MARKET DISEASES OF FRUITS AND VEGETABLES 45 



RHIZOPUS SOFT ROT 



(Rhizopus tritici Saito and R. nigricans Ehr.) 



Rhizopus soft rot is a common transit and market decay of either 

 bunched or topped carrots and is frequently of importance on topped 

 carrots in common or farm storage. The affected tissues have a 

 brownish water-soaked appearance and are soft and watery. The 

 early stages of decay are distinguished from those of bacterial soft 

 rot by the presence of the fungus threads, which can readily be 

 demonstrated by gently pulling apart the diseased tissues. In later 

 stages of decay the coarse white mycelium of the pathogen can be 

 found growing over the surface of the lesions. The black fruiting 

 bodies of the causal fungus may or may not be present. 



Extensive storage tests have shown that Rhizopus nigricans is of 

 much less importance on carrots than is R. tritici. The optimum 

 temperature for the development of decay of carrots by the latter 

 species was found to be around 90° F. ; no decay developed in roots 

 stored at temperatures lower than 66°. In fact, seldom did any type 

 of rhizopus soft rot, resulting from natural infections, occur below 

 54°. The decay is of most importance on carrots that have been 

 subjected to unusually high temperatures. (See Beans, Rhizopus 

 Soft Rot, p. 27.) 



(See 188.) 



WATERY SOFT ROT 



This disease is illustrated in plate 12, C, D. (See also Celery, 

 Watery Soft Rot, p. 56.) 



Celery 



Celery (Apium graveolens L.) is grown for its leafstalks. The 

 celery plant consists of a short thickened stem or crown on which are 

 borne the fibrous root system below and the succulent leafstalks above. 

 The latter grow in whorls about a terminal bud within the central 

 part or "heart" of the plant. Each leafstalk bears three pairs of 

 leaflets and a terminal leaflet. Celeriac (Apium graveolens L. var. 

 rapaceum DC), also known as turnip-rooted celery, is a form in 

 which the leaves are borne on a thickened, turniplike crown that is 

 the edible part of the plant. 



The marketability of celery depends chiefly upon its tenderness, 

 crispness, and color, and its freedom from blemishes and decay. 

 Tenderness is determined to a great extent by the variety, the local 

 growing conditions, and the weather during the growing season. 

 Lack of crispness may be due to excessive transpiration or drying out 

 during the period of growth, harvest, transportation, or storage. 

 Color is determined by the variety, the method of blanching used, 

 and the duration of the blanching process. 



Most of the injuries and diseases to which the celery plant is 

 subject not only occur in the field but are of direct importance on the 

 market either as blemishes or as decays of the leaves or the leafstalks. 

 These include bacterial soft rot. bacterial blight, black-heart, brown 

 stem, cracked stem, early blight, freezing injury, late blight, phoma 

 root rot, tarnished plant bug injury, and watery soft rot. 



