298 THE PEANUT— THE UNPREDICTABLE LEGUME 



mature plants are attacked there is no evidence of an invasion of the 

 fruit (23). 



When not otherwise e\'ident the infection may be detected in cross 

 sections of stems and roots. Dark-brown spots are usually evident in the 

 cut xylem and pith regions (143) though healthy appearing plants may 

 be filled with bacteria without any discoloration of the vessels (106). 



Organism and pathogenicity. Since about 1911 Bacterium solana- 

 cearum (E.F.S.) E.F.S. has seemed definitely established as the patho- 

 gen of the bacterial wilt of peanuts. Inoculation tests have established that 

 a typical slime disease is produced when peanuts are inoculated with B. 

 solanacearum isolated from peanuts or other plants (87, 136). The nomen- 

 clature of the pathogen of slime disease is not definitely established, how- 

 ever, and it has been placed in four genera other than the genus Bac- 

 terium. 



With a number of plants reportedly susceptible the existence of dif- 

 ferent strains of the bacterium seems likely. Early observations in the 

 East Indies suggested the existence of a strain equally pathogenic to pea- 

 nuts, tobacco and tomatoes (23, 122) and another strain more pathogenic 

 to eggplant, potatoes and local species (122). 



In the United States, B. solanacearum has been investigated most 

 frequently in connection with the "Granville wilt" of tobacco, and bac- 

 terial wilt of peanuts was first noted on peanuts grown in rotation with 

 tobacco (47) . The bacterium from tobacco was successfully cross inocu- 

 lated into peanuts. Further studies showed that numerous other species 

 of cultivated plants and weeds are susceptible to the bacterium ( 131, 136) . 

 In South Africa cross-inoculation tests indicated that tomatoes and only 

 one variety of tobacco were partially susceptible to the bacterium attacking 

 peanuts (87). These results suggest the existence of dififerent strains of 

 the bacterium in the three widely separated peanut-producing areas, and 

 this may explain the apparent unimportance of the slime disease of 

 peanuts in the United States. 



Factors most frequently suggested as aflfecting the pathogenicity of 

 B. solanacearum on peanuts are soil type, soil moisture, and rotation 

 practices. The virulence of the organism on peanuts in the East Indies 

 was found to be higher on more moist soils, on heavy clay soils, and on 

 soils planted to peanuts for several successive years (106). Continuous 

 cultivation on irrigated soils resulted in an apparent increase in infections 

 in dry seasons (121). In South Africa repeated cropping to peanuts in- 

 creased the severity of the disease which was apparently restricted to the 

 heavier loamy soils (87) . This emphasis on soil texture and drainage sug- 



