252 



ON FORMS OF THE HOP {HUMULUS LUPULUS L.) 



RESISTANT TO MILDEW {SPHAEROTHECA 



HUMULI (DC.) BURR.); HI. 



By E. S. salmon, 

 Mycologist, S.E. Agricultural College, Wye, Kent. 



In previous articles (i) (2) I have pointed out that certain seedlings of the 

 wild hop obtained from Italy show immunity, or resistance, to the 

 attacks of the mildew Sfhaerofheca Humuli (DC.) Burr. 



Under conditions in which other seedlings of the same parentage 

 and age (to the number of several hundreds) became severely infected 

 with mildew, certain individual seedlings remained persistently immune 

 throughout the growing season for the two consecutive years 1916 and 

 1917. The present paper deals with the behaviour of these and several 

 other seedlings during 1918 and previous years. The manner in which 

 these plants when grown in the greenhouse were artificially inoculated 

 and otherwise exposed to infection has already been described in 

 detail ((i), p. 456). 



The facts observed as to the degree of immunity shown by the 

 various seedlings can best be described if we take the plants in groups 

 and record their behaviour each season for the years during which 

 they have been under observation. In the annual record of each seedling 

 the following abbreviations are used: 



G = grown in greenhouse, I = immune, 



H = „ hop garden, S = susceptible. 



The figures 1 to .3 indicate the amount of mildew present, 1 = mere trace of 

 mildew; 2 = fair amount of mildew; 3 - plant very mildewed. The plants are all 

 seedlings of the wild hop, raised at Wye from seed obtained from Vittorio, Italy. 



Group 1. 4 seedlings (1-4) sex unknown. 



j-lOKi G(I), 



Plants 1,2, :i, 41. 1!»17 (J (I), 



U9I8 G(I). 



These four seedlings, 1 -year-old in 1915, have proved persistently 

 immune as 2-, 3-, and 4-year-old plants (non-floworing) in the green- 

 ^ These are four of the .seven seedlings noted iti (1), p. 45G and (2), p. 88. 



