212 Diseases of Truck Crops 



lent on early spring or fall radish. The greatest 

 damage done by this trouble is to the seed crop. 



Symptoms. On the leaves, white rust is manifested 

 as white raised pimples or sori (fig. 33 b) character- 

 istic of all white rusts. When the surface of the 

 sori breaks open a white powder, which consists of the 

 spores of the fungus, is liberated. On the flower 

 organs of the radish, the symptoms of the disease are 

 especially striking. The ovary sacs, the stamens, 

 corolla, and calyx become hypertrophied and dis- 

 tended, resembling abnormal leaves. 



It has been questioned whether the white rust of 

 the radish is the same as that which attacks other 

 crucifers such as cabbage, mustard, etc. While 

 much remains to be learned, the investigations of 

 Melhus throw much light on the subject. Melhus 1 

 had no trouble in infecting the rat-tail radish (Raph- 

 anus caudatus) with conidia taken from ordinary radish 

 (Raphanus sativus). Melhus also secured infection 

 by sowing conidia from the radish on white mustard 

 (Brassica alba) and cabbage {Brassica oleracea). At 

 no time, however, was it possible to infect more 

 than fifty per cent, of the cotyledons or leaves of the 

 white mustard which were inoculated. With the 

 cabbage it was still more difficult to secure infection. 

 Of the fifteen varieties inoculated less than one per 

 cent, of the plants became infected. 



No infection could be obtained when sowing spores 

 of Cystopus candidus from radish on ten varieties of 



1 Melhus, T. E., Wisconsin Agr. Expt. Sta. Research Bui., 15: 25- 

 83,1911. 



