The influence of natural disturbances on developmental patterns in Acadian mixedwood forests from 1946 to 2008

We used dendrochronological analyses to identify periods of natural disturbance and resulting growth responses in 32 mixed species stands in the Acadian forest. Stands represented five different development patterns, based upon 1946 softwood (SW) content (70–80%, termed SW versus 30–60%, termed mixedwood (MW)) and change in SW content from 1946 to 2006: SW-stable, SW-declining, MW-fluctuating, MW-stable, and MW-declining. Standardized growth chronologies were developed from 1163 increment cores sampled from balsam fir (Abies balsamea), red spruce (Picea rubens), yellow birch (Betula alleghaniensis), and sugar maple (Acer saccharum). Growth chronologies clearly identified three spruce budworm (Choristoneura fumiferana) outbreaks from 1914 to 1921, 1954 to 1961, and 1975 to 1984, and birch dieback from 1938 to 1948. Stand developmental patterns were caused by species characteristics and multiple interacting disturbances, resulting in mortality, growth reductions, releases, and establishment of new cohorts. Balsam fir was present in all stands, but its tendency to establish and release from advanced regeneration following budworm-caused mortality resulted in cyclical proportions of fir in the canopy. Red spruce was less vulnerable to spruce budworm and longer lived, allowing them to persist and better withstand disturbance. Periodic growth index values less than 0.9 for fir and spruce were correlated with mortality of softwoods caused by defoliation, which resulted in release and growth index values >1.1 for sugar maple. Our results demonstrated substantial variation in mixedwood development patterns over a 60-year period within a small (45 km) area.     

Morphological and Molecular Identification of Phytophthora tropicalis as Causal Agent of Crown and Root Rot on Albizia julibrissin

Isolates of a Phytophthora sp. were obtained from soil and root baiting of declining Albizia julibrissin plants grown in soil in an Italian nursery. Identification was performed on the basis of morphological, pathological and molecular features. As main characteristics, isolates did not grow at 35°C, were poorly pathogenic when inoculated on bell pepper plants, and had the average sporangium pedicel length longer than 100, being similar to Phytophthora tropicalis. A comparative study of internal transcribed spacer, beta‐tubulin, translation elongation factor‐1 alpha and cytochrome c oxidase subunit II (CoxII) sequences supported the identification of the isolates as P. tropicalis. Comparison included all the European isolate sequences available in GenBank. Pathogenicity tests reproduced symptoms of root and crown browning and rotting and wilting as originally observed on nursery plants. Considering all the results, we identified P. tropicalis as the causal agent of A. julibrissin decline, crown and root rot. To our knowledge, this is the first report of this host–pathogen combination in Italy or elsewhere. P. tropicalis has to be considered a serious threat to agricultural and natural environment because it is highly polyphagous and easy to spread due to its caducous sporangia.     

Stand-level distribution and movement of Platypus quercivorus adults and patterns of incidence of new infestation

Abstract 1 Flying populations of an ambrosia beetle, Platypus quercivorus (Murayama), a vector of an ambrosia fungus Raffaelea quercivora, which causes deciduous oak diebacks in Japan, were determined by sticky screen traps. 2 Platypus quercivorus beetles tended to move upwards along slopes. The highest concentrations of flying beetles usually occured at the upper forest margins. 3 During the period when the number of flying beetles was increasing, the incidence of newly infested trees spread from the epicentre into the forest. During the period when the number of flying beetles was decreasing, the epicentre shrank into the upper forest edge. Newly infested trees did not occur in this period because most trees had already been infested. 4 Near the upper forest edge, where many beetles were highly concentrated throughout the season, the number of new entry holes decreased greatly after the initial attack early in the season, although many adults were present throughout the period.     

Differences among avocado cultivars in susceptibility to polyphagous shot hole borer (Euwallacea spec.)

Polyphagous shot hole borer (PSHB) (Euwallacea spec.; Coleoptera: Curculionidae: Scolytinae) has recently invaded southern California, USA. Along with its associated fungi, the beetle causes branch dieback and tree mortality in more than 200 host tree species, including avocado (Persea americana Mill., Lauraceae) and many important native, urban landscape, and nursery stock trees. As PSHB spreads into the avocado‐growing regions of southern California, there is a pressing need for more information for effective management of the insect/fungus complex. The objective of this study was to examine avocado cultivars to see whether there were differences in susceptibility to attack and gallery development from PSHB. We conducted choice and no‐choice trials with cut branches in the laboratory, artificially infested avocado saplings with PSHB, and also surveyed attack rates for two cultivars of field‐grown avocado subject to natural attack by PSHB. Laboratory and field trials showed similar patterns for preference among avocado cultivars indicated by beetle attack rates and gallery formation. Among the common commercial cultivars, Fuerte, Gwen, and Bacon most often had lower attack rates and lower rates of gallery formation. Zutano most frequently indicated high attack rates and much gallery formation, indicating that it may be the most susceptible to PHSB of the commercial cultivars.     

Characterizing the production of a wild-type and benomyl-resistant Fusarium lateritium for biocontrol of Eutypa lata on grapevine

Benomyl-resistant (BR) and wild-type (WT) strains of Fusarium lateritium were examined for their tolerance to benomyl on potato dextrose agar (PDA) containing benomyl and control of the Eutypa lata in grapevine bioassays. The WT strain grew on PDA containing 1 μg/ml benomyl at 13, 26 and 29°C. The BR strain grew on PDA containing 10 μg/ml benomyl at 4°C, on PDA containing 100 μg/ml benomyl at 29°C, and on PDA containing 1000 μg/ml benomyl at 13 and 26°C. The BR strain was also able to colonize grapevine segments and control E. lata in the presence of 1000 μg/ml benomyl. Both strains were amenable to production via liquid fermentation and both achieved 100% control of E. lata in grapevine bioassays. Neither the duration of fermentation nor incubation temperature during grapevine bioassays influenced the efficacy of either strain against E. lata. The results suggest that application of BR F. lateritium alone or in combination with benomyl may provide good control of E. lata. Journal of Industrial Microbiology & Biotechnology (2001) 26, 151–155. Received 22 December 1999/ Accepted in revised form 20 October 2000     

Development of a multiplex PCR assay to discriminate native Hymenoscyphus albidus and introduced Hymenoscyphus fraxineus in Britain and assess their distribution

Two Hymenoscyphus species are associated with ash (Fraxinus) in Europe; the recently arrived ash dieback pathogen Hymenoscyphus fraxineus and apparently native Hymenoscyphus albidus. However, in parts of Europe invasive H. fraxineus appears to be replacing H. albidus which may, therefore, face extinction. We designed primers based on calmodulin sequences for use in singleplex and multiplex PCR assays to detect and discriminate between these two morphologically very similar species. The multiplex assay was tested against 50 isolates and 26 apothecial field samples of H. albidus/H. fraxineus from Europe and Asia, plus isolates of Hymenoscyphus fructigenus, Hymenoscyphus koreanus and Hymenoscyphus occultus. Use of the assay confirmed both H. albidus and H. fraxineus were present across southern Britain between 2014 and 2015, with H. albidus detected at eight geographically distinct sites. The sensitivity, specificity and potential applications of the multiplex assay are discussed.     

Enzymatic detoxification of eutypine, a toxin from Eutypa lata, by Vitis vinifera cells: partial purification of an NADPH-dependent aldehyde reductase

Eutypine, 4-hydroxy-3-(3-methyl-3-butene-1-ynyl) benzaldehyde, is a toxin produced by Eutypa lata (Pers.: Fr.) Tul., the causal agent of dying arm disease of Vitis vinifera L. (grapevine). Previously, we have shown that eutypine is involved in the development of disease symptoms. In the present study, the effects of V. vinifera cell-suspension cultures on the biological activity of the toxin were investigated. Eutypine was converted by grapevine tissues into a single compound, identified by mass spectrometry and nuclear magnetic resonance as 4-hydroxy-3-(3-methyl-3-butene-1-ynyl) benzyl alcohol, designated eutypinol. This compound was found to be non-toxic for grapevine tissues. Unlike eutypine, eutypinol failed to affect the oxidation rate or membrane potential of isolated mitochondria. In grapevine cells, reduction of eutypine into the corresponding alcohol is an NADPH-dependent enzymatic reaction. An enzyme which reduced eutypine was partially purified, over 1000-fold, using a five-step purification procedure. By gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the protein was found to have a molecular mass of 54–56 kDa. The enzyme exhibited an apparent K _m for eutypine of 44 μM, and was active between pH 6.8 and 7.5 with a maximum at pH 7.0. The eutypine reductase activity was improved by Mn²⁺ and Mg²⁺ and inhibited by disulfiram and p-hydroxymercuribenzoate. The possible role of the eutypine-detoxification mechanism in the defense reactions of V. vinifera cells is discussed. Received: 20 April 1998 / Accepted: 22 September 1998     

A low‐cost,yet simple and highly repeatable system for acoustically surveying cryptic species

Accurate determination of the population density of key focal species is necessary for monitoring the success of management programs and ecosystem health across a wide range of contexts. Unfortunately, many key taxa are visually cryptic and thus difficult to count using traditional observation‐based techniques. Bell miners (Manorina melanophrys), are just such a species. They are widespread throughout south‐eastern Australia, yet they are critical to monitor given their association and potential causal link to spreading vegetative dieback in this region. A new passive acoustic monitoring technique was trialled by testing its ability to determine population densities of bell miner colonies via counting the distinctive ‘tink’ vocalization of this species. This call was given at a constant rate per individual, and at a common amplitude across 10 colonies throughout the entire geographic range of the species. Theoretical sound transmission and playback trials through typical habitat determined that any bird within a 50‐m radius of the recorders used would be louder than 70 dB, enabling this threshold amplitude to be used to determine the number of birds in a 50 m radius of the recorder. Field trials of the acoustic protocol versus human observers using traditional visual surveys found that passive acoustic monitoring was able to detect more individuals, using a less expensive protocol that drastically reduced the need for observer training or expertise. Sound therefore offers a reliable method for determining the density of this vocal, but visually cryptic species. We present methods for calibrating recording devices and detecting calls louder than species‐specific thresholds using readily available freeware, enabling our methods to be easily adapted to census a variety of acoustically distinctive species, offering a more effective, yet lower cost and in our case more efficient census technique for surveying difficult species.