158 Journal of Agricultural Research voi. x, no. 4 



INOCULATION EXPERIMENTS 



Seedlings of the Purple Top variety of turnips, which had been de- 

 veloped in pots in the greenhouse, were sprayed with a suspension of the 

 fungus spores in water. For this purpose a bean-pod culture, covered 

 with the pink spore mass, was shaken in sterilized water. The suspension 

 was then poured into a sterile atomizer used for spraying. At the same 

 time similar seedlings were sprayed with sterile water, and both lots 

 were covered with bell jars during the first four days. On the fourth day 

 dark water-soaked spots began to appear on the plants sprayed with the 

 spore suspension. The spots soon became very numerous and faded to 

 the light-straw color characteristic of naturally infected spots. The 

 control plants, sprayed with sterile water, remained free from the disease. 



On March 15 several plants of mixed varieties from seed sown in the 

 field the previous autumn were transferred to pots and carried into the 

 greenhouse. After the plants had recovered from the transplanting and 

 had begun to grow, they were inoculated as described above. Abundant 

 infection was obtained on all varieties, indicating that probably no 

 varieties of turnips are immune. Not only the leaves but also the stems 

 and seed pods showed infection. Some of the very young seed stalks 

 were killed, the whole outer surface being covered with anastomosed spots. 



Inoculations were also made in a similar manner on radish (Raphanus 

 sativus), cabbage (Brassica oleracea capitata), collard {Brassica oleracea 

 viridis), and lettuce (Laciuca saliva). The inoculations on radish plants 

 gave abundant infection. The radish seemed to be fully as susceptible 

 as the turnip. On cabbage a few spots developed, but not nearly so 

 abundantly as on turnip and on radi^. Collards seemed to be slightly 

 more susceptible than cabbage, but no naturally infected plants of either 

 have ever been found in the field. The lettuce plants showed no sign of 

 infection, though inoculated on various occasions. 



A few cross-inoculations have been made in studying the relation of 

 this fungus to other allied forms. Several turnip plants in each of five 

 pots were inoculated as follows: No. i with the Colletotrichum from 

 turnip, No. 2 with conidia of Glomerella cingulata from pear, and No. 

 3 with conidia of Glomerella gossypii from cotton bolls. The two others 

 were not inoculated, but were given otherwise similar treatment to serve 

 as control plants. On the fifth day spots began to appear on the plants 

 of pot I sprayed with the Colletotrichum from turnip, and after a few 

 days infection became so abundant that all the leaves were killed on 

 these plants. No spots ever occurred either on the control plants or on 

 the plants of pots 2 and 3. 



At the same time three sound bean pods were sprayed with a water 

 suspension of conidia of the Colletotrichum from turnip, five others 

 were likewise sprayed, after being pricked or scratched with a sterile 

 needle, and similar numbers to serve as controls were sprayed with sterile 



