Abstract
Studies on physiologic specialization of stem rust of wheat (Puccinia graminis tritici (Pers.) Erikss. et Henn.) were carried out with 56 uredosorial samples collected from various parts of Japan during 1957 to 1960. These isolates revealed the presence of three races in Japan; namely physiologic race 56 collected twice in Nagano Pref. in 1957, physiologic race 21 most frequently and widely distributed all over the country, and race closely related to 11, being collected twice in Nagano Pref. in 1959, and once in Niigata Pref. in 1960.
The seedling reactions of many wheat varieties and related plants were examined to each race. Most of them were susceptible to all three races. Triticum timopheevi and its derivatives were immune or highly resistant to all three races. It needs introducing of wild wheat genes for breeding stem rust resistant varieties.
It draws our attention that the race compositions of wheat stem rust in Japan is very simple in contrast to wheat leaf rust. This may be attributed, at least as a part, to scarceness of passage through alternate hosts, owing to absence of susceptible barberries, and poor germinability of teliospores.
