Epidermal cell response to rust hyphae and the resistance mode of tropical maize to southern corn rust (Puccinia polysora underwood)

Abstract

Southern Corn Rust (SCR), caused byPuccinia polysora Underwood, is found primarily in the tropics, occurring especially during wet and cool winters in Hawaii. Whereas Hi38-71, a tropical Hawaiian super sweet corn, is resistant to SCR, the G24 inbred is susceptible. Anatomical traits are distinct in these two lines, with differences evident in their epidermal cell shapes, cell types, epidermal cell walls, hairs, and bulliform cells. Trichomes are found on the leaves of Hi38-71 plants and their epidermal surface cells are flat. In contrast, the epidermal surfaces of G24 leaves are circular, rough, and woolly, and are uniform in their size and pattern. These woolly epidermal leaf surfaces on the susceptible G24 provide access for disease infection while the trichomes and smooth leaves may confer more resistance in Hi38-71. Our genetic study utilized Generation Mean Analysis (GMA) of progenies derived from crosses of these two inbred lines. Resistance to SCR was scaled from 1 (resistant) to 9 (susceptible) in the winter and spring in Hawaii. Average scores for Hi38-71 and G24 were 3.1 and 6.9 respectively, while the F1 and F2 hybrids were both highly resistant to the rust. Both additive and dominant effects for SCR resistance were highly significant, as were their epistatic interactions [aa] and [dd]. However, the additive x dominance interaction was not. Therefore, a single dominant gene in inbred line Hi38-71 might be involved in determining its high resistance to SCR.