PEANUT DISEASES 275 ■ 



infection. Small spots of initial infection serve as the starting point from 

 which secondary infection spreads over almost unlimited areas. 



Conidia are primarily windborne (94) and other means of dissemi- 

 nation are of little significance. Under ideal conditions conidia germinate 

 within 3 to 8 hours (68) , The conidia do not germinate if completely cov- 

 ered by water, or if there is insufficient moisture. Infection takes place 

 through either surface of the leaflet, but most infection probably is 

 through the lower surfaces since they are not subject to rapid dessication. 



Penetration of the germ tube is through epidermis or stomata. Cer- 

 cospora arachidicola has intercellular mycelium but no haustoria. Host 

 cells die rapidly in advance of the mycelium, and the hyphae penetrate 

 the dead cells. Mycelium of Cercospora personata leafspot organism re- 

 mains intercellular with branched or botryose haustoria which may be 

 found in apparently normal cells. 



The early leaf-spot organism develops consistently but the late leaf- 

 spot organism is sporadic, being widespread some years, and again rarely 

 found or entirely missing. It appears that, when occurring, the late leaf- 

 spot organism causes a more rapid defoliation (68, 171). The regular 

 occurrence of early leafspot and harvesting of many peanuts before late 

 leafspot reaches epiphytotic proportions indicate that in lower southeast- 

 ern United States early leafspot is more destructive. In this region early 

 leafspot usually becomes epiphytotic in August ; late leafspot sometime in 

 September (68). 



Factors influencing the severity and spread of infection by leaf-spot 

 organism have been studied and discussed (94). Various fertilizer pro- 

 grams have no apparent efifect on the disease. Age of plants, rate of early 

 growth, method of weed control, and frequency of rainfall appear to be 

 influencing factors. Infection is usually more severe on peanuts following 

 peanuts every year or every other year than when 3-year rotations are 

 practiced. 



Control. Field sanitation can offer no great hope for control of peanut 

 leafspot. Resistance has been reported sporadically, but at present no 

 definite resistance exists in any standard variety of peanuts. The possi- 

 bilities along this line have been discussed by Higgins (61, 62) who noted 

 an apparently independent inheritance of resistance to the two types of 

 leaf spotting. Recently, Miller has reported the existence of physiological 

 races within each species (93) which may complicate breeding programs. 

 Resistant varieties may result from some of the current breeding pro- 

 grams, but present-day control measures must center in preventing 

 spread of infection. 



