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BULLETIN" 3 3, PORTO RICO EXPERIMENT STATION 



unless the trees are suffering also from a lack of moisture or nutri- 

 tion. The remedy is, of course, to keep the tree growing, which is 

 not always possible because of climatic conditions. The tree, there- 

 fore, must be constantly watched and the dead tips and branches 

 pruned off at the termination of a dormant period. New growth 

 may start from the live tissue, and the dead parts may drop, but 

 very frequently the decay continues unless the dead tissue is removed 

 by pruning. Wounds following the removal of branches one-fourth 

 inch in diameter or over should be dressed. 



Two decays cause appreciable damage to citrus fruit in Porto 

 Eico after it is picked. One decay is clue to the blue mold (Penicil- 

 Mvm italiawm) and sometimes to the green mold {P. digitatum) . 

 These fungi do not usually enter the rind of the fruit unless it has 

 been bruised or mechanically injured and do not seriously attack 

 grapefruit because the rind does not bruise readily. They are a 

 very serious pest of oranges having a thin rind, especially oranges 

 grown in the mountain districts. The avoidance of bruises is not 

 always possible under local conditions, and dipping bruised fruit in a 

 borax or sodium bicarbonate solution is not very advantageous. 

 Even cooling to a temperature of 40° F. or below does not prevent 

 bruised fruit from decaying. The method suggesting itself for 

 stabilizing the mountain-orange industry is that of handling with- 

 out bruising, whenever that is possible, and precooling and shipping 

 under refrigeration. The oranges of the mountain districts are of 

 fine quality and can be grown cheaply and should therefore be 

 entered on the market in competition with oranges from elsewhere. 



The other decay is the so-called stem-end rot caused by the fungus 

 Diplodia natalensis, which results in great loss to grapefruit growers 

 in Porto Rico. Like the Penicillium fungi, the Diplodia fungus 

 does not usually enter the rind of fruit unless it has been bruised. 

 Since it is usually found about the stem the name stem-end rot has 

 been given to it. The fungus may enter through the stem end before 

 the fruit is picked, in which case it almost invariably drops soon after. 

 Usually very little fruit drops because of Diplodia infection in Porto 

 Rico. After the fruit is picked the fungus enters through the stem 

 scar or through the stem cavity after the button loosens. The latter 

 is the usual mode of entrance because the space under the calyx al- 

 ways harbors dirt and fungus spores. Two remedies have been tried 

 to control stem-end rot in Porto Rico. One consists in disinfecting 

 and sealing with shellac the cut end of the stem at the time the fruit 

 is picked, but it did not prove to be efficient for the reason that respi- 

 ration of the fruit is very high in the usual air temperature in Porto 

 Rico. When respiration is vigorous the gas exchange is very much 

 greater through the stem end than through any part of the rind; 

 consequently sealing does not endure and infection readily takes place 

 once the seal is broken. The other remedy tried consists in removing 

 the button and sealing the stem cavity, but that has not been found 

 successful locally, at least not with the early fruit. In removing the 

 button from fruit that is not thoroughly mature the rind is torn on a 

 great many specimens, and infection follows. 



Diplodia will be much less of a problem in the future since precool- 

 ing and a more efficient refrigeration are now available on the 

 steamers. 



