REPORT OF THE SOCIETY 



79 



to adverse conditions and are known to be able to live over in the soil at least 

 three years. 



Before leaving this discussion men- 

 tion should be made of dry rots fol- 

 lowing S. suhterranea. If, in the 

 development of the pustule, it hap- 

 pens that the cork layer which cuts 

 off the parasite is not laid down, 

 drying-out or dessication follows in 

 storage. The severity of this de- 

 pends upon the number of pustules 

 on the surface of the tubers which 

 are not limited by a cork laj^er. It 

 often happens that the spore balls 

 are still present in the pustule in sto- 

 rage and if the temperature condi- 

 tions are satisfactory for germination, 

 the spores in the balls will germinate 

 and the resulting plasmodia will des- 

 troy' cells surrounding the old pustule. 



Naturally such pustules are open 

 places for the entrance of wound pa- 

 rasites and one of the most impor- 

 tant of these, Phoma tuherosa Melhus 

 et al, causes serious dry-rot injur3^ 



It must be pointed out that, se- 

 condary Spongospora injury, dry-rot 



Fig. 6 — Black-stem of potato. Note the black- 

 ened tissues at A and also the rolling of the leaves. 

 (Aiter Coons, Mich. Bull. 85; Fig. 7 also.) 



and dessication may occur together in some cases. 



Varietal Susceptibility 



Nothing can yet be said regarding resistance to this disease since it is pro- 

 bable that all the well-known potato varieties may be affected. Seasonal differ- 

 ences may account for some varieties escaping infection during one season but 

 being affected another. 



Other Hosts 



It is interesting to note that the roots of tomato are susceptible to infection 

 by S. suhterranea and that galls are formed similar to those on potato roots. 



