Diplodia shoot blight and asymptomatic persistence of Diplodia pinea on or in stems of jack pine nursery seedlings

Diplodia pinea (syn. Sphaeropsis sapinea) is known as a major cause of damage to red pine (Pinus resinosa) seedlings in nurseries. The fungus can also be a latent pathogen of red pine seedlings, persisting in the absence of gross symptoms and later proliferating under conditions that induce host stress. In the fall of 2004, three nurseries in Wisconsin were surveyed to determine the potential for the occurrence of Diplodia shoot blight on jack pine (Pinus banksiana) seedlings and the persistence of D. pinea on or in asymptomatic seedlings of this species. Incidence of shoot blight was quantified in five 1 m long segments of an interior row in each of two survey areas in each nursery. The pathogen was identified on symptomatic seedlings collected in these areas on the basis of presence of characteristic pycnidia and conidia. Five groups of 20 asymptomatic seedlings were also collected in each of the two survey areas in each nursery. A segment of the lower stem/root collar from each of these asymptomatic seedlings was surface‐disinfested and culturally assayed using tannic acid agar. The mean incidence of shoot blight (as high as 9%) and mean frequency of cultural detection from asymptomatic seedlings (as high as 20%) were greatest in proximity to red pine windbreaks which are a source of inoculum. Only D. pinea was confirmed from subsets of symptomatic and asymptomatic seedlings which were tested using mt SSU rDNA polymerase chain reaction (PCR) primers that allow differentiation of D. pinea from D. scrobiculata and other fungi in the genus Botryosphaeria and related anamorphic fungi. Jack pine seedlings inoculated with D. pinea isolates obtained from asymptomatic nursery seedlings developed shoot blight symptoms in greenhouse trials. Thus, the ability of D. pinea to damage jack pine seedlings in nurseries has been documented and the potential for virulent strains of this latent pathogen to be distributed on asymptomatic jack pine seedlings from nurseries has been confirmed.     

PCR primers for identification of Sirococcus conigenus and S. tsugae,and detection of S. conigenus from symptomatic and asymptomatic red pine shoots

Regions of diversity in the internal transcribed spacer (ITS) sequences of Sirococcus species were exploited to design primer pairs used in a PCR-based method for the identification of the conifer shoot blight pathogen Sirococcus conigenus and the closely related fungus Sirococcus tsugae. The specificity of each primer pair for the respective fungus, detection limits and utility for detection from host material were confirmed. The S. conigenus primers were then used to detect this pathogen in tissues of symptomatic or apparently healthy red pine shoots collected at six locations in Wisconsin and Michigan and results compared with those obtained using a cultural assay. For needles, bark and wood of symptomatic shoots, the mean frequencies of detection of S. conigenus using the PCR-based methods were consistent (≥7.5 out of 10) and always greater than for the cultural assay. Detection from symptomatic shoots using the cultural assay was more frequent from needles than from bark or wood. Both the PCR-based method and the cultural assay detected S. conigenus in similar frequencies from asymptomatic shoots, although less frequently than from symptomatic shoots. The efficiency of the PCR-based method and its utility for direct testing of host material should make it particularly useful in areas where multiple shoot blight pathogens are found.     

Association of Sphaeropsis sapinea with insect‐damaged red pine shoots and cones

The association of the shoot blight and canker pathogen Sphaeropsis sapinea with red pine (Pinus resinosa) shoots and cones damaged by insects (especially Dioryctria sp.) was investigated. Samples from a single plantation approximately 35 years old, in Sauk Co., Wisconsin and also from three plantations, between approximately 40 and 50 years old, located in an area of pine shoot moth activity in the preceding year in Adams Co., Wisconsin were visually examined. Samples were arbitrarily collected from trees felled in the first plantation in May. Pycnidia of S. sapinea and insect damage were observed on 56 of 91 (62%) of closed cones and 17 of 165 (7%) of previous year's shoots. In the absence of insect damage, pycnidia of the pathogen were identified only on eight of 91 (9%) closed cones and never on previous year's shoots. In each of the other three plantations, 10 trees were located at intervals along transects in mid‐June; one branch from the lower half of the crown per tree was pruned off, and both current and previous year's shoots were examined. Insect damage and S. sapinea pycnidia were too rare on current year's shoots to draw any conclusions. Insect damage occurred on 20–40% of over 2000 previous year's shoots that were examined, but pycnidia of the pathogen were identified on only about 5%. Although infrequent, S. sapinea was identified in association with insect‐damaged previous year's shoots from these three plantations three times more frequently than those without insect damage. Random amplified polymorphic DNA (RAPD) markers from eight randomly selected isolates were consistent with the A group of S. sapinea, which can be aggressive on red pine. This ability to exploit insect‐damaged shoots may facilitate long‐term persistence of S. sapinea at low disease incidence and severity. The potential role of insect wounds as infection courts and insects as vectors of this important pathogen of pines deserves further study.     

Excised shoots of top-pruned red pine seedlings,a source of inoculum of the Diplodia blight pathogen

Diplodia pinea causes shoot blight and collar rot diseases of pines in forest tree nurseries and sporulates on colonized seedling needles and stems. In late summer 2005, pycnidia of D. pinea were observed on shoots that had been excised by top pruning red pine seedlings earlier that summer during the third season of growth. This observation prompted surveys to determine the incidence and abundance of D. pinea conidia on excised shoots. At each of two nurseries, excised shoots were collected from the seedling canopy and adjacent alleyway soil in two subplots in each of five beds (plots). Excised shoots from both nurseries bore pycnidia with conidia of D. pinea. A water washing and filtration technique was used to quantify D. pinea conidia extracted from these shoots. Excised shoots collected from the seedling canopy yielded more D. pinea conidia than shoots collected from adjacent alleyway soil. Collection and removal of excised shoots resulting from top pruning of pine nursery seedlings should be considered as a means of reducing inoculum in areas where D. pinea is present.     

Site-related influences on cone-borne inoculum and asymptomatic persistence of Diplodia shoot blight fungi on or in mature red pines

The shoot blight and canker pathogens Diplodia pinea and D. scrobiculata sporulate abundantly on cones of many pine hosts. Variation in incidence and abundance of potential inoculum from cones and frequency of asymptomatic persistence on or in shoots was examined for mature red pines in sites differing in dominant presettlement vegetation and soil type in Bayfield and Douglas counties in northern Wisconsin. Collections were made in each county from 6 plantations, 3 each in areas historically vegetated with jack pine and soils mapped as sands and three in areas historically vegetated with red pine with soils mapped as loamy sands. At each site, 5 cones were collected from each of 5 red pines and 10 shoots were collected from up to 5 red pines. Conidia from cones were quantified with a water wash and filtration technique. Diplodia species were cultured from surface-disinfested asymptomatic shoots. A species-specific PCR assay was used to identify the Diplodia species from cones and shoots. Although cones and asymptomatic shoots from each county yielded D. pinea and D. scrobiculata, D. pinea was detected more frequently. More conidia were obtained from cones from Douglas Co., where there is a history of severe shoot blight damage, than cones from Bayfield Co. In Douglas Co., more conidia were obtained from cones from plantations in areas of more sandy soil and presettlement jack pine dominance than cones from plantations in areas of less sandy soil and presettlement red pine dominance. The numbers of conidia and frequencies of cultural detection of Diplodia species from asymptomatic shoots at a site were positively correlated. These results provide evidence for site-related influences on abundance of pathogen inoculum and asymptomatic persistence on or in red pine crowns that may contribute to differences in frequency and severity of damage from Diplodia shoot blight.     

Sphaeropsis shoot blight and altered nutrition in red pine plantations treated with paper mill waste sludge

During 1993 progressive, severe shoot blight and canker disease in crowns of mature, merchantable red pines (Pinus resinosa) in central Wisconsin was noted in plantations in which paper mill waste sludge previously had been applied. For eight treated plantations and six non‐treated plantations, incidence of shoot blight attributed to the pathogenic fungus Sphaeropsis sapinea (syn. Diplodia pinea) was quantified during 1993 or 1994. Foliage and soil samples also were collected for analyses. Sphaeropsis shoot blight was more frequent in treated plantations than in the non‐treated stands (means of 81% of trees and 10.2% of shoots compared with 7% of trees and 0.1% of shoots, respectively). Consistent with other reports of damage caused by some diseases of conifers in situations of altered host nutrition, mean foliar N concentrations were higher in treated plantations (1.61%) than non‐treated plantations (1.31%) (p < 0.001). Mean foliar Zn, Mn, Cu, and Al concentrations were lower in treated plantations than non‐treated plantations, and mean soil P, Ca, and Mg concentrations were higher in treated plantations than non‐treated plantations.     

First report of Sydowia polyspora causing disease on Pinus pinea shoots

The fungus Sydowia polyspora is frequently isolated from conifers worldwide and is considered a pathogen on several hosts. Stone pine (Pinus pinea) is one of the most important forestry species throughout the Mediterranean basin due to the value of the edible pine nut. Stone pines showing tip dieback, needles with tan‐ to yellow‐coloured lesions and shoot death, observed in stands in Portugal, were sampled for analysis. Fungal colonies covered with cream‐coloured spore masses, were consistently obtained. Morphological and phylogenetic analyses of the ITS rDNA region enabled identification of these isolates as S. polyspora. Inoculation tests showed that the fungus caused lesions on excised P. pinea shoots. The symptoms observed might have a negative effect on pine nut production, and thus, evaluation of the impact of this disease is of relevance to future research. This paper is the first to report S. polyspora causing disease on P. pinea.     

Detection of Diplodia pinea in asymptomatic pine shoots and its relation to the Normalized Insolation index

Diplodia pinea (syn. Sphaeropsis sapinea), a common pathogenic fungus, causes considerable damage in Italy, particularly to pine stands in which trees are subjected to environmental stress. The occurrence of D. pinea in symptomless Pinus nigra shoots was investigated and related to the amount of radiation received by the trees growing on a site in a year, expressed as the Normalized Insolation index (NIi). Twenty‐seven pines were selected from nine locations in Trentino (northern Italy). For each pine the incidence of the fungus in apparently healthy shoots was determined by both culturing on an agar medium and application of real‐time PCR. The incidence of D. pinea determined by culturing samples taken from asymptomatic trees was 59% (16 of 27 trees), compared with 85% found using real‐time PCR (23 of 27 trees). Detection of the pathogen in healthy pine tissue was positively correlated (p < 0.05) with the NIi values, using both detection methods.     

Longevity of inoculum production by Diplodia pinea on red pine cones

In summer of 2004, pycnidia of Diplodia pinea were observed on cones of Pinus resinosa that had matured and opened during previous years, but had been retained in canopies of trees at a mature red pine plantation in southern Wisconsin. Surveys during the winter and early summer of three consecutive years (2005–2007) to determine incidence and abundance of D. pinea conidia on cones of different ages in this stand. Cones from each age class consistently bore pycnidia with conidia of D. pinea. Although cones collected in June of the year after their maturation tended to yield more D. pinea conidia than older cones, large numbers of conidia were obtained from cones even 3 years after maturation. Perennial availability of inoculum due to persistence of D. pinea on cones of several ages in the overstory or in adjacent stands should be considered when regenerating red pine in areas where this pathogen is known to be present.     

Sources of Diplodia pinea endophytic infections in Pinus patula and P. radiata seedlings in South Africa

Diplodia pinea, an opportunistic and latent pathogen, can significantly affect Pinus productivity worldwide. Despite being studied in South Africa for almost 100 years, the source of D. pinea inoculum responsible for seedling infection is unknown. The aim of this study was to determine the role of seed in vertical transmission of D. pinea and to investigate sources of inoculum leading to horizontal transmission to pine seedlings. Surface‐disinfected seeds were inoculated with spore and mycelium suspensions of D. pinea to determine its effect on germination. In addition, isolation of the fungus was performed from surface‐disinfected seeds, asymptomatic seedlings collected from nurseries, plantations where pines naturally regenerate and recently established fields, to assess transmission and incidence of endophytic D. pinea infections. Inoculation of seeds with D. pinea spore suspensions affected speed and rate of germination. The fungus was isolated from surface‐disinfected seeds in only a few instances (2–3%) and was not found in healthy seedlings collected from greenhouses and nurseries, suggesting that vertical transmission of the fungus does not occur or is rare. In contrast, D. pinea was isolated from 40% of seedlings obtained from the understory of mature P. patula trees showing that horizontal transmission from mature to young trees sustains the D. pinea inoculum in South African pine plantations.     

Sirococcus shoot blight on Picea spinulosa in Bhutan

During a recent survey of forest tree diseases in Western and Central Bhutan, Sirococcus shoot blight and an associated Sirococcus sp. were found on saplings and mature trees of Eastern Himalayan spruce (Picea spinulosa). Based on morphological characteristics and DNA sequence comparisons of the ITS region of the rDNA operon, representative isolates from Bhutan were unequivocally identified as Sirococcus conigenus. The DNA sequence data also showed that these isolates belong to the P group of S. conigenus. To our best knowledge, this is the first report of Sirococcus shoot blight from the Himalayas or any other part of Asia. Sirococcus conigenus does not appear to cause dramatic damage at the moment, but this fungus has the potential to cause severe disease problems on P. spinulosa in Bhutan.     

Histology of Diplodia pinea in diseased and latently infected Pinus nigra shoots

Diplodia tip blight is a serious disease of >30 conifer species worldwide. Symptoms are particularly severe on non‐native, two‐needled Pinus species, and typically include stunted, necrotic needles and shoots and a general decline of the tree. Latent Diplodia pinea infections occur in current‐year shoots of some symptomless pines, and in some apparently healthy current‐year shoots of diseased pines. Latent infections also occur in symptomless terminal buds. A histological approach was used to investigate the nature of latent infections in shoot stems and terminal buds of landscape Pinus nigra. Fungal colonization was compared in healthy, diseased and latently infected tissues. A nested‐PCR technique that is specific for D. pinea was used to differentiate latently infected tissues from uninfected ones. Latent D. pinea infections were localized in the outer stem cortex, usually in the vicinity of needle scales at leaf axes. In contrast, pathogenic D. pinea infections were characterized by fungal colonization throughout the shoot stem tissues, even very early in symptom development. The presence of necrophylatic periderms in two of the latently infected samples suggests that host defences play a role in the production and maintenance of latent stem infections. Latent infections of terminal buds appeared to originate from the distal bud scales of axillary buds in the terminal bud cluster, and not from the subtending shoot. Fungal tissues were never observed inside asymptomatic, PCR‐negative shoots.     

An effective medium for isolating Sphaeropsis sapinea from asymptomatic pines

The pathogen Sphaeropsis sapinea can persist in stems and branches of asymptomatic pines and can later induce disease when triggered by host stress. Several experiments were conducted to test if:(i) medium amended with tannic acid (TA) can increase the frequency of cultural detection of this shoot blight and canker pathogen from asymptomatic red pine (Pinus resinosa) stems, and (ii) S. sapinea can persist in asymptomatic red pine in the field following artificial inoculation. TA (0.5% w/v) in 2% (w/v) water agar proved to be the best medium for isolation of S. sapinea among a larger number of tested media. The addition of TA had little or no effect on the growth of two group A and two group B isolates of S. sapinea. However, when TA was added, 11 other fast‐growing fungal isolates from stems/branches of red or jack pines (P. banksiana) were inhibited and grew more slowly (p < 0.05) than both S. sapinea groups. The TA‐amended medium improved cultural detection of S. sapinea from 2‐year‐old, asymptomatic red pine nursery seedlings compared with two other methods used for the cultural detection of S. sapinea (32%vs. 8.5% and 18% recovery; p < 0.001 and p = 0.031, respectively). A field test using the TA‐amended media established that S. sapinea can persist asymptomatically in red pine trees for at least 1 year. This medium significantly reduces the frequency of false‐negatives from asymptomatic field material.     

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.     

Red pine harvest debris as a potential source of inoculum of Diplodia shoot blight pathogens

A high incidence of Diplodia shoot blight (site means ranging 85-100%) was observed on recently planted red pine (Pinus resinosa) seedlings where mature red pine stands previously had been clearcut. An investigation of the potential of harvest debris as a source of inoculum of Diplodia pathogens then was conducted. Cones, bark, needles, stems from shoots bearing needles, and stems from shoots not bearing needles (both suspended above the soil and in soil contact) were collected from harvest debris left at sites where clearcutting occurred. Conidia were quantified, and their germination rate was assessed, and Diplodia species were identified using PCR. Conidia of Diplodia species were found at all study sites and conidia counts increased from samples collected from 6 to 18 months after harvest. Germinable conidia were obtained from debris collected 6 months to 5 years after harvest. Fewer conidia were obtained from debris collected at intervals of up to 4-5 years after harvest and the percentage of germinable conidia was lower after longer intervals following harvest. More conidia were obtained and a greater percentage germinated from debris collected above the soil than from debris in soil contact. The host substrate also influenced the number of conidia and the percentage that germinated. Planting red pine seedlings next to debris infested with Diplodia pathogens could provide a persistent source of inoculum. Results should prompt further consideration by land managers and researchers of the potential forest health risks, in addition to benefits, that may be associated with harvest debris.     

Infection of Norway spruce container seedlings by Gremmeniella abietina

First‐ and second‐year containerized Norway spruce seedlings were inoculated with conidia of type A (large tree type) and type B (small tree type) of Gremmeniella abietina var. abietina at different times during the summer. The appearance of symptoms after artificial inoculation and natural infection on spruce seedlings were recorded the following spring and compared with the disease symptoms on Scots pine seedlings. The proportion of diseased seedlings after inoculation reached as high as 80%. The susceptible period during the summer began later on the first‐year seedlings than on the second‐year seedlings, and was similar for the pine seedlings. Susceptibility of first‐year seedlings was highest in August and on second‐year seedlings in July. The accumulated temperature sum, relative humidity and height growth for first‐ and second‐year seedlings was assessed. Natural infection in 2002 caused more disease on pine than on spruce seedlings. Experimental thinning of seedlings had no effect on disease incidence. In a preliminary comparison between the ability of A and B types to cause disease in Norway spruce seedlings, type B caused more damage than type A after inoculation. However, type A caused a high disease frequency in other experiments in this study. Symptoms on Norway spruce seedlings often first occurred in the mid‐section of the shoot, and were similar to those observed on pine seedlings: needles turned brown, starting at the needle base, in the spring following inoculation. On first‐year spruce, diseased needles were shed rapidly, in contrast to a slower rate of shedding on first‐year pine seedlings. Pycnidia developed about 2 years after inoculation (on pine 1 year after inoculation). On Norway spruce seedlings the lower part of the shoot, including the lateral shoots, often remained alive. The experiments show that G. abietina can cause disease on containerized Norway spruce seedlings under nursery conditions in Finland. The coincidence of spore dispersal, seedling susceptibility and predisposing factors are important in disease development.     

Surveys for asymptomatic persistence of Sphaeropsis sapinea on or in stems of red pine seedlings from seven Great Lakes region nurseries

The fungus Sphaeropsis sapinea persists on or in stems of asymptomatic red pine (Pinus resinosa) nursery seedlings, and proliferates to cause collar rot and mortality after planting. In the spring of 2002, seven nurseries were surveyed to determine the potential range in frequency of asymptomatic persistence: three operated by Wisconsin Department of Natural Resources (DNR), two by Minnesota DNR, one by Michigan DNR, and one by USDA Forest Service (in Michigan). At each nursery five groups of 20 asymptomatic red pine seedlings were collected near an inoculum source (red pine windbreak), if present, and five groups of 20 asymptomatic seedlings were collected away from such a source (1400 seedlings total). A segment of the lower stem/root collar from each seedling was surface disinfested and incubated on tannic acid agar. Transfers were made from resulting colonies and the pathogen identified from pycnidia and conidia produced in culture. The pathogen was identified from asymptomatic seedlings collected in all Wisconsin and Minnesota nurseries, but was never detected from seedlings from the Michigan DNR or USDA Forest Service nurseries. Frequencies of detection were greater (as high as 88%) from asymptomatic seedlings near red pine windbreaks including diseased trees than from seedlings distant from such windbreaks. A subset of isolates from asymptomatic seedlings was characterized using inter‐simple sequence repeat–polymerase chain reaction analysis. Most isolates were the A group of S. sapinea, but B group isolates (recently named Diplodia scrobiculata) were also obtained from one nursery. One Minnesota nursery was more extensively sampled in 2003, with 17–44 groups of five asymptomatic red pine seedlings collected in four separate fields (525 seedlings total). The mean frequency of detection of the pathogen in these four fields ranged from 40 to 71%. Persistence of S. sapinea on or in asymptomatic seedlings continues to be problematic, not only because of the potential for subsequent seedling mortality, but also as a means by which a pathogen may be widely distributed.     

Seedling shoot,needle and bud development in three provenances of Pinus sylvestris and Pinus contorta cultivated in northern Sweden

The patterns of current‐year shoot, needle and terminal bud elongation in seedlings of three Scots pine (Pinus sylvestris L.) and three lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) provenances were compared during the third and fourth growing seasons after planting. Lodgepole pine produced longer shoots and buds than did Scots pine, mainly because lodgepole pine formed more stem units and elongated at a faster rate. Stem unit length and the duration of shoot and bud elongation differed relatively little between species and provenances. Lammas or polycyclic growth occurred in some lodgepole pine provenances, but not in any Scots pine provenance, and was associated with enhanced shoot elongation. Needle elongation commenced earlier, proceeded at a faster rate, and was greater in lodgepole pine than in Scots pine, but ceased about the same time in all species and provenances. The heat sum required to attain 50% of final length was lower for shoots and needles in lodgepole pine than in Scots pine, and for shoots in northern provenances than in southern ones. Mitotic activity in the apical meristem of the terminal bud, which occurred less than one week after the seedlings were free from snow, started and ceased about the same time in each species, but was higher in lodgepole pine than in Scots pine early in the shoot elongation period.     

Phylogeographic variation among isolates of the Sirococcus conigenus P group

In this study the phylogeographic variation among isolates of the Sirococcus conigenus P group and the phylogenetic relationships of S. conigenus with Sirococcus clavigignenti‐juglandacearum and other species previously placed in the genus Sirococcus were investigated. A collection of 33 isolates originating from Picea, Pinus and Larix in Europe, North America and Bhutan were characterized by sequence analyses of the internal transcribed spacer (ITS) region (including ITS1, 5.8S ribosomal DNA, ITS2) of the nuclear rDNA and a portion of the β‐tubulin gene. In phylogenetic analyses most isolates from pine, spruce and larch formed a distinct clade, representing the P group of S. conigenus, which was separated from the T group of this pathogen. Four isolates from Picea in Europe and Canada formed a third clade within S. conigenus and these isolates are referred to as the S group. The P group consisted of five distinct ITS haplotypes, which partly differed in their optimum growth temperature and their growth rates at 25°C on malt extract agar. Nested clade analysis resolved the five haplotypes into three distinct clades and revealed significant genetic/geographic associations for some of the haplotypes. Parsimony analysis of the small subunit (18S) ribosomal DNA sequences confirmed the phylogenetic affinities between S. conigenus and S. clavigignenti‐juglandacearum. In contrast, Godronia cassandrae and Hormococcus conorum, which formerly had been placed in the genus Sirococcus, were found to be only distantly related to S. conigenus and S. clavigignenti‐juglandacearum.