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, 1913, 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 III .—Results of inoculation of green plums with Sclerotinia cinerea through 
uninjured cuticle 
Variety. 
June 14. 
June 16. 
June 17. 
Etopa 
Plums inoculated... 
1 infection spot 
Opata 
Topa., 
do 
do 
10 infection spots... 
AX W 15 
B X W 21 
do 
do 
15 infection spots... 
No infection spots... 
B X W 15.do 
Americana .do 
seedling 
No. 1. 
_do. 
1 through curculio 
wound. 
5 infection spots on 2 
plums. 
5 fruits rotting. 
3 fruits completely rotted; 
2 have 1 spot each. 
Spots spreading slowly. 
2 clean; 3 one spot each; 
not spreading rapidly. 
No infection spots. 
4 clean; 1 completely rot¬ 
ted through curculio 
wound. 
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 with which the varieties of plums are infected, as 
well as the rapidity with which the fruit tots after infection has taken 
