Accumulation of 3-deoxyanthocyanidin phytoalexins and resistance to Colletotrichum sublineolum in sorghum

3-Deoxyanthocyanidins are the principal phytoalexins that accumulate in sor ghum in response to fungal infection. Two cultivars which differed in their reaction to: Colletotrichum sublineolum, the pathogen causing the anthracn ose disease in sorghum, were examined for their phytoalexin response and ex pression of defense-related genes. In the incompatible interaction, fungal development in the host was contained during early stages of pathogenesis. When compared to the susceptible cultivar, defense responses in the resista nt cultivar were characterized by a greater:and faster:accumulation of phyt oalexins and an earlier induction of defense-related genes encoding chalcon e synthase and pathogenesis-related protein PR-10. In the compatible intera ction, the pathogen was able to colonize the host with the proliferation of primary and secondary hyphae. In addition to the quantitative and timing d ifferences, there were qualitative differences between the cultivars in the ir phytoalexin response. Thus, the resistant cultivar accumulated a complex phytoalexin mixture, including luteolinidin and 5-methoxyluteolinidin, nei ther of which was produced by the susceptible cultivar following fungal ino culation. These compounds were shown previously to exhibit higher fungitoxi city than other phytoalexin components in sorghum. Our results demonstrate that 3-deoxyanthocyanidin phytoalexins represent major components of resist ance to C. sublineolum in sorghum. (C) 1999 Academic Press.