6 Bacterial Disease of the Mango 



leaves have newly fallen. The first appearance of disease in the stem 

 is a discolouration of the tissues. This is accompanied by gummosis 

 and the formation of deep longitudinal cracks. The discolouration is 

 not merely superficial but penetrates some distance iDto the stem 

 (Plate III). 



The disease is especially evident on the peduncles and pedicels ; 

 frequently, by the time the fruit is half grown, the whole inflorescence 

 is affected. The stalks to which the mangoes are attached become 

 black and dead, and consequently the fruit all falls to the ground 

 (Plate VI). 



As has been mentioned above, although the spots on the leaves and 

 stems are often very numerous, they do not noticeably affect the general 

 health of the tree. Their chief importance is as a source of infection 

 for the fruit which is seriously injured by the disease. Large numbers 

 of mangoes fall to the ground, and the small percentage which remains 

 on the trees is so disfigured as to be practically useless (Plate IV). 

 The mangoes on the windward side of the tree suffer most. The 

 diseased spots first appear on the most exposed side of the fruit or else 

 at the spot where two mangoes on the same bunch are in contact and 

 where a drop of water would lodge after rain. The first sign of infection 

 is a small water-soaked area round the white spot which indicates the 

 presence of a stoma, or near a slight wound ; this spreads considerably 

 and then begins to discolour. Cracking takes place in several directions 

 and the surface of the diseased area becomes very much roughened. 

 If infection takes place during a period of rapid growth, deep longi- 

 tudinal cracks are formed, running almost the whole length of the fruit 

 in bad cases (Plate V). 



The discoloured spots vary much in size ; they are 1 mm. to 15 mm. 

 in diameter and are irregular in shape, and the discolouration penetrates 

 to a depth of 8 — 15 mm. 



Especially noticeable in the case of infections near the point of 

 attachment of the fruit is the exudation of gum which runs over the 

 surface of the mango. This substance is highly infectious and diseased 

 spots are developed wherever it touches the surface of the fruit. 



When a mango has once become diseased the slightest air movement 

 detaches it from the tree, and the ground becomes strewn with decaying 

 fruit. 



