48 MISC. PUBLICATION 440, U. S. DEPARTMENT OF AGRICULTURE 



otherwise be subjected to warm, humid conditions. Once the stock 

 has become thoroughly cooled the decay should make little progress 

 during, transit. Precooling either before or after loading reduces 

 the likelihood of decay. 



(See 160, 177, ISO, 189, 212, 225, 226.) 



BLACK-HEART 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Black-heart is found in all sections of the country where celery is 

 grown commercially. It is probably of most importance in the Flor- 

 ida and California crops but has frequently been found to a serious 

 extent in other States. 11 Although primarily a field disease it is at 

 times of considerable importance on the market. 



The first symptom of black-heart is the appearance of brown lesions 

 on the outer margins of the youngest and tenderest leaves at the 

 center of the celery plant. The affected tissues in these lesions may 

 dry out, retain their brown color, and remain sharply set off from the 

 healthy tissues; the plant may then recover and continue growth. 

 This may occur several times during the growing season. Or there 

 may be a darkening of the affected tissues accompanying the exten- 

 sion of the lesions throughout the leaflets and petioles of the heart 

 leaves so that the entire central part of the plant is blackened and 

 killed (pi. 15). 



In the more advanced stages of black-heart the affected tissues are 

 frequently invaded by various secondary soil organisms and a soft 

 rot develops. Black-heart should not, however, be confused with 

 the "heart rot" or "crown rot" types of bacterial soft rot, (See Bac- 

 terial Soft Rot, p. 46). 



Although occasionally the outer leaves become yellowed or chlorotic 

 before other symptoms of black-heart appear, usually there is no 

 external evidence of the disease even though the early symptoms 

 could be demonstrated by cutting open the plant. This, together with 

 the fact that slight external evidence of the disease may be overlooked, 

 makes possible the occurrence of advanced stages of black-heart on 

 the market in celery that was presumed to be free of the disease at the 

 time of shipping. Black-heart may become more serious during 

 transit or on the market, but it originates in the field. 



CAUSAL FACTORS 



Although considerable information has been obtained regarding 

 the conditions that favor the appearance of black-heart it cannot be 

 said that the cause is fully understood. Undoubtedly the disease is 

 the result of a very complex physiological disturbance in the plant. 



Development of black-heart usually follows periods of drought or 

 of excessive soil moisture. It has been suggested that these extremely 

 different conditions may have the common effect of killing the root 

 hairs. Once the soil-moisture conditions approach a point favorable 

 for the occurrence of the disease, any factor that increases the rate of 



u FOSTER. A. <'. ni.Ai'MiKAUT DISEASE OF cklkkv. U. S. Bur. Plant Indus., Plant Dig. 

 Rptr. IS : 177-185. 1934. [Mimeographed.] 



