Impact of Temperature, Osmotic Potential, and Osmoregulant on the Growth of Three Ectotrophic Root-Infecting Fungi of Kentucky Bluegrass.

Abstract

Two isolates each of Magnaporthe poae, Gaeumannomyces incrustans, and Leptosphaeria korrae were grown at 25°C in liquid shake culture in minimal salts medium (-0.12 MPa) or minimal salts medium adjusted to -0.5 MPa with KCl, MgCl2, or polyethylene glycol (PEG). Fungal dry weight of all three species was greater in minimal salts medium amended to -0.5 MPa with MgCl2 than in nonamended medium, and dry weight in medium amended with PEG was not different from dry weights in nonamended medium or medium amended with KCl. Fungi were incubated at varying temperatures on a minimal salts solid-agar medium (-0.12 MPa) adjusted to osmotic potentials ranging from -0.5 to -5.0 MPa with KCl or MgCl2. Optimum growth of M. poae, G. incrustans, and L. korrae on nonamended medium occurred at 30, 30, and 25°C, respectively. At optimum temperatures for each species, fungal growth was greatest at the higher osmotic potentials tested (-0.5 to -1.0 MPa) and decreased in a linear manner as osmotic potential decreased. In most cases, growth was detected at the lowest osmotic potential measured (-5.0 MPa). The relationship of fungal growth to osmotic potential depended on both temperature and osmoregulant. At temperatures optimal or nearly optimal for fungal development, the growth of all three fungi declined more rapidly with decreasing osmotic potential when grown on medium amended with MgCl2 than on medium amended with KCl. At the highest temperature evaluated for growth of M. poae and L. korrae (35 and 30°C, respectively), growth on medium amended with KCl was curvilinear and peaked at osmotic potentials of -2.5 to -3.0 MPa. Furthermore, between osmotic potentials of -2.0 and -5.0 MPa, M. poae grew best at 35°C. When maintained on nonamended minimal salts medium (-0.12 MPa) in liquid culture at 25°C or on nonamended solid-agar medium at temperatures optimal for growth, M. poae grew at a faster daily rate than L. korrae.