MARKET DISEASES OF FRUITS AND VEGETABLES 43 



from which it spreads to the seedling, foliage, crown, and root of 

 the plant. Nothing comparable to this has been observed in this 

 country. 



Carrot roots are susceptible to infection by the black rot fungus 

 anywhere in an approximate temperature range from 31° to 93° F., 

 but development is slow near the lower limit of this range. The 

 optimum temperature for infection and decay is approximately 82°. 



CONTBOL MEASURES 



Losses from black rot can probably be reduced by avoiding excessive 

 bruising, particularly at the crown, during harvesting operations. 



Although carrots cannot be stored below the temperature range of 

 infection without danger of freezing, infection and decay can be re- 

 tarded by storage at temperatures of 32° to 35° F. 



(See 187, 191.) 



FUSARIUM ROT 



(Fusarium spp. ) 



Topped carrots held for some time at farm storage temperatures 

 frequently become affected with a shallow spongy decay caused by 

 Fusarium spp. The decay follows wounds at the crown and sides of 

 the taproot and may be recognized by the sparse development of white 

 mold both in cavities within the diseased tissue and over the surface 

 of the lesion. Bacterial soft rot is frequently associated with it. Lim- 

 ited tests indicate that fusarium rot is of little commercial importance 

 at temperatures below 46° F. 



This type of decay is seldom found affecting bunched carrots on the 

 market. However, there is a type of fusarium injury that occasionally 

 constitutes an important market blemish of California bunched car- 

 rots. 9 With this injury the taproots are apparently invaded at the 

 point of emergence of secondary roots by weakly pathogenic species 

 of Fusariumrb and an irritation is set up which results in the formation 

 of shallow corky or scabby areas (pi. 13, B). During growth and ex- 

 pansion of the taproot the lesions enlarge by extending around the 

 circumference of the taproot. The lesions are of chief importance 

 as a blemish of the taproots, although occasionally a shallow decay 

 develops that seldom penetrates deeper than one-eighth of an inch. 



(See 188.) 



GRAY MOLD ROT 



(Botrytis spp.) 



Gray mold rot is a common decay of topped carrots, parsnips (pi. 

 12, A ) , and to a much less extent celery when these have been held for 

 some time in cold storage. Only occasionally is it of importance on 

 bunched carrots or on celery that has not been stored. Infected tis- 

 sues are light brown and water-soaked at first ; later they may become 

 somewhat spongy. In advanced stages of decay a grayish-white mold 

 develops over the surface of the lesions. When conditions become 

 favorable for spore production the decay may be readily identified by 



9 Ramsey, G. B. fruit and vegetable diseases on the Chicago market in 1936. U. S. 

 Bur. riant Indus., Plant Dis. Rptr. Sup. : 101, 81-96. 1937. [Mimeographed.] 



