Organic Agriculture is especially affected by the increasing spread of stem rust in rye (Puccinia graminis f. sp. secalis) because there is a lack of resistant cultivars in Germany. To analyze the virulence situation of rye stem rust, 71 single-pustule-isolates were established and 30 of those were tested with a differential set consisting of 19 lines. The isolates could be classified into 22 different pathotypes. Only seven pathotypes could be found more than once. Most of the isolates showed a complexity of five virulences. In a preliminary analysis a Simpson index of 0,98 was found indicating a high level of diversity of German stem rust populations. Nine of 19 tested lines reacted fully resistant in seedling stage. In 2011, 70 and 30 rye populations, were cultivated under organic conditions at three and five field sites, respectively, to determine the level of adult-plant resistance. The most common cultivars Recrut, Conduct, Amilo, Firmament®, Lichtkornroggen®, Rolipa, and Lautenbacher were highly susceptible to stem rust under artificial infection with disease severities of about 50%. Twelve rye populations contained resistant plants in varying frequencies resulting in disease severities ranging from 6-34%
