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A BACTERIAL BLIGHT OF PEAR BLOSSOMS 

 OCCURRING IN SOUTH AFRICA. 



By ETHEL M. DOIDGE, M.A., D.Sc, F.L.S. 



{Mycologist, Union Department of Agriculture.) 



(With 7 Text-figures.) 



During the seasons 1914 — 15 it was observed by fruit growers in 

 the Stellenbosch district that a large percentage of the pear blossoms 

 blackened and then died, and that in some varieties only a very small 

 number of mature fruits were produced. The blackening was at first 

 attributed to Fnsicladiiwi, but winter spraying seemed to have no 

 effect on the prevalence of the trouble and specimens were therefore 

 sent to this Laboratory for examination. The discoloured tissues were 

 found to. be swarming with innumerable bacteria ; from these a pure 

 culture was readily obtained of an organism which caused blackening 

 in pear blossoms, artificially inoculated within a few days. The organ- 

 ism was re-isolated, and studied with a view to comparing it with the 

 two organisms which are known to cause blight in frnit blossoms and 

 which will be referred to in detail presently ; one of these is the well 

 known ''Fire Blight" organism. Bacillus amylovorns, which occurs 

 commonly in America, and the other a Bacterium recently described by 

 Barker and Grove, as causing a blight of fruit blossoms in England. 

 The South African organism proved to be distinct from either of these. 



It is interesting to note that during some experiments carried out 

 at the Elsenberg Agricultural College, in an orchard which has since 

 been found to be heavily infected with the blossom blight, it was found 

 that if the flowers were covered with paper bags before they opened 

 almost 100 % set, as many as 32 to one truss in some cases ; whereas 

 when the floweis were not covered a large percentage fell. This was 

 attributed to the fact that the blossoms were sheltered by the bags 

 from high winds and sudden changes of temperature, but it seems 

 more probable that it was due to the flowers being protected from the 



