Research PaperA pathosystem is a subsystem of an ecosystem and is characterised by the phenomenon of parasitism. The bean-Pythium pathosystem consists of the host (bean), the pathogen (Pythium) and their host-pathogen relation. Of interest is how the pathogen causes pathogenicity on other crops and beans. To investigate this, screen house experiments were set up to test the pathogenicity of Pythium species derived from bean and other crops grown in association with beans. Pathogenicity was tested on maize (Zea mays), millet (Eleusine corcana), sorghum (Sorghum bicolor), peas (Pisum satium), susceptible bean variety (CAL 96) and resistant bean variety (RWR 719). The results indicated that distinct symptoms were observed in the roots and shoots of test crop species which are characteristic of Pythium infection. For instance peas had brownish watery stems and roots Also bean-derived pathogenic Pythium spp. were found to be more virulent than Pythium spp. derived from other crop species.Sorghum and peas had the highest disease scores upon infection by Pythium spp. We can conclude that there is cross pathogenicity among Pythium spp. especially affecting sorghum and peas. This phenomenon may account for the current root rot epiphytotics in south western Uganda and other similar agroecologies. An integrated disease management strategy that will deploy multi-non hosts to Pythium root rot is recommended.A pathosystem is a subsystem of an ecosystem and is characterised by the phenomenon of parasitism. The bean-Pythium pathosystem consists of the host (bean), the pathogen (Pythium) and their host-pathogen relation. Of interest is how the pathogen causes pathogenicity on other crops and beans. To investigate this, screen house experiments were set up to test the pathogenicity of Pythium species derived from bean and other crops grown in association with beans. Pathogenicity was tested on maize (Zea mays), millet (Eleusine corcana), sorghum (Sorghum bicolor), peas (Pisum satium), susceptible bean variety (CAL 96) and resistant bean variety (RWR 719). The results indicated that distinct symptoms were observed in the roots and shoots of test crop species which are characteristic of Pythium infection. For instance peas had brownish watery stems and roots Also bean-derived pathogenic Pythium spp. were found to be more virulent than Pythium spp. derived from other crop species.Sorghum and peas had the highest disease scores upon infection by Pythium spp. We can conclude that there is cross pathogenicity among Pythium spp. especially affecting sorghum and peas. This phenomenon may account for the current root rot epiphytotics in south western Uganda and other similar agroecologies. An integrated disease management strategy that will deploy multi-non hosts to Pythium root rot is recommended
