MARKET DISEASES OF FRUITS AND VEGETABLES 57 



on celery and a wide variety of other vegetable crops and is found 

 wherever they are grown. It may occur as a damping-off of young 

 plants or as a basal rot of the stem and leaves of older plants. 

 Occasionally it is found on the upper parts of the plant several inches 

 from the ground. 



The symptoms of watery soft rot on market products are water 

 soaking and softening of the affected tissues. The color changes 

 vary with the commodity ; in celery, finocchio, and other light-colored 

 vegetables the decaying tissues are light brown with a pinkish-brown 

 border (pi. 14, C) . There is no characteristic odor. The decay 

 occurs frequently at the base of the leafstalks of celery and finocchio, 

 although it occurs as well elsewhere on the leafstalk or on the leaflet 

 petioles. On bunched carrots it is of more frequent occurrence on 

 the taproots than on the tops. The most important diagnostic char- 

 acter in the advanced stages of decay on all commodities is the pres- 

 ence of the white cottony mold growth of the pathogen. In hampers 

 of peas and beans this is responsible for the so-called nests of decay, 

 in which decayed individuals are covered and held together by the 

 mold. In later stages of decay the resting bodies or sclerotia of the 

 causal fungus are formed either over the surface or in cavities within 

 the affected commodity. These are white at first, then bluish, and 

 finally black. They are particularly abundant under field or storage 

 conditions. There is usually considerable leakage from decaying 

 tissues along with a shriveling of affected plant parts so that the 

 final stage of decay, particularly in root crops such as carrots and 

 parsnips, may be the formation of a wrinkled dry mummy. 



CAUSAL FACTORS 



Watery soft rot is caused chiefly by the fungus Sclerotinia sclero- 

 tiorum. At times, however, either 8. minor I. C. Jagger or S. inter- 

 media Ramsey may be responsible for the decay. These fungi live 

 over from crop to crop as sclerotia either on diseased plant refuse 

 or in the soil. Under favorable moisture and temperature conditions 

 mycelium develops from them and spreads out through the soil to 

 attack young plants of the current crop. Under conditions favorable 

 for their development, small mushroomlike structures, known as 

 apothecia, may be formed from sclerotia buried in the soil. These 

 fruiting bodies of the pathogen push up through the soil and produce 

 innumerable spores that are discharged and are carried by air 

 currents to healthy plants. 



The presence of moisture is essential for the germination of the 

 sclerotia, the growth of the mycelium, the production of the apo- 

 thecia, and the infection of plants. Spore production and discharge 

 are favored by moderately low temperatures and are prevented at 

 temperatures above 80° F. Where moisture and temperature con- 

 ditions are ideal for spore development the disease may become 

 widespread throughout the field. Such conditions apparently oc- 

 curred in 1936 in the Sarasota region of Florida. 17 Following a 

 period of cold wet weather favorable for the development of the 



17 Tisdale, W. B., and Kelbert, David, G. A. pink rot of celery in Florida. U. S. 

 Bur. Plant Indus., Plant Dis. Rptr. 20: 134-135. 1036. [Mimeographed.] 



