EXPERIMENT STATION BULLETINS. 581'" 



SPORE AND PYCNIDIUM MEASUREMENT. 



Spore Pycnidium 



Klebahn 3-4 x 1.2—1.8 microns 90-240 microns 



Quanjer and Slagter 4 x 1.5 microns 98-210 microns 



Author 3-3.8 x 1-1.6 microns 80-100 x 100-250 microns 



The pycnidia, as shown by the above table, are subject to great variation 

 in size. Quanjer and Slagter (6) found that spores produced in pure culture 

 were smaller than those on the host, a thing which has not been noted in 

 any culture used in this work. 



TROOP OF PATHOGENICITY. 



The organism causing "Scab" of celeriac was isolated by Klebahn (5) 

 and its pathogenicity proved by inoculation experiments. Coons (2) iso- ' 

 lated a Phoma from diseased celery plants and proved its causal relationship 

 to Root Rot. Regarding this organism he says: "This fungus was ob- 

 tained in pure culture and typical lesions were obtained in inoculation ex- 

 periments. The etiological relation of the Phoma thus obtained has been 

 fully cstabhshed." 



The author has obtained a Phoma from celery from a number of sources. 

 Single spore isolations have been made from diseased plants from Kalamazoo, 

 Portage, and North Muskegon, as well as from a number of diseased plants . 

 which were found in the greenhouse at the Michigan Agricultural College. 

 Inoculations with these cultures have given characteristically diseased plants 

 in a large percentage of cases. The organism has been reisolated from celery, 

 parsnip, and parsley and the identity of the different cultures proved by com- 

 parison of cultural characteristics and by inoculation followed by typical 

 signs of disease. Repeated inoculations and isolations leave no doubt as to 

 the pathogenicity of the organism and its causal relationship to the disease. 



NAME OF ORGANISM. 



European writers have been unanimous in ascribing the cause of "Scab" 

 of celeriac to Phoma apiicola Kleb. A culture of this organism was obtained 

 from Dr. Johanna Westerdijk of the Centralstelle fur Pilzkulturen, Amster- 

 dam, by Dr. G. H. Coons who compared this culture with the Phoma which 

 he isolated from celery. As a result of this comparison he states that, ' 'The 

 fungus (the one isolated in Michigan) in culture and pathological habit 

 greatly resembles Phoma apiicola described by Klebahn as producing the 

 'Scab' of Celeriac." 



The author has further compared this European culture with the ones 

 which have been isolated in Michigan in an effort to find morphological or 

 physiological differences. In the earlier work it was found that the European 

 culture produced distinctly lighter colored mycelium. Later it was foand 

 that Michigan strains grown on artificial media lost color so that the cultures 

 from the two different sources could not be separated on the basis of any 

 color difference. Pycnidial and spore differences have not been found, and 

 each strain has exactly the same host range, both attacking celery, celeriac, 

 parsnip, carrot, parsley and caraway. Thus, the European fungus which 

 causes "Scab" of celeriac seems to be identical with the Michigan Root Rot 

 organism. 



