From the Editor

Abstract

In 2001 large areas of Pinus sylvestris L. stands in Sweden were attacked by Gremmeniella abietina (Lagerb.) Morelet. The resultant damage was assessed in five genetic field trials and one clonal seed orchard, with the aims of quantifying the genetic variation in tree responses to G. abietina, studying the genetic relationship between G. abietina susceptibility and growth traits, and examining the implications of the results for P. sylvestris breeding. A comparison of G. abietina damage between plus-tree progenies and seed stand check-lots in each of four tree classes (dominant, co-dominant, subordinated and suppressed) found no significant differences except in the suppressed tree class, where plus-tree progenies were damaged less severely than trees from the seed stands. Narrow- and broad-sense heritability for G. abietina damage traits were in the range 0.22–0.42. Genetic correlations between G. abietina damage and growth traits were weak and not significantly different from zero. The results imply that selection for growth capacity in P. sylvestris breeding programmes using plus-tree selection or field progeny tests does not increase susceptibility to G. abietina. In addition, there is scope for selecting genotypes with increased resistance if this is required in the future.     

In vitro growth of Gremmeniella abietina isolates (European race) at different temperatures

The mycelial growth of 24 isolates of types A and B of Gremmeniella abietina (Lagerb.) Morelet, collected in northern Finland and the Kola peninsula, Russia, was studied on malt agar plus pine needle extract at 18°C and 5°C. Great variation occurred within both types, and the results suggest that several isolates per stand are needed to represent one local isolate, if responses of G. abietina mycelia are studied on artificial media.     

Precipitation and temperature as factors in Gremmeniella abietina epidemics

The combination of temperature and precipitation during the growth season could be correlated with the occurrence of Gremmeniella abietina epidemics in Denmark. The Gremmeniella index value (GIV) is the result of the monthly rain in mm divided by average monthly temperature in centigrade (mm/°C) and it was created to facilitate easy prediction of epidemics in Denmark. The two most severe outbreaks of G. abietina in pine and other conifers in Denmark took place in 1963–64 and 1984–85, following years where low average temperatures and high precipitation in May combined with the same weather patterns in either August or September. These meteorological conditions were not fulfilled from 1874 to 1900, in which period Pinus nigra was pronounced unsuitable for Danish forestry because of recurring problems with fungal disease. However, the earlier epidemics seemed to coincide with cold and rainy weather (high GIV) in August. In addition, severity of epidemics may also depend on the presence of dense stands between 30 and 40 years of age, as high GIV in August has occurred without disease outbreak in periods with low frequency of susceptible stands. Gremmeniella abietina attacks in Denmark are initiated by the climatic conditions expressed by the Gremmeniella index value, although it does not explain the biological process behind this phenomenon. Nevertheless, the method could be useful for other regions, where epidemics of G. abietina may be related to weather.     

Conidial germination and formation of necrosis in pine seedlings by Gremmeniella abietina at low temperatures

The germination of conidia of G. abietina on water agar reached the same germination percentage at 0°C as at 5 °C to 12.5 °C, but required more time. The fungus caused necrosis even at - 4 °C in pine seedlings.     

Effects of associated fungi Sclerophoma pythiophila and Cenangium ferruginosum on Gremmeniella abietina dieback in Spain

The interactions between Gremmeniella abietina and either Sclerophoma pythiophila or Cenangium ferruginosum, fungi frequently isolated from diseased twigs along with G. abietina, were studied under laboratory (dual cultures) and greenhouse conditions (double‐inoculations). Virulence of each species was also evaluated in greenhouse experiments by means of single‐inoculations. In vitro interactions were assessed on Petri dishes containing malt agar with pine needle extract, and greenhouse experiments were performed on 1‐year‐old Pinus halepensis seedlings. In vitro growth of G. abietina was inhibited by both fungi when grown in dual culture. In single‐inoculations, G. abietina caused the greatest necrosis length on P. halepensis seedlings, followed by S. pythiophila, whereas C. ferruginosum did not cause significant necrosis. In double‐inoculations, C. ferruginosum was able to reduce the length of necrosis caused by G. abietina on the P. halepensis seedlings. In contrast, necrosis length was greater in seedlings inoculated with both S. pythiophila and G. abietina than in those inoculated with G. abietina alone. Therefore, S. pythiophila seems to play a role in disease expression caused by G. abietina on P. halepensis in Spain.     

Crown transparency, tree mortality and stem growth of Pinus sylvestris, and colonization of Tomicus piniperda after an outbreak of Gremmeniella abietina

In the year 2000, large areas of forest in Sweden, mainly 30-50 year old Pinus sylvestris (L.) stands, were attacked by the fungus Gremmeniella abietina (Lagerb.) Morelet. The aims of this study were to investigate: (i) the relationship between G. abietina-induced tree crown transparency (CT) and P. sylvestris (L.) tree mortality; (ii) the influence of CT levels on stem growth; (iii) the recovery of the crown; and (iv) the association of CT and colonization by Tomicus piniperda (L.). Thirty-five permanent sample plots were established in five P. sylvestris stands (38-46 years old), infested by G. abietina, and 23 plots in four reference stands, not obviously infested.During the 5 years following the attack, the total mortality amounted to 454 trees ha⁻¹ and 7.8 m² ha⁻¹, on average, in the five infested stands, corresponding to 42% of the trees and 34% of the basal area at the time of the attack. Most of the mortality occurred within 2 years of the attack. The mortality of individual trees (2002-2005) was found to be related to the crown transparency (CT), the position of needle loss within the crown and the tree diameter at breast height. Based on our modeling, the probability of mortality was substantially increased if the initial CT-value was higher than 85%.Growth reductions were detected for individual trees with an initial CT of >c. 40%. In contrast, trees with a low initial CT (<c. 40%) were not affected and even exhibited increased growth. In the five infested stands, the reductions in basal area and volume increment were estimated to be 26-58%, and, 42-73%, respectively, during the five growing seasons after the attacks.The trees in the infested stands that were still alive in spring 2005 had started to recover in terms of CT. Breeding of T. piniperda on the P. sylvestris (L.) stems occurred almost exclusively on stems with a CT > 90%.The data from this study suggest that when a P. sylvestris (L.) stand has been attacked by G. abietina, trees with a CT above 80% should be felled; the remaining trees will have a high probability of survival and resistance to successful breeding by the T. piniperda.     

La maladie à Brunchorstia. II. Répartition en France

The Brunchorstia disease. 2. Its distribution in France . Since 1966 the Brunchorstia disease caused by Gremmeniella abietina (Lagerb.) Morelet [Conidial stage: Brunchorstia pinea (Karst.) Höhn.] has been observed in 33 departments. It occurs mainly near Verdun. Various pine species are attacked and the damage is usually more important than damage caused by Dothistroma septospora.     

Effect of fungicides,endophytes and fungal filtrates on in vitro growth of Spanish isolates of Gremmeniella abietina

The effect of eight fungicides and 15 endophytes isolated from twigs of healthy Pinus halepensis trees on the growth rate of four Spanish isolates of the pathogen Gremmeniella abietina was evaluated in vitro. In the fungicide experiments, four doses of each fungicide tested were added to the growth medium. In the endophyte experiments, dual cultures endophyte‐pathogen were paired in Petri dishes. Furthermore, growth of three G. abietina isolates was evaluated on malt agar with pine needle extract amended with filtrates from cultures of endophyte E14, which produced a brownish compound apparently inhibiting G. abietina growth. The results obtained suggested that chlorothalonil and daconil were the most suitable fungicides at low doses to reduce growth of G. abietina isolates from Spain. Four of the endophytes tested in vitro showed strong antagonistic activity against G. abietina and deserve further testing in vivo. The endophyte E14 produced in vitro a brownish compound which almost completely inhibited mycelial growth of G. abietina isolates from Spain.     

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.     

Scleroderris canker in New York State: Attempts to justify and cope with regulatory action

Pinus resinosa, P. sylvestris, P nigra, Pseudotsuga menziesii, and Picea glauca seedlings in three sites and Pinus thunbergii in two sites in New York State were inoculated with conidia of Gremmeniella abietina twice in 1986. Percent infection therefrom was determined in spring of 1987, Some members of each species of Pinus became infected at one site within the current range of the disease and in other sites 84 and 300 km south of the current range. P. glauca and P. menztesii were not infected. Results of experiments to test efficacy of postharvest treatments to eradicate G. abietina from infected seedlings suggested that immersion in hot (55°C) water and applications of dilute sodium hypochlorite would eradicate the pathogen with little or no effect on retention or color of foliage of P. resinosa and P. sylvestris.     

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.     

Growth reactions of a Gremmeniella abietina isolate and Scots pine embryogenic tissue cultures differ in a host–parasite in vitro system

Summary The aim of this study was to screen Scots pine embryogenic tissue culture material to Gremmeniella abietina. According to the results Scots pine (Pinus sylvestris) embryogenic tissue lines (27 lines) could be ranked based on significant differences in G. abietina effects estimated by changes in glucosamine concentrations, growth, and dry matter contents of inoculated tissue pieces. The ranking order of the extreme tissue lines stayed basically similar, regardless of the variable measured. These findings imply a possibility to use the ranked embryogenic tissue lines in more detailed investigations of interactions between G. abietina and its host. This is the first report of using embryogenic tissue cultures in studying host–parasite interaction between Scots pine and G. abietina.     

Tree mortality caused by Gremmeniella abietina in a subalpine afforestation in the central Alps and its relationship with duration of snow cover

Tree survival and causes of mortality were studied in an experimental afforestation in the upper subalpine forest zone in the Swiss Alps. A total of 59.8% of Pinus cembra and 45.6% of Pinus mugo were killed by Gremmeniella abietina during the first 20 years after planting, compared to 1.5% of Larix deddua trees. The mortality rates caused by G. abietina were highly correlated with the duration of snow cover in spring. Tree losses were lowest at sites where the snow melted early and highest at sites where the snow ablation was delayed in spring. Tree mortality varied greatly between years. In the year after the coldest summer of the observation period mortality due to G. abietina infections was highest, suggesting high susceptibility of trees in poor condition. Phaddium infestans, which was the second most important factor for mortality in P. cembra, killed trees irrespective of their condition. Other biotic and abiotic causes of tree mortality had negligible influence compared with the impact of G abietina and P. infestans. Excluding anthropogenic impacts, the diverse spatial pattern of forested and treeless sites close to the subalpine timberline may predominantly result from the action of parasitic fungi, depending on the ablation pattern of the snow cover in spring.     

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.     

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.     

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.     

Impacts of inoculation with Herpotrichia pinetorum,Gremmenia infestans and Gremmeniella abietina on Pinus nigra subsp. pallasiana and Cedrus libani seedlings in the field

Herpotrichia pinetorum, Gremmenia infestans and Gremmeniella abietina were inoculated onto 2‐year‐old Anatolian black pine (Pinus nigra subsp. pallasiana) and Taurus cedar (Cedrus libani) seedlings planted in a high mountain forest (1800 m a.s.l) in south‐western Turkey, to determine the effects of these fungi during winter. In June, 8 months after inoculation, 39.9% of experimental plants were dead and 20.4% of the surviving plants failed to flush. Gremmeniella abietina and H. pinetorum caused the most fatalities. Prevention of new shoot formation on surviving plants, however, was mainly an effect of G. abietina infections, although many surviving plants inoculated with G. infestans or H. pinetorum also failed to flush. All three pathogens had the potential to severely damage young plants of P. nigra subsp. pallasiana and C. libani growing at high elevations near to forests with heavy inoculum loads. The implications of this finding for P. nigra afforestations at high altitudes in Turkey are discussed. This study is also the first to report that G. infestans can infect and cause disease on young C. libani plants.     

Occurrence of Gremmeniella abietina damage on Scots pine along a pollution gradient from Monchegorsk nickel smelter to western Lapland

Gremmeniella abietina damage was studied at stand and tree level on the Kola Peninsula and in northern Finland. At stand level, damage was recorded in four areas in Finland, while only individual damaged trees were found in Russia. According to the results of branch analysis, there was no sign of endemic epidemics in any of the areas. There was a significant negative correlation between the average G. abietina damage and modelled SO₂ deposition and temperature sum along the gradient. The results suggest that G. abietina is distributed all over northern Finland and the Kola Peninsula in natural stands of Scots pine, and that the direct effect of SO₂ deposition from the Monchegorsk nickel smelter on the damage may be minimal.     

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.