Effect of osmotic stress on growth of Gaeumannomyces graminis strains differing in hyphal pigmentation

The effect of osmotic stress on mycelial growth was determined for melanize d and nonmelanized strains of Gaeumannomyces graminis var. tritici and var. graminis using a minimal salts medium, both in liquid and solid form. The osmotica used were KCl and sucrose. Growth measurements obtained from mycel ia grown in solid media bore no obvious relationship to data obtained from liquid media at 25 C. In liquid media, all four strains exhibited minimum g rowth rates at the highest osmotic potential (-0.39 MPa). In solid media, m inimum growth rates were measured at the lowest osmotic potential (-4.34 MP a). Addition of sucrose to liquid media doubled the growth rates of all str ains, but no similar increase in growth rate was observed in solid media su pplemented with sucrose. A suboptimal growth temperature (30 C) for the G. g. var. tritici strains increased the level of osmotic stress tolerated by these strains. This was not observed for the G. g. var. graminis strains. T here was no consistent relationship between melanization and osmotic stress .