Phycomyces blakesleeanus BURGEFF and several wood‐decay fungi in a bioassay for growth factor resources in fresh and microbially precolonized timber

Abstract

The presence of the essential growth factor thiamine in timber was ascertained with the determination of the mycelial growth figures of several indicator fungi on the respective timber substrates. The behaviour of the absolutely thiamine-dependent phycomycete, Phycornyces bkizkesleeanus BURCEFF (Pb), as well as of 6 strains of basidiomycetous wood-decay fungi (WBF) that did or did not depend on exogenous vitamin supply proved in accordance that (i) both sapwood and heartwood material of 14 native timber species examined were able to furhish fiinlri with xnv deyee of vitamin dependence with the essential growth factor(s); (ii) both fresh timber and timber pre-colonized by bacteria, ascomycetous discolouration fungi, and WBF contained thiamine resources above the saturation level of 50 fig per kg; (iii) neither a thiamine supply of 2 to 20 mg per kg total weight nor the residues of microbial pre-colonizers added to the vitamin pool of timber in that the growth of the test fungi could be further stimulated; (iv) the depressive growth of WBF on vitaminfree liquid media was not observed on vitamin-free solid media such as fertilized builder's sand. A vitamin supply did not improve the vigour of WBF of any degree of vitamin dependence, but it was a prerequisite for the growth of Pb on these substrates.It is concluded that vitamins in timber have, on their permanent excessive presence, no ecological significance. They do not add to host wood specificity, to the election of the fungus' host range, to the specialization for gymnosperm wood, to the preference for sapwood or heartwood within the stem, to the establishment of pathogenesis on standing timber, and to the preference for fresh or pre-colonized wood material.The long-term cultivation of mycelia of wood-destroying basidiomycetous fungi (WBF) in vitamin-free liquid media revealed that about 30 % of the strains of brown-rot fungi and 70:/, of the strains of white-rot fungi depend on exogenous vitamin supply. In the permanent absence of the B-Vitamins, thiamine and biotin, their mycelial dry weight production dropped to less than 25 7; to normal. In several strains the growth vigour even collapsed irreversibly (GRAMSS 1990). The partial dependence of WBF on exogenous vitamin supply is a well-known fact (e.g., FRIES 1938, SCHOPFER and BLUMER 1940). Wood-decay fungi share this dependence with basidiomycetous ground fungi (LINDEBERG 1939, RA-WALD 1962) and ectomycorrhizal fungi (MELIN and NYMAN 1940). Within the group of basidiomycetes, vitamin requirements are restricted to thiamine, the thiamine moieties thiazole and pyrimidine, and sometimes to biotin ( JENNISON 1952, VOLZ and BENEKE 1969, EUL and SCHWANTES 1985. It is suggested that fresh timber substrates meet the thiamine requirements of WBF (JENNISON 1952).ZIFGLER and ZIECLER (1962) demonstrated in a bioassay with auxotrophic bacteria that the assimilate sap stream of 37 tree and shrub species thoroughly contained, besides other water-soluble vitamins, 0.11 to 1 .O mg per litre thiamine, 0.1 1 to 1 pg per litre ...