The capacity in Heterobasidion annosum s.l. to resist overgrowth by the biocontrol agent Phlebiopsis gigantea is a heritable trait

The necrotrophic pathogen Heterobasidion annosum sensu lato (Fr.) Bref. causes severe root rot on coniferous trees in the boreal and temperate forests. The annual economic losses caused by this fungus in Europe are estimated to at least 790 million €. In managed forests, the major route of infection is via stump surfaces from which the H. annosum s.l. grows through the roots and attacks adjacent healthy trees. A biocontrol method to reduce H. annosum s.l. infection is to apply the wood degrading fungus Phlebiopsis gigantea in a spore solution (Rotstop) directly on the freshly cut stumps immediately after cutting. We investigated the potential risk for a build-up in the capacity of H. annosum s.l. to resist overgrowth by P. gigantea. Wood blocks of Picea abies, precolonized with the two fungal species, were juxtaposed on top of agar and the overgrowth of the P. gigantea strain (Rotstop) on the H. annosum s.l. was measured periodically. We found a natural variation in Heterobasidion parviporum to resist overgrowth by P. gigantea. There was no difference between homo- and heterokaryotic strains. In a mapping population of 91 progenies from a H. annosum hybrid strain we were able to identify one quantitative trait locus (QTL) which controls the examined resistance capacity. We estimated the broad sense heritability to 0.336 for the capacity to resist the P. gigantea overgrowth. We conclude that there exists a theoretical risk for resistance build-up in the H. annosum s.l. population towards its biological control agent P. gigantea.     

New labdane resin acids from Pinus elliottii

Slash pine needles and cortex oleoresin have been found to contain a new major diterpene constituent, imbricataloic acid. The closely related imbricatoloic acid, previously reported only in Araucaria imbricata, was found to be present in small amounts in slash pine needle extract. Spectral data are given for an unidentified diterpene alcohol isolated from the cortex oleoresin.     

Plant and fungal responses to elevated atmospheric carbon dioxide in mycorrhizal seedlings of Pinus sylvestris

The effects of elevated CO₂ concentration upon the mycorrhizal relationships of Scots pine (Pinus sylvestris) seedlings were investigated. Plants were grown for 4 months with their shoots exposed to ambient (C_AMB=360 μl l⁻¹) or elevated (C_ELEV=700 μl l⁻¹) CO₂ environments while their root systems, either colonised by the mycorrhizal fungi Paxillus involutus or Suillus bovinus, or left in the non-mycorrhizal condition, were maintained in sealed dishes. In one series of these plants the effects of C_ELEV upon the extent of mycorrhizal development and upon their growth and nutrition were determined, while another series were transferred from the dishes after 1 month, to transparent observation chambers before being returned to the two CO₂ environments. In these chambers, the effects of C_ELEV upon development of the external mycelial systems of the two mycorrhizal fungi was determined by measuring the advance of the hyphal fronts of the mycorrhizal fungi across non-sterile peat from the colonised plants. The dry mass and number of mycorrhizal tips were significantly higher in C_ELEV than in the C_AMB condition in plants colonised by both fungi in the dishes. Yields of whole plants and of shoots were higher in the C_ELEV treatment whether or not they were grown in the mycorrhizal condition, but the greater yields were not associated in these sealed systems with enhanced nutrient gain. The dry mass of non-mycorrhizal plants was greater than that of those colonised by mycorrhizal fungi under elevated CO₂. This is thought to be attributable to the energetic cost of production of the larger mycorrhizal systems in this treatment. The extent of development of the mycorrhizal mycelial systems of both fungi was greatly increased in C_ELEV relative to that in C_AMB environments. It is hypothesised that increased allocation of carbon to mycorrhizal root systems and their associated mycelia would provide the potential for enhancement of nutrient acquisition in open systems of greater fertility.     

Quantitative comparison of chemical, biological and mechanical induction of secondary compounds in Pinus pinaster seedlings

Chemical elicitors and mechanical treatments simulating real insect herbivory have been increasingly used to study induced defensive responses in woody plants. However, simultaneous quantitative comparisons of plant chemical defences elicited by real and simulated herbivory have received little attention. In this paper we compared the effects of real herbivory, simulated herbivory using two chemical elicitors, and mechanical damage treatments on the quantitative secondary chemistry of Pinus pinaster juveniles (namely on non-volatile resin in the stem and total phenolics in the needles). The real herbivory involved phloem wounding by Hylobius abietis and defoliation by Brachyderes lusitanicus (two pine weevils); the chemical elicitors to simulate herbivory induction were 40 mM methyl jasmonate (MJ) and 20 μM benzothiadiazole (BTH); and the mechanical treatments included phloem wounding and needle clipping. We also performed an additional experiment for assessing at what extent insect extracts could increase plant responses over mechanical damage. Chemical induction with MJ, mechanical wounding and real phloem herbivory by H. abietis all produced quantitatively similar results, increasing the concentration of resin in the stem and total phenolics in the needles by equivalent magnitudes. Exogenous application of BTH increased the concentration of phenolic compounds in pine needles, but did not show the same effect on stem resin. Contrastingly, we did not find significant changes in the concentration of resin in the stem or phenolics in the needles after needle clipping and B. lusitanicus feeding. Mechanical damage followed by the application of extracts from the insects B. lusitanicus and H. abietis on the injured tissues did not increase the responses in comparison to mechanical damage alone. The fact that strong induced responses elicited by phloem wounding insects are equally elicited by phloem injuries suggests that defences in pine trees are raised with low specificity regarding biotic enemies. Results from this paper support future methodological approaches using chemical elicitors and mechanical damage as simulated herbivory treatments for the experimental induction of conifer defences.     

Identification of volatiles from felled Pinus radiata and the electroantennograms they elicit from Sirex noctilio

Volatiles emanating from Pinus radiata show only minor changes in composition with time after felling even though attractiveness of the felled timber to the wood wasp Sirex noctilio changes markedly over the first 3 weeks. Monoterpene hydrocarbons account for more than 95% of the volatiles and show little change in relative composition during this time. Oxygenated components (camphor, pinocamphone, isopinocamphone and trans-pinocarveol), which are absent or present in trace amounts immediately after felling, are produced in increasing amounts and account for 1% of the volatiles after 3 weeks. Their presence in the volatile fraction significantly increases the response from the antenna of S. noctilio. The major monoterpene hydrocarbons and oxygenated components were identified by chromatographic and spectral techniques.

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Résumé Les composés volatils émanant de Pinus radiata ne montrent que de faibles changements dans leur composition après l'abattage, bien que l'attractivité des arbres abattus à l'égard de Sirex noctilio change nettement au-delà de 3 semaines. Pendant les premières 3 semaines suivant l'abattage les monoterpènes hydrocarbons représentent plus de 95% des composés volatils et leur composition varie peu durant cette période. Les composants oxygénés (camphor, pinocamphone, isopinocamphone et trans-pinocarveol) qui sont absents ou seulement présents à l'état de traces immédiatement après l'abattage, sont produits en quantités croissantes et représentent 1% des substances volatiles au bout de 3 semaines. Leur présence dans la fraction volatile accroît de facon significative la réponse antennaire de Sirex noctilio. Les principaux monoterpènes hydrocarbonés et les composants oxygénés ont été identifiés par les techniques chromatographiques et spectrographiques.

     

Late Holocene ecological history of Pinus pinaster forests in the Sierra de Gredos of central Spain

This article describes the patterns and processes of vegetation change and fire history in the Late Holocene (c. 2400 calendar year BP) palaeoecological sequence of Lanzahíta, Sierra de Gredos in central Spain, and provides the first Iberian pollen sequence undertaken within a monospecific Pinus pinaster woodland. These new data reassess not only the autochthonous nature of this pine species in the region and the Iberian Peninsula, but also the naturalness of well-developed cluster pine forests. Conflicts of palaeoecological evidence with phytosociological models of vegetation dynamics in the study region, and the relationships of P. pinaster with fire occurrence in Mediterranean-type ecosystems, are discussed.     

Jasmonic acid inhibition of in vitro shoot organogenesis in Pinus radiata cotyledons

The effect of jasmonic acid (JA) onde novo shoot formation in excised cotyledons of radiata pine (Pinus radiata D. Don), was examined. JA had no effect on shoot-forming (SF) tissues at concentrations up to 10⁻⁶ mol · L⁻¹. At concentrations greater than that, JA caused a reduction in the number of shoots formed, as well as the lengths of the shoots and fresh and dry masses of the tissues. Reciprocal transfer of excised radiata pine cotyledons from a SF medium with 10⁻⁵ mol · L⁻¹ JA to a SF medium without JA and vice versa showed that any exposure of the cotyledons to JA either during the shoot induction phase (days 0-21) or the shoot development phase (beyond day 21) led to a reduction in shoot formation. However, the JA effect was significantly less if the cotyledons were not exposed to JA during the initial 10 days in culture; indicating that the JA effect was mainly during shoot primordia formation and the subsequent development into shoots.     

Effect of tree age on needle morphology and anatomy of Pinus uliginosa and Pinus silvestris – species-specific character separation during ontogenesis

Differences in morphological and anatomical characters of needles between seedlings, saplings and adult trees of the endangered Pinus uliginosa from the Węgliniec Nature Reserve in SW Poland were examined biometrically and statistically assessed using the Student's t-test, Tukey–Kramer test, step-wise discrimination and agglomeration on Euclidean distances according to Ward's method. Pinus sylvestris adults and seedlings were used as comparative material. The results show that needles of all three P. uliginosa generations differ significantly from each other. In seedling needles, several anatomical characters were similar to those of P. sylvestris growing in the vicinity of the reserve. However, P. uliginosa had a lower number of resin canals, lower frequency of fibre-like sclerenchyma cells and higher frequency of thin-walled sclerenchyma cells with large lumens in the spaces between vascular bundles. Needle characters of saplings and adult trees of both species were distinctly more different than it was the case in the seedling stage.