Microbial populations in wetwood of European white fir (Abies alba Mill.): (Quantification of microbial populations; wetwood; European fir dieback; forest decline; Protaminobacter; Pseudomonas; yeasts)

A method for extraction of microbial populations from wood samples was worked out which gave good recovery of both aerobic and anaerobic microorganisms in agar shake dilution and plating enumerations. This method was applied to the quantification of microbial populations in three European white firs (Abies alba Mill.) which were afflicted with the European fir disease. Low numbers of aerobic microorganisms (10²−10⁴ colony- forming units (cfu) per g fresh tissue) were detected in sapwood irrespective of the degree of affliction. Anaerobic bacteria were usually 1–2 orders of magnitude less frequent. Wetwood of highly diseased firs contained significantly higher numbers of aerobic microorganisms (10⁵−10⁷), whereas the number of anaerobes was not enhanced significantly. Among the prevalent aerobic microorganisms in wetwood were Protaminobacter, Pseudomonas strains, and a yeast. In anaerobic counts from wetwood, Klebsiella and Vibrio strains predominated. The sapwood contained Bacillus, Beijerinckia, Staphylococcus, and Clostridium spp. High numbers of aerobic microorganisms were also detected in the roots and lower stem of a diseased vine plant (Vitis vinifera L.). The importance of microbial populations in wetwood formation and disease expression is discussed.