BEHAVIOR OF LEGUME BACTERIA 309 



THE BEHAVIOR OF LEGUME BACTERIA IN ACID 

 AND ALKALINE MEDIA. 



RAYMOND C. SALTER. 



Several investigators have noted a very marked difference in 

 the resistance of various legumes to soil acidity. Vast areas 

 of cultivated land in the United States show an acid reaction, 

 and as lime is expensive in some localities it has heen suggested 

 that much can be saved by the choice of acid tolerant crops. 1 

 Red clover, crimson clover, soy bean, cowpea, hairy vetch, lu- 

 pine and serradella have been reported as acid tolerant, while 

 on the other hand, alfalfa, one of our most useful forage crops, 

 is found to be very sensitive to acid. 



This sensitiveness may be due to many factors concerning the 

 nutrition of the plant. Since leguminous plants obtain nitro- 

 gen by a symbiotic relation with certain bacteria, it seems prob- 

 able that the ill effects of the acid may be directly upon the 

 symbiotic bacteria and only indirectly upon the higher plant. 



The influence which the acid constituents of the soil may 

 exert on plant growth has been studied chiefly with reference 

 to the growth of higher plants. From the nature of the re- 

 sults of these investigations, it seemed advisable to extend the 

 study to the lower plants. Probably one of the most striking 

 examples of the interdependence of higher plants and bacteria, 

 is the legumes and legume bacteria. Any agent affecting the 

 one will have a corresponding effect on the other. 



The growth of legume bacteria can be measured directly by 

 plate counts, and their virulence can be tested by the formation 

 of nodules on the host plant. This property of the organism 

 makes it well suited for a study of the effect of acid and alkali 

 on its development. An increase or decrease which might re- 

 sult will be noted, especially if the result is compared with that 

 from a neutral culture. 



Experiments were planned to study and compare the effect 

 of acid and alkali on the bacteria and host plant. Since legumes 

 are found to vary in resistance, the acid tolerant red clover 



iCoville, F. V., Bui. 6, United States Dept. Agr. Bur. Plant [ndust. 



