Deterioration of mycorrhizal short roots and occurrence of Mycelium radicis atrovirens on declining Norway spruce in Bavaria

From four locations in Bavaria, the only known pathogenic fungi identified from fine roots (< 2mm dia) of declining Norway spruce (Picea abics) were Cylindrocarpon destructans and Mycelium radicis atrovirens, the latter being much more common (25 vs. 95 isolations from 219 root segments). Norway spruce from six additional locations were sampled for mycorrhizae and fine roots. There were always more active mycorrhizal root tips (1.28 to 3.44 fold) on spruce which were less symptomatic of decline P(T) = 0.0156]. However, the occurrence of inactive mycorrhizae and M. r. atrovirens were similar on all spruce that were sampled. In tins study, no evidence was found that a root pathogen is causing the deterioration in the fine root system of declining Norway spruce.