Dothistroma spp. in Western Ukraine and Georgia

Dothistroma needle blight (DNB) is among the most serious foliar diseases affecting Pinus spp. globally. Infected needles were collected from potential host species in four locations in western Ukraine and in four locations in eastern Georgia during spring–summer 2015 to update the knowledge on pathogen distribution in these countries. Dothistroma spp. were detected using isolation, sequencing and species‐specific priming (SSPP) PCR. Two new hosts for Dothistroma spp. were recorded in western Ukraine: D. septosporum on Pinus nigra var. australica and D. pini on P. nigra var. mollet. D. septosporum was found on 15‐year‐old P. strobus in western Ukraine. New hosts for D. septosporum were recorded in Georgia on 5‐ to 10‐year‐old naturally regenerated P. sylvestris var. hamata and on 40‐ to 50‐year‐old P. ponderosa trees. D. pini was found for the first time in Georgia on 30‐ to 40‐year‐old P. nigra trees. The work confirmed the presence of both D. septosporum and D. pini in western Ukraine and Georgia, and demonstrated new hosts for both Dothistroma species.     

Detection of pine needle diseases caused by Dothistroma septosporum,Dothistroma pini and Lecanosticta acicola using different methodologies

Dothistroma and Lecanosticta needle blight are among the most damaging foliage diseases in plantations and natural pine stands worldwide, and are therefore listed as quarantine organisms in numerous countries. The aim of this study was to validate different methodologies used for the detection of both diseases. Based on multiplex quantitative PCR (qPCR), simultaneous detection and discrimination of the three pathogens Dothistroma septosporum, Dothistroma pini and Lecanosticta acicola were possible in symptomatic needles. Additionally, the same set of needles was analysed for the presence of all three pathogens using novel end‐point PCR assays followed by enzymatic digestion of PCR products. Results were compared with the qPCR data, and for validation, collected needles were screened morphologically for the presence of typical fruiting bodies and spores. Differences in detection sensitivity were found between the detection tools. The qPCR‐based detection allowed for specific and efficient identification and quantification of all three pathogens simultaneously. At the same time, conventional PCR assays, which target the multicopy ITS region, showed increased detection sensitivity and can be conducted without the use of expensive infrastructure and reagents.     

First report of Lecanosticta acicola on non‐native Pinus mugo in southern Sweden

In 2017, severe symptoms of brown spot needle blight, similar to those caused by Lecanosticta acicola, were observed on needles of non‐native Pinus mugo var. Hesse planted in an arboretum in southern Sweden. Microscopic characterization and molecular diagnostics of isolates obtained from diseased needles confirmed the identity of L. acicola. This is the first report of the quarantine pathogen L. acicola in Sweden. Subsequent surveys are urgently needed to assess the presence and extent of the L. acicola invasion in Scots pine (Pinus sylvestris) stands in Sweden and other Scandinavian countries.     

Artificial inoculation and susceptibility of Pinus armandii to Dothistroma septosporum

Dothistroma needle blight (DNB) is a serious needle disease of conifers that primarily affects pine species (Pinus spp.). Dothistroma septosporum is one of the DNB pathogens that has a diverse range of host species excluding Pinus armandii. In 15 inoculated P. armandii seedlings, D. septosporum acervuli were observed in 43 infected needles of ten seedlings with a mean disease severity of 1.11% at 25 weeks after inoculations, demonstrating the potential of D. septosporum to cause symptoms on the needles of P. armandii via artificial inoculation. The disease severity of P. armandii was similar to the positive control, Pinus nigra (median 0.75 for P. armandii to 0.70 for P. nigra), thus, P. armandii acts under artificial conditions as a susceptible host species.     

Needle blight of pine caused by two species of Dothistroma in Hungary

Dothistroma septosporum and D. pini cause the serious pine needle disease, Dothistroma needle blight (DNB). Of these, D. septosporum has a global distribution, while D. pini is known only from the USA, Russia, Ukraine and France. During a study of D. septosporum isolates from Pinus nigra in Hungary, microsatellite markers revealed the presence of a second Dothistroma species. The aim of this study was to identify the DNB pathogens occurring in Hungary using four different molecular techniques. These included sequencing of the rDNA ITS region, a species‐specific ITS‐RFLP, mating type primers and a diagnostic microsatellite marker, Doth_A. Results showed that both D. septosporum and D. pini occur in Hungary and that both DNB pathogens were present on the same trees and in some cases, the same needles. Mating types MAT1 and MAT2 of D. septosporum were shown to be present in Hungary, but only the MAT2 of D. pini was found. In addition, examination of needles with DNB symptoms from Russia revealed the presence of D. pini on Pinus pallasiana and P. nigra as well as on a new host, Pinus mugo. The molecular markers applied in this study were sufficiently robust to identify and differentiate between the two DNB pathogens, both in culture and directly from needles. They will consequently be useful to document the geographical range and to monitor the spread of D. septosporum and D. pini in future studies.     

Modelling of the spread of Dothistroma septosporum in Europe

Dothistroma needle blight (DNB), a disease affecting several pine species, is currently generating great concern in Europe. Caused by Dothistroma pini and Dothistroma septosporum, DNB affects pine needles and causes premature defoliation, which results in growth reduction and, in extreme cases, mortality. The disease has increased in importance in Europe over the last 20 years, with an increase in the number of observations of DNB in regions with large areas of Pinus sylvestris in northern Europe. This article presents a cell‐based spatiotemporal model for predicting the likelihood and intensity of the future spread of D. septosporum in Europe. Here, “spread” includes both invasion of new regions and infection of healthy stands within already‐colonized regions. Predicted spread depends on the availability of host species, climatic suitability of different regions to D. septosporum and dispersal of sexual and asexual spores from infected trees to surrounding forests via water splash, mist and wind. Long‐distance spread through transport of infected seedlings is also included in the model. Simulations of spread until 2007 and 2015 were used to validate the model. These simulations produced similar patterns of spread to those observed in Europe. Simulations for 2030 suggested that additional and new outbreaks are likely to occur in Scotland, southern Norway, southern and central Sweden, northern parts of Germany and Poland, Estonia, Latvia and south‐west Finland. Preventing the delivery of infected seedlings would be an effective method for reducing the spread of D. septosporum in the Nordic countries, Scotland and Ireland, the Baltic countries, and parts of Germany, Poland and Belarus. In these states, prevention of transport of infected seedlings can reduce the probability of additional spread by 15%–40%.     

New host and country records of the Dothistroma needle blight pathogens from Europe and Asia

Dothistroma needle blight (DNB) is a serious disease of pines (Pinus spp.), with a worldwide distribution. It is caused by the ascomycete fungi Dothistroma septosporum (teleomorph: Mycosphaerella pini) and Dothistroma pini (teleomorph unknown). Recently, DNB was found on Pinus peuce in Austria, Pinus pallasiana in Ukraine and the European part of south-western Russia, as well as on Pinus radiata and Pinus wallichiana in Bhutan. Based on DNA sequence comparisons of the internal transcribed spacer and β-tubulin gene regions, isolates from Austria and Bhutan were identified as D. septosporum, while isolates from Ukraine and south-western Russia were identified as D. pini. Additional isolates studied from Pinus mugo in Hungary confirmed the presence of D. septosporum in this country. The record of D. septosporum on exotic P. peuce in Austria represents a new host report of this needle blight pathogen in Europe. Likewise, DNB and the associated pathogen, D. septosporum are reported from Bhutan, eastern Himalayas, for the first time. In addition, D. pini was found in two European countries and on a new host, P. pallasiana. These European records represent the only reports of D. pini from outside the north-central USA. Morphological examination of selected specimens from different hosts and countries showed that D. septosporum and D. pini overlap in the length of their conidia, while the width is slightly wider in D. pini than in D. septosporum. The differences in conidial width are so small, however, that identification of the two Dothistroma species solely based on morphology is virtually impossible. The new host and country records provided here are consistent with the continuing trend of reports of the DNB pathogens from new hosts and new geographical areas during the last two decades, particularly in the northern hemisphere.     

First report of Mycosphaerella dearnessii in Switzerland

Brown-spot needle blight caused by Mycosphaerella dearnessii [syn. Scirrbia acicola; anamorphic state: Lecanosticta acicola (syn. Septoria acicola)] was observed for the first time in Switzerland. So far, the disease seems to be confined to planted Pinus mugo and Pinus uncinata near Zurich. Pinus sylvestris adjacent to diseased P. uncinata did not show any disease symptoms.     

First molecular detection of Lecanosticta acicola from Poland on Pinus mugo

The presence of quarantine pathogen Lecanosticta acicola, the causal agent of brown spot needle blight, was confirmed using molecular methods for the first time in northern part of Poland on the coastal area adjacent to the Baltic Sea. This area includes sandy beaches, where Pinus mugo and P. sylvestris were planted. Symptomatic needles were collected in 2017 from 20 P. mugo trees growing in one stand in Ustka. Typical symptoms of brown spot needle blight infection, including dead needle tips and central zones with yellow or reddish brown, circular spots in green tissue, were observed on all samples. Only, the asexual stage of L. acicola was obtained during this work. The pathogen species identity was confirmed using classical morphological methods (microscopic examination of the infected needles), real‐time and species‐specific priming (SSPP) PCR, and ITS sequencing. Analysis of mating‐type (MAT) genes showed the presence of both mating types in northern Poland.     

Invasive brown spot needle blight caused by Lecanosticta acicola in Estonia

Lecanosticta acicola (Thüm.) Syd., a serious foliage pathogen of pines in many regions of the world, is an emerging invasive species in northern Europe. After the first record of L. acicola on Pinus ponderosa Dougl. ex Laws. in northern Estonia in 2008, monitoring was started to investigate the spread and host range of the fungus in the country. By the beginning of 2015, L. acicola was also recorded on P. uncinata Mill. ex Mirb., P. mugo Turra and on P. mugo var. pumilio (Haenke) Zenari, being the northernmost records of the fungus in Europe. So far, the single native pine species Pinus sylvestris L. has not been found to be infected. Molecular analysis proved infection of L. acicola on pines in five different localities of Estonia: in Tallinn (mainly in the Botanic Garden, northern Estonia), in Tori and Kärdla (western Estonia), in Vasula and Kärevere (east-central Estonia). The sexual state (teleomorph) of the fungus was not found, but the existence of the both mating types, MAT1-1 and MAT1-2, was confirmed.     

Needle blight caused by Dothistroma pini in Slovakia: distribution,host range and mating types

Dothistroma needle blight (DNB) has been observed in Slovakia during the last two decades. Up until 2017, Dothistroma septosporum has only been detected and molecularly confirmed to cause DNB in Slovakia. Here, we report the detection of Dothistroma pini at six localities around Slovakia, representing different plantation types. Four pine species (Pinus sylvestris, P. nigra, P. mugo and P. jeffreyi) were confirmed as hosts of D. pini in Slovakia, of which only P. mugo has been previously reported as host in Slovakia. Three gene regions (ITS, EF1 –α, and ß-tubulin) of each of the 13 isolates were sequenced and assigned as D. pini. Based on ITS sequences, the studied isolates represent the haplotypes Dp_HAP.1, Dp_HAP.2. Both mating types were detected but at different localities. Our results suggest that in addition to D. septosporum, D. pini may contribute to DNB also in Slovakia.     

Pathogenicity of Heterobasidion annosum (Fr.) Bref. sensu stricto on coniferous tree species in Turkey

Two‐year‐old seedlings of Pinus brutia, P. brutia var. eldarica, Pinus pinea and 3‐year‐old seedlings of Pinus radiata, Pinus sylvestris, Pinus nigra and Cedrus libani were inoculated on the lower stem with isolates of Heterobasidion annosum s.s. collected from the Black Sea and Mediterranean regions of Turkey. In total, 315 seedlings were inoculated in April 2014 and incubated in a growth chamber for 7 weeks at 18–20°C. All isolates were pathogenic on the seven different hosts and had the ability to grow in living sapwood. The isolates had a greater growth on C. libani, P. sylvestris and P. radiata seedlings compared to plants of the other species tested. The least affected species were P. brutia and P. nigra. The isolates originating from the Black Sea region caused longer lesions on the hosts. Overall mortality during 7 weeks of incubation was 4%.     

The hosts and geographic range of Dothistroma needle blight in Slovakia

The occurrence and distribution of Dothistroma needle blight (DNB) were studied in 2014–2017 around Slovakia. A total of 84 localities, both native and planted, were investigated, and the presence of DNB was confirmed in 73 of them. In all positive locations, symptoms typical of DNB were observed and the Dothistroma species was confirmed using species‐specific primers either from fungal cultures or directly from needles. Both Dothistroma species—D. septosporum and D. pini—were identified. Both species occurred together in 29 locations, only D. septosporum in 42 and only D. pini in two locations. The host range of D. septosporum included 10 pine species and two spruce species. The host range of D. pini comprised the same number of pine hosts but only one spruce species. Five pine hosts, P. aristata, P. coulteri, P. densiflora, P. jeffreyi, P. × schwerinii, and one spruce host P. abies are new hosts species of D. pini. P. densiflora and Picea pungens have earlier been reported to be susceptible for DNB. In this study, D. septosporum was found from both tree species.     

Fungicide sensitivity of Dothistroma septosporum isolates in the UK

Dothistroma septosporum, a causal agent of Dothistroma needle blight (DNB), is a damaging fungal pathogen of pines that has recently started to affect native Scots pine woodlands in the UK. In addition to silvicultural methods, fungicide spraying of forest nursery stock can help prevent the spread of DNB. However, the effectiveness of modern single‐site fungicides against D. septosporum and the risk of fungicide resistance evolution remain largely unknown. In this project, we aimed to establish sensitivity profiles of D. septosporum to some widely used single‐site fungicide classes in vitro, and to determine whether fungicide resistance is already present, as this could increase the spread of D. septosporum genotypes on planting stock in native woodlands. For this purpose, we compared isolates of D. septosporum, originating from pine stands unexposed to fungicides, with isolates from nursery outbreaks, for sensitivity to a range of commonly applied fungicides. Most of the fungicides we tested were effective in vitro and we observed no significant shifts in sensitivity in forest nurseries. Although further tests in planta are required to confirm effectiveness of single‐site fungicides against D. septosporum, our results suggest that they can be successfully used in DNB control, although appropriate measures to prevent the evolution of fungicide resistance are strongly recommended.     

Resistance levels of Spanish conifers against Fusarium circinatum and Diplodia pinea

Pitch canker, caused by Fusarium circinatum, and Diplodia shoot blight, caused by Diplodia pinea, are both damaging to pines (Pinus spp.) grown in plantations throughout the world, including Spain. To assess the potential for interspecific differences in susceptibility to contribute to the management of pitch canker and Diplodia shoot blight in the Atlantic region of Spain, the present study was undertaken to characterize the susceptibility of six pine species (P. sylvestris, P. nigra, P. pinaster, P. radiata, P. halepensis and P. pinea) and Douglas‐fir (Pseudotsuga menziesii) to F. circinatum and D. pinea. Based on inoculations of 2‐year‐old trees, Ps. menziesii, P. pinea and P. nigra were the most resistant to F. circinatum, with lesion lengths ranging from 3.7 to 21.5 mm, 2.2 to 12.6 mm and 2.8 to 30.9 mm, respectively. At the other extreme, Pinus radiata was the most susceptible, sustaining lesions that ranged from 8.5 to 74.8 mm in length. Pinus sylvestris, P. pinaster and P. halepensis showed an intermediate response to F. circinatum. Broadly similar results were observed in inoculations with D. pinea, with Ps. menziesii being relatively resistant and P. radiata being highly susceptible. Consistent with these results, field surveys revealed no pitch canker in stands of Ps. menziesii and low severity of Diplodia shoot blight, whereas P. radiata was severely affected by both diseases. Our findings suggest that selection of appropriate species can greatly reduce the risk of damage from two important canker diseases affecting pine plantations in the Atlantic region of Spain. Furthermore, intraspecific variation in susceptibility implies that selection may allow for the enhancement of resistance in otherwise susceptible species.     

Microspatial genetic diversity of Dothistroma septosporum

The distribution of genetic diversity in a local population of Dothistroma septosporum was determined on a microspatial geographical scale. The study was conducted in a seed orchard of Pinus nigra divided into four plots, each of 0.84 ha in area. Ninety‐two isolates were obtained from needles with red band needle blight symptoms. Molecular variance, Mantel test and autocorrelation spatial analyses were performed with the use of random amplified microsatellites markers to test the null hypothesis of a random distribution of genotypes. The groups of isolates from individual plots demonstrated small differences as regards intrapopulation variation. The mean contribution of polymorphic loci for isolate groups was almost 77%, genetic diversity 0.270, while the Shannon coefficient was 0.389. The Mantel test demonstrated a significant, positive correlation between Huff's genetic distance and geographical distance. Significant spatial genetic structure was detected with autocorrelation coefficients being significant in the first two distance classes up to about 8–12 m.     

Dothistroma Needle Blight in Slovenia is caused by two cryptic species: Dothistroma pini and Dothistroma septosporum

Dothistroma Needle Blight (DNB) has been known in Slovenia since 1971, but the disease symptoms have intensified in recent years. With this study, the DNB symptoms in Slovenia are for the first time connected to both phytopathogenic Dothistroma species: D. pini and D. septosporum. Based on the ITS‐rDNA comparisons, the Slovenian isolates of D. pini group with the D. pini isolates from France, Hungary and the USA and not with the D. pini isolates from Russia and Ukraine. Both mating types MAT1 and MAT2 of D. septosporum are present in Slovenia, while for D. pini, only MAT2 was found. The current widespread occurrence of D. pini in native forest stands indicates the prolonged presence of this species in Slovenia.     

Dothistroma septosporum on firs (Abies spp.) in the northern Baltics

In the spring of 2008, Dothistroma septosporum, a damaging quarantine pathogen of pine foliage, was documented in Järvselja (southeastern Estonia), apparently for the first time, on white fir (Abies concolor). Thus, a new host species and genus for the fungus were recorded. Infection of white fir by D. septosporum, and also of some other fir species, was monitored annually on a transect proceeding from southeastern Estonia to northern Latvia. As a result, D. septosporum was detected also on silver fir (Abies alba). It is not clear why this fungus with a worldwide distribution appeared on this new host genus definitely in northern Europe.     

The hosts and potential geographic range of Dothistroma needle blight

Dothistroma needle blight, one of the most important foliar diseases of Pinus spp., is caused primarily by the fungus Dothistroma septosporum (Dorog.) Morelet, and to a lesser extent by Dothistroma pini Hulbary. The potential distribution and abundance of Dothistroma spp. was determined by (i) developing a process-oriented model of potential distribution of Dothistroma spp. from known locations, (ii) compiling a comprehensive list of susceptible host species from existing scientific literature and (iii) determining the distribution of susceptible hosts in areas predicted to be suitable for range expansion of Dothistroma spp. Using these three sources of information regions at risk were identified as those that were predicted to be suitable for range expansion by Dothistroma spp. and included significant areas of susceptible host species.     

One-hundred-year foliage comparison of Pinus ponderosa and Pinus sylvestris under dry growing conditions in Brandenburg,Germany

Abstract

The dynamics of six different needle parameters of Pinus sylvestris L. and Pinus ponderosa Dougl. ex P. & C. Laws. were examined retrospectively for a 112-year-old mixed stand in Brandenburg, Germany, using the needle trace method. Similarities were found in needle production, needle loss and needle density. However, needle age, needle retention and total number of needles revealed significant differences between the tree species, with higher values for P. ponderosa. Pinus ponderosa yielded approximately twice as much mean whole-crown needle dry mass as P. sylvestris. Furthermore, different branching systems could be detected between the species, with both pines following “Corner's rule”. The results suggest that under identical growing conditions, P. ponderosa exhibits more efficient water use and can therefore maintain a bigger crown (as the basis for increased growth) than P. sylvestris.