STUDIES ON THE PHYSIOLOGIC SPECIALIZATION OF YELLOW RUST (PUCCINIA GLUMARUM (SCHM.) ERIKSS. & HENN.) IN GREAT BRITAIN
Abstract
During 1945‐8, 223 British collections of yellow rust were determined on Gassner & Straib's differential hosts, with the addition of the wheat variety Wilma. Physiologic races 2, 3, 5, 6, 7, 8 and 17 were obtained from wheat, race 46 from barley, race 33 from Hordeum murinum and race 28 from Agropyron repens. Three new races, 6x from wheat, M from H. marinum and G from Dactylis glomerata were also isolated. High temperatures increase the susceptibility of some differential hosts to certain wheat races, but decrease that of others. Biotypes of races 2, 6 and 8, differing from the ‘type’ cultures of those races, were isolated. Of the commoner wheat races, nos. 6 and 8, occurring on many wheats, were widespread, but races 5 and 7, on fewer varieties, were confined to the north of Britain, and races 2 and 3, on very few varieties, to the south. Certain grasses are partially susceptible to some of the cereal races. The uredospores of race 2 germinate less well than those of races 5 or 8, other wheat races being intermediate. The optimum temperature for spore germination of race G is 22‐5 C, that of all other races 10–13 o C. Twelve wheat varieties were inoculated in the field with each of the eight wheat races, and some varieties developed field resistance to certain races. The races attacking a variety the most severely in the field inoculations were usually the races isolated from that variety in collections received.