JOiNAL OF AGEICDLTIKAL RESEARCH 



DEPARTMENT OF AGRICULTURE 

 Vol. V Washington, D. C, October II, 1 91 5 No. 2 



PERENNIAL MYCELIUM IN SPECIES OF PERONOSPO- 

 RACEAE RELATED TO PHYTOPHTHORA INFES- 

 TANS 



By I. E. Melhus, 



Pathologist, Cotton and Truck Disease Investigations, 



Bureau of Plant Industry 



INTRODUCTION 



Phytophthora infestans having been found to be perennial in the Irish 

 potato (Solamcm tuberosum), the question naturally arose as to whether 

 other species of Peronosporaceae survive the winter in the northern part 

 of the United States in the mycelial stage. As shown in another 

 paper (13)/ the mj^ceUum in the mother tuber grows up the stem to the 

 surface of the soil and causes an infection of the fohage which may result 

 in an epidemic of late-blight. 



Very little is known about the perennial nature of the mycelium of 

 Peronosporaceae. Only two species have been reported in America: 

 Plasmopara pygmaea on Hepatica acutiloha by Stewart (15) and Phytoph- 

 thora cactorum on Panax quinque folium by Rosenbaum (14). Six have 

 been shown to be perennial in Europe: Peronospora schachtii on Beta 

 vulgaris and Peronospora dipsaci on Dipsacus follonum by Kiihn (7, 8); 

 Peronospora alsinearum on Stellaria media, Peronospora grisea on Veronica 

 hederae folia, Peronospora effusa on Spinacia oleracea, and A triplex hor- 

 tensis by Magnus (9); and Peronospora viticola on Vitis vinifera by 

 Istvanffi (5). 



Many of the hosts of this family are annuals, but some are biennials, 

 or, like the Irish potato, are perennials. Where the host lives over the 

 winter, it is interesting to know whether the mycelium of the fungus may 

 also live over, especially where the infection has become systemic and 

 the myceHum is present in the crown of the host plant. The absence or 

 sparse production of oospores in some of the species of Peronosporaceae, 

 coupled with the appearance of the fungus as soon as the host puts out 

 foliage in the spring, suggests that the mycelium may play an important 



' Reference is made by number to " Literature cited," p. 68-69. 



Journal of Agricultural Research, Vol. V, No. 2 



Dept. of Agriculture, Washington, D. C. Oct. 11, 1915 



ac G — 57 



(59) 



