Salinity and Salinity Tolerance Alter Rapid Blight in Kentucky Bluegrass, Perennial Ryegrass, and Slender Creeping Red Fescue

Abstract

Rapid blight, caused by Labyrinthula terrestris (D. W. Bigelow, M. W. Olsen, and Gilb.), occurs on cool-season grasses in arid and coastal regions of the USA with elevated irrigation salinity. The impacts of irrigation salinity and cultivar salinity tolerance on rapid blight were examined in greenhouse experiments. Four cultivars each of Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and slender creeping red fescue (Festuca rubra spp. littoralis (G. F. W. Meyer) Auquier), known to differ in rapid blight susceptibility, were irrigated daily with solutions of 0.2, 1.3, 2.5, 3.6, and 4.8 dS/m, with or without inoculation with L. terrestris. Treatment effects were assessed by rating chlorotic leaf tissue and calculating area under the leaf chlorosis curve (AULCC). Rapid blight had little effect on AULCC of any grass at = 2.5 dS/m. Perennial ryegrasses and Kentucky bluegrasses had substantial rapid blight-induced AULCC at >= 2.5 dS/m. Leaf chlorosis due to rapid blight was less and slower to develop in 'North Star' Kentucky bluegrass and 'Hawkeye' and 'Peregrine' perennial ryegrasses than in other cultivars of these species. Leaf chlorosis due to salinity of 4.8 dS/m without inoculation correlated well with leaf chlorosis due to rapid blight at 2.5 dS/m, suggesting mechanisms imparting salinity and rapid blight tolerance may be similar. Irrigation water management practices reducing rootzone salinity and selection of tolerant species and cultivars are recommended to lessen rapid blight.