Histological characterization of the early‐stage infection events of Setosphaeria turcica in maize

Abstract

AbstractNorthern corn leaf blight (NCLB) caused by Setosphaeria turcica is a major foliar disease of maize. The early‐stage infection events of this pathogen on maize leaves are unclear. We investigated the optimum temperature for conidial germination and appressorium formation, and characterized penetration and growth of S. turcica in maize leaf sheath and onion epidermis cells, including use of histological staining to assess plant cell viability. The results showed that the optimum temperature for conidial germination and appressorium formation was 20°C. On the maize leaf sheath, the appressoria were formed by germinated conidia, and penetration on the epidermal cells occurred at 8 h postinoculation (hpi). Round vesicles developed beneath the appressoria. Between 16 and 24 hpi, the branched invasive hyphae invaded three to five adjacent cells at most infection sites. The invasive hyphae tended to move along the cell wall and crossed from one cell to another. In the onion epidermis cells, the appressoria formed at 8 hpi, and in most cases the epidermal cells were penetrated through the juncture of the cell walls. At 16–24 hpi, the primary hyphal terminus swelled to a vesicle. The maize leaf sheath cells died at 8 hpi, whereas the onion cells did not. Our findings documented in detail the penetration and invasive hyphal growth in maize leaf sheath and onion epidermis, as well as viability of plant cells, at the early stages of infection, and provide a foundation for elucidating the underlying mechanism of S. turcica–maize interactions.