48 MISC. PUBLICATION 4 9 3, U. S. DEPT. OF AGRICULTURE 



fruit rarely occurs in the field except in pineapples allowed to ripen 

 fully on the plant. 



Observations made on the New York city market show that about 

 three-fourths of the decay originates at the base of the fruit, the 

 fungus entering through the cut stem. Most of the remainder of the 

 decay starts at the side of the fruit, although an occasional fruit is 

 invaded through the crown leaves. The decay in the fruit is charac- 

 terized by a slightly brown water-soaked appearance of the affected 

 tissue. It early becomes very soft and almost liquid with the skin of 

 the fruit forming a brittle shell. If the decay starts at the stem the 

 fungus grows rapidly through the water-conducting strands in the 

 core of the fruit producing no external evidence of decay except for 

 slight softening at the base. In later stages the fruit becomes so 

 completely disintegrated that it yields to the slightest pressure. On 

 broken or otherwise exposed surfaces, decayed tissue becomes covered 

 with a black crust composed of macrospores of the fungus. These 

 also form in the decayed tissue near the core of the fruit, turning it 

 black (pi. 19. B). Under warm conditions the vascular strands in 

 the fruit are not disintegrated as rapidly as the remaining tissue, 

 thus giving a decided stringiness to the decayed portion. A sweetish 

 odor of fermentation accompanies the decay. 



CAUSAL FACTORS 



Black rot is caused by the fungus Ceratostomdla paradoxa, better 

 known by the name of its imperfect stage. Thielaviopsis paradoxa 

 (De Seyn.) Hoehn. This organism is widely distributed, in tropical 

 and subtropical countries whore it causes important diseases of pine- 

 apple, sugarcane, bananas, and other plants. The organism lives and 

 sporulates freely on dead plant parts in the pineapple field; thus 

 abundant inoculum is usually present at harvesttime when the cut 

 made at the base of the fruit as it is removed from the stalk affords a 

 point of easy entry for the fungus. It may enter the fruit through 

 insect punctures or through injuries received during the harvesting, 

 packing, and marketing processes. Much of the rot on the side fol- 

 lows packing bruises that conld be reduced by proper sizing of fruit. 

 Although it is probable that the fungus cannot penetrate the unin- 

 jured surface of the fruit, very small, invisible cracks between the 

 eyes may allow infection if they come in contact with decayed tissue 

 from a neighboring fruit in a crate. 



Moisture conditions in the field at harvest are very important 

 factors in decay development. When high percentages of decay oc- 

 cur in a shipment it is usually found that the fruit was harvested 

 either during or immediately after prolonged rainy periods. In 

 fact, the relation between moisture and the decay is so marked that 

 in some sections it is called water rot. 



The fungus develops in the fruit very rapidly at temperatures be- 

 tween 70° and 90° F.. but becomes almost quiescent below 50°. It 

 develops more rapidly in ripe than in green fruit. At room tempera- 

 ture, a ripe fruit may become entirely decayed in 3 or 4 days. 



CONTROL MEASURES 



A control measure frequently used is to expose the cut surface of 

 planting material immediately after removal from the parent plant 



