Intraspecific genetic variation of acid phosphatase activity in monokaryotic and dikaryotic populations of the ectomycorrhizal fungus Hebeloma cylindrosporum

Abstract

Intraspecific variability of acid phosphatase activity and mycelial growth of the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi was examined because of the role of this enzyme activity in the phosphate nutrition of the fungus and consequently of mycorrhizal host plants. Interstrain variation was studied with 11 wild strains, and intrastrain variability was studied with 20 sib-monokaryons and 50 reconstituted dikaryons, progeny of the HC1 fruiting strain. The range of variation of acid phosphatase activity among wild dikaryotic mycelia was the same as that among sib-monokaryons or dikaryons belonging to the progeny of a single strain. The total phosphatase activity of the wild strains ranged from 5.70 to 96.0 total milliunits (TmU). It ranged from 11.1 to 120.5 TmU within sib-monokaryons and from 34.2 to 178.1 TmU for reconstituted dikaryons. Specific phosphatase activity of wild dikaryons ranged from 48.5 international milliunits (ImU) to 675.6 ImU, whereas the ranges of variation among sib-monokaryons and reconstituted dikaryons were, respectively, 85.3–791.0 and 270.7–816.1 ImU. On average, sib monokaryons and reconstituted dikaryons had lower activity than their parental dikaryon. However, four reconstituted dikaryons had a higher specific activity than the original dikaryon HC1. The growth of the studied mycelia also varied, but in a narrower range (from 97.1 to 151.6 μg protein per culture for wild dikaryons, from 130.1 to 199.1 μg for sib-monokaryons, and from 160.6 to 275.9 μg for reconstituted dikaryons). No correlation could be detected between specific acid phosphatase activity and growth rate in pure culture within the different monokaryotic or dikaryotic populations studied. These results demonstrate the possibility of obtaining, by intrastrain crossings, mycelia having higher phosphatase activity than the parental wild strains. The characteristics of the different mycelia are discussed in relation to a selection program and their putative spatial distribution in natural conditions. Key words: acid phosphatase, ectomycorrhizal fungus, intraspecific variation, monokaryon, dikaryon, Hebeloma cylindrosporum.