146 



ON FORMS OF THE HOP {HUMULUS LUPULUS L.) 



RESISTANT TO MILDEW {SPHAEROTHECA 



HUMULI (DC.) BURR.); V^ 



By B. S. salmon, 

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



Seedlings raised at Wye from seed of the "wild hop''' 

 {H. Lupulus L.) obtained from Vittorio, Italy. 



In previous articles^ it has been recorded that certain seedhng hop- 

 plants of the origin given above are resistant to the attacks of the mildew 

 Sphaerotheca Humuli (DC.) Burr. The further observations made during 

 the season of 1920, and recorded below, bring the investigations, which 

 have been continued through seven seasons (1914-1920) to a close. The 

 facts observed during 1920 will be given first, and then a general sum- 

 mary of the results obtained since the investigations were started in 1914. 



Observations made during the season 1920. 



Cuttings of certain seedlings of the "wild hop" from Italy were grown 

 in pots in the greenhouse and tested for resistance to mildew under the 

 conditions described in previous experiments. 



The following table gives a list of these seedlings, together with the 

 number of cuttings ("clone-plants") used. 



Not one of these 200 plants, raised vegetatively from 23 different 

 seedlings, showed a trace of mildew on any part throughout the growing 

 season, although inoculated with conidia both artificially on several 

 occasions, and naturally almost continuously by currents of air carrying 

 conidia from several hundred mildewed hop-plants closely surrounding 

 them. 



Some of the hop-plants surrounding them were cuttings of other 

 seedlings of the same origin as the 23 " immune " seedlings noted above. 



^ A grant in aid of publication has been received for this communioation. 

 ^ See Annals of Applied Biology, vi, 293-310 (1920), where a complete Bibliography is 

 given. 



