Cultural and PCR-based identification of the two most common fungi from cankers on container-grown Norway spruce seedlings

Abstract

Assays were made to identify the most common fungi in cankers occurring on container seedlings of Norway spruce. The fungi isolated from cankers were first separated into morphological groups based on colony color, growth rate, and pattern on malt extract agar. Profiling of 18S rDNA indicated that several operational taxonomic units (OTUs) inhabited the cankers, some (OTU1 and OTU2) of which could be linked to mycelial cultures also isolated from the cankers. In addition, OTU1 could be linked to isolates originating from damped-off seedlings. Although the cultures linked to OTU1 differed morphologically from each other, the random amplified microsatellite analysis showed that they were genetically highly similar and represented a single species. Later, when these cultures were kept in natural sunlight, they all produced conidia morphologically similar to Sirococcus conigenus. Also, their partial 18S rDNA sequence was identical to that of S. conigenus in GenBank. The other common fungus (OTU2) was not possible to identify to species level, but based on comparisons with sequences in GenBank, it was closely related to Phoma herbarum. In preliminary tests, both S. conigenus (OTU1) and P. herbarum related fungus (OTU2) were pathogenic to Norway spruce seedlings.