568 Journal of Agricultural Research voi. xiii, no. n 



While' final conclusions are not yet justifiable, the results of these 

 experiments make it reasonably certain that under Wisconsin conditions 

 the practical cherry grower need have no serious concern regarding 

 infection of cultivated cherries by Coccomyces spp. from wild hosts, with 

 the possible exception of P. pennsylvanica. So fev/ sweet cherries are 

 grown in the State that infection of P. avium from P. pennsylvanica is of 

 little importance except as it relates to the possibility of infecting P. 

 cerasus by way of the sweet cherry. The direct cross from P. pennsyl- 

 vanica to P. cerasus was effected but once in 10 trials. It seems improb- 

 able, therefore, that such infection would be important. If P. mahlaleh, 

 however, were of common occurrence within the State, it should be listed 

 as a dangerous harborer of infectious material. In the case of the plums 

 it is evident that the native P. americana may be a harborer of infectious 

 material for cultivated species. 



SUMMARY 



This paper is a report of progress on more than i ,000 cross-inoculation 

 tests with Coccomyces spp. from certain of the more common species of 

 Prunus of Wisconsin. 



From the standpoint of host relationships, the strains of fungi studied 

 are tentatively grouped as follows, according to the hosts from which they 

 were procured: (i) P. cerasus, P. avium, P. mahaleb, and P. pennsyl- 

 vanica, (2) P. domestica, (3) P. virginiana, and (4) P. serotina. It is 

 realized that minor variations in pathogenicity occur among strains 

 within these groups. 



The plants inoculated varied widely both in the range and the degree 

 of their susceptibility to inocula from the various sources. P. mahaleb 

 was notable for its wide range of susceptibiHty, being infected in varying 

 degrees by inocula from all the host sources tested. Among the plums, 

 P. insititia was notably susceptible, while the results of the two incidental 

 inoculations of P. cerasifera suggest that it has likewise a wide range of 

 susceptibility. P. serotina and P. virginiana, on the other hand, were 

 notable for their resistance to cross infection, while P. padus, the host 

 upon v/hich Karsten^ originally described Cylindrosporium padi, was 

 infected only by strains from P. virginiana. P. salicina, A . persica, P. 

 armeniaca and A . persica nectarina were notable for their resistance to all 

 the strains tested. 



While results are listed as positive only in cases where fructifying 

 lesions were induced (p. 544), flecking and spotting without fungal fructifi- 

 fication frequently resulted from inoculations on uncongenial hosts. It 

 is tentatively assumed that such manifestations represent aberrant infec- 

 tion, all gradations of which probably occur. 



1 Karsten, p. a. loc. cit. 



