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.     

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.     

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.     

Development of fruiting bodies of large tree type of Gremmeniella abietina var. abietina and timing of infection on Scots pine inn northern Finland

The formation and maturing of the large tree type Gremmeniella abietina var. abietina fruiting bodies and their sporulation were investigated for 3 years on Scots pine (Pinus sylvestris) in northern Finland. This was done by monthly assessment of shoots in the field and in the laboratory. Infection caused by G. abietina var. abietina was dated on Scots pine by monthly covering with pollination bags and exposing branches during the growing season. Pycnidia appeared between August and September, 1 year after infection, and they started to release conidia between late June and early July, 2 years after infection. Fresh pycnidia and microconidia were formed during the following August and September in the infected shoots. The causal large tree type of G. abietina var. abietina did not produce apothecia on branches within 3 years of infection. Monthly covering and exposing branches showed that infection took place mainly between June and July.     

The effect of late season damage on the apical bud development of Scots pine seedlings

The effect of Lygus rugulipennis Popp. feeding and artificial damage on the apical bud of Scots pine (Pinus sylvestris L.) late in the growing season was studied on two-year-old seedlings. Lygus feeding in late July and August caused inhibition of bud formation in the subsequent year's shoots, which led to loss of apical dominance and formation of interfascicular buds. Mechanical damage caused by piercing the apical bud with a needle in July, August and October produced scars and malformations on subsequent year's shoots and buds, but did not inhibit bud formation. Damage to the apical meristem could not be detected visually on the dormant bud before shoot elongation.     

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.     

Risk from Sirococcus conigenus to understory red pine seedlings in northern Wisconsin

Interest in development of multicohort stands of red pine (Pinus resinosa) in the Great Lakes region of North America prompted an investigation of the potential impact of the shoot blight pathogen Sirococcus conigenus (syn. S. strobilinus) on understory red pine seedlings. In May 2002 and 2003 healthy, 1‐year‐old red pine seedlings were planted in the understory of a maturing red pine plantation in northern Wisconsin in an area with a history of presence of this pathogen. Occurrence of shoot blight symptoms was recorded periodically during the summer, and in each year seedlings were harvested in fall and examined for signs of shoot blight pathogens. By fall 2002 and 2003, respectively, shoot blight incidence was 89% and 98% and most seedlings were dying. Pycnidia with conidia of S. conigenus were present on almost all of the symptomatic seedlings. The conifer shoot blight and canker pathogen Diplodia pinea (syn. Sphaeropsis sapinea) was also detected, though less frequently. Pycnidia of S. conigenus tended to be found more frequently on symptomatic current year's shoots than symptomatic previous year's shoots; the opposite was true for pycnidia of D. pinea. Risk from S. conigenus to understory red pine seedlings should be considered in any plans for development of multicohort red pine stands in areas where the pathogen is present.     

Infection experiments with Gremmeniella abietina on seedlings of Norway spruce and Scots pine

Conidia of Gremmeniella abietina infected and caused disease symptoms in annual shoots of both Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings. In Norway spruce shoots the infection remained largely latent, with only a few seedlings showing symptoms. Mycelial growth inside the shoots was faster in Scots pine than in Norway spruce and was favoured by low temperature in both hosts. The shoots of Norway spruce seedlings had higher endophyte populations than those of Scots pine, and the populations were decreased by low temperatures. Reductions in the normal epiphytic or endophytic flora by acid mist treatments seemed to favour the development of G. abietina.     

Morphological and Ecological Variation of Gremmeniella abietina var. abietina in Pinus sylvestris,Pinus contorta and Picea abies Sapling Stands in Northern Finland and the Kola Peninsula

The morphological and ecological variation of two types of Gremmeniella abietina var. abietina causing scleroderris canker on conifers was investigated in Pinus spp. and Picea sp. sapling stands in northern Finland and the Kola Peninsula. Small - tree type (STT or B type) of G. abietina was detected alone in 13 Scots pine, three lodgepole pine and two Norway spruce sapling stands out of 26 stands investigated, both STT and large - tree type (LTT or A type) were observed in six Scots pine stands, and LTT was detected alone in two Scots pine stands. For the first time, G. abietina was found to injure Norway spruce saplings in a respective plantation in northern Fennoscandia. STT isolates produced statistically significantly more conidia in vitro than LTT isolates. Morphological variation in conidia septation revealed that STT produced conidia with more than five septa more frequently than did LTT. There was a greater range in variation in septation in STT than in LTT, with overlapping between the types. Isolates of both types were equally associated with cankers, coloured wood, pycnidia or apothecia in the infected saplings.     

Boron retranslocation in Scots pine and Norway spruce

We previously traced 10B-enriched boric acid from shoots to roots to demonstrate the translocation of boron (B) in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings. To gain a more detailed understanding of B translocation, we sought: (1) to demonstrate B retranslocation directly, by showing that foliar-applied 10B is located in the new growth after dormancy; and (2) to assess whether shoot-applied B affects growth in the long term. We applied 10B-enriched boric acid to needles of Scots pine and Norway spruce seedlings. After a dormancy period and 9 weeks of growth, small but significant increases in the 10B isotope were found in the new stem and needles of both species. In Scots pine, the total B concentration of the new stem was also increased. Both species contained polyols, particularly pinitol and inositol. Boron-polyol complexes may provide a mechanism for mobilizing B in these species. To determine the long-term effects of applied B, seedlings were grown for two growing seasons after the application of 10B to shoots. In Norway spruce, the proportion of 10B in the root systems and current needles of the harvest year was slightly higher than in the controls, and in Scots pine root systems, marginally so. The B treatment had no effect on growth of Norway spruce seedlings. In Scots pine seedlings, the B treatment caused a 33% increase in total dry mass and significantly increased the number of side branches.     

Patterns of Stem Damage by Moose (Alces alces) in Young Pinus sylvestris Stands in Sweden

The incidence of recent moose browsing of the main stem on young Scots pine (Pinus sylvestris L.) trees, and correlations with tree or stand characteristics, were examined using data from a large-scale survey in Sweden. On average, 10% of all Scots pine main stems showed one or more types of recent damage, with browsing of the apical leader accounting for about 75% of all damage recorded. Stripping of bark off the main stem occurred most frequently in the southern area, where site productivity is highest. Apical leader browsing was negatively correlated with height of the main stems, length of the apical leader and incidence of pre-commercial thinning, whereas bark stripping and stem breaking were positively correlated with the same variables. All types of recent stem damage correlated positively with the extent of previous stem damage and also with the extent of recent browsing of lateral shoots.     

Interference of bracken (Pteridium aquilinum L. Kuhn) with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) seedling establishment

The nature of interference of bracken with Scots pine and Norway spruce seedling establishment was considered in three field experiments. In a seeding experiment, it was found that Scots pine germination was highest on exposed mineral soil and lowest when intact bracken litter and humus were present, suggesting adverse effects of litter and humus on pine regeneration probably due to phytotoxicity. In a second experiment, smothering by bracken caused high mortality of Scots pine seedlings while Norway spruce seedlings were relatively unaffected. Mortality for both Scots pine and Norway spruce seedlings was low when planted in a adjacent Scots pine-bilberry stand with no bracken. Annual shoot growth of Norway spruce was higher in bracken than in Scots pine-bilberry vegetation while no differences in shoot growth between these two vegetation types occurred for Scots pine. In a third experiment, activated carbon was added to the ground under Norway spruce seedlings planted in bracken to adsorb possible phytotoxic compounds released by bracken. The addition of carbon had no effect on seedling mortality or growth rate, indicating that the seedlings were not susceptible to allelochemicals released by bracken. Since large Norway spruce seedlings were relatively unaffected by bracken interference in this study, artificial regeneration with containerized Norway spruce seedlings is suggested to achieve an acceptable conifer tree establishment on clear-cuts invaded by bracken.     

Assessment of seedling storability of Quercus robur and Pinus sylvestris

Pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.) seedlings were lifted on several occasions during autumn 1997 to determine the relationships between storability and frost hardiness. On each lifting date their physiological status was determined by assessment of shoot and root electrolyte leakage and frost hardiness, assessed as freeze-induced electrolyte leakage. Additional seedlings were simultaneously cold-stored for field planting and assessment of preplanting root growth potential in April 1998. First year field performance was determined the following winter. Storability and cold acclimation patterns differed between the two species. Both were negatively affected by early lifting, but oak was less sensitive with respect to survival, and pine attained tolerance to cold storage more rapidly and earlier with respect to growth increment. The correlations between shoot frost hardiness and performance suggest that freeze-induced shoot electrolyte leakage (SEL_diff?20) below a threshold of 5% is a good storability predictor for Scots pine in Denmark. A completely reliable criterion for pedunculate oak could not be established.     

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.     

Damage by pine weevil Hylobius abietis to conifer seedlings after shelterwood removal

Abstract

Pine weevil (Hylobius abietis L.) damage to seedlings after overstorey removal was investigated in a survey study in six shelterwoods in the south–central part of Sweden. The shelterwoods predominantly consisted of Scots pine, except at one site where the shelter trees mainly consisted of Norway spruce. Before final cutting, 10 plots were laid out at each site and measurements of shelter trees and marked seedlings were taken. The seedlings were examined during the 2 years after final cutting. The study showed that removal of shelter trees increases the risk of severe damage by pine weevil and the variable that was most strongly correlated with the risk was the seedling root collar diameter. Both Scots pine and Norway spruce seedlings were severely damaged by pine weevil, and most of the feeding occurred during the first year after cutting. The amount of debarked area was significantly larger for Scots pine than for Norway spruce seedlings. Vitality (growth of the leading shoot before final cutting) of the seedlings also affected the probability of damage. Seedlings with high vitality were less damaged by pine weevil than seedlings with low vitality. For Scots pine the shelterwood density before final cutting was correlated to the intensity of pine weevil feeding after cutting. In conclusion, after the final cutting of a pine or spruce shelterwood, pine weevils will probably invade the area. To avoid serious damage, Norway spruce and Scots pine seedlings should have reached a diameter of at least 10–12 mm.     

Effects of nickel and copper on growth and mycorrhiza of Scots pine seedlings inoculated with Gremmeniella abietina

Scots pine (Pinus sylvestris) seedlings were planted in soil originating from two localities with different background levels of nickel and copper. In addition, some of the seedlings were exposed to additional nickel (20.5 mg Ni/l of soil) or copper (63.5 mg Cu/l of soil), or a combination of both Ni and Cu, via soil without direct shoot exposure during their second growing period. The seedlings were either irrigated with spring water (pH 6) or got only natural rain during the whole field experiment. All seedlings were inoculated with conidia of a shoot‐pathogen Gremmeniella abietina during their third growing season, and harvested the following spring. Lengths of shoots of different year‐classes were used as growth estimates. In roots, the proportion of fungal (assumedly mycorrhizal) biomass was estimated by measuring ergosterol concentration. Guajacol peroxidase activity was measured. Short roots were classified into two groups according to their condition and the composition of the mycorrhizal community was expressed as a proportion of morphotypes in the roots. The seedlings exposed to additional Ni had higher shoot growth than the seedlings in the other treatments. The mean Ni concentration in the roots of seedlings exposed to additional Ni was 79 p.p.m. and in other seedlings 16 p.p.m. Additional Ni also decreased the frequency of clearly senescent short roots and the proportion of the mycorrhizal morphotype with the thinnest mantle. These results indicate that the Ni exposure levels used in this experiment had some positive effects on the seedlings. The relative fungal biomass was about 6% lower (p = 0.0981) in the fine roots of seedlings treated with additional Cu. The mean Cu concentration in the roots of seedlings exposed to additional Cu was 256 p.p.m. and in other seedlings 29 p.p.m. Peroxidase activity, which was used as a general stress indicator in this study, was not affected by any of the treatments. The shoot growth and the relative biomass of fungi in the fine roots were positively correlated in all seedlings, and this correlation was stronger in seedlings exposed to additional Ni that were not irrigated compared with seedlings not exposed to additional Ni that were irrigated. The frequency of asymptomatic infections of G. abietina was positively correlated with the proportion of senescent short roots in the irrigated seedlings but not in not‐irrigated seedlings. The general condition of seedlings may be an important factor for infection by G. abietina when moisture is high enough for the fungi to infect seedlings by conidia.     

Effect of uninucleate Rhizoctonia on Scots pine and Norway spruce seedlings

One‐year‐old container‐grown seedlings were planted in spring on clear cut areas: the Norway spruce (Picea abies) on a moist upland site (Myrtillus‐type) and Scots pine (Pinus sylvestris) on a dryish upland site (Vaccinium‐type). While still in the nursery, half of the seedlings of each species had been inoculated during the previous summer, with a uninucleate Rhizoctonia sp., a root dieback fungus. At outplanting all the seedlings appeared healthy and had a normal apical bud, although the height of the inoculated seedlings was less than that of the uninoculated control seedlings. At the end of the first growing season after planting, the mortality of inoculated Scots pine and Norway spruce seedlings was 25 and 69%, respectively. After two growing seasons the mortality of inoculated seedlings had increased to 38% for Scots pine and 93% for Norway spruce. The mortality of control seedlings after two growing seasons in the forest was 2% for Scots pine and 13% for Norway spruce. After outplanting the annual growth of inoculated seedlings was poor compared with the growth of control seedlings. These results show that, although Rhizoctonia‐affected seedlings are alive and green in the nursery, the disease subsequently affects both their survival and growth in the forest.     

Responses of conifer species of the Great Lakes region of North America to inoculation with the pitch canker pathogen Fusarium circinatum

Five conifer species grown in the Great Lakes region of North America were examined for their susceptibility to Fusarium circinatum, (syns. Fusarium subglutinans f. sp. pini and F. moniliforme var. subglutinans), the causal agent of pitch canker. Three‐year‐old (3‐0) seedlings of red (Pinus resinosa), jack (P. banksiana) eastern white (P. strobus), Scots (P. sylvestris) and Austrian (P. nigra) pine were planted in 4 l pots in a greenhouse at Auburn University in November 1998. In April and June 1999, seedlings were inoculated by removing a needle fascicle approximately 5 cm from the terminal bud and placing a drop containing F. circinatum conidia on the wound. Resin production, canker length and seedling mortality were recorded 12 weeks later. Jack, Scots and eastern white pine were the most susceptible with Austrian and red pine more resistant to the fungus. F. circinatum was re‐isolated from 37% to 96% of inoculated seedlings. The susceptibility of jack, Scots and eastern white pine indicates a potential risk to these important species of the region if F. circinatum were to be introduced into the area.     

Studies on anastomosis groups of Rhizoctonia solani isolates causing disease in two forest nurseries in Poland

Thirty‐eight isolates of Rhizoctonia spp. were isolated from Scots pine (Pinus sylvestris) seedlings with damping‐off symptoms, originating from two forest nurseries in central‐west Poland (Wronczyn and Jarocin) and from diseased seedlings grown in soil from Wronczyn nursery. Majority of these isolates (79%) had multinucleate cells and were identified as Rhizoctonia solani. The remaining isolates were recognized as binucleate Rhizoctonia spp. R. solani isolates were characterized using hyphal anastomosis and were divided into five anastomosis groups (AG). The most prevalent was AG5 (37% of isolates), followed by AG2‐1 (30%) and 27% of the isolates were identified as AG4. Groups AG1‐IB and AG2‐2 were only represented by single isolates. The virulence recorded as mortality (in percentage) was comparatively high for binucleate and multinucleate isolates of Rhizoctonia spp. Sequence analysis of the polymerase chain reaction (PCR)‐amplified internal transcribed spacer (ITS) rDNA region was used for phylogenetic analysis. The dendrogram showed that isolates were distinctly separated based on their AG types and there was no relationship between pathogenicity on Scots pine seedlings and the AG to which the isolates belong to. The results are discussed with respect to pathogenic potential of the various AG groups.     

Growth and visible responses of Scots pine (Pinus sylvestris L.) seedlings to simulated summer frost

Scots pine seedlings, 20–30 days old, were exposed to simulated summer frost in controlled environment growth chambers. The responses observed showed extreme variation between individual seedlings; seedlings suffering from needle-necrosis, healthy-looking, and dead seedlings were found in the same treatment. Four days exposure to temperatures below –4.5°C caused multiple-leaders maximally in 7.7 % of the pine seedlings and resulted in decreased shoot and root dry weight and shoot length.