Susceptibility of different provenances of Pinus sylvestris,Pinus Contorta and Picea abies to Gremmeniella abietina

In a randomized block factorial experiment, 1200 seedlings from four provenances, each of Pinus sylvestris, Pinus contorta and Picea abies were inoculated with conidia (2 × 10⁴ and 1 × 10⁶ conidia/seedling) of Gremmeniella abietina (Brunchorstia pinea), isolated from P. contorta plantations in northern Sweden. A further 600 seedlings were left as controls. The occurrence of symptoms and the extension of dead tissues on the annual shoots were recorded 13 months after inoculation. Only the higher spore dose resulted in significant infection. P. sylvestris and P. contorta seedlings were equally susceptible (53% infected), and significantly more infected than P. abies seedlings (39%). The annual shoots of P. sylvestris and P. abies were affected to 43% and 37% of their length, which was significantly more than 15% of the length of P. Contorta shoots. The frequency of affected seedlings differed between the most southern and northern provenances of P. sylvestris and P. abies, and between the northwestern and the south-eastern provenance of P. contorta Twenty-six months after inoculation, a higher proportion of P. contorta seedlings than P. sylvestris and P. abies seedlings had recovered, and a lower proportion of P. contorta than P. sylvestris and P. abies seedlings had died. This paper discusses why P. sylvestris was found to be more susceptible to G. abietina than P. contorta in this experiment, while the reverse is found in plantations in northern Sweden.     

Survival and vitality of Gremmeniella abietina on Pinus sylvestris slash in northern Sweden

Survival and vitality of Gremmeniella abietina on Pinus sylvestris slash was studied in northern Sweden during 2003 and 2004. Once a month between September 2003 and April 2004, two to three trees were cut down and debranched. Shoots with pycnidia were sampled at the felling date and then at every consecutive month. The percentage of germinated conidia from each shoot was calculated after 24, 48 and 72 h incubation. The vitality of G. abietina pycnidia in the slash remained high the whole period. Intact pycnidia were found on slash several months after the time of conidial sporulation, which indicates that new pycnidia may be produced on dead pine branches. Sampling of shoots from slash on 13‐ to 18‐month‐old clear‐cuts showed conidial germination capacity as high as in pycnidia collected in fresh slash. Due to survival of G. abietina in slash it is recommended to postpone planting of P. sylvestris seedlings in northern boreal areas to the third vegetation period after sanitary clear‐cuts.     

RAPD variation in Gremmeniella abietina attacking Pinus sylvestris and Pinus contorta in northern Sweden

Genomic DNA from 81 isolates of Gremmeniella abietina collected from eleven plantations each of Pinus sylvestris and Pinus contorta in northern Sweden was studied using RAPD markers. The DNA variation between and within populations and the race and type distribution of G. abietina populations, causing symptoms similar to those of the North American race, were studied. The degree of genetic similarity was greater among G. abietina isolates from the same geographical areas than among isolates from different geographical areas, regardless of whether they were isolated from P. sylvestris or P. contorta. RAPD variation was greatest in the central parts of northern Sweden, suggesting that sexual reproduction has been somewhat more important there than further north or south. Only the RAPD fragments characteristic of the EU race of G. abietina were found in the material tested. The RAPD pattern described as characteristic of the northern type within the EU race was identified in 62% of the isolates. Divergence from the expected profile was due to differences in occurrence of fragments OPA12-1400 and 12-1500. This indicates that this part of the RAPD profile cannot be treated as diagnostic for the northern type. A conclusion of practical importance is that there is a considerable risk of G. abietina spreading from infected P. contorta plantations to adjacent areas with indigenous P. sylvestris regeneration, and vice versa, owing to the indicated lack of host-specificity of the pathogen. It is possible, however, that host-specific strains exist, but do not differ in their RAPD profiles.     

Effect of slash removal on Gremmeniella abietina incidence on Pinus sylvestris after clear-cutting in northern Sweden

The Gremmeniella abietina outbreak in Sweden in 2001-2003 forced forest owners to sanitary clear-cut large areas of middle-aged Pinus sylvestris stands. There is, however, little knowledge of effective reforestation of P. sylvestris on G. abietina-infected sites. Gremmeniella abietina disease incidence on P. sylvestris seedlings planted in 2003 was studied with and without (control) removal of infected P. sylvestris slash. Removed slash was piled in stacks around the regeneration plots. The seedlings were planted within 1 year after sanitation felling on three sites in northern Sweden. One year after planting, G. abietina pycnidia were found on 32% of the control seedlings and total infection, including stem cankers, reached 44%. Total and G. abietina-induced mortality was 15 and 10%, respectively. The method of removing and piling the infected slash reduced the number of infected seedlings by 50% and seedling mortality by 27% 1 year after planting, compared with control. Consequently, even if there is a clear sanitation effect of removing infected slash to the sides of the regeneration area, it does not eradicate the infection source from the stands. Postponed planting, slash burning or complete removal of the infected slash is needed to minimize the infection risk. The positive correlation found between slash coverage and infection rate indicates that clear-cuts with large amounts of infected slash should be given priority for slash treatment.     

The ability of Gremmeniella abietina to hydrolyze polygalacturonic acid

Gremmeniella abietina grew well in media with pectin as the sole carbon source. The fungus secreted at least one enzyme with polygalacturonase activity, and this was induced by addition of pectin to the culture medium.     

Resistance of Pinus contorta to the European race of Gremmeniella abietina

Pinus contorta seedlings, together with Pinus resinosa and Pinus banksiana seedlings, were planted adjacent to 25‐year‐old red pine trees infected by the European (EU) race of Gremmeniella abietina. Resistance to this race was assessed over 5 years. All P. resinosa seedlings were dead after that period while 65% of P. contorta and 86% of P. banksiana seedlings appeared resistant to the disease. The tip blight that occurred on P. contorta was slightly longer than that observed on P. banksiana. In microscopy, one, two, or even more suberized boundaries were seen to be initiated near the surface of the shoot at the base of healthy needles where they extended downward in the direction of the vascular cambium. Suberized boundaries occasionally crossed the xylem and joined together in the pith region to form continuous barriers around necrotic tissues. However, in most cases, these suberized barriers were not continuous across the shoot and compartmentalization was then completed by other barriers mainly constituted of parenchyma cells and xylem tracheids that accumulated phenolic compounds. Meristematic‐like cells were observed adjacent to the necrophylactic periderm. Tissue regeneration, restoration of cambial activities and formation of traumatic resin canals also seemed to be associated with the defence system of P. contorta against the EU race of G. abietina.     

Comparison of Gremmeniella abietina isolates from Pinus sylvestris and Pinus contorta in terms of conidial morphology and host colonization

Gremmeniella abietina isolates from Pinus contorta in northern Sweden produced, in vitro, shorter conidia with fewer septa compared with isolates from Pinus sylvestris in the southern part of the country. After mycelial inoculation of shoots with G. abietina isolates from both host species, the resulting necroses were longer in P. sylvestris than in P. contorta. Keeping seedlings in artificial mild winter climate or detaching shoots from the seedling before inoculation caused longer necroses. No host specificity in colonization was found. Isolates from P. sylvestris caused longer necroses than did isolates from P. contorta, and both types of isolates caused longer necroses in P. sylvestris than in P. contorta. The differences found between the two G. abietina populations probably reflect regional variation in the fungus.     

Incidence of Gremmeniella abietina in planted seedlings of Picea abies and Pinus sylvestris in northern Finland

The ascomycete Gremmeniella abietina causes a disease (scleroderris canker) on conifers. The pathogen kills terminal shoots and branches of Pinus sylvestris and Picea abies, sporulates on host shoots and causes leader changes (i.e. dieback). Damage caused by G. abietina was investigated in young P. abies and P. sylvestris plantations in northern Finland. Side branches from seedlings of both species and the main stems of P. sylvestris were collected from three sites in two locations (Poksa 1 and 2, Kivalo) in northern Finland. The number of cankers and leader changes was counted in branches of each age (i.e. year) in a total of ca. 6300 shoots of P. abies and 1200 shoots of P. sylvestris. Cankers were common on both P. abies and P. sylvestris in Poksa 1 (2002–2008) and on P. abies in Poksa 2 (1998–2001). In Kivalo, cankers occurred only sporadically on P. sylvestris. Leader changes were most frequent in 1999–2009 in Poksa 1, in 2001–2009 in Poksa 2 and in 2003 in Kivalo. Cankers and other symptoms of infection were more obscure on P. abies than on P. sylvestris. According to both conidial morphology and molecular analysis, the strain of G. abietina infecting both P. abies and P. sylvestris was small‐tree type (STT). This is the first report of G. abietina, STT or B type, injuring P. abies in plantations.     

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.     

Formation and growth of stem cankers caused by Gremmeniella abietina on young Pinus contorta

From 1990 to 1995, the formation and growth of stem cankers caused by Gremmeniella abietina on Pinus contorta var. latifolia was studied in three stands in northern Sweden. The stands were planted in 1976–80. The total number of cankers on 756 trees that were individually followed increased from 233 to 477 during the 5‐year period. With 42.0% of the cankers, the pathogen entered through or from the base of diseased branches, and 33.6% through visually undamaged bark. Most of the cankers were within 100 cm of the ground. In one of the three areas, the cankers were evenly distributed within 180 cm of the ground. The frequency of cankers facing north exceeded those facing south. The average vertical length of cankers had increased, 55.6% of cankers had increased their percentage coverage of the stem girth; 13.8% had fully girdled the stem. At two of the sites, there was a negative correlation between canker coverage of the stem circumference and tree height increment.     

Susceptibility of four conifer species to Gremmeniella abietina

G. abietina causes severe dieback in pole-stage stands of Scots pine in Britain. The susceptibility of ll provenances of Scots pine and of three other conifer species was tested by inoculations. Significant differences in susceptibility were found amongst Scots pine provenances, with those originating from a native Scottish pinewood at Loch Maree showing the highest levels of disease. Corsican pine was shown to be the most susceptible species tested although sporulation was greatest on Scots pine. Norway spruce was also shown to be susceptible when inoculated late in the growing season. Infection in lodgepole pine was negligible. High levels of β-phellandrene were tentatively linked with resistance among trees in a single stand of Scots pine.     

Differential reaction in Pinus spp. to inoculation by various isolates of Ascocalyx (Gremmeniella) abietina

Stem inoculations of 3 species of pole-size pines with 4 diverse isolates of Ascocalyx (Gremmeniella) abietina revealed Pinus pinea to be more susceptible than either P. pinaster or P. nigra in terms of canker length. Isolate type and geographical aspects considered more briefly, also have some effect.     

Susceptibility of Six Scots Pine Clones to the Pathogenic Fungus Gremmeniella abietina

Genotypic variation in susceptibility to Gremmeniella abietina, an economically important fungal pathogen of conifers, was studied by artificially inoculating 23 - yr - old grafted plants of six Scots pine (Pinus sylvestris L.) clones in a seed orchard. Two fungal isolates were used. The mycelium was inserted into the current year shoots in late winter and the length of the necrotic lesion caused by the fungus was measured the next spring. The growth and male flower production of the experimental shoots were also measured. The development of symptoms did not vary among the clones, but the location of the grafts within the orchard statistically significantly affected the length of necrosis. The clones differed significantly in regard to height and the production of male and female flowers. Differences in flowering intensity among the clones were not connected with the development of G. abietina. At the level of the single shoot, the production of male flowers correlated positively with the length of necrosis. The length of necrosis correlated negatively with the length of current and previous year shoots. The ability of the two fungal isolates to cause necrosis differed significantly.     

Capability of the European and North American race of Gremmeniella abietina to hydrolyse polygalacturonic acid in vitro

Polygalacturonase was found to be one of the first enzymes secreted by a pathogen during infection. The polygalacturonic-acid hydrolysing activity was compared between the North American and the European race of Gremmeniella abietina in vitro. Isolates were grown in pure pectin media from which the enzyme activity was analysed. Altogether, 29 isolates were tested in five experiments (experimental runs in a growing chamber). The data were analysed using variance-component models that included fixed-race effects and random-experiment, isolate, flask and measurement effects. The European race secreted more polygalacturonic-acid hydrolysing enzyme than the North American race and the mycelial dry weight produced was smaller for the European race. The differences between races were of the same order of magnitude as the variation between isolates within races; variance components relating to experimental errors were quite large. No correlation was found between the activity and mycelial dry-matter production within the races. Logarithmic transformation removed the apparent racial differences in the variability of the activity and mycelial dry weight. Results from the additionally tested A- and B-type of Finnish isolates indicated differences in dry-matter production.     

Effect of temperature on the ability of Gremmeniella abietina to survive and to colonize host tissue

Gremmeniella abietina was able to survive in vitro for four weeks at average temperatures less than 30° C. At higher temperatures, survival time was inversely proportional to temperature. The fungus survived for 23–28 months inside asymptomatic trees. Freezing, or freezing and thawing, of inoculated trees, may have promoted symptom development.     

Susceptibility of six pine species to Gremmeniella abietina isolates from Spain

Inoculation experiments were performed in order to evaluate the virulence of Gremmeniella abietina isolates from Spain on the main pine species planted in the Iberian Peninsula, as well as the influence of seedling age on this virulence. Two different experiments were carried out with four isolates of G. abietina from Spain. The greenhouse experiments consisted of seedling inoculations. One‐ and 2‐year‐old seedlings of the following five pine species were used: Pinus halepensis, Pinus pinea, Pinus pinaster, Pinus sylvestris and Pinus uncinata; also, 1‐year‐old seedlings of P. nigra were inoculated. The relative necrosis length (RNL) caused by the pathogen after 130 days was used as a response variable. The laboratory experiments were performed on 2‐ to 6‐year‐old internodes of the above pine species excluding P. uncinata. The necrosis length after 6 weeks of incubation was measured. The results have shown that all G. abietina isolates were pathogens on seedlings of these six pine species and seedlings of P. halepensis were consistently the most susceptible ones, although it is important to take into account that all the isolates used in the present work were isolated from P. halepensis, the only pine species in Spain where G. abietina has been recovered up to now. The susceptibility of the other pine species depended on the age of the seedlings.     

Effects of sulphuric acid and heavy-metal deposition on frequency of asymptomatic infections of Gremmeniella abietina in Scots-pine seedlings

The isolation frequency of Gremmeniella abietina was measured from asymptomatic 4-year-old Scots-pine seedlings. The seedlings had been subjected to simulated sulphuric deposition (pH 3.1 or 4.1) or control treatments (irrigation with spring water (pH 6), or no irrigation) during the three previous growing seasons. The seedlings were planted in soil originating from two localities with different backround levels of copper (Cu) and nickel (Ni), and the soil was further amended with Cu (63.3 mg/1 of soil) and Ni (20.5 mg/1 of soil), or a combination of the two. The seedlings were inoculated with conidia of G. abietina during their third growing season in the field. Asymptomatic infections of G. abietina were recovered frequently from seedlings that had received water irrigation. The addition of sulphuric acid to the irrigation water, and/or the lowered pH (pH 3.1 and 4.1) resulting from this addition, mitigated the effect of water application. The effect of Ni-treatment on the recovery of G. abietina depended on the irrigation treatment; with no irrigation, Ni-treatment increased isolation frequency, but, in irrigated seedlings the response was the opposite. Only 10.6% of the seedlings had symptoms caused by G. abietina; most of the seedlings had become infected before the application of the various treatments.     

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.     

Studies of the life cycle of Gremmeniella abietina on Scots pine in southern Sweden

Aspects of the life cycle of Gremmeniella abietina (Lagerb.) Morelet were studied from 1988 to 1990 in stands of Pinus sylvestris L., 16–32 years old, in southern Sweden, initiated in 1988 with a widespread outbreak of the disease. Pycnidia started to release conidia in late spring and apothecia began to release ascospores in summer. Latent infections could still be detected one year after their establishment by cultivation of healthy looking shoots on agar petri dishes. G. abietina appeared to have a mainly biennal life cycle, as most spores were released two years after infection of the shoot.