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

3-Deoxyanthocyanidins are the principal phytoalexins that accumulate in sorghum in response to fungal infection. Two cultivars which differed in their reaction to: Colletotrichum sublineolum, the pathogen causing the anthracnose disease in sorghum, were examined for their phytoalexin response and expression 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 resistant cultivar were characterized by a greater:and faster:accumulation of phytoalexins and an earlier induction of defense-related genes encoding chalcone synthase and pathogenesis-related protein PR-10. In the compatible interaction, the pathogen was able to colonize the host with the proliferation of primary and secondary hyphae. In addition to the quantitative and timing differences, there were qualitative differences between the cultivars in their phytoalexin response. Thus, the resistant cultivar accumulated a complex phytoalexin mixture, including luteolinidin and 5-methoxyluteolinidin, neither of which was produced by the susceptible cultivar following fungal inoculation. These compounds were shown previously to exhibit higher fungitoxicity than other phytoalexin components in sorghum. Our results demonstrate that 3-deoxyanthocyanidin phytoalexins represent major components of resistance to C. sublineolum in sorghum. (C) 1999 Academic Press.