The Anthracnose Disease of the Raspberry 175 



to obtain spores of Plectodiscella veneta in culture. Typical lesions were 

 formed on the drupelets after an incubation period of from fifteen to 

 forty-eight hours. 



During the summer of 19 13 the writer conducted a series of inoculation 

 experim.ents on young raspberry canes of the Columbian variety, which 

 were emerging from the ground. Cotton-plugged lamp chimneys were 

 placed over these shoots, and when they were about six to eight inches 

 high they were sprayed with a suspension of P. veneta conidia in water. 

 The conidia were taken from the lesions on older canes, and in a few 

 cases from pure cultures on potato agar, but in no case did more than 

 thirty or forty per cent of them germinate. All inoculations were made 

 in the evening, to avoid the evaporation of the drops of water containing 

 the spores, and the lamp chimneys were allowed to remain over the young 

 plants for two or three days. Check plants were used. Many of these 

 experiments were destroyed, as they were conducted in a field which was 

 being continuously cultivated. The final data obtained, therefore, were 

 relatively few and scattered. 



Inoculations were made on the following dates: May 26, June 20 and 

 23, July 16, 18, and 29, and September i. Fifty-six of these experiments 

 were completed but infection occurred only in eighteen cases. The 

 incubation period was three days for seven experiments, four days for 

 four, five da3^s for five, and seven days for two. The shortest period 

 was during the warmest weather, while during cool weather no infections 

 occurred. Aside from climatic conditions, the causes of the low per- 

 centage of infection were possibly poor germination of the conidia, the 

 drying of the drops of water, and the condition of the host plant. When 

 the host tissue becomes hard, infection does not take place. Other factors, 

 not sufficiently understood, no doubt entered into the experiments. 



Inoculations with spores front the ascigerous stage 



In order to make certain the connection between the ascigerous form 

 and Gloeosporium venetum Speg., a series of inoculation experiments 

 were conducted. The use of ascospores as an inoculum was impossible, 

 since very few could be collected owing to the scarcity of the ascocarps 

 and their irregularity in time of maturing. Also, it is difficult to make 

 certain that the ascospores are separated from the conidia unless the 

 former are collected by causing them to be ejected on plates of agar. 

 The most satisfactory method appeared to be the use of conidia for 

 inoculation from a culture of the fungus that had been developed from a 

 single ascospore. 



Such a culture was obtained, and was grown on three-per-cent potato 

 agar until large, sclerotia-like masses were formed. These fungous 



-'85 



