94 PARASITES BELONGING TO THE GENUS GLOMERELLA. 



PARASITISM OF GLOMERELLA. 



That Glomerella is an active parasite in certain races and under 

 certain conditions would never be questioned by one who has had 

 an opportunity to observe a severe attack of bitter-rot of the apple 

 such as occurred in an orchard near Vienna, Va., in 1911. Several 

 trees of Willow Twig apples well cared for and in a thrifty condition 

 and bearing a good crop of fruit were attacked in July when the fruit 

 was about half grown. Within a week or two nearly every apple 

 on these trees showed bitter-rot spots which developed rapidly and 

 soon destroyed the crop. This result was apparently due to a com- 

 bination of favorable factors, the presence of a virulent race of the 

 fungus, a susceptible variety of fruit (other varieties immediately 

 adjoining showed little or no bitter-rot), and optimum conditions 

 of temperature and moisture for infection and development. 



Many races of Glomerella under ordinary conditions appear to be 

 rather weak parasites. The different degrees and manifestations of 

 parasitism among the fungi are so numerous and varied that it is 

 very difficult to classify them satisfactorily in this respect. The 

 possession of dormant hibernating hyphse which infest the seeds of 

 some annual plants, as in the case of the cotton and bean anthracnoses, 

 the shoots of perennials, as in orange, and the leaves of evergreens, 

 as in the case, of the rubber plant, coffee, tea, citrus fruits, and other 

 subtropical plants, indicates a considerable degree of specialization 

 which would appear to give Glomerella a higher rank among para- 

 sites than the Fusarium forms of Nectria and closely related organ- 

 isms. On the other hand, its ready growth on artificial culture media, 

 dead organic matter and matured fruits suggests a low form of para- 

 sitism. As already mentioned, Appel and Wollenweber (1) have 

 suggested that the fact that an organism will complete its life history 

 on artificial culture media or dead organic matter is an indication that 

 it is a saprophyte. As has already been pointed out, this suggestion 

 does not seem to accord with the known facts. 



The majority of the inoculation experiments which have been 

 reported were performed by puncture of mature or nearly mature 

 fruits. This method does not furnish the best proof of the parasitism 

 of the organism. It is quite possible that the fungus would grow 

 and develop rot under such conditions but still might not under nat- 

 ural conditions be able to gain entrance through the unbroken surface 

 of the fruits. 



The experiments of Edgerton (28), Rolfs (66), Barre (7, 8), Hassel- 

 bring (45), Bessey (13) and others, as well as some of those of the 

 present writers, have shown that cross-inoculations can be success- 

 fully made by the application of spores to the uninjured stems, leaves, 

 and flowers of living plants. Hasselbring (45) has shown a way in 



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