“Definitive senescence” in stock cultures of basidiomycetous wood-decay fungi

Abstract

For 7 cultures of basidiomycetous wood-decay fungi the decline of the following vitality marks were recorded over a 6-year period: (i) Consumption of sterilized beech wood substrate within a time unit as an indicator of the overall vigorousness of the fungus, (ii) decline of the competitive saprophytic ability (kratovirulence), which enables the fungus to colonize natural nonsterile substrates, (iii) capacity for sexual reproduction, (iv) several morphological features of the fungal colony. The reference strains kept growing at + 1 … 2°C on fertilized wood dust substrate retained in 5 of 7 cases all of their juvenility marks, although the wood-decay capacity gradually dropped back to 65 to 34% that of the initial value. The substrains maintained on liquid still cultures at 23°C lost their vitality marks after a period of continuous decline rather abruptly. With the loss of kratovirulence and fruiting capacity the strains were no longer viable under field conditions, and with the drop of the sterile wood-decay capacity to less than 3% by dry weight the formation of aerial mycelium and melanin pigments virtually ceased. In several fungal species the colonies segregated into coexisting sectors of extreme senescence and comparative juvenility, and a spread of senescence to the juvenile sectors did not occur. It is concluded that stock cultures of wood-decay fungi are subject to progressive senescence even under optimum conditions of strain preservation. Their current vitality should be examined in a sterile wood decay test before they are used in biotechnology or research.