300 THE PEANUT— THE UNPREDICTABLE LEGUME 



The peanut rust organism is found chiefly on the undersurface of 

 leaves ( 10) , where it appears, first, as necrotic flecks and later as yellow- 

 ish spots on the upper surface. Spores form in typical sori rupturing the 

 lower epidermis. 



While these necrotic spots do not enlarge much, the infected leaves 

 soon appear as though burned or scalded (74), and premature defoliation 

 results (9). It is reported that premature ripening of fruits, and under- 

 developed, shriveled seeds also result from rust infection (9). 



Organism and pathogenicity. There is no agreement as to the proper 

 name for the causal organism of peanut rust. Arthur, in 1925 (10) re- 

 ferred it to Puccinia arachidis Speg. as it was originally described. 



According to Arthur (9) telia of this organism have been found only 

 once. It may be presumed that this was in connection with the type speci- 

 men collection. Pycnia are unknown, and the organism does not have an 

 aecial stage. 



Peanut rust has no alternate host. The uredinial and telial stages 

 are found on peanuts. 



Although not cited specifically, it is presumed that the pathogenicity 

 of this organism on peanuts has been proven by artificial inoculations. 

 Arthur (10) lists Arachis hypogaea as the only host. West (159) dis- 

 cussing the rust in breeding plots in Florida reports it on A. nambyquarae 

 Hoehne; A. prostrata Benth. and a hybrid of A. hypogaea X A. namby- 

 quarae. KenKnight's report from Texas (74) indicates, indirectly, that 

 selection and natural hybrids within A. hypogaea may sometimes be 

 highly susceptible. 



The organism appears to be seed-borne. It appears to have been 

 brought into Florida recently on seeds from Brazil (159), although the 

 rust had been reported from Florida twice previously (8, 129). 



Some factors have been indicated as affecting the virulence of the 

 organism. Arthur (9) concluded that peanut rust is more prevalent in wet 

 seasons, with very little damage when infection is accomplished late in the 

 growing season. In the West Indies the degree of infestation appears to 

 depend largely on climate and condition of the soil (104). When con- 

 ditions favor growth and vigor of peanuts only leaves approaching senility 

 are infected. Under less favorable conditions infection is higher and 

 results in death of the entire plant. 



Control. Spraying with Bordeaux mixture has been reported as in- 

 creasing the yield of rust-infected peanuts in the West Indies ( 104) . In a 

 3-year experiment ( 104) it was finally concluded that while two applica- 

 tions of Bordeaux produced some beneficial results, it could not be said 



