Effect of mannitol on the in vitro growth, temperature optimum, and subsequent ectomycorrhizal infectivity of Pisolithus tinctorius

Abstract

The effect of mannitol on in vitro growth, temperature optimum, and subsequent ectomycorrhizal infectivity of Pisolithus tinctorius isolate T1069 was investigated. In vitro growth on mannitol as a sole carbon source was 50–140% of that on equimolar glucose. The pH optimum for growth on mannitol was 6.0 with a minor peak at 4.0. A lag period of 5–10 days before the onset of growth was observed with mannitol, but no lag was observed with glucose. In addition, growth on mannitol after 4 weeks was greater if the inoculum had previously been grown on mannitol than if it had previously grown on glucose. These observations suggest adaptation of the fungus to mannitol. The optimum temperatures for growth of the fungus on mannitol and glucose were 27 and 21 °C, respectively. At 23 °C, the ability of the fungus to form ectomycorrhizae on Pinus mugo seedlings was low, regardless of whether the inoculum had been grown on mannitol or on glucose. At 33 °C, however, infectivity was substantially increased. At the higher temperature, mannitol and glucose grown inoculum caused 35 and 55% of the short roots to become infected, respectively.