Fungal Biology 123 (2019) 887e894 Contents lists available at ScienceDirect Fungal Biology journal homepage: www.elsevier.com/locate/funbio Adaptation of subpopulations of the Norway spruce needle endophyte Lophodermium piceae to the temperature regime * Michael M. Müller a, , Leena Hamberg a, Tatjana Morozova b, Alexander Sizykh b, Thomas Sieber c a Natural Resources Institute Finland (Luke), Natural Resources and Bioproduction, P.O. Box 2, 00791, Helsinki, Finland b Russian Academy of Sciences, Siberian Branch, Siberian Institute of Plant Physiology & Biochemistry, Irkutsk, 664033, Russia c Department of Environmental Systems Science, Institute of Integrative Biology, Forest Pathology and Dendrology, ETH Zürich, Switzerland article info abstract Article history: Lophodermium piceae represents the most common Norway spruce needle endophyte. The aim of this Received 8 May 2019 study was to find out whether subpopulations of L. piceae in climatically different environments (in Received in revised form which Norway spruce occurs natively) are adapted to local thermal conditions. L. piceae’s ability for 16 September 2019 thermal adaptation was investigated by determining growth rates of 163 isolates in vitro at four different Accepted 18 September 2019 temperatures: 2, 6, 20 and 25 C. Isolates were obtained between 1995 and 2010 from apparently healthy Available online 28 September 2019 needles sampled in Finland, Poland, Switzerland, Italy and southeastern Siberia. The sampling sites Corresponding Editor: Brenda Diana represent seven climatically distinct locations. Results were evaluated in relation to the age and Wingfield geographic origin of the isolate, in addition to the highest and lowest average monthly temperature of the sampling location. We found a significant correlation between the growth rate and the age of the Keywords: isolate at 25 C. Variation in growth rates between subpopulations was low compared to within sub- Climate populations. Only at 2 C did statistically significant differences between the average growth rates of Distribution subpopulations emerge. These results suggest that L. piceae covers the whole distribution area of Norway Fitness spruce but that generally the thermal reaction norm of its subpopulations has not changed according to Fungi local temperature ranges, despite high contrast in thermal conditions across this vast area. Therefore, it Picea abies fi Thermal reaction norm would appear that the thermal environment is not a crucial factor in assessing the tness of this fungal species within the native range of Norway spruce. © 2019 British Mycological Society. Published by Elsevier Ltd. All rights reserved. 1. Introduction Similarly, Venturia fraxini, the most frequently found endophytic fungus in leaves of the European ash (Fraxinus excelsior)in Temperature is an essential abiotic factor influencing the bio- Switzerland and Northern Italy, seems to be scarce or even absent logical, ecological and evolutionary processes of any organism in its in Norway (Schlegel et al., 2018; Hietala et al., 2018). As it is unclear environment. Fungi living in the tree canopies of boreal forests have whether direct effects of the northern temperature range restrict to cope, as do their hosts, with high diurnal and seasonal temper- their propagation northwards, it is difficult to predict if global ature variations which can, for instance in Finland, span up to 60 C warming will extend their distribution area in the future. It remains (Finnish Meteorological Institute, 2019). Not all native forest an intriguing, largely unanswered question as to whether fungal pathogens occur throughout the distribution range of their main parasites and pathogens in general are as adaptable in the face of native host species, but relatively little is known about how the climatic fluctuations as their main host plant species are. For local temperature pattern can restrict the survival of plant- instance, do environmentally highly tolerant tree species with associated fungi. For instance, Heterobasidion annosum s.s. and extremely wide distribution ranges, such as the Norway spruce Diplodia sapinea are not present in the most northern Scots pine (Picea abies L. Karst.), host the same parasitic fungi throughout their (Pinus sylvestris L.) forests in Europe (Müller et al., 2018a, 2018b). entire native area? Norway spruce is indigenous to the boreal forests of northern Europe and the mountainous areas of Central Europe. It gradually * Corresponding author. transforms morphologically along its distribution area towards the E-mail address: [email protected] (M.M. Müller). https://doi.org/10.1016/j.funbio.2019.09.008 1878-6146/© 2019 British Mycological Society. Published by Elsevier Ltd. All rights reserved. 888 M.M. Müller et al. / Fungal Biology 123 (2019) 887e894 northeast and its eastern variant (or Siberian subspecies) is called P. perform differently at both the high and low ends of their active abies ssp. obovata (Ledeb.). This subspecies’ presence spans the Kola temperature range, i.e., that their selection is based among others, Peninsula in northern Europe through Siberia to the coast of the on the local temperature regime. L. piceae was chosen as the model Okhotsk Sea of the Pacific Ocean. It can therefore be said that species because it is found abundantly on Norway spruce needles, is Norway spruce and its Siberian subspecies thrive in widely differing easy to isolate and to cultivate on ordinary growth media. climatic conditions, including mild coastal sites at sea level in Furthermore, L. piceae has a simple life cycle compared, for Fennoscandia, continental areas in Siberia, as well as, harsh instance, to plant pathogenic rust fungi, so using only one trait, i.e., mountainous sites up to 2000 m a.s.l. in the Alps, Altai and Sayan mycelial growth rate in vitro, may be sufficient in measuring the (Schütt et al., 2006). degree of adaptation to site-specific thermal conditions (Pringle Lophodermium piceae (Fuckel) Hohn€ is the most common and Taylor, 2002). endophyte endemic to Norway spruce needles in European forests. The infection frequency increases with needle age and often over 2. Material and methods 50 % of needles are colonized by this fungus (Barklund, 1987; Sieber, 1988; Solheim, 1995; Müller and Hallaksela, 1998). L. piceae infects 2.1. Needle sampling and fungal isolation needles via its air-driven ascospores (Osorio and Stephan, 1991), and it only colonizes small spatial domains in the needle tissue, Sampling and isolation of all but the Swiss isolates were per- meaning a single intact needle can accommodate over 30 different formed as follows. Third year twig segments (delimited by terminal L. piceae individuals (Müller et al., 2001). The number of L. piceae bud scars in previous years) were cut from twigs of mature Norway individuals inhabiting a single spruce tree is therefore potentially spruces at 1.5e3 m in height and transported in plastic bags (as immense, exceeding the number of needles on the tree. In general, hand luggage or by mail) to the laboratory where they were sub- the fungus causes no visible harm to its host. jected to the isolation procedure within three weeks of being cut The adaptation of fungal subpopulations to the local tempera- from their trees. Samples were obtained from four European ture range of their environment has been documented in form of countries and from southeastern Siberia (Table 1 and Fig. 1S). Fungi altered thermal reaction norms (temperature-dependent pattern of of these samples were considered to represent seven sub- an activity like growth rate, sporulation etc.) in a number of fungal populations based on geographical distance and/or distinct differ- species associated with various plants (Manici et al., 1995; Laine, ences in climatic conditions of the sampling locality. 2008; Zhan and McDonald, 2011; Mboup et al., 2012; Stefansson The twig segments were surface sterilized with sodium hypo- et al., 2013; Müller et al., 2015; Robin et al., 2017). In some cases, chlorite, as described by Müller and Hallaksela (1998). Four slices of thermal adaptation (being manifested as increased performance, approximately 0.5 mm were cut from the base of symptomless such as growth rate or reproduction success, of a strain or sub- green needles after removal of the petiole. These needle slices were population at different thermal conditions than in its initial/native incubated on water agar for one month at 20 C in darkness. Single environment) has been shown to proceed rapidly (de Crecy et al., hyphal tips were removed under the microscope from the plates 2009; Lendenmann et al., 2016). Rapid thermal adaptation within with a modified Pasteur pipette and transferred to modified orange a few years or decades is not necessarily based solely on changes in serum (MOS) agar plates (Müller et al., 1994). After cultivation at the relative abundance of individual genotypes in a population. In 20 C for three to four weeks, small hyphal samples from colony the case of Cryphonectria parasitica, adaptation has been known to edges were removed and transferred to fresh MOS agar plates. Agar occur in clonal lineages after their range expansion to a number of plugs with hyphal samples were transferred after three to four areas in France over a couple of decades (Robin et al., 2017). weeks into 2 ml Cryo-vials (Nalgene, SigmaeAldrich, Saint Louis, Intraclonal adaptation has also been witnessed in Phytophthora USA) and preserved at 5 C until experimental use. infestans (Mariette et al., 2016) in regard to the latent period, lesion Swiss isolates were obtained as follows. Ten healthy five-year- growth and spore production which varied between strains ac- old needles were collected from ten trees at the Gandberg cording to local temperatures at their origin. (465804000N90600000E) and the Albis (471703000N82905300E) sites, We can hypothesize that especially the fungal species colonizing i.e. 100 needles per site. At the Creux du Van site (465505900N the upper canopy of trees must demonstrate higher adaptability to 64302500E), 20 healthy five-year-old needles were collected from variable temperatures than species dwelling in the roots and basal six trees, i.e.