Searching thePinus taedafoliar mycobiome for emerging pathogens among brown spot needle blight and needlecast outbreaks in the Southeast United States

Abstract

AbstractNeedle pathogens cause the discoloration, death, or premature abscission of conifer foliage, which reduce growth and vigor, and repeated defoliation may eventually result in tree mortality. Since 2016, forest managers in the southeast United States have reported an increasing scale, frequency, and severity of needle disease outbreaks on the region’s principal timber species, loblolly pine (Pinus taedaL.). These recent outbreaks are raising concern throughout the region, as needle diseases are not traditionally considered a threat toP. taeda.Lecanosticta acicola(Thum.) Syd., the native causal agent of brown-spot needle blight, has been recovered from some outbreaks, however, the full array of fungi associated with symptoms has not been explored. In this research,P. taedafoliage was collected from affected stands throughout the region and analyzed to identify fungi associated with needle disease symptoms. We employed both targeted molecular diagnostics, to confirm the presence or absence ofL. acicola, and DNA metabarcoding, to characterize the foliar mycobiome and screen for other potential pathogens.Lecanosticta acicolawas detected among symptomatic needles from multiple states, particularly in western portions of theP. taedarange but rarely from stands in eastern states. Fungal ITS1 metabarcoding revealed multiple pathogens in symptomatic needles and identified associations between known pathogens fungi and differing symptoms. Additionally, the fungal community composition of needles varied with patterns of symptom presentation. This study is the first regionwide assessment of fungi associated with recent large-scale needle disease outbreaks onP. taedaand identifies multiple pathogens that warrant study in greater detail.