274 THE PEANUT— THE UNPREDICTABLE LEGUME 



eflfects. The interrelationships between time of infection, severity of in- 

 fection, beginning of defoliation, and severity of defoliation have not been 

 extensively studied. In Georgia, leafspot appears sometimes in June on 

 peanuts planted in late April (172), and without control spotting in- 

 creases rapidly during July so that defoliation is noticeable by August. A 

 close relationship is observed to exist between the amount of leaf spotting 

 and the amount of defoliation (94). 



Comparative studies (68, 171) have shown that late leafspot usually 

 appears 3 to 4 weeks later than early leafspot. 



Organisms and pathogenicity. Woodroof (171) has clarified the 

 synonomy and nomenclature of the conidial stages of the peanut leafspot 

 organism. Her studies established Cercospora arachidicola Hori as the 

 correct name for the early leaf-spot organism, and C. personata (B. and 

 C. ) E. and E. as the correct nanie for the late leafspot organism. Jenkins 

 (68) studied the development of both organisms and connected them 

 with Mycosphaerella perithecial stages which were found to develop only 

 on overwintered material. 



The pathogenicity of both organisms has been proven (68). The first 

 infection is from ascospores formed on overwintered peanut debris. 

 There have been reports that the disease is seed-borne (94) but most ob- 

 servers feel that it is not. Following initial infection and an "incubation" 

 of 2 to 3 weeks (68) the lesions become evident and the organisms pro- 

 duce conidia in abundance. These conidia then spread infection rapidly. 



There is a leafspot of the common coflfee weed {Cassia tor a L.) of 

 the southeastern United States caused by a Cercospora sp., but attempts 

 at cross inoculation of this Cercospora sp. with peanuts have failed^. 

 Possibly other weeds are hosts of the peanut leaf-spot organism and thus 

 may serve as additional sources of ascospores for initial infection. As a 

 rule, however, there is more than enough peanut debris to provide an 

 abundance of initial inoculum. 



The production of perithecia of the organisms on overwintering ma- 

 terial has been studied (68). It appears that even under ideal conditions 

 perithecia are formed sparingly. Rapid disintegration of the substratum 

 may be a factor in this, and temperature may be a limiting factor since 

 mature perithecia are not found in Georgia before June. Some rainfall 

 during the period of spermagonial discharge is also necessary. Asci al- 

 most always mature gradually so that ascospores are discharged over a 

 considerable period of time. Initial infections usually are scattered in the 

 southeastern United States (68), but peanut fields rarely, if ever, escape 



s Unpublished results, Georgia Experiment Station. 



