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XXIX. 



THE SOUECES OF INFECTION OF POTATO TUBERS WITH THE 

 BLIGHT FUNGUS, PHYTOPHTHOBA INFESTANS} 



By PAUL A. MUEPHY, B.A., A.E.C.Sc.L, 

 Assistant in the Seeds and Plant Disease Division, Department of Agriculture 

 and Technical Instruction for Ireland. 



[Read June 28. Published August 29, 1921.] 



I. — Peevious Work on the Manner of Tuber Infection. 



In his important paper on the control of potato blight, Jensen^ distinguishes 

 between two periods during which infection of the tubers occurs. The first 

 is while they are still in situ in the soil ; and the decay set up by the parasite 

 is generally obvious at digging time, or at the latest by about one week after 

 that operation. The second occurs during lifting, a copious development 

 of Phytophthora rot setting in about one week after the potatoes have been 

 dug. 



Jensen, if he was not the first to draw attention to the danger of digging 

 the crop while any green foliage remains on diseased plants, appears to have 

 been the first, at any rate, to emphasize the magnitude of the danger, to give 

 a rational explanation of it, and to suggest a remedy. 



According to this author, " si Ton arrache les pommes de terre avant que 

 les fanes soient completement mortes et pendant que les feuilles portent 

 encore des quantites de spores capable de germer, ces spores vont tomber en 

 quantity sur les tubercules . . . et une semaine apres ou un pen plus tard, 

 si la temperature est basse, I'effet fatal s'en fera sentir." And it is further 

 stated : " si Ton retarde I'arrachage jusqu'a ce que les spores soient mortes, 

 c'est a dire environ deux semaines apres le dessechement des fanes,, tout 

 danger est evite." 



There are quoted in support of this view the results of two experiments 



' Acknowledgment is made to the Department of Agriculture of the Dominion of 

 Canada for permission to publish in advance the results of experiments carried out in 

 that country. 



^ Jensen, J. L. : "Moyens de combattre et de detruire le Peronospora de la pomme 

 de terre." M6m. Soc. nat. d' Agriculture de France, t cxxxi. 1887. 



gClENT. PBGC. K.D.S., VOL. XVI, NO. XXIX. 8 U 



