MARKET DISEASES OF FRUITS AND VEGETABLES 25 



on the stem lesions, and dries to form a glistening crust. In severe 

 attacks the petioles are killed, which causes the blossoms and young 

 pods to drop. 



The pathogen, Phytomonas vignae, enters the plant through the 

 stomata and extends downward into the tissues, causing death of the 

 cells. Frequent rains and temperatures between 80° and 86° F. are 

 most favorable for the dissemination of the organism and the develop- 

 ment of the disease. 



Since it is thought that the bacteria are carried over winter in in- 

 fected seed, the selection of disease-free seed appears to be the most 

 promising method of control. 



(See 66, 90, 91, H7.) 



BACTERIAL WILT 



(Phytomonas ffaccumfaciens (Hedges) Bergey et al.) 



Bacterial wilt in some respects is so similar to bacterial blight that 

 it has been confused with the latter in many bean-growing regions. 

 The pathogen has been found in bean seed from many States, but gen- 

 erally it does not cause as much loss as the blight organisms. Green 

 beans on the market do not often show this disease. 



As the name implies, the disease is primarily a wilt. Infection pro- 

 ceeds systemically through the vascular system of the plant into 

 the pods and seed. At times the pods bearing infected seed seem per- 

 fectly healthy ; at others, the infection follows the seed-bearing suture 

 causing dark-green water-soaked elongated areas. In immature pods 

 the diseased areas may be yellowish green and somewhat withered. 

 The lesions are more conspicuous on mature pods, where they appear 

 as greenish-brown areas in the normal yellow of the pod. No pod 

 spots of the blight type are produced. 



On the seeds the lesions are essentially like those caused by Phyto- 

 monas phaseoli, with a marked tendency toward yellow discoloration 

 at the point of attachment of the seed. 



The causal organism lives in bean seed and can retain its virulence 

 for at least 5 years. When infected seed is planted and conditions 

 favor growth of the organism, it spreads into the vascular tissue of 

 the growing plant, causing wilt. By way of the vascular tissues it 

 proceeds into the pod and on through the hilum into the seed. 



Control is most easily effected by planting seed selected from wilt- 

 free fields. 



(See 71, 102, 103, 119, 156.) 



COTTONY LEAK (WILT) 



(Pythium butleri Subr.) 



Cottony leak is sometimes a market factor in the shipment of snap 

 beans from Florida and other Southern States. During rainy weather 

 the pods become infected, apparently by contact with the causal 

 fungus in the soil, and large water-soaked lesions are produced, 

 which often enlarge greatly during the transit and marketing period. 

 If beans are harvested and packed while wet, the causal organism fre- 

 quently grows profusely over the surface of the beans, matting the 



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