Protein crop plants such as soybean and lupin attract increasing attention because of their potential use as forage, green manure or for the production of oil and protein for human consumption. While soybean production only recently gained more importance in Germany and within the whole EU in frame of protein strategies, lupin production already is well established in Germany. The cultivation of lupins is impeded by the hemibiotrophic ascomycete Colletotrichum lupini, the causing agent of anthracnose disease. Worldwide, soybean is also a host for a variety of Colletotrichum species, but so far this seems not to be the case in Germany. Cross-virulence between lupin and soybean infecting isolates is a potential threat, especially taking into consideration the overlap of possible soybean and lupine growing areas in Germany. To address this question, we systematically investigated the interaction of different Colletotrichum species isolated from soybean in Brazil on actual German soybean and lupin plant cultivars. Conversely, we tested the interaction of a German field isolate of C. lupini with soybean. Under controlled conditions, Colletotrichum species from soybean and lupin were able to cross-infect the other host plant with varying degrees of virulence, thus underpinning the potential risk of increased anthracnose diseases in the future. Interestingly, we observed a pronounced plant growth-promoting effect for some host-pathogen combinations which might open the route to the use of beneficial biological agents in lupine and soybean production.