12 Bacterial Disease of the Mango 



On the 26th January, Mr van der Bijl paid his final visit to Bar- 

 berton in connection with the spraying experiments. The fruit on 

 both sprayed trees and controls had nearly all fallen, and most of those 

 which remained were diseased. It is therefore evident that Hycol is 

 useless in preventing the spread of the disease. 



This was again a dry season. About 2| inches rain fell between the 

 first and second sprayings, and about 2 inches accompanied by hail 

 between the second and third. The fruit was slightly injured by the 

 hailstones. 



Mr Winter reported that the disease has this season spread through 

 the valley, and that he has noticed diseased fruit on his farm at some 

 distance from the village. 



From the account of spraying experiments given above, it is evident 

 that the sprays used up to the present are useless in combating this 

 disease; and that iron sulphide is worse than useless as it injures the 

 foliage and thus promotes the spread of infection. The mango being an 

 evergreen tree it is impossible to check the disease by pruning as in the 

 case of "fire blight" and other diseases of deciduous trees. 



The risk of infection can be slightly reduced by gathering and 

 burning all diseased fruit and leaves and by keeping the soil under trees 

 damp with some germicide which will prevent the dust from blowing 

 about in the wind and carrying with it the infective bacteria ; but no 

 remedial measures used up to the present can be recommended as being 

 really effectual. 



The cause of the disease. 



A large number of diseased plants have been examined, and in every 

 case the tissues of the discoloured areas in the leaves, stem and fruit 

 were crowded with bacteria. 



An organism was isolated from a diseased fruit from Barberton in 

 November, 1909; as it occurred in the host it was a short rod with 

 rounded ends about 1*5 x -6 /a. A pure culture was obtained without 

 any difficulty. The same organism has since been isolated dozens of 

 times from fruit and leaves of trees growing in Warmbaths, Barberton 

 and several localities in Natal ; in every instance an almost pure culture 

 was obtained at once, except in the case of very old infections on the 

 fruit where a number of yeasts and bacilli have established themselves. 



The method used in isolating the organism was as follows: A fairly 

 young infection on the fruit was selected, the surface seared with a hot 

 knife, then a portion of the underlying tissues was cut out with a hot 



