Application of methyl jasmonate reduces growth but increases chemical defence and resistance against Hylobius abietis in Scots pine seedlings

Scots pine (Pinus sylvestris L., Pinaceae) produces a terpenoid resin which consists of monoterpenes and resin acids that offer protection against herbivores and pathogen attacks. Methyl jasmonate (MJ) is a potential plant elicitor which induces a wide range of chemical and anatomical defence reactions in conifers and might be used to increase resistance against biotic damage. Different amounts of MJ (control, 10 mm , and 100 mm ) were applied to Scots pine to examine the vigour, physiology, herbivory performance, and induction of secondary compound production in needles, bark, and xylem of 2‐year‐old Scots pine seedlings. Growth decreased significantly in both MJ treated plants, and photosynthesis decreased in the 100 mm MJ treated plants, when compared to 10 mm MJ or control plants. The large pine weevil (Hylobius abietis L.) (Coleoptera: Curculionidae) gnawed a significantly smaller area of stem bark in the 100 mm treated plants than in the control or 10 mm treated plants. The 100 mm MJ treatment increased the resin acid concentration in the needles and xylem but not in the bark. Furthermore, both MJ treatments increased the number of resin ducts in newly developing xylem. The changes in plant growth and chemical parameters after the MJ treatments indicate shifts in carbon allocation, but MJ also affects plant physiology and xylem development. Terpenoid resin production was tissue‐specific, but generally increased after MJ treatments, which means that this compound may offer potential protection of conifers against herbivores.     

Long-term impacts of elevated carbon dioxide and transgenic Bt cotton on performance and feeding of three generations of cotton bollworm

A field screening trial undertaken in Uganda showed that a number of Musa L. (Musaceae) cultivars and hybrids displayed high levels of resistance to banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), while most highland banana cultivars tended to be susceptible to weevil attack. In this study, research was undertaken to determine modalities of resistance to banana weevil. Laboratory studies suggested that all cultivars were attractive to the weevil and that females freely oviposited on all cultivars. While some differences were found between cultivars in attractivity and egg numbers, these were not related to subsequent damage. Therefore, antixenosis does not appear to play an important role in host‐plant resistance to banana weevil. Larval survivorship rates in living corms were, for the most part, low on resistant cultivars, suggesting that antibiosis mechanisms offer the primary avenues of resistance. In the laboratory, development was slower on some resistant cultivars although survivorship rates on excised corm material were not as well related to levels of resistance as that on living material. Sap appeared to play a minor role in reducing egg eclosion rates on some resistant cultivars. Methanol extracts from Kayinja, a resistant cultivar, inhibited larval development on corms of susceptible cultivars in the laboratory.     

Use of Shrubs as Nurse Plants: A New Technique for Reforestation in Mediterranean Mountains

Common techniques currently used for afforestation in the Mediterranean basin consider the pre‐existing vegetation (mainly shrubs) as a source of competition for trees, and consequently it is generally eliminated before planting. Nevertheless, it has been demonstrated that woody plants can facilitate the establishment of understory seedlings in environments that, like the Mediterranean area, are characterized by a pronounced dry season. In this study, we experimentally analyze the usefulness of shrubs as nurse plants for afforestation of two native conifers, Pinus sylvestris L. (Scots pine) and Pinus nigra Arnold (black pine). Two‐year‐old seedlings were planted in four microhabitats: (1) open interspaces without vegetation (which is the usual method used in afforestation programs), (2) under individuals of Salvia lavandulifolia, (3) under the north side of spiny shrubs, and (4) under the south side of spiny shrubs. Pine survival was remarkably higher when planted under individuals of the shrub S. lavandulifolia (54.8% for Scots pine, 81.9% for black pine) compared with open areas (21.5% for Scots pine, 56.8% for black pine; chi square, p < 0.05). The survival of both pines was also higher when planted on the north side of spiny shrubs, although the survival on the south side was similar to that found in open areas. In addition, pine growth was not inhibited when planted in association with shrubs. This pattern appears to result from the combination of abiotic conditions imposed by the presence of a nurse shrub, which leads to improvement in seedling water status and therefore reduced summer mortality by drought. The results show that the use of shrubs as nurse plants is a technique that offers both economic and ecological advantages, in terms of savings in labor and plant material and reduced and even negligible impact on the pre‐existing vegetation.     

Effects of green tree retention, prescribed burning and soil treatment on pine weevil (Hylobius abietis and Hylobius pinastri) damage to planted Scots pine seedlings

1 Feeding damage and mortality caused to planted Scots pine seedlings by the pine weevils Hylobius abietis and Hylobius pinastri were studied on burned and unburned sites with 0, 10 and 50 m³ per hectare levels of green tree retention from the second to the fourth summer after logging and burning of the sites. 2 The rate of severe feeding damage to pine seedlings caused by pine weevils was higher on burned clearcut sites than on unburned ones, whereas burning did not increase the feeding damage rate on sites with groups of retention trees. The damage rate in the fourth summer was approximately the same on burned and unburned sites. 3 Pine weevil feeding was the major cause of mortality of freshly planted pine seedlings on unburned sites. On burned sites, mortality was higher than the rate of severe feeding damage, particularly in the second summer after burning, possibly owing to fungal attack and abiotic factors. 4 At a retention tree level of 50 m³, feeding damage to the seedlings was lower than on clearcuts and at a 10 m³ retention tree level. Furthermore, on sites with 50 m³ of retention trees, scarification of the soil was found to decrease feeding damage more effectively than on clearcuts and 10 m³ sites. If the seedlings were situated in the centre of scarified patches, scarification alone was as effective as insecticide treatment on unscarified soil for decreasing feeding damage and mortality. 5 The results suggest that when burning is applied as silvicultural treatment after clear‐cuts, retention of trees is recommended to reduce the damages caused by pine weevils on pine seedlings.     

Mutual benefit interactions between banded pine weevil Pissodes castaneus and blue‐stain fungus Leptographium serpens in maritime pine

• 1 Ecological interactions between banded pine weevil Pissodes castaneus and blue‐stain fungus Leptographium serpens, when simultaneously sharing the same host plant (maritime pine Pinus pinaster) in winter and spring, were investigated. Temporal components of the interaction were taken into account by either introducing the weevils and the pathogen simultaneously or sequentially, with the weevils being introduced 1 month after the fungal inoculation.
• 2 We measured larval mortality, development time, offspring number, sex ratio and body size of P. castaneus. Phloem phosphorus and nitrogen concentrations were also assessed. Furthermore, we tested whether: (i) emerging offspring transported propagules of the fungus; (ii) artificially‐contaminated weevils may transmit the disease to healthy trees; and (iii) field collected P. castaneus carry the fungus.
• 3 The fungus enhanced weevil colonization and brood production in both seasons. During winter and spring, adults from trees where the pathogen was inoculated prior to weevil introduction emerged earlier than weevils from trees where they had been introduced simultaneously with the fungus. During winter, weevils from pre‐inoculated trees were also larger. Sex ratio and larval mortality were not affected. Leptographium serpens did not affect phloem nitrogen content but phosphorus content was greater in plants inoculated with the pathogen, which may explain the findings on weevil growth.
• 4 Sixty‐five percent of the weevils that emerged from inoculated trees carried spores of L. serpens, although no successful isolation was made from field collected weevils. The fungus was recovered from 25% of the trees infested with artificially‐contaminated weevils.
• 5 These results suggest that P. castaneus benefits from the presence of L. serpens and may contribute to its spread.

     

Evaporative demand determines branchiness of Scots pine

Analysis of the branch area/stem area ratio of Scots pine growing in different climatic conditions in Europe and Siberia indicates that the branch area supported by a stem increases in warmer and drier conditions. The ratio was significantly correlated with several climatic variables, especially with potential evapotranspiration (E _p). The ratio was negatively correlated with stand density (d _s). A regression model combining E _p and d _s accounted for 85% of the total variation. These trends are believed to reflect hydraulic segmentation of trees and may represent a strategy to avoid cavitation in the tree, especially in the branches.     

Molecular cloning and functional expression of a stress-induced multifunctional O-methyltransferase with pinosylvin methyltransferase activity from Scots pine (Pinus sylvestris L.)

Formation of pinosylvin (PS) and pinosylvin 3-O-monomethyl ether (PSM), as well as the activities of stilbene synthase (STS) and S-adenosyl-l-methionine (SAM):pinosylvin O-methyltransferase (PMT), were induced strongly in needles of Scots pine seedlings upon ozone treatment, as well as in cell suspension cultures of Scots pine upon fungal elicitation. A SAM-dependent PMT protein was purified and partially characterised. A cDNA encoding PMT was isolated from an ozone-induced Scots pine cDNA library. Southern blot analysis of the genomic DNA suggested the presence of a gene family. The deduced protein sequence showed the typical highly conserved regions of O-methyltransferases (OMTs), and average identities of 20–56% to known OMTs. PMT expressed in Escherichia coli corresponded to that of purified PMT (40 kDa) from pine cell cultures. The recombinant enzyme catalysed the methylation of PS, caffeic acid, caffeoyl-CoA and quercetin. Several other substances, such as astringenin, resveratrol, 5-OH-ferulic acid, catechol and luteolin, were also methylated. Recombinant PMT thus had a relatively broad substrate specificity. Treatment of 7-year old Scots pine trees with ozone markedly increased the PMT mRNA level. Our results show that PMT represents a new SAM-dependent OMT for the methylation of stress-induced pinosylvin in Scots pine needles.     

Simulated roots and host feeding enhance infection of subterranean insects by the entomopathogenic nematode Steinernema carpocapsae

Steinernema carpocapsae can be effective against root-feeding insects despite its reputation as a sedentary ambusher. In pot experiments, using twigs as surrogate roots and pine weevil larvae as targets, we tested the hypothesis that roots serve as physical routeways and conduits of feeding-associated stimuli, thus enhancing the success of S. carpocapsae applied at the surface against subterranean hosts. Insect mortality was lowest (25%) in the absence of plant material, increased to 48% when twigs linked nematodes and insects, and further increased to 69% when the insects were allowed feed on the twigs. This is the first experimental support for the root-routeway hypothesis.     

Root disturbance of common ash, Fraxinus excelsior (Oleaceae), leads to reduced foliar toughness and increased feeding by a folivorous weevil, Stereonychus fraxini (Coleoptera, Curculionidae)

Abstract.

• 1 Bioassays were carried out to examine differences in the feeding of a folivorous weevil, Stereonychus fraxini De Geer, on leaves from ash saplings with undamaged roots, and those with damaged roots. Beetles ate significantly more of the leaves of root-damaged saplings in a choice experiment.
• 2 A separate study of the effect of root damage on leaf toughness was carried out on a second group of ash saplings. Saplings with damaged roots had less tough leaves than control saplings. Decreased leaf toughness in hypothesized as a mechanism to explain the preference of weevils for leaves from damaged trees.
• 3 Both chemical and physical changes may occur in the tissues of ash trees in response to environmental stress such as drought and root damage.
• 4 Root damage caused by agricultural disturbance is hypothesized as a mechanism making mature ash trees in hedgerow ecosystems more susceptible to insect herbivores.

     

Sequential patterns of colonization of coarse woody debris by Ips pini (Say) (Coleoptera: Scolytidae) following a major ice storm in Ontario

Abstract

• 1 It is widely known that many bark and wood‐boring beetle species use nonresistant coarse woody debris (CWD) created by disturbances; however, the ability of these secondary species to cause mortality in healthy trees following a build‐up of their populations remains unclear. We characterized the pattern of colonization by Ips pini (Say) following a major ice storm that created large amounts of CWD varying in resistance to colonization (i.e. ranging from snapped tops with no resistance to heavily damaged trees with intact root systems). A major question was how the beetles responded to the different types of storm‐damaged material and whether healthy undamaged trees were colonized and killed following increases in beetle populations.
• 2 Six red pine, Pinus resinosa Ait., plantations in eastern Ontario were monitored from 1998 to 2001 inclusive: three with high storm damage (approximately 120 m³/ha CWD) and three with minimal damage (approximately 20 m³/ha CWD). Transects (200 × 2 m) were sampled yearly in each plantation to assess the type and amount of damaged pine brood material colonized by the pine engraver beetle, I. pini.
• 3 Beetles preferentially infested the most nonresistant material available each year (i.e. all snapped tops in year 1, all standing snags, up‐rooted trees and many bent trees by year 2, but still less than 50% of trees blown over but with intact root systems by year 3). By years 3 and 4, the majority (approximately 75%) of severely damaged trees (with > 50% crown loss) died prior to beetle colonization.
• 4 The size of the beetle population tracked the abundance of available woody material from year‐to‐year within a plantation; populations were very large in the first 2 years, and declined significantly in the last 2 years.
• 5 Healthy standing red pines were apparently resistant to colonization by the beetles, despite the significant build‐up in their populations. Hence, the results of the present study suggest that native bark beetle populations will not cause further tree mortality following such a disturbance in this region.

     

Comparison of the initial demographies of pine and oak populations in rural pine forests in Korea and Japan

In order to understand the human impact upon demographic change in plant population in rural forests, we examined the population trends ofPinus densiflora andQuercus serrata inP. densiflora forests viewing their seedlings and saplings in rural Korea and Japan. The most prominent factor affecting the regeneration of the pine and oak was the intensity of management activity which controlled the vegetation stratification and its light environment. Open spaces, such as graveyard or cleaned area that allow the long-term direct daylight in dry season to accelerate the surface heat of soil, were unfavorable habitats for germination and growth of both species. The negative effects of the presence of litter and evergreen trees were related to the failure of early seedling and sapling growth of pine. Cover of litter is, especially, another factor related to the growth of pine saplings. It is considered that successful germination and sapling growth of pine and oak in early successional stages is determined by vegetation structures and light condition.     

Resistance and response of <Emphasis Type="Italic">Pinus pinaster</Emphasis> seedlings to <Emphasis Type="Italic">Hylobius abietis</Emphasis> after induction with methyl jasmonate

Experimental induction of plant chemical defences with methyl jasmonate (MeJa) is a valuable tool for understanding the ecology of plant defensive responses. However, few studies have examined whether MeJa-induced defences in conifers are effective against insect herbivores. We studied, in 17 half-sib Pinus pinaster families, (i) the effect of MeJa application on plant growth and on the induction of diterpenoid resin in different sections of the stem; (ii) whether MeJa-induced defences increase the resistance of living pine juveniles against the large pine weevil Hylobius abietis in an in vivo bioassay and (iii) the induction of resin content after weevil wounding. Resin concentration was greater in the upper section of the stem compared with basal sections in both MeJa-induced and non-induced seedlings. Sixty days after MeJa application, treated plants showed 40% greater resin content all along the stem, but reduced height growth compared to control plants. MeJa-induction was effective against the pine weevil, as induced seedlings were 21% less damaged than control plants. Wounding activity by H. abietis produced a strong local defensive response after 48 h, where resin concentration was double that observed in the basal and apical sections not exposed to the insects.     

Genetic variation in resistance of Norway spruce seedlings to damage by the pine weevil <Emphasis Type="Italic">Hylobius abietis</Emphasis>

Regeneration of northern conifer forests is commonly performed by reforestation with genetically improved materials obtained from long-term breeding programs focused on productivity and timber quality. Sanitary threats can, however, compromise the realization of the expected genetic gain. Including pest resistance traits in the breeding programs may contribute to a sustainable protection. Here we quantified the variation in different components of resistance of Norway spruce to its main pest, the pine weevil Hylobius abietis. We followed insect damage in two large progeny trials (52 open-pollinated families with 100–200 individuals per family and trial) naturally infested by the pine weevil. Pine weevils damaged between 17 and 48% of the planted seedlings depending on the trial and year, and mortality due to weevil damage was up to 11.4%. The results indicate significant genetic variation in resistance to the pine weevil, and importantly, the variation was highly consistent across trials irrespective of contrasting incidence levels. Individual heritability estimates for the different components of seedling resistance were consistently low, but family heritabilities were moderate (0.53 to 0.81). While forward selections and breeding for higher resistance seem not feasible, backwards selections of the best parent trees emerge as a putative alternative to reduce weevil damage. A positive genetic correlation between early growth potential and probability of being attacked by the weevil was also observed, but the relationship was weak and appeared only in one of the trials. Overall, results presented here open the door to a new attractive way for reducing damage caused by this harmful pest.     

Eriophyoid mites (Acari: Eriophyoidea) on coniferous trees: is the occurrence of one species associated with the other?

Although Eriophyoidea is one of the most important phytophagous mite taxa owing to its negative impact on plants, reports on associations between occurrences of eriophyoid species are scarce. The aim of this paper is to test the hypothesis that the occurrence of one species is correlated with the occurrence of another in some predictive manner. Analyses are carried out for two popular coniferous trees in Poland, i.e., Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). Observations were made in four locations in Poland, from three age groups of trees, namely adult trees (thirty 15-cm shoot samples from each of ten trees), young trees (ten 15-cm shoot samples from each of ten trees) and seedlings (100 whole-seedling samples). The associations were estimated by Yule’s V index. Among four eriophyoid species observed on Scots pine, and the same number of species on Norway spruce, in general no association pattern was observed. It means that their occurrence is independent. The most likely explanation for the absence of co-occurrence is the abundance of microhabitats on coniferous trees for eriophyoid mites, combined with the low mite density on these plant hosts.     

Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality

Key message

The retrospective analysis of wood anatomical features evidences how a long-term deterioration of hydraulic performance and carbon use portend drought-induced mortality in Scots pine.

Abstract

Widespread episodes of drought-induced tree mortality are predicted to become more frequent as climate becomes warmer and drier. Nevertheless, growth trends and their links to changes in wood anatomy before tree dies are still poorly understood. Wood anatomical features provide valuable information that can be extracted to infer the mechanisms leading to tree death. In this study, we characterize drought-induced mortality affecting two Scots pine (Pinus sylvestris) sites (Prades and Arcalís) located in the North Eastern Iberian Peninsula. Co-occurring now-dead and living Scots pine trees were sampled and their wood anatomical features were measured and compared. We aimed to detect differences in anatomical features between living and dead trees, and to infer past physiological performances that might have determined their subsequent death or survival. Now-dead trees showed lower tracheid and resin duct production, and smaller radial lumen diameters than co-occurring living trees. At the more xeric Prades site, these anatomical differences were larger and chronic, i.e. were observed over the three studied decades, whilst they were less pronounced at the other, more mesic Arcalís site, where tree mortality episodes were more recent. This indicates that dead trees’ hydraulic conductivity was severely affected and that carbon investment in xylem formation and resin duct production was constrained prior to tree death. Our findings show that both hydraulic deterioration and low carbon allocation to xylem formation were associated to drought-induced mortality in Scots pine. Nevertheless, the temporal dynamics of these processes differed between populations as a function of site climatic conditions.     

Survival and growth of eastern white pine shoot apical meristemsin vitro

Shoot apical meristems of seedling and mature eastern white pine trees were excised and grownin vitro. Placing the meristems on filters instead of directly on agarose-solidified nutrient medium enhanced survival of both juvenile and mature meristems. Applying forcing treatments to mature branches improved survival and growth of dissected meristems compared with meristems from non-forced branches in experiments conducted over two years. No consistent differences were observed among 2-, 4-, and 6-week forcing treatments. Including 5.37 nM (0.001 mg l^-1) l-naphthaleneacetic acid in the culture medium did not affect meristem survival or growth. Some meristems from seedlings grew rapidly, produced primary leaves, underwent internode elongation, and in three cases, produced adventitious roots. Meristems from mature trees did not grow as rapidly as seedling meristems. The leaves produced by mature meristems appeared to be scale leaves and a few of these had brachyblast primordia in the axils. The shoots derived from mature meristems did not produce adventitious roots.     

Developmental patterns of above-ground hydraulic conductance in a Scots pine (Pinus sylvestris L.) age sequence

Hydraulic resistance to water flow was measured in branches and stems of Scots pine trees ranging from 7 to 59 years of age in Thetford (East Anglia, UK). On the basis of these measurements, tree above-ground conductance was calculated and related to the amount of leaf area sustained by each tree. Branches at the crown bottom had a lower proportion of sapwood area and a lower total hydraulic conductance than branches of the same diameter at the tree top. Within branches, most of the hydraulic resistance was located near the needles. Tree above-ground conductance was positively related to tree diameter and inversely related to tree height. Compared with young trees, mature trees had about 4 times less above-ground conductance per unit of leaf area. Apparently, the increase in pathway length associated with tree height growth could be only partially compensated for by the increase in conductive capacities resulting from diameter growth. We argue that this reduction may account for reported decreases of stomatal conductance with tree age. It is suggested that the increase in branchiness associated with tree maturation may represent a compensation mechanism to reduce the overall resistance to water flow in the crowns.     

The effect of bark phenols upon mountain hare barking of winter-dormant Scots pine

Due to high numbers of mountain hares in recent winters in northern Finland the barking of winter dormant Scots pines was widespread. The hares fed selectively upon upper crown bark of grafted pines, nitrogen fertilized trees and trees in poor condition. Bark of preferred upper crown branches and physiologically mature scions contained less total phenols than lower parts. However, there were no differences between total phenols concentrations of graft bark preferred by hares and nearby unbarked juvenile phase Scots pine. Neither decrease in resistance after nitrogen fertilization n- or stress was correlated with bark total phenolic concentration. Thus, total phenolic concentration is not a reliable predictor of the susceptibility of Scots pine to winter barking by the mountain hare.     

Ants protect conifer seedlings from feeding damage by the pine weevil Hylobius abietis

• 1 Ants that protect food resources on plants may prey on (or deter) herbivores and thereby reduce damage. Red wood ants (of the Formica rufa group) are dominant ants in boreal forests of Eurasia and affect the local abundance of several herbivorous species.
• 2 The pine weevil Hylobius abietis (L.) is a herbivore that causes severe damage by feeding on the bark of coniferous seedlings within areas of forest regeneration.
• 3 We investigated whether ants can protect conifer seedlings from pine weevil feeding. In a manipulative experiment, ants were attracted to sugar baits attached to spruce seedlings and the damage caused by pine weevils was compared with control seedlings without ant‐baits.
• 4 The feeding‐scar area was approximately one‐third lower on the seedlings with ant‐baits compared with the controls. Besides red wood ants, Myrmica ants were also attracted in high numbers to the ant baits and the relative effects of these species are discussed.
• 5 The results obtained in the present study support the trophic cascade hypothesis (i.e. damage to herbivores is suppressed in the presence of predators). The decreased pine weevil feeding on the baited seedlings was probably a result of nonconsumptive interactions [i.e. the presence of (or harassment by) ants distracting pine weevils from feeding].
• 6 Understanding the role of ants may have important implications for future strategies aiming to control pine weevil damage. For example, maintaining suitable conditions for ants after harvesting stands may be an environmentally friendly but currently unexploited method of for decreasing weevil damage.