MARKET DISEASES OF FRUITS AND VEGETABLES 35 



margins. On the pods the spots are more nearly circular in shape, 

 are larger, and have light centers with dark-brown borders. Gold- 

 yellow or salmon-tinted spore masses are produced in the center of the 

 pod lesions and in the elongated stem lesions. 



The causal agent, C olletotrichum pisi, is a close relative of the fungi 

 that cause anthracnose of beans and of cucurbits. The spores are 

 disseminated primarily by water, insects, and man. At 75° F. the 

 spores can germinate, penetrate the epidermis, and establish the fungus 

 in about 36 hours. It is not known how the fungus overwinters, 

 although it is not unlikely that it remains alive in infected seeds and 

 in plant refuse left in the field. 



No control methods have been worked out for this disease. In view 

 of the possibility of the fungus living over in the pea seeds, it is ad- 

 visable to take precautions to reject all discolored pea seed. 



(See 111, 112.) 



BACTERIAL BLIGHT 



(Phytomonas pisi (Sack.) Bergey et al.) 



Bacterial blight has been reported from practically all pea-growing 

 States. It is especially severe in regions that have high humidity. 

 The disease usually becomes apparent first on the lower part of the 

 plant and may eventually affect all above-ground parts. Early infec- 

 tions of seedlings may result in death; later ones may cause a reduc- 

 tion of the crop ; and the market value of the pods is often seriously 

 affected because of the conspicuous spots produced upon them. 



Infections may take place through stomata or through wounds. 

 Early stages of infection on pods appear as small water-soaked spots; 

 the more advanced stages usually found during marketing are slightly 

 sunken greasy or water-soaked spots of irregular outline with gray 

 or grayish-brown centers (pi. 10, B). Small spots overlooked at pack- 

 ing time and infections starting through wounds during the harvesting 

 and packing process probably account for the high percentage of in- 

 fected stock sometimes found upon the market. The lesions present 

 at time of shipment may enlarge somewhat during transit, but it is 

 not known whether any new infections can take place. In advanced 

 stages of decay the bacteria may penetrate the pod wall and discolor 

 the seed, but this stage is seldom found on the market. The stem and 

 leaf lesions appear as water-soaked green or greenish-brown areas 

 somewhat similar to those found upon the pods. 



The causal organism (Pkytomonas pisi) is carried over from year 

 to year in and on affected seeds. Experimental evidence indicates that 

 the organism does not live over in the soil. Spreading of the bacteria 

 in the field is thought to be due to spattering rain and to insects. 



Pea seed grown in the Western States under dry conditions is not 

 likely to harbor the blight organism. This kind of seed is recom- 

 mended for planting in regions having climatic conditions favoring 

 the development of bacterial blight, There are indications of con- 

 siderable varietal variation in susceptibility to this disease; conse- 

 quently, resistant varieties may be developed eventually by breeding 

 and selection. 



(See 101, 106, 122, Ul, 11$.) 



