16 



BULLETIN 684, U. S. DEPARTMENT OP AGRICULTURE. 



these two varieties were nearly healed over, and in the dead bark 

 remaining the fungus was no longer alive. 



Although these experiments seemed to show rather conclusively 

 that the branches of the Yellow Newtown, the chief commercial apple 

 whose fruit is susceptible to bitter-rot in Virginia, are resistant to 

 the disease, it was also thought possible that the fungus found in 

 Virginia might not be capable of causing cankers. This, hovfever, 

 proved not to be the case, as is shown by the series of inoculations 

 listed in Table II. In fact, in these experiments the fungus isolated 

 from Virginia fruits attacked the branches more vigorously than 

 that isolated from bitter-rot cankers from Arkansas. The results of 

 these inoculations did not differ materially from those of the pre- 

 vious experiments. 



Table II. — Comparison of results of inoculations of apple brandies tcitli Mtter- 

 rot fungus cultures from fruits (jroion in Virginia and in Arkansas, at Ar- 

 lington Farm, Va., on August 21, 1916. 



Source of culture used. 



Apple variety. 



Age of 

 bBanch. 



Number 

 of inocu- 

 lated 

 slits. 



Width of blackened 

 band. 





On Aug. 29. 



On Sept. 15. 





Ben Davis 



Yearn. 

 2 

 3 

 2 

 2 

 4 

 2 

 1 



6 

 6 

 6 



4 

 4 

 4 

 4 



Mm. 



1 

 1 

 



2 to 3 

 1 



0to2 

 1 



Mm. 

 6 to 20 





...do 



lto2 



Do 



do ; 











3 to 10 



Do 



. do 



4 to 10 





...do 



0to5 





Yellow Newtown 



4 









The importance of cankers as sources of infection is also greatly in- 

 creased by the enormous number of spores which a single canker is 

 capable of producing in a season. The writer estimated that the 

 number of conidia in one canker 7 cm. long by 2 cm. wide, not a large 

 specimen by any means, was not less than nine millions. When one 

 considers that during moist hot weather the production of spores may 

 be almost continuous, he realizes that the number produced from a 

 single canker during one season must be enormous. 



SUMMARY OF KNOWLEDGE EEGAEDING BITTEE-EOT CANKERS. 



Knowledge of the bitter-rot cankers may be summarized as 

 follows : 



(1) Discovered by Simpson in 1902 and shown by Spaulding and Von Schrenk, 

 in 1906, to be due to Glomerella cingulata. 



(2) May occur perennially on older branches of susceptible varieties and 

 may survive many years. 



(3) Infections on younger branches develop rapidly but do not survive. 



(4) Slow-growing cankers are more apt to survive. 



(5) Varieties differ in susceptibility to the canker disease; the Yellow New- 

 town and York Imperial are nearly immune. 



