(iO Bacterial BlUjht of Pear Blossoms in South Africa 



Varieties affected. 



Some of the late flowering varieties are the most susceptible. 

 Winter Nelis and Beurre Superfine are very badly affected, also the 

 Kastanje liergamot; a number of other varieties including the Keiffer, 

 Beurre Diel and Bon Chretien are also affected but not to the same 

 extent as those above mentioned. The Duchesse d'Angouleme appears 

 to be practically immune, as no sign of the disease could be found on 

 trees standing in an adjacent row to a number of Keift'ers which were 

 badly affected. 



Symptoms and spread of infection. 



So far as can be ascertained up to the present the disease is confined 

 to the flowers, peduncles and very young fruits. No infections have as 

 yet been found on leaves or twigs, and I have failed to produce artificial 

 infections on these parts. 



Infection almost invariably takes place through the receptacles; 

 it usually takes place at more than one spot, a number of minute dark 

 spots appear on the receptacle, these rapidly increase in size, becoming 

 black and spreading until the whole receptacle is involved. Less 

 frequently the tissues of the receptacle are very completely invaded 

 before any blackening occurs, the whole assuming a greenish brown, 

 water-soaked appearance and later turning black. 



When the receptacle is invaded the infection and blackening fre- 

 quently spreads to the styles and the ovary, and less frequently to the 

 flower stalk. Infected flowers fafl, and in the case of susceptible 

 varieties in such numbers as to seriously affect the crop. 



The rapidity with which the disease spreads from flower to flower 

 suggested that the infection is carried through the agency of bees. 

 With the assistance of Mr Neethling, the lecturer in Botany at the 

 Elsenberg Agricultural College, this point was satisfactorily settled. 

 He kindly co-operated with me in this matter by capturing a number of 

 bees which were working in the neighbourhood of the infected trees ; 

 some of these were allowed to walk over some nutrient agar and then 

 released ; from others the mouth part's were excised, and dropped into 

 tubes of melted agar which were then set on the slant. The tubes 

 thus infected were then posted to me at Pretoria for examination. 



Cidtures of the causal organism were readily obtained from all five 

 of the tubes containing the bee traces ; of the others the organism was 

 found in one into which the head and prothorax of the bee had been 



