Simon F. Shamoun

Standardizing the Nomenclature for Clonal Lineages of the Sudden Oak Death Pathogen, Phytophthora ramorum

Phytophthora ramorum, the causal agent of sudden oak death and ramorum blight, is known to exist as three distinct clonal lineages which can only be distinguished by performing molecular marker-based analyses. However, in the recent literature there exists no consensus on naming of these lineages. Here we propose a system for naming clonal lineages of P. ramorum based on a consensus established by the P. ramorum research community. Clonal lineages are named with a two letter identifier for the continent on which they were first found (e.g., NA = North America; EU = Europe) followed by a number indicating order of appearance. Clonal lineages known to date are designated NA1 (mating type: A2; distribution: North America; environment: forest and nurseries), NA2 (A2; North America; nurseries), and EU1 (predominantly A1, rarely A2; Europe and North America; nurseries and gardens). It is expected that novel lineages or new variants within the existing three clonal lineages could in time emerge.

Growth, sporulation, and conidia discharge of Valdensinia heterodoxa a foliar pathogen of salal, as influenced by temperature and photoperiod in vitro

Four day/night temperature regimes (11/6, 14/9, 17/12, 20/15 °C), three photoperiods (0, 12, 24 h d −1 ), and four continuous temperature regimes (10, 13, 16, 19°) were evaluated for their effects on growth, sporulation, and conidia discharge of two isolates of Valdensinia heterodoxa , a foliar pathogen of salal ( Gaultheria shallon ). All temperature regimes supported mycelial growth; however, growth rates were faster at higher temperatures. Sporulation and conidia discharge in both isolates was generally highest at 17/12° (day/night) or 16° constant compared with other temperature regimes. Photoperiods of 12 and 24 h d −1 resulted in faster growth and significantly greater sporulation and discharge compared with a continuous dark treatment. The study shows that temperature and light conditions have a moderate effect on mycelial growth but are crucial for sporulation of V. heterodoxa. Possible implications for the use of V. heterodoxa as a potential biological control agent for salal are discussed.

Contrasting research approaches to managing mistletoes in commercial forests and wooded pastures.

Many mistletoe species are pests in agricultural and forest ecosystems throughout the world. Mistletoes are unusual “weeds” as they are generally endemic to areas where they achieve pest status and...

Forest pathogens: friend or foe to biodiversity?

Biological diversity in forest ecosystems results from evolutionary processes driven by ecological imperatives linked to pathogens, symbionts, fire, climate, and competition or impacts from other agents of disturbance. To understand the behavior of microorganisms and microbial pathogens, it is necessary to have a comprehensive appreciation for the diversity of their functional attributes in their natural habitats. Where niches are complex, evolution is guided by more than simple host–pathogen relationships. Moreover, the negative attributes of a pathosystem are not always obvious at different scales or in different contexts. Deleterious impacts on one species (e.g., mortality, parasitism) may benefit another species through reduced competition or enhanced nutrient cycling. Species with pathogenic behavior also display mutualistic and symbiotic benefits (e.g., mycorrhizal fungi and endophytic antagonists found in grasses) or useful attributes as biological control agents. Preserving the diversity of natural areas while controlling forest pests is both a challenge and an opportunity. The challenge is to understand pest niches more thoroughly, while the opportunity is to have a wiser use of both timber and nontimber forest resources.

Colonisation of leaves and twigs of Rubus parviflorus and R. spectabilis by endophytic fungi in a reforestation site in British Columbia

A study was designed to isolate and identify the endophytic mycobiota in leaves and twigs of Rubus spectabilis and R. parviflorus, the long-term goal being biological control of these plants with endophytes. Endophytic fungi were isolated from healthy-looking leaves and twigs collected from each species on Vancouver Island, British Columbia, Canada. More than 90% of the leaves of both species were colonised by endophytes. In addition, one third of the twig samples of each species were also colonised. Most isolates belonged to Phomopsis, and five species were identified and characterised according to morphology of the cultures and fructification structures. All Phomopsis species occurred on both Rubus species, but, one primarily colonised R. parviflorus, whereas another preferentially colonised R. spectabilis. The suitability of the isolated endophytes to inhibit growth of R. spectabilis and R. parviflorus, which compete with conifers in reforestation sites, is discussed.

Effects of culture media, temperature, pH, and light on growth, sporulation, germination, and bioherbicidal efficacy of Phoma exigua, a potential biological control agent for salal (Gaultheria shallon)

Abstract In order to evaluate the potential use of Phoma exigua isolate PFC 2705 (PFC2705) as a biological control agent for salal (Gaultheria shallon), effect of cultural and environmental parameters on growth, conidia production, and pathogenicity of P. exigua were characterized in studies conducted under laboratory and greenhouse conditions. Within a range of 5–30°C, the optimum growth and germination temperature range was 20–25°C. The effect of pH on mycelial growth and conidial germination was not significant from pH 5 to 10. Fluorescent light significantly enhanced sporulation of the fungus on most agar media tested, yet was not necessary for growth. The type of culture media significantly affected mycelium growth, sporulation, and conidia germination. Age of mycelia used as inoculum affected the disease severity on salal. PFC2705 suppressed the growth of mature salal plant by inciting lesions on leaves, branch tips, and axillary buds and caused 56% death of the total biomass above ground. Characteristics such as easy inoculum production, wide range of growth environments, and high infectivity on salal increased the potential of P. exigua as a biocontrol agent for management of salal.

Effects of potato dextrose broth and gelatin on germination and efficacy of Phoma exigua, a potential biocontrol agent for salal (Gaultheria shallon)

The role of a combination of four gelatin concentration levels (0.0%, 0.2%, 0.5%, and 0.8%) and eight potato dextrose broth (PDB) concentration levels (0.0%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%) on water evaporation, water absorption, conidial germination, and biocontrol efficacy of conidia of Phoma exigua isolate PFC2705 for salal was evaluated. PDB and gelatin reduced water evaporation. After 3 h of evaporation at 23 °C and 22% RH, the water content of gelatin–PDB combinations increased compared with PDB alone. The relationships between the amounts of absorbed water and PDB concentration at all gelatin concentration levels were linear (p < 0.001) after 60 min in a 100% RH environment. After 240 min, the mass of absorbed water was 11.8 times the dry mass of the 0.5% gelatin and 1.5% PDB combination, and this relationship did not change significantly over the following 16 h. PDB and gelatin increased conidial germination and might have provided nutrition for conidia of P. exigua PFC2705 at different RH environments. Conidia of PFC2705 did not germinate in sterilized ion-free water, germinated somewhat (4% to 10%) in gelatin suspensions, and germinated well (average 89%) in suspensions of different concentrations of PDB or gelatin–PDB combinations after 24 h at 23 °C. The average conidial germination at 24 h was 76% in 100% RH, 12% in 97.5% RH, and 0.0% at 92.5% RH; at 48 h it was 44.4% in 97.5% RH and 20% in 92.5% RH. No conidia germinated when RH was lower than 92.5% over 48 h. Conidia in the gelatin–PDB combinations smeared on slides stored for 4 weeks at 23 °C with 22% RH had an average conidial germination rate of 20% after 16 h incubation at 100% RH. Gelatin–PDB combinations with 0.5% gelatin and 1.5% to 2.5% PDB caused significantly larger lesions on detached young salal leaves (20 to 25 days old) than other gelatin–PDB combinations.

In vitro germination and development of western hemlock dwarf mistletoe

A procedure for in vitro culture of the parasitic flowering plant western hemlock dwarf mistletoe, Arceuthobium tsugense (Rosend.) G.N. Jones subsp. tsugense, is described. A factorial experiment evaluated the effects of media (Harveys medium (HM) and modified Whites medium (WM)), temperatures (15 °C and 20 °C), presence or absence of light, and plant growth regulators (the auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the cytokinin 6-benzylaminopurine (BAP) at varying concentrations (0.001 mg l−1 to 1 mg l−1)). Seed explants germinated in less than one week in culture and produced radicles. Optimal conditions for radicle elongation were WM at 20 °C in the presence of light and without plant growth regulators. Some of the radicles split at the tip to yield callus while others swelled to become spherical holdfasts. Holdfasts were also produced at the tips of radicles, and callus arose from split holdfasts. Factors that promoted holdfast production were Harveys medium, light, and 2,4-D at 1 mg l−1. Callus development from split radicles and split holdfasts was optimal on WM with 0.5 mg l−1 2,4-D and 1 mg l−1 BAP at 20 °C in the dark.

Evaluation of an Inoculum Production and Delivery Technique for Valdensinia heterodoxa, a Potential Biological Control Agent for Salal

Inoculum production of Valdensinia heterodoxa Peyr. (isolate PFC 3027), a foliar pathogen of salal (Gaultheria shallon Pursh.), was evaluated on various solid substrates. Incubation on salal leaf pieces resulted in the greatest number of discharged conidia, which is deemed a suitable indicator for sporulation and inoculum dispersal of V. heterodoxa. Subsequently, V. heterodoxa inoculum of two isolates (PFC 2761 and PFC 3027) was produced on salal leaf pieces using four different growth periods (0, 4, 8, or 12 days) and three different cold storage treatments (0, 4, or 8 weeks) following harvest of colonised leaf pieces. Overall, the maximum number of discharged conidia was obtained with a growth period of 4 or 8 days, whereas the effect of a cold storage treatment was inconclusive between the fungal isolates and various growth periods. Conidia discharge from salal leaf piece inoculum of V. heterodoxa (PFC 2761 and PFC 3027) applied on pot soil level resulted in 8-41% leaf damage of intact salal plants. Results from this study indicate the potential of salal plant tissue as both a growth substrate and a suitable delivery technique for V. heterodoxa to control salal.

Assessment of Neonectria neomacrospora (anamorph Cylindrocarpon cylindroides) as an inundative biocontrol agent against hemlock dwarf mistletoe

A field trial was conducted on Vancouver Island to evaluate the efficacy of the native fungus Neonectria neomacrospora as a biocontrol agent of hemlock dwarf mistletoe (Arceuthobium tsugense), a conifer parasite. Treatments consisted in formulated inoculum of N. neomacrospora applied to unwounded and wounded A. tsugense swellings. After 10 months, the amount of bark necrosis for the wounded, inoculated treatment was significantly greater than for the other treatments. Similarly, sporodochia were more common (present on 50% of swellings) for the wounded, inoculated treatment than the other treatments (present on less than 10% of swellings). Neonectria neomacrospora was isolated from 55.0% of unwounded, inoculated swellings and from 73.7% of those wounded and inoculated, while isolated from 20.0% of unwounded, uninoculated swellings and from 35.0% of those wounded and uninoculated. These results suggest that, although some infection does occur when inoculum is applied to unwounded swellings of hemlock dwarf mistletoe, wounding significantly enhances infection. Hemlock dwarf mistletoe swellings with confirmed N. neomacrospora infection (isolation of the fungus and (or) presence of sporodochia) had their numbers of healthy mistletoe shoots significantly reduced (by 1.6, or about 36%) when compared with mistletoe swellings with unconfirmed infection (P = 0.014).