MARKET DISEASES OF FRUITS AND VEGETABLES 47 



narily characteristic. The decay may affect the crown, the leaf- 

 stalks, or the leaflets. The decayed areas may be continuous or 

 scattered over the plant. The rot develops rapidly under warm, 

 humid conditions and serious market losses often occur in infected 

 stock. 



CAUSAL FACTORS 



Bacterial soft rot of celery and other vegetables is caused by 

 Erwinm carotovora and other closely related species of bacteria. 

 The causal organisms are all soil inhabitants and will grow on a 

 wide variety of plant products. They are readily carried over from 

 season to season on stored stock and are found as contaminants of 

 plant debris in places where diseased stock has previously been stored. 

 The practice of allowing plant trash to accumulate aids in increasing 

 the number of bacteria that are readily available for dissemination 

 to growing or harvested stock. These are undoubtedly spread by 

 tools, insects, domestic animals, and running or splashing water. 

 Inoculation may result from direct contact with infested soil or 

 infested plant trash. Plants that become infected early in the season 

 serve as a readv source from which bacteria are spread later in 

 the field. 



Celery plants may become inoculated during harvesting and pack- 

 ing operations through contact with contaminated cutting knives, 

 hands, tools, and wash water. Although the decay may be spread in 

 transit and storage through contact with diseased plants, much of 

 what appears there undoubtedly had its inception in the field. 



The causal organisms enter the plant through wounds, insect 

 punctures, and lesions of other diseases. Moisture is essential for 

 the growth and reproduction of the bacteria, and they are sensitive 

 to desiccation and direct sunlight. Wet weather usually favors the 

 decay by increasing the rate of multiplication and dissemination 

 of the causal organisms and by moistening the plant tissues. It 

 has been found in Minnesota, however, that celery is more susceptible 

 to heart rot in the field during dry periods. This is believed to 

 be due to variation in the activities of the insect carrier during 

 periods of dry weather. 



The decay is usually favored by high temperatures provided the 

 humidity is high. Under conditions of high humidity the most 

 favorable temperature for decay is in the range of 77° to 86° F., 

 although there is a wide temperature range within which the decay 

 may progress actively. At temperatures of about 45° or lower the 

 decay is checked. 



CONTROL MEASURK8 



Control measures include the adoption of general sanitary prac- 

 tices around storage houses, pits or cellars, and during harvesting 

 and packing operations. Any practice that will reduce the likelihood 

 of contamination by the soft rot bacteria should be of help in reduc- 

 ing losses from the disease. 



The most important measure for the control of bacterial soft rot 

 is that of temperature control during transit and storage. Conse- 

 quently promptness in placing the celery under desirable transit or 

 storage temperatures is advantageous, particularly if the celery would 



