Family Chenopodiaceac 119 



Symptoms. The disease does not usually manifest 

 itself until the roots are nearly half grown. Abnormal 

 outgrowths or galls (fig. 20 a) appear which vary in 

 size from that of a garden pea to nearly two inches in 

 diameter, depending on the severity of the attack. 

 The galls are usually attached to the beet by a narrow 

 string. In light cases of infection there may be but 

 one gall on the root; in severe cases, however, the 

 roots may be covered with numerous galls. 



The Organism. The cause of crown gall is a bac- 

 terial organism, Pseudomonas tumefaciens Sm. and 

 Town. It is a short rod, multiplying by fission, which 

 moves about by means of polar flagella. On agar or 

 gelatine it forms small round white colonies. Under 

 unfavorable conditions it readily develops involution 

 forms; in pure culture the organism is short lived. 

 P. tumefaciens lives over in the soil from year to 

 year. 



Control. Although crown gall is known to attack 

 a large number of plants, it has never been found as a 

 parasite on grain crops. Gardens or fields which 

 refuse to grow beets because of the disease, should be 

 given a rest for at least three years by planting sweet 

 corn instead. According to Dr. Smith 1 the follow- 

 ing truck crops are susceptible to crown gall : Tomato, 

 potato, cabbage, beet, radish, and salsify. In infected 

 fields, these crops should be left out when planning a 

 rotation which is aimed at starving out the organism 

 in the soil. 



'Smith, E. P., et. al., " Crown Gall of Plants," U. S. Dept. Agr., 

 Bur. PI. Ind., Bui. 213 : 13-200, 1911. 



