May6, i9i8 Yellow-Leafblotck of Alfalfa 325 



Table II. — Result of the inoculation of alfalfa leaves with ascospores of Pyrenopeziza 

 medicaginis from dead leaves 



Results of this kind have been obtained repeatedly with inoculations 

 from ascospores under conditions of pure culture, as v^^ell as from dead 

 leaves. When only very young vigorous leaves are chosen for inocula- 

 tion and the material used discharges spores in abundance, a 100 per cent 

 infection can usually be obtained. Either the upper or lower surface of 

 the leaf can be infected. 



The failure to get a 100 per cent infection in all cases appears to be due 

 in part to the variable and often very low percentage of germination of 

 ascospores. It has been noted especially with ascospores discharged 

 from leaves that not more than i or 2 per cent of the first spores to be 

 discharged after the leaf is soaked fail to germinate more, while 25 per 

 cent of those discharged a few hours later may germinate. But sufficient 

 observation of germination under these conditions has not been made 

 to warrant the opinion that this is a general rule. 



The time required for the yellow-leafblotch to appear after inocula- 

 tions in the greenhouse is approximately two weeks. In case a great 

 number of viable spores has been placed on the leaf, the yellowing 

 begins a few days earlier; but if the number of spores is small, giving 

 rise to but a few penetrations, the yellowing is delayed until a few days 

 later. Heavy infection may produce yellowing prior to the develop- 

 ment of pycnidia, and, in fact, the leaf may be killed before pycnidia 

 can be formed. When infection is light, a leaf may not show a yellow 

 blotch until very shortly before the pycnidia are formed. Under green- 

 house conditions the diseased leaf tissue usually dries out so early that 

 no apothecia develop. Only in a single case, vi^here the inoculated plants 

 were growing in a dense mat that maintained a constant condition of 

 high humidity, did apothecia appear. 



