respiration rates of the tested Rhizobi um strains were significantly depressed by 50 mM NaN3, whereas the res piration rates of the strains Lobab Z, Bukkony 75/4 and Bab 5/3 at 30 mM NaN3 were higher than the control. However, 50 mM NaN3 was signific antly high and depressed the respiration rates of Rhizobium strains at P = 0.05.