SUMMAKY. 37 



SUMMARY. 



The aim of this bulletin is to present in concise form what is known 

 about disease resistance of potatoes. Much of this information is from 

 European sources. 



Certain minor diseases of obscure nature, but apparently nonpara- 

 sitic, are tirst considered— the internal brown spot, filosite, and leaf- 

 spot. Among remedial measures for each is the selection of resistant 

 varieties. 



Scab diseases of tubers are in most, and perhaps in all, cases of para- 

 sitic origin — fungous or bacterial. Apparentl}' the variet}^ of these is 

 greater in Europe than in America, but the severity is less in Europe. 

 It is undecided to what extent the American type of scab occurs in 

 Europe, so a close comparison of conditions and remedies is not prac- 

 ticable. In Germany certain varieties are known to be more scab 

 resistant than others, among them being Richter's Imperator, Profes- 

 sor Wohltmann, and Irene. The same is true in America, Cambridge 

 Russet leading the list, so far as is known. Other American varie- 

 ties showing a considerable degree of resistance are Carmen No. 3, 

 American Giant, Sir Walter Raleigh, and Irish Cobbler. Scabproof 

 and Aurora are also highly commended for scab resistance. 



Various stem diseases of the potato are known. The commonest 

 t3^pe in Europe is termed blackleg (Schwarzbeinigkeit), a bacterial 

 disease. It is not known to occur in America, but it resembles certain 

 maladies which do occur here and which are as yet imperfectly under- 

 stood. Varietal resistance to blackleg is not full}^ established, but 

 apparently Dabersche and certain similar, thick-skinned, starch-rich 

 late varieties are more resistant than thin-skinned, starch-poor early 

 I varieties of the Rose t^^pe. Factor and Up-to-Date showed a consider- 

 able degree of resistance to blackleg in England. La Czarine and 

 other varieties are reported to show resistance to a bacterial stem 

 disease in France. 



The late-blight and rot due to the fungus PJujtophthora infestans 

 occurs more commonl}^ in Europe than in America. Attention has been 

 given for many years to relative varietal susceptibilit}- to this disease, 

 especially in Great Britain and in Germany. Varieties of superior 

 disease resistance are known in both countries, and a number of the 

 most promising from these and other European sources have been 

 imported for trial. 



The following statements are tentatively formulated as to the nature 

 of resistance toward blight and rot and the character of the varieties 

 exhibiting it: 



(1) Disease resistance in potatoes is relative, not absolute, no variety 

 known being wholly proof against late-blight and rot. 



