May 6, 1918 



Yellow-Leaf blotch of Alfalfa 



323 



TabIvE I. — Time required for the germination of ascospores of Pyrenopeziza medicaginis 



<» Germinating spores rare; growth not continued. 



PATHOGENICITY 



INOCULATIONS WITH CONIDIA 



Inoculations with conidia were begun when the disease was first found 

 in order to determine if the conidia found so abundantly in diseased 

 areas belonged to the organism causing the disease. In no case was any 

 degree of success in producing infection obtained. When the fungus had 

 been cultured and had been shown to be the cause of the disease, further 

 efforts to secure infection with conidia were made. Various methods of 

 making inoculations were followed. Spores from diseased leaves or from 

 pure cultures were sprayed over the plants in a water suspension. The 

 plants were kept in a moist chamber for at least 24 hours. In order to 

 get large numbers of spores on selected leaves, diseased leaf fragments 

 from which conidia were oozing were placed on moistened alfalfa leaves 

 for about 24 hours in a moist chamber. When these leaves finally 

 became dry, the mass of conidia appeared as a slight white incrustation. 

 This likewise failed to produce any diseased condition. In order to make 

 conditions more severe, other leaves were slightly wounded by abrading 

 the cuticle before inoculation was made. This likewise was unsuccessful. 

 No conditions were found under which these conidia were viable and 

 capable of producing infection. However, negative evidence of this kind 

 must be kept open to question. 



INOCULATIONS WITH ASCOSPORES 



In contrast with the results obtained from inoculations with conidia, 

 no inoculation with ascospores has yet failed to give a larger or smaller 

 percentage of infection. A few of the earlier inoculations in the green- 

 house in the late summer were not absolutely conclusive, because at that 

 time all plants showed a few infections, probably from spores blown in 

 49385°— 18 2 



