MARKET DISEASES OF FRUITS AND VEGETABLES 55 



and parsnip. Dill was not affected. In Europe it is known chiefly as 

 a disease of celeriac. 



Losses from phoma root rot are sporadic and largely confined to 

 the field. In several instances, however, the disease has been re- 

 sponsible for approximately a 50-percent loss either in storage or 

 on the market. 



The field symptoms of the disease are wilting, yellowing, and dying 

 of the outer leaves, followed either by stunting or by the death of 

 the plants. The decay usually begins near the base of the leafstalks 

 and progresses through the crown, affecting the roots in close 

 proximity thereto. Affected roots turn brown and soon disintegrate. 

 The diseased tissues of the crown and leaflet petioles are first bluish 

 green and later black. The decay never extends far up the leafstalk 

 or far down the root system, being chiefly confined to the crown of 

 the plant. Where the disease is severe the affected tissues are usually 

 completely disintegrated by secondary soft rot organisms. 



As observed on celery in storage and on the market the decay is 

 likewise confined to the basal part of the plant. Unless other decays 

 are also present the affected tissues are only moderately softened and 

 are black with a greenish-black color at the advancing edge of the 

 lesion. 



CAUSAL FACTORS 



Phoma root rot is caused by the fungus Phoma a/pilcola. The 

 pathogen overwinters in plant debris in the soil and occasionally is 

 carried over from season to season on the seed. The disease fre- 

 quently originates in the greenhouse or coldframe, but it may origi- 

 nate directly in the field. 



The black fruiting bodies (pycnidia) of the fungus are formed 

 in abundance over the decayed areas of the crown. The spores re- 

 leased from the pycnidia are carried by surface water to nearby 

 healthy plants. The fungus is able to penetrate directly the healthy 

 tissues, particularly in young plants. 



The most favorable temperature for the growth of the pathogen 

 is within the approximate range of 61° to 68° F. The maximum 

 temperature for growth is around 82°. It is therefore essentially 

 a low-temperature organism. The disease is important in the field 

 only during the spring and fall, and is most severe during unusually 

 cold and wet seasons. Celery that was apparently healthy when 

 placed in commercial storage at 32° has been known to show a high 

 percentage (18 to 90 percent) of phoma root rot when it was re- 

 moved 7 to 9 weeks later. The fact that 45 percent of the plants 

 in one carlot were affected with this decay on the market 16 likewise 

 suggests that healthy-appearing celery from diseased fields may be 

 already inoculated with the pathogen at the time of packing and con- 

 sequently exhibit heavy losses after storage. 



CONTROL MEASURES 



No way is known of insuring complete control of the disease. 

 Where it is prevalent, care should be taken to use disease-free seed 



w Wiant, James S. new york market pathology notes. U. S. Bur. Plant Indus., 

 Plant Dis. Rptr. 16 : 1-2. 1932. [Mimeographed.] 



