Nov. 29. 1915 Varietal Resistance of Plums to Brown-Rot 



375 



(1889), however, had no trouble in bringing about infection in ripe 

 peaches when he sowed the spores in a drop of water on the uninjured 

 skin. Cordley (1899) obtained similar results with plums and cherries. 



Field observations indicate that infection of green plums may take 

 place through the uninjured surface if conditions are very favorable. 

 These cases are comparatively rare, the greatest number of infections in 

 green fruit taking place through curculio or other wounds. It is not rare, 

 however, to find in a rotting condition uninjured green plums which are 

 in contact with a rotting plum that is producing spores. In the ripe fruit 

 it is not at all uncommon to find rot due to infection through uninjured 

 cuticle which is not in contact with that of other plums. 



Cooley (1914, p. 322-323) concluded from infection experiments that 

 "The brown-rot organism will infect fruits which are immature, even 

 penetrating those which are not more than half -grown or those in which 

 the pits are still soft, provided the skin is punctured." He had no trouble 

 in infecting ripe fruits without injuring them. 



In the following infection experiments, carried on to determine the rela- 

 tive resistance of varieties, results were obtained which differ somewhat 

 from those of Cooley. 



On June 14, 191 3, five plums of each of seven varieties were put into a 

 sterile chamber and sprayed with distilled water containing Monilia 

 spores. The results are set forth in Table III. 



Table HI. — Results of inoculation of green plums with Sclerotinia cinerea through 

 uninjured cuticle 



These results show very clearly that infection can take place through 

 the injured skin of very young plums. This experiment was repeated 

 from time to time until the plums were ripe, and at no time, if the tem- 

 perature was favorable, was any difficulty encountered in obtaining 

 infection through the uninjured surface of certain varieties. 



The results given in Table III also indicate that there is considerable 

 difference in the ease wdth which the varieties of plums are infected, as 

 well as the rapidity with which the fruit rots after infection has taken 



