28 MISC. PUBLICATION 4 4 0, U. S. DEPARTMENT OF AGRICULTURE 



In active stages of development rhizopus rot is always more or 

 less soft and watery. In many instances enough water is liberated 

 to cause a leaky condition, but in very dry atmosphere sometimes 

 the water is lost rapidly enough by evaporation to cause shriveled, 

 moderately dry areas. Under moist conditions there is produced 

 pn the surface of lesions a coarse, white, stringy mycelium, which 

 bears glistening, white, spherical heads (sporangia) that soon turn 

 black and break open, releasing thousands of dustlike black spores. 

 This bushy growth of mycelium often extends an inch or more from 

 the surface and is sometimes called "whiskers." Eventually this mold 

 collapses and becomes matted and black from the liberated spores. 

 These characteristics of the fungus usually serve to identify the decay. 



The fungus spreads readily by contact between diseased and 

 healthy beans or peas in the center of moist hampers during transit. 

 The masses of pods surrounded and held together by this mold are 

 known as "nests" (pi. 9). 



CAUSAL FACTORS 



Various species of Rhizopus are ever present in the air, soil, and 

 water in all regions; consequently, most products are exposed to 

 inoculation at some time during the harvesting, packing, and shipping 

 period. Wounds or bruises and surface moisture on beans, peas, 

 and other products greatly favor infection by Rhhopvs. The later 

 development of decay depends largely upon temperature conditions. 

 Snap or green beans have been found showing rhizopus rot through- 

 out a range of temperatures from 54° to 96° F. with most active 

 development taking place near 80° to 85°. The temperature range 

 varies among different species of Rhizopus* but generally speaking 

 rhizopus rot is not a serious factor in cars of produce unless tempera- 

 tures therein are well above 50°. 



CONTROL MEASURES 



It is recommended that insofar as possible all excessively wounded 

 and bruised stock and that showing any sign of disease at time of 

 packing be discarded. Beans and peas should be cooled and surface- 

 dried as soon as possible after picking, and shipped under refrigera- 

 tion sufficient to keep the warmest part of the load below 50° F. 



(See 117.) 



RUSSETING 



Russeting is a surface discoloration of snap bean pods that develops 

 primarily after harvest. It also occurs in the field to some extent 

 on both green pod and wax pod varieties but is much more common 

 in the latter. It is very objectionable from the market standpoint 

 because of the appearance of the stock. 



The lesions consist of chestnut -brown surface discolorations of 

 various shapes and sizes, sometimes involving the entire pod (pi. 

 7, G). At times discolored streaks are more or less parallel, like 

 those of sunscald, but they differ from these in that they are not as 

 red and occur on both sides of the pods. The brownish discolora- 

 tions result from the death of three or four outer layers of cells. The. 

 dead tissues are not sunken, and they do not decay unless invaded 

 by bacteria or fungi. 



