Effects of water potential on accumulation and exudation of carbohydrates and glycerol during sclerotium formation and myceliogenic germination in Sclerotinia sclerotiorum

Abstract

On KCl- and NaCl-adjusted media, linear extension rates of Sclerotinia sclerotiorum mycelia measured over 2–3 days decreased with decreasing water potential, with zero growth at −6.0 MPa. Increasing the incubation period to 4–5 days at −2.0 to −6.0 MPa resulted in an increase in extension rates over those at 2–3 days. On the same media, sclerotium numbers fell with decreasing water potential as did the amount of fluid exuded by each sclerotium. However, the average weights of individual sclerotia increased. Sclerotia contained (in order of amounts present) mannitol, glycerol, glucose, arabitol and trehalose. Exudates similarly contained mannitol, glycerol, arabitol and glucose. Totalled concentrations of these solutes in both sclerotia and exudates increased linearly with decreasing substratum water potential. Sclerotia produced at different water potentials showed differences in subsequent germination behaviour on water agar. Those formed at low potentials germinated more vigorously and exuded greater amounts of water, mannitol, glycerol and glucose than those from higher potentials. In addition, during germination they lost more dry weight and tended to produce secondary sclerotia. These observations are discussed in relation to osmoregulation during sclerotium morphogenesis and germination.