Assessing the role of bark- and wood-boring insects in the decline of Scots pine (Pinus sylvestris) in the Swiss Rhone valley

Abstract.  1. In several dry inner Alpine valleys higher mortality levels of pine have been observed in recent years. This paper evaluates the role of xylophagous insects in the current pine decline and the influence of climate change on the infestation dynamics.
2. More than 200 trees of different levels of crown transparency (needle loss) were felled between 2001 and 2005 and sections of them incubated in insect emergence traps. Colonisation densities were related to the transparency level of each host tree at the time of attack.
3. Trees with more than 80% needle loss were colonised most frequently, but the breeding density was highest in trees with 65–80% needle loss.
4. The scolytine Ips acuminatus and the buprestid Phaenops cyanea colonised trees with 30–90% needle loss in high densities. The bark beetle Tomicus minor was less aggressive, preferring trees with 60–85% needle loss. The hymenopteran Sirex noctilio and the cerambycid Acanthocinus aedilis were restricted to greatly weakened trees with 50–85% needle loss. Most species colonised trees that had experienced a decline in vigour, that is an increase in crown transparency shortly before attack.
5. The infestation dynamics of P. cyanea covaried with the drought index as well as with temperature.
6. Increased temperatures not only trigger a drought stress rendering the host trees susceptible to insect attack, but also accelerate insect development. As more frequent drought periods are likely as a result of climate change, even trees only slightly or temporarily weakened will be more subject to attack by aggressive species such as I. acuminatus and P. cyanea .     

Differential roles of glucosinolates and camalexin at different stages of Agrobacterium‐mediated transformation

Agrobacterium tumefaciens is the causal agent of crown gall disease in a wide range of plants via a unique interkingdom DNA transfer from bacterial cells into the plant genome. Agrobacterium tumefaciens is capable of transferring its T‐DNA into different plant parts at different developmental stages for transient and stable transformation. However, the plant genes and mechanisms involved in these transformation processes are not well understood. We used Arabidopsis thaliana Col‐0 seedlings to reveal the gene expression profiles at early time points during Agrobacterium infection. Common and differentially expressed genes were found in shoots and roots. A gene ontology analysis showed that the glucosinolate (GS) biosynthesis pathway was an enriched common response. Strikingly, several genes involved in indole glucosinolate (iGS) modification and the camalexin biosynthesis pathway were up‐regulated, whereas genes in aliphatic glucosinolate (aGS) biosynthesis were generally down‐regulated, on Agrobacterium infection. Thus, we evaluated the impacts of GSs and camalexin during different stages of Agrobacterium‐mediated transformation combining Arabidopsis mutant studies, metabolite profiling and exogenous applications of various GS hydrolysis products or camalexin. The results suggest that the iGS hydrolysis pathway plays an inhibitory role on transformation efficiency in Arabidopsis seedlings at the early infection stage. Later in the Agrobacterium infection process, the accumulation of camalexin is a key factor inhibiting tumour development on Arabidopsis inflorescence stalks. In conclusion, this study reveals the differential roles of GSs and camalexin at different stages of Agrobacterium‐mediated transformation and provides new insights into crown gall disease control and improvement of plant transformation.     

A high‐resolution approach for the spatiotemporal analysis of forest canopy space using terrestrial laser scanning data

Forest canopies and tree crown structures are of high ecological importance. Measuring canopies and crowns by direct inventory methods is time‐consuming and of limited accuracy. High‐resolution inventory tools, in particular terrestrial laser scanning (TLS), is able to overcome these limitations and obtain three‐dimensional (3D) structural information about the canopy with a very high level of detail. The main objective of this study was to introduce a novel method to analyze spatiotemporal dynamics in canopy occupancy at the individual tree and local neighborhood level using high‐resolution 3D TLS data. For the analyses, a voxel grid approach was applied. The tree crowns were modeled through the combination of two approaches: the encasement of all crown points with a 3D α‐shape, which was then converted into a voxel grid, and the direct voxelization of the crown points. We show that canopy occupancy at individual tree level can be quantified as the crown volume occupied only by the respective tree or shared with neighboring trees. At the local neighborhood level, our method enables the precise determination of the extent of canopy space filling, the identification of tree–tree interactions, and the analysis of complementary space use. Using multitemporal TLS data recordings, this method allows the precise detection and quantification of changes in canopy occupancy through time. The method is applicable to a wide range of investigations in forest ecology research, including the study of tree diversity effects on forest productivity or growing space analyses for optimal tree growth. Due to the high accuracy of this novel method, it facilitates the precise analyses even of highly plastic individual tree crowns and, thus, the realistic representation of forest canopies. Moreover, our voxel grid framework is flexible enough to allow for the inclusion of further biotic and abiotic variables relevant to complex analyses of forest canopy dynamics.     

The size at reproduction of canopy tree species in central Africa

Size at reproduction is a key aspect of species life history that is relatively understudied for long‐lived tropical trees. Here, we quantified reproductive diameter for 31 major timber species across 11 sites in Cameroon, Congo, and Central African Republic. Specifically, we examined whether (1) between‐species variability is correlated with other species traits; (2) reproductive diameter varies within‐species among sites; (3) reproductive status varies with crown exposure; and (4) the minimum cutting diameter limits (MCDL) imposed by national forest regulations enable seed trees to persist after logging operations. Consistent with studies conducted elsewhere in the tropics, we found great variability in diameter at reproduction among species, which correlated with adult stature (maximum diameter and height). For some species, reproductive diameter thresholds substantially varied between sites, and crown exposure had a significant positive effect on reproductive status. Most MCDLs were found to be suitable, with trees having a high probability of being seed trees at MCDL. Our findings have implications for the sustainable management of production forests, and they highlight questionable MCDLs for some species and between‐site variation in reproductive diameter. The study also highlights the need for long‐term phenological monitoring of tree species spanning a large range of ecological strategies to address both theoretical (species life history, allocation trade‐offs) and practical questions (MCDL).     

Transformation of five grape rootstocks with plant virus genes and a virE2 gene from Agrobacterium tumefaciens

Summary To facilitate the development of transgenic grapevines that are resistant to grapevine fanleaf virus (GFLV), grapevine leafroll-associated closterovirus (GLRaV-3) and crown gall diseases, we developed a rapid system for regenerating root-stocks: Couderc 3309, Vitis riparia ‘Gloire de Montpellier’, Teleki 5C, Millardet et De Grasset 101-14, and 110 Richter via somatic embryogenesis. Embryo culture and grape regeneration were accomplished with four media. Embryogenic calluses from anthers were induced in the initiation medium [MS basic medium containing 20 g sucrose per L, 1.1 mg 2,4-dichlorophenoxyacetic acid (2,4-D) per L, 0.2 mg N⁶-benzyladenine (BA) per L, and 0.8% Noble agar). The percentage of anthers that developed into embryogenic calli ranged from 2 to 16.3% depending on the rootstock. Calluses with early globular stage embryos were cocultivated with Agrobacterium tumefaciens strain C58Z707 containing the gene constructs of interest. The genes were sense-oriented translatable and antisense coat protein genes from GFLV and GLRaV-3, a truncated HSP90-related gene of GLRaV-3 (43K), and a virE2 del B gene from A. tumefaciens strain C58. Twenty independent transformation experiments were performed on five rootstocks. After 3–4 mo. under kanamycin selection, secondary embryos were recovered on differentiation medium (1/2 MS salts with 10 g sucrose per L, 4.6 g glycerol per L, and 0.8% Noble agar). Embryos that were transformed were regenerated on a medium containing MS salts with 20 g sucrose per L, 4.6 g glycerol per L, 1 g casein hydrolysate per L, and 0.8% Noble agar. Elongated embryos were then transferred to a rooting medium supplemented with 0.1 mg BA per L, 3 g activated charcoal per L, 1.5% sucrose, and 0.65% Bacto agar. A total of 928 independent putative transgenic plants were propagated in the greenhouse. All plants were tested for neomycin phosphotransferase II expression by enzyme-linked immunosorbent assay (ELISA). The presence of transgenes was assessed by polymerase chain reaction and Southern analysis. ELISA revealed various levels of expression of GFLV coat protein in transgenic plants of Couderc 3309. The transgenic rootstocks that have been generated are being screened to determine whether transgenes have conferred resistance to the virus and crown gall diseases.     

Enantioselective determination of FCE 28833, a new potential antiischemic agent,in gerbil plasma using column switching HPLC with UV detection

A sensitive and selective high performance liquid chromatographic method using an automated column switching technique for the determination of FCE 28833 enantiomers in gerbil plasma was developed. After solid-liquid extraction using a Supelcosil C₁₈ cartridge FCE 28833 was eluted on a clean-up column (Spherisorb CN) and the enantiomers were separated using an analytical chiral column (Crownpack CR(+)). The mobile phase (15% methanol in HClO₄ 1 mM) was directed through the columns at a flow rate of 1 ml/min and the fraction eluted between 13 and 40 min was transferred from the clean-up column into the analytical column. FCE 28833 enantiomers were monitored at 257 nm. The limit of quantitation of the method was 20 ng/ml plasma for both enantiomers and proved to be linear, precise, and accurate for the assay of both enantiomers in the 20–6,000 ng/ml concentration range. No interference from the blank gerbil plasma sample was observed. The suitability of the method was assessed using plasma samples obtained from male gerbils treated with a single oral dose (400 mg/kg) of FCE 28833. Chirality 9:133–138, 1997. © 1997 Wiley-Liss, Inc.     

Infection process of Gaeumannomyces graminis var. graminis on the roots and culms of rice

Crown sheath rot, caused by the ascomycete Gaeumannomyces graminis var. graminis that infects the root and the base of the culm of rice, causes early grains maturation, tiller death and reduced yield. As a paucity of information exists in the literature on the rice‐G. graminis var. graminis interaction at the microscopic level, this study aimed to gain novel insights into the infection process of this pathogen in the root and culm of rice using both light and scanning electron microscopy. In the roots, the fungus initially colonized the epidermal, exodermal and sclerenchyma cells. At 15 days after inoculation (dai), fungal hyphae colonized the cortex and clusters of perithecia were observed in the roots. At 20 dai, the fungus reached the central cylinder, and an intense fungal colonization at the base of the culm was observed that resulted in the formation of a mycelial mat on both adaxial and abaxial surfaces of the leaf sheaths. At 25 dai, fungal growth was noticed in the parenchyma cells, vascular bundles and airspaces. Perithecia emerged through the base of prophyllum and from the first leaf sheath at 30 dai. The results of this study provide new insights into the infection process of G. graminis var. graminis in rice and may help to find better control measures in reducing crown sheath rot development.