Abstract
It has been generally thought that teleutospores of wheat leaf rust (Puccinia recondita Rob. et Desm. f. sp. tritici (Erikss.)) are not formed on young wheat seedlings, but only on adult plants in place of uredospores. While the authors collected a number of uredosorial samples of wheat leaf rust from various parts of Japan and cultured them at a green-house with the study on physiologic specialization of this fungus, one isolate named P 130 (physiologic race 37 B) was found to from teleutospores on the first leaves of young seedlings of wheat. With this as a clue, the authors inoculated to the first leaf of young seedlings of many wheat varieties, including the standard differential hosts to identify physiologic races, at about 1.5 leaf stage, with many fungus isolates belonging to the main races which prevail in Japan, and observed teleutospore formation.
The isolate P 130 had a greater ability to form teleutospores on young wheat seedings than many other isolates containing some isolates belonging to race 37 B. It formed teleutosori on many varieties of wheat until twenty days after inoculation, and other isolates also formed teleutosori on some varieties until twenty-five days after inoculation, except races 1 A and 1 B which never formed a uredinial pustule on almost all tested varieties. Contrary to popular belief, most of the leaf rust fungi found in Japan, form teleutospores on the first leaf of young wheat seedlings rather easily. The degree of the teleutospore formation is not related with physiologic races of the fungus, but varies remarkably according to fungus isolates and wheat varieties. The difficulty of teleutospore formation on young wheat seedlings, therefore, seems to be due to the combination of fungus isolate and wheat variety. Teleutosori hardly formed on highly resistant varieties, but easily on the varieties which showed moderate resistance, especially, X-type reaction rather than highly susceptible varieties.
Teleutospore formation on young seedlings was divided into seven types. Most commonly, uredosorial ring formed secondarily as a concentric circle around the normal uredosori originated from the first infection, and was replaced by teleutosori which was formed under the uredosori. The teleutosori were formed, therefore, as a intermittent or a continuous ring. Generally, they were not covered with epidermis different from those on adult wheat plants, and the teleutospores were rather short with round tops. They could germinate soon after their formation, as they do on adult plants.
