Evidence of the Involvement of in Herpotrichia Needle Browning of .

Herpotrichia needle browning (HNB) is a disease that affects several species of fir trees in Europe and North America. HNB was first described by Hartig in 1884, who isolated a fungal pathogenic agent identified as responsible for the disease. This fungus was later named but is currently named . However, the identity of the pathogens causing HNB is regularly questioned and, to date, the true causal agent of this disease has not been definitely established. The present study aimed to identify the fungal populations present in needles of Christmas fir trees () and to correlate them with needle health status using robust molecular methods. PCR primers specific to allowed detection of the presence of this fungus in DNA samples from symptomatic needles. Furthermore, high-throughput sequencing (Illumina MiSeq) clearly showed that was associated with symptomatic needles. However, high-throughput sequencing results revealed that the presence of other species such as and sp. may also correlate with the development of HNB. A diagnostic tool, based on quantitative PCR using a probe, was then developed to detect and quantify in DNA samples. The efficacy of this molecular approach was validated through the detection of the pathogenic agent in symptomatic needle samples as well as in nonsymptomatic needles collected in trees affected by HNB. In contrast, could not be found in needles from healthy trees. The present study argues for the importance of in causing HNB symptoms.