Timo Kurkela

Development of needle retention in Scots pine (Pinus sylvestris) in 1957-1991 in northern and southern Finland

The needle trace method was used to study retrospectively the long-term latitudinal variation in needle retention in Scots pine (Pinus sylvestris L.) in Finland. The mean annual summer needle retention (ANR) along the main stem varied from 3.4 to 6.0 needle sets during the period 1957–1991. The lowest values were observed in southern and the highest in northern Finland. The length of the growing season, expressed as the thermal sum (threshold value +5 °C), was negatively correlated with the mean ANR (r=-0.96). The geographical needle retention pattern (NRP) for the period 1957–1991 showed a clearly increasing trend from 1957 to 1969 (southern Finland) and to 1975 (northern Finland); thereafter, the NRP tended to decrease close to its minimum value recorded in 1991. The general level of the NRP was approximately 5.0 needle sets in northern Finland and 3.5–4.0 needle sets in southern Finland. The NRP, with its 6–12 year cycle for southern Finland, was clearly periodical. Differences in the NRP among the ten stands in southern Finland were small, whereas the said periodicity was missing and the differences were high among the stands in northern Finland. The results indicate that variation in the number of needle sets, viz. defoliation of pines, is a normal phenomenon. The role of net carbon assimilation as a regulator of the number of needle sets is discussed.

The number of Cladosporium conidia in the air in different weather conditions

The effect of varying weather conditions on the hourly number of airborne Cladosporium conidia was studied in forest environments during three summers. All factors having diurnal periodicity correlated significantly with the number of spores. Because of the great variation in weather and the interaction of weather factors, the most important factors were not the same for each summer. Temperature was important in each year. Relative humidity was most important in the first rainy summer, and precipitation was more important during the two drier summers than in the first summer. The maximum spore counts were obtained at the onset of rain, indicating the effectiveness of the first rain drops in detaching conidia. The amount of water precipitated also promoted the production of conidia, since it correlated positively with the number of spores in the air several hours later. Spore detachment also seemed to be closely related to decreases in relative humidity and increases in wind velocity which occurred in the ...

Inoculation of known and potential alternate hosts with Peridermium pini and Cronartium flaccidum aeciospores

The ability of Peridermium pini and Cronartium flaccidum aeciospores and mycelium to infect known (Vincetoxicum spp., Pedicularis spp., Paeonia spp.) and potential (Melampyrum spp., Pyrola sp., Dactylorhiza sp., Solidago sp., Salix sp., Geranium sp. and Maianthemum sp.) alternate hosts was tested. None of the mycelial cultures and only 10% of the aeciospore samples produced uredinia or telia on the tested species suggesting that most aeciospores in Finland belong to the autoecious P. pini. Aeciospores from three locations in northern Finland, however, produced uredinia or telia on Vincetoxicum mongolicum, V. nigrum, V. fuscatum, Paeonia anomala, three P. officinalis cultivars, Melampyrum sylvaticum and Pedicularis palustris either in vitro or in vivo, indicating that these aeciospores belong to the heteroecious C. flaccidum, which occurs sporadically in Finland. Interestingly, the host-specificity of C. flaccidum encountered in Finland was very low (e.g. one sample produced uredinia or telia on eight species). This, added to the wide distribution of Melampyrum spp. over northern Fennoscandia, suggests that the main alternate hosts for C. flaccidum in Finland may be in Melampyrum rather than Pedicularis.

Revealing past needle density in Pinus spp.

The number of short shoots per shoot length, or needle density, is species typical, and it shows year‐to‐year variation within species. By modification of the needle trace method, long‐term needle density chronology was produced in a Scots pine (Pinus sylvestris L.) stand, located at the northern timberline in Finland. Treewise, needle density varied between 9 and 14 short shoots per long shoot (stem internode) centimetre, the annual minimum and maximum values being 5 and 37 short shoots cm−1. The stand‐specific long‐term average was 10.5 short shoots cm−1, and the mean annual value varied between 17 and 8 short shoots cm−1 in 1951 and 1984, respectively. The long‐term pattern in needle density was one of decline with time between 1950 and the mid‐1970s, then to slightly increase on entering the 1990s. The years when the density was relatively high were 1957, 1968 and 1981, indicative of some climatic extremes.

Revealing past needle retention inPinusspp.

Needle retention in conifers is affected by several environmental factors, e.g. climate, mineral nutrition, other edaphic conditions, and more recently by air pollution. This paper describes a meth...

Pyrenopeziza betulicola and an anamorphic fungus occurring in leaf spots of birch.

We isolated ascospores and conidia of fungi associated with leaf spots common in birch leaves, and prepared mycelial cultures from them. The taxonomic positions of the fungi were determined by analysing morphological characteristics with photomicroscopy. The relationship between the teleomorph and anamorph was tested using random amplified microsatellite fingerprints, in which the variation was not explained by the origin of isolates (e.g. ascospores or conidia). This suggested that the ascospores and conidia would have been produced by the same biological species. In pathogenicity tests birch leaves inoculated with mycelia derived from ascospores developed spots showing that the fungus could be the cause of the leaf spots. The anamorph was isolated from the developing spots. Based on these results and on review of the literature we concluded that the causative agent of the leaf spot disease of birch in Finland is Pyrenopeziza betulicola, the anamorph of which belongs to Cylindrosporium.

Morphological measurements and ITS sequences show that the new alder rust in Europe is conspecific with Melampsoridium hiratsukanum in eastern Asia

Three species of Melampsoridium have been reported to infect hosts in genus Alnus. An epidemic of foliar rust affecting A. glutinosa and A. incana began in Europe in the mid-1990s, and the associated pathogen was identified as Melampsoridium hiratsukanum based on morphology. In this investigation we analyzed the morphology and genetic variation of alder rusts from Europe and Japan and the host specificity of the European epidemic rust. Our results showed that two rusts occur on the leaves of alders native to northern Europe; in Scotland an endemic rust indistinguishable from M. betulinum occurs, whereas alders in areas of Europe affected by the current epidemic were infected by M. hiratsukanum. M. hiratsukanum from naturally infected alder in Finland produced aecia on all Larix species tested but did not infect Betula leaves.

North American populations of Entoleuca mammata are genetically more variable than populations in Europe

Entoleuca mammata (syn. Hypoxylon mammatum) is a damaging pathogen of Populus tremuloides and P. grandidentata in North America and P. tremula in Europe, where the fungus occurs only sporadically in alpine regions and Scandinavia. It has been hypothesized that E. mammata was introduced to Europe from North America. In this study, E. mammata isolates collected from Europe and North America were compared by a sequence analysis of two DNA markers derived from DNA fingerprints. The objective of the study was to elucidate the relationship between North American and European E. mammata populations by testing two hypotheses: (1) North American and European isolates are conspecific; and (2) the fungus was introduced between continents causing both a founder effect and a genetic bottleneck. North American populations were found to be more polymorphic, but no major phylogenetic differences between fungal isolates collected from different continents were found. This result combined with the historical observations of the disease in Europe implies that E. mammata was introduced to Europe several centuries ago.

The occurrence of an undescribed species of Venturia in blighted shoots of Populus tremula

Morphological characters and genetic markers from 35 single-ascospore isolates of a Venturia sp. collected from Populus tremula were analysed. The morphological data were compared with the literature, and genetic markers were amplified for comparison with isolates of V. populina, V. macularis and V. ditricha. According to ascospore morphology the fungus resembled V. populina, but the morphology of the conidia was closer to Pollaccia radiosa (the anamorph of V. macularis). Analysis of 49 RAMS markers, variation within the internal transcribed spacer (ITS) sequence of the ribosomal gene cluster and a single marker locus derived from RAMS fingerprint suggested that the Venturia is a previously undescribed species.

Needle Retention, Age, Shedding and Budget, and Growth of Scots Pine Between 1865 and 1988

Four northern Finnish Scots pines (Pinus sylvestris L.) were felled, sectioned into 1-year bolts and planed with an electric planing machine in order to examine the needle history of the trees. By using the vascular bundle method, the retention, age and shedding of the needles as well as the needle budget in the main stem of pines were defined for the period of 1865–1988. No descending change in needle retention was found from 1868 to 1988. The number of needle sets varied between 1.2 and 4.2, being mostly between 2.0 and 3.5. Needles had been over three growing seasons in the shoots on the average. The whole set of needles were shed very seldom during the same year. Annual shedding of needles varied from nil to two needle sets. Needle factors were compared with the annual radial increments of the same trees. The use of the vascular bundle method for forest health studies is discussed.