CHAPTER XXII 



DISEASES OF MINOR FRUIT TREES 



Avocado. 



This fruit-tree occurs throughout the islands, grown only in a 

 scattered way. The leaves very commonly bear roundish patches 

 of the alga of " red rust " Cephaleuros mycoidea. Withering 

 of the tips and edges of the leaves, sometimes involving a good 

 deal of leaf surface, occurs in dry situations. The tree is very 

 susceptible to Rosellinia root disease, and where, as in some 

 districts of St. Lucia, it has been planted as shade for cacao it 

 very often forms the originating centre of groups of affected 

 cacao trees. Apart from this disease certain other fungi have 

 been found on the roots and collars of dying trees, under con- 

 ditions suggesting their complicity in that condition. Diplodia 

 dieback (see Cacao) occurs on the twigs and branches. 



Anthracnose. 



Blossom blight, leaf injury, and fruit rot of avocado occur 

 which are due to the attacks of a fungus possibly identical with 

 that which produces similar effects on the mango, both being 

 regarded by some authorities as belonging to the species Colleto- 

 trichum glceosporioides found on citrus trees. 



According to J. B. Rorer, the disease is very prevalent in 

 Trinidad, so that it is almost impossible to buy a fruit in the 

 market which does not show signs of infection. These are of 

 little importance on the fresh fruit, but result in complete decay 

 during shipment. 



Quoting Rorer's account of the attack on the fruit : " The 

 disease appears first as a very small brown spot. If the attack 

 takes place when the fruit is green, the diseased spot ceases to 

 grow and becomes somewhat sunken, and the fruit cracks around 

 the margin ; small black pimples may be noticed in the centre 

 of the brown tissue. If the attack is bad, the young fruits fall 

 to the ground prematurely, otherwise the fruit may reach 

 maturity, but the skin is cracked at the various places adjacent 

 to the brown spots. When soft-skinned fruits are attacked, the 

 fungus penetrates into the flesh and forms a cone-shaped mass of 

 diseased tissue, which may extend all the way into the seed, and 

 gradually rots the whole fruit. When attack takes place on ripe 

 fruits, they rot very quickly, as shown in the figure. (Fig. 85 .) 

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