Red Needle Research Articles

Combined use of spectral and structural characteristics for improved red band needle blight detection in pine plantation stands

Current trends in research for detection of infections in forests almost exclusively involve the use of a single imaging sensor. However, combining information from a range of sensors could potentially enhance the ability to diagnose and quantify the infection. This study investigated the potential of combining hyperspectral and LiDAR data for red band needle blight detection. A comparative study was performed on the spectral signatures retrieved for two plots established in lodgepole pine stands and on a range of LiDAR metrics retrieved at individual tree-level. Leaf spectroscopy of green and partially chlorotic needles affected by red band needle blight highlighted the green, red and short near-infrared parts of the electromagnetic spectrum as the most promising. A good separation was found between the two pine stands using a number of spectral indices utilising those spectral regions. Similarly, a distinction was found when intra-canopy distribution of LiDAR returns was analysed. The percentage of ground returns within canopy extents and the height-normalised 50th percentile (height normalisation was performed to each tree’s canopy extents) were identified as the most useful features among LiDAR metrics for separation of trees between the plots. Analysis based on those metrics yielded an accuracy of 80.9%, indicating a potential for using LiDAR metrics to detect disease-induced defoliation. Stepwise discriminant function analysis identified Enhanced Vegetation Index, Normalised Green Red Difference Index, percentage of ground returns, and the height-normalised 50th percentile to be the best predictors for detection of changes in the canopy resulting from red band needle blight. Using a combination of these variables led to a substantial decrease of unexplained variance within the data and an improvement in discrimination accuracy (96.7%). The results suggest combining information from different sensors can improve the ability to detect red band needle blight.

Canopy temperature from an Unmanned Aerial Vehicle as an indicator of tree stress associated with red band needle blight severity

Monoculture plantation woodlands are particularly vulnerable to disturbance events as species uniformity makes such stands highly susceptible to pests and diseases. Red band needle blight (caused by the fungus Dothistroma septosporum) is a disease which has a particularly significant economic impact on pine plantation forests worldwide, affecting diameter and height growth. However, monitoring its spread and intensity is complicated by the fact that the diseased trees are often only visible from aircraft in the advanced stages of the epidemic. Remote sensing could potentially aid in the detection of infected stands and in monitoring disease development and spread. Thermography is one of the techniques that can be used for monitoring changes in the physiological state of plants following infection. However, the use of thermography in forestry has so far been restricted by poor spatial resolution (satellite-based sensors) or high data acquirement costs (airborne sensors). This paper investigates the use of Unmanned Aerial Vehicle (UAV)-borne thermal systems for detecting disease-induced canopy temperature increase and explores the influence of the imaging time and weather conditions on the detected relationship. Furthermore, the potential of a number of airborne LiDAR-derived structural metrics for detection of changes in the canopy structure following the infection are investigated. The study was located in a diseased Scots pine (Pinus sylvestris) stand in Queen Elizabeth II Forest Park (central Scotland, UK), where 60 sample trees were surveyed. The thermal imagery was acquired at six different times of a day from an altitude of 60 m. Statistically significant correlation between canopy temperature depression (CTD) and disease levels was found for most of the flights (R2 between 0.27 and 0.41), which may be related to the needle damage symptoms caused by the disease, i.e. loss of cellular integrity, necrosis and eventual desiccation. Furthermore, the standard deviation of the crown temperature exhibited weak but statistically significant correlation (R2 between 0.11 and 0.13). The combination of CTD and standard deviation of crown temperature in a partial least squares regression (PLSR) further improved the observed relationship with the estimated disease level. Inclusion of LiDAR structural metrics was also investigated but only provided a slight improvement. A change in environmental conditions altered the magnitude of differences between canopy temperatures; no significant correlation with disease level was found in the morning flight, whilst the strongest relationship was obtained at the time of highest solar radiation, which coincides with the time of maximum photosynthetic activity.

Validating outsourced high throughput automated qPCR for increased research outputs from forest pathology trials

Needle diseases of Pinus radiata caused by Phytophthora pluvialis and Phythophthora kernoviae have been increasingly recognised since the discovery of red needle cast in 2008. There is a need for rapid diagnostic screening of numerous samples, but sample processing time, equipment and staff availability limit the throughput and utilisation of diagnostic qPCR analysis in the research environment. Automated and high-throughput capable DNA extraction and real-time PCR provides the opportunity to expand the capacity of research trial analysis and a potential alternative to laborious isolation and plating but must be thoroughly validated before results can be used with confidence. The use of a high-throughput format for qPCR assays targeting Phytophthora pluvialis and Phythophthora kernoviae was validated on a robotic platform, proving to be consistently more sensitive than isolation, achieving qPCR detection down to 1% diluted inoculated material for Phytophthora kernoviae and 10% for Phytophthora pluvialis. Plating results yielded a 60% detection rate of Phythophthora pluvialis in inoculated needle fragments, whereas qPCR yielded a 100% detection on the same material. High throughout automated qPCR can therefore be utilised with confidence in forest pathology research trial analyses in future.

Assessing the genetic variation of tolerance to red needle cast in a Pinus radiata breeding population

Breeding for disease resistance or tolerance is a viable option for disease management programmes and is important for the continued success and resilience of planted forests. Red needle cast (RNC) is a disease that affects radiata pine (Pinus radiata) and is caused by Phytophthora pluvialis. Knowledge is still very limited regarding the potential for genetic tolerance to this pathogen. The application of controlled screening techniques is clearly required. Using a detached needle assay, we screened 392 clonally replicated individuals (clones) from an elite P. radiata population for quantitative tolerance to RNC. Data was highly skewed and required logarithmic data transformation and Poisson distributions for the estimation of best linear unbiased predictions. These estimates revealed a broad range in susceptibility/tolerance to RNC, and enabled the identification of clones that were clearly susceptible and clones that were clearly tolerant. There was a high correlation between the number and length of lesions that developed in response to inoculation with P. pluvialis. Broad-sense heritability estimates were low to moderate, indicating that there is potential for improving tolerance through breeding. These results provide evidence that breeding for tolerance to P. pluvialis is possible, although continued work into understanding and minimising causes for variance are required.

A dynamical systems model for poly-cyclic foliar forest pathogens

A simple systems model is proposed to understand and quantify the onset and epidemiology of red needle cast in radiata pine. This disease is impacting much of the New Zealand forestry estate being driven through the production of self-replicating spores which are dispersed with water. The model is at present deterministic, not spatially or age-structured, nor dependent on environmental or seasonal effects. This model shows the clear existence of calculable thresholds for disease proliferation and elimination, showing it has captured the essential components of the biological mechanisms. It is to be used to identify thresholds for infection to spread or retract. Further it will provide a base model from which we can fit and then predict experimental outcomes. References C Lee Campbell, Laurence V Madden, et al. Introduction to plant disease epidemiology. John Wiley and Sons., 1990. Margaret Anne Dick, Nari Michelle Williams, Martin Karl-Friedrich Bader, Judy Frances Gardner, and Lindsay Stuart Bulman. Pathogenicity of phytophthora pluvialis to pinus radiata and its relation with red needle cast disease in new zealand. New Zealand Journal of Forestry Science, 44(1):6, 2014. Heidi S Dungey, Nari M Williams, Charlie B Low, and Graham T Stovold. First evidence of genetic-based tolerance to red needle cast caused by phytophthora pluvialis in radiata pine. New Zealand Journal of Forestry Science, 44(1):31, 2014. RJ Ganley, NM Williams, CA Rolando, IA Hood, HS Dungey, PN Beets, LS Bulman, et al. Management of red needle cast, caused by phytophthora pluvialis, a new disease of radiata pine in new zealand. N. Z. Plant Protect.-SE, 67:48–53, 2014. Wake GC. Private communication, 2017. Christopher A Gilligan. An epidemiological framework for disease management. Advances in botanical research, 38:1–64, 2002. MJ Jeger. Asymptotic behaviour and threshold criteria in model plant disease epidemics. Plant Pathology, 35(3):355–361, 1986. Nurul S Abdul Latif, Graeme C Wake, Tony Reglinski, and Philip AG Elmer. Modelling induced resistance to plant diseases. Journal of theoretical biology, 347:144–150, 2014. Nurul S Abdul Latif, Graeme C Wake, Tony Reglinski, Philip AG Elmer, and Joseph T Taylor. Modeling induced resistance to plant disease using a dynamical systems approach. Frontiers in plant science, 4, 2013. Laurence V Madden, Gareth Hughes, Frank Bosch, et al. The study of plant disease epidemics. American Phytopathological Society (APS Press), 2007. CA Rolando, MA Dick, J Gardner, M Bader, NM Williams, et al. Chemical control of two phytophthora species infecting the canopy of monterey pine (pinus radiata). Forest Pathology, 47(3), 2017. Carol Rolando, Robyn Gaskin, David Horgan, Nari Williams, and Martin KF Bader. The use of adjuvants to improve uptake of phosphorous acid applied to pinus radiata needles for control of foliar phytophthora diseases. New Zealand Journal of Forestry Science, 44(1):8, 2014.

Genetic diversity of Phytophthora pluvialis, a pathogen of conifers, in New Zealand and the west coast of the United States of America

Phytophthora pluvialis is the causal agent of red needle cast on Pinus radiata in New Zealand. It was first isolated in 2008 but had previously been recovered from tanoak (Notholithocarpus densiflorus) and Douglas‐fir (Pseudotsuga menziesii) trees in Oregon, USA in 2002. Phytophthora pluvialis was subsequently described as a new species in 2013 and classified as a clade III Phytophthora species. The aim of this study was to gain a better understanding of the genetic diversity, population structure and origin of this pathogen. A total of 360 P. pluvialis isolates were collected from the USA and New Zealand. The genome sequences of two P. pluvialis isolates were used to identify 27 single nucleotide polymorphism (SNP) markers that were then used to genotype the two populations. The genotypic data showed that the USA population of P. pluvialis had twice the genetic diversity and a greater number of multilocus genotypes (MLGs) compared to the New Zealand population, with 126 and 24 MLGs, respectively. The majority of the subpopulations within the USA and New Zealand showed linkage disequilibrium. All subpopulations had a negative fixation index, indicating that clonal reproduction is prevalent in both countries. A minimum spanning network (MSN) showed two unique clusters of isolates in the New Zealand population, suggesting two potential introductions of P. pluvialis into New Zealand from the USA. There was no significant structure within the New Zealand or USA populations. This study provides novel insight into the genetic structure of P. pluvialis in New Zealand and the USA.

Climate change induced drought impacts on plant diseases in New Zealand

Climate change is expected to increase the frequency and duration of drought in many parts of New Zealand. This may affect the natural lifecycles of plant pathogens, influence host predisposition to infection or disease expression, shift the natural ranges of the pathogens, and alter the rate of genetic change in pathogen populations. Collectively, these influences are likely to affect a range of pathosystems of significant economic importance to New Zealand’s productive sectors. We undertook analyses of potential drought impacts on several diseases of plants important to New Zealand: pea root rot (caused by Aphanomyces euteiches), onion white rot (Sclerotium cepivorum), wheat take-all (Gaeumannomyces graminis var. tritici), wheat crown rot (Fusarium spp.), brassica black leg (Leptosphaeria maculans), grapevine black foot (Ilyonectria/Dactylonectria spp.), kiwifruit sclerotinia rot (Sclerotinia sclerotiorum), and radiata pine red needle cast (Phytophthora pluvialis). For most pathosystems, increased drought is expected to increase disease expression. However, drought may reduce the severity of some diseases, such as Scelerotina rot of kiwifruit and red needle cast of radiata pine. To exemplify how drought can affect different components of the host-pathogen-environment interaction, a case study on red needle cast of radiata pine is presented. We recommend that land-based productive sectors need to better prepare for the deleterious impacts or beneficial opportunities of increased drought for plant diseases in New Zealand.

Phytophthora pluvialis Studies on Douglas-fir Require Swiss Needle Cast Suppression.

Phytophthora pluvialis is associated with early defoliation and shoot dieback in Douglas-fir in Oregon and New Zealand. In 2013, P. pluvialis was described from mixed tanoak-Douglas-fir forests in the Pacific Northwest and concurrently recognized as the main causal agent of red needle cast (RNC) in New Zealand radiata pine plantations. Little is known about its infection cycle and impact on host physiology. P. pluvialis studies in Douglas-fir are challenging due to the ubiquitous presence of the endophyte Phaeocryptopus gaeumannii, which produces similar symptoms and premature defoliation with persistent needle wetness, known as Swiss needle cast (SNC). Nonetheless, our study showed P. pluvialis infection in the presence of SNC. Exclusive expression of P. pluvialis is difficult to achieve as both diseases are promoted by high humidity. Here we established a 'dry leaf' strategy to suppress SNC when inoculating Douglas-fir needles for RNC studies. Sheltering plants along with drip irrigation to avoid needle wetness during the P. gaeumannii sporulation period suppressed its development in the new season flush. The diminished endophyte inoculum enabled bias-reduced studies of P. pluvialis impacts on Douglas-fir without the confounding effects of stomatal blockage and premature defoliation caused by P. gaeumannii.

Emerging Needle Blight Diseases in Atlantic Pinus Ecosystems of Spain

Red band needle blight caused by Dothistroma septosporum and D. pini, and brown spot needle blight caused by Lecanosticta acicola provoke severe and premature defoliation in Pinus, and subsequent reduction of photosynthetic surfaces, vitality, and growth in young and adult trees. The recurrent damage results in branch and tree death. Until recently, pine needle blight diseases have had only minor impacts on native and exotic forest trees in the North of Spain, but in the past five years, these pathogen species have spread widely and caused severe defoliation and mortality in exotic and native plantations of Pinus in locations where they were not detected before. In an attempt to understand the main causes of this outbreak and to define the effectiveness of owners’ management strategies, four research actions were implemented: a survey of the management activities implemented by the owners to reduce disease impact, the evaluation of specific symptoms and damage associated with infection, and the identification of the causative pathogenic species and their reproductive capacity. Morphological characteristics of the fungus and molecular identification were consistent with those of Lecanosticta acicola and Dothistroma spp., D. septosporum, D. Pini, and both mating types were present for the three identified pathogens. The local silvicultural management performed, mainly pruning and thinning, was not resulting in the expected improvement. The results of this study can be applied to establish guidelines for monitoring and controlling the spread of needle blight pathogens.

UAV-BORNE THERMAL IMAGING FOR FOREST HEALTH MONITORING: DETECTION OF DISEASE-INDUCED CANOPY TEMPERATURE INCREASE

Abstract. Climate change has a major influence on forest health and growth, by indirectly affecting the distribution and abundance of forest pathogens, as well as the severity of tree diseases. Temperature rise and changes in precipitation may also allow the ranges of some species to expand, resulting in the introduction of non-native invasive species, which pose a significant risk to forests worldwide. The detection and robust monitoring of affected forest stands is therefore crucial for allowing management interventions to reduce the spread of infections. This paper investigates the use of a low-cost fixed-wing UAV-borne thermal system for monitoring disease-induced canopy temperature rise. Initially, camera calibration was performed revealing a significant overestimation (by over 1 K) of the temperature readings and a non-uniformity (exceeding 1 K) across the imagery. These effects have been minimised with a two-point calibration technique ensuring the offsets of mean image temperature readings from blackbody temperature did not exceed ± 0.23 K, whilst 95.4% of all the image pixels fell within ± 0.14 K (average) of mean temperature reading. The derived calibration parameters were applied to a test data set of UAV-borne imagery acquired over a Scots pine stand, representing a range of Red Band Needle Blight infection levels. At canopy level, the comparison of tree crown temperature recorded by a UAV-borne infrared camera suggests a small temperature increase related to disease progression (R = 0.527, p = 0.001); indicating that UAV-borne cameras might be able to detect sub-degree temperature differences induced by disease onset.

Spore Dispersal byDothistroma septosporumin Northwest British Columbia

We studied spore dispersal by Dothistroma septosporum, causal agent of a serious outbreak of red band needle blight in lodgepole pine plantations in northwest British Columbia. Spore abundance was assessed at different distances and heights from inoculum sources and microclimatic factors were recorded during two consecutive years. Conidia were observed on spore traps from June to September during periods of rainfall. It was rare to detect spores more than 2 m away from inoculum sources. The timing and number of conidia dispersed were strongly tied to the climatic variables, particularly rainfall and leaf wetness. Should the trend toward increased spring and summer precipitation in the study area continue, the results suggest that disease spread and intensification will also increase. Increasing the planting distances between lodgepole pine trees through mixed species plantations and overall reduction in use of lodgepole pine for regeneration in wet areas are the best strategies to reduce the spread of the disease and enhance future productivity of plantations in the study area.

First Record of Dothistroma pini on Pinus nigra in Switzerland.

The mitosporic ascomycetes Dothistroma septosporum s.s. (Dorog.) Morelet and D. pini Hulbary are closely related species (1) causing red band needle blight on Pinus spp. D. septosporum (teleomorph Mycosphaerella pini Rostr.) is considered as a cosmopolitan species, whereas D. pini (no teleomorph known) seems to have a more restricted distribution area. Detected in the United States on Pinus nigra for the first time, it was later found in Russia, Ukraine, Hungary, and France on different pine species (P. radiata, P. mugo, P. pallasiana) (3). In Switzerland, Dothistroma sp. (species not further determined) was recorded in 1989 for the first time and since then only damages on planted pines (mainly P. mugo and P. nigra) in urban areas were reported (R. Engesser, personal communication). In September 2012 and in April 2013, several planted mature trees and naturally regenerated young trees of P. nigra with Dothistroma needle blight were detected on a climatically mild forest site on limestone at the shore of Lake Walensee (47°07'48.0″ N, 9°13'54.4″ E, 420 m asl). In 2012, symptomatic needles were collected from the litter under one planted mature P. nigra tree and in 2013, symptomatic needles were collected from green twigs from a 2 m tall naturally regenerated P. nigra specimen. Conidiomata were frequently observed in the red bands but no conidia were detected. For fungal isolation, the surface of infected needles was shortly disinfected with 95% ethanol. The epi- and hypo-dermis covering the still closed conidiomata was removed and small tissue samples from the mesophyll (less than 0.5 mm length) were placed on malt extract agar (15 g/liter agar, 20 g/liter malt extract) amended by 50 mg/liter oxytetracycline. Conidia were observed after one year at 4°C in the resulting pure colonies (3 to 4 cm diameter on malt extract agar medium). The conidia formed by strain OH_120923_2_1_1 (KJ878557 = D. pini) were hyaline, smooth, thin-walled, 2- to 4-celled, and 31.6 (22 to 37) × 2.8 (2 to 3.5) μm. While conidial morphology of both Dothistroma species overlap, DNA was extracted and the internal transcribed spacer (ITS) region (primers ITS 1 and ITS 4) sequenced (KJ878557 to 81). From the 25 obtained ITS sequences, seven were identical with AY808275 (D. septosporum from P. radiata, South Africa, CMW 684), three were identical with AY808302 (D. pini from P. nigra, Michigan, CMW 10951), and 15 were identical with DQ926964 (D. pini from P. pallasiana, Ukraine, CMW 23767). The North American and Ukrainian D. pini sequences (AY808302 and DQ926964) showed only 1 bp difference. In addition, mating type genes were amplified using the method described by Groenewald et al. (2) for D. pini and scored using gel electrophoresis. Analyses showed that both D. pini ITS-sequence variants (e.g., KJ878557 and KJ878558) and both mating types were sometimes present in the same needle. In two cases, both mating types and ITS-sequence variants were also present within the same lesion. Interestingly, D. pini and D. septosporum were found on the same tree but not on the same needles. This is the first report of D. pini in Switzerland. Although symptoms of red band needle blight (species not determined) were repeatedly observed on this site during the last 20 years, the disease level always remained low and no tree mortality was noted. However, due to the presence of two ITS-sequence variants and both mating types, the incidence of D. pini in Switzerland deserves attention.

First evidence of genetic-based tolerance to red needle cast caused by Phytophthora pluvialis in radiata pine

Red needle cast (RNC) is a new needle disease of Pinus radiata D. Don (radiata pine) in New Zealand that is causing significant, but as-yet un-quantified, loss of growth and productivity. This foliar disease has recently been attributed to the infection of the needles by Phytophthora pluvialis Reeser, Sutton & E Hansen. Genetic improvement is seen as a possible solution to mitigate the effects of this needle disease on forest productivity. To quantify the ability of genetics to provide a solution, RNC was assessed on a single clones-within-families genetics trial using two methods: the percentage needle cast that was attributable to red needle cast symptoms; and the percentage needle cast where the causal agent was not clearly identifiable. Both needle cast assessment methods were found to be heritable (ĥ 2 0.21-0.31). Selecting for tolerance to RNC is likely to deliver healthier trees. More assessments across a number of sites and seasons are required to confirm this result.

Four New Host and Three New State Records of Dothistroma Needle Blight Caused by Dothistroma pini in the United States.

During 2010 and 2011, Dothistroma needle blight (DNB), also known as red band needle blight, was observed for the first time in Cass and Pembina counties in North Dakota (ND). In Pembina Co., DNB was observed in two sites in the Jay V. Wessels Wildlife Management Area (JWWMA). In September 2009, yellow spots on green needles were observed on some trees along the western edge of one planting. By June 2010, DNB was found on third- and fourth-year needles in both JWWMA plantings. Symptoms had developed into dark brown bands or spots on necrotic needles that contained erumpent black acervuli. In June 2011, similar DNB symptoms were observed on Pinus nigra, P. flexilis, P. ponderosa, P. cembra, and P. albicaulis in the Dale E. Herman Research Arboretum, Cass Co., ND. DNB was collected in July 2011 in Brookings Co., South Dakota (SD), from a seed source provenance planting of P. ponderosa. To identify the species causing the infections, symptomatic needles were collected in 2010 from both sites in JWWMA and then again from all four locations in 2011 on all pine species infected. Needles of P. nigra from a private residence near Fairland in Shelby County, Indiana (IN), were also included in the sample set. The rDNA-ITS was PCR-amplified either directly from conidia obtained from acervuli on the needles or from cultures obtained from isolations. Amplicons were sequenced and a BLAST search was performed in GenBank. The sequences of samples obtained from P. nigra, P. flexilis, P. cembra, and P. albicaulis in ND, P. ponderosa in SD, and P. nigra from IN showed 100% sequence homology with Dothistroma pini (Accession No. AY808302). These isolates were identical to all previously assayed isolates of D. pini from Nebraska, Minnesota, and Michigan in the United States. The P. ponderosa isolates from all three sites in ND differed from the other isolates and contained a 1-bp point mutation from a C to a T at site 72 (sequence deposited in GenBank, accession KJ933441). Mating type was determined using species-specific mating type primers for D. pini (3). All 26 samples from ND and SD were of the MAT-1 idiomorph, while the sample from IN contained the MAT-2 idiomorph. All cultures are maintained at FABI, University of Pretoria, South Africa. The two species that cause DNB, D. septosporum (G. Dorog.) M. Morelet and D. pini Hulbary, are morphologically indistinguishable and molecular characterization remains essential for correct species identification (1). Host and geographical distribution range determinations of Dothistroma spp. made without molecular methods are not valid. To date, species confirmed using DNA sequences in the United States include D. septosporum in the Pacific Northwest states of Oregon and Idaho on P. ponderosa, in Montana on P. contorta v. latifolia, and D. pini in the North Central states of Nebraska, Minnesota, and Michigan on P. nigra (1). This study documents the presence of D. pini in three additional states, including a first report of DNB in ND and SD. It also includes new records of D. pini infecting P. flexilis, P. cembra, P. albicaulis, and P. ponderosa. Results of this study have expanded the documented host range of D. pini in the United States from one (P. nigra) to five species. Globally, D. pini is now known to infect a total of 10 pine hosts (2,4,5).

First Report of Dothistroma pini, a Recent Agent of the Dothistroma Needle Blight, on Pinus radiata in France.

Dothistroma needle blight (DNB), also known as red band needle blight, is an important fungal disease of Pinus spp. that occurs worldwide. On the basis of molecular and morphological studies of the anamorphic stage, Barnes et al. (1) showed that two closely related species were involved in DNB: Dothistroma septosporum (Dorog.) Morelet and D. pini Hulbary. D. septosporum (teleomorph: Mycosphaerella pini Rostr.) has a worldwide distribution and is reported as the species that caused past epidemics of DNB. This species is reported on more than 80 different pine species, and Pinus radiata D. Don (Monterey pine) is classified as a highly or moderately susceptible species, depending on the published sources (4). D. pini (telemorph: unknown) was initially found on needles of P. nigra J. F. Arnold collected from 1964 to 2001 in the north central United States (Minnesota, Nebraska, and Michigan). It was subsequently found in Ukraine and southwestern Russia, where it has been associated with the emergence of DNB on P. nigra subsp. pallasiana (Lamb.) Holmboe, in Hungary on P. nigra, and in Russia on P. mugo Turra (1). In France, D. pini was reported for the first time on P. nigra, and was sometimes found in association with D. septosporum on the same needles (3). Later on, a more intensive survey of DNB was launched in France and 216 stands of Pinus sp. were studied. D. septosporum and D. pini were detected in 133 and 123 stands, respectively. Both species co-occurred in 40 stands but D. pini was only found on P. nigra (subsp. laricio and austriaca) (2). Up to now, D. pini was therefore only reported on European pine species, mainly on the different allopatric subspecies belonging to the black pine complex and on one occasion on P. mugo, which belongs to the same section and subsection as P. nigra. In March 2011, typical symptoms of DNB (needles with orangey-red brown distal ends, dark red bands, and green bases; small and black fruit bodies within the bands) were observed in a 50- to 60-year old P. radiata stand of ~3 ha located in Pyrénées Atlantiques close to the Spanish border (1°36'08″ W, 43°19'51″ N). The density of pine was relatively low and patches of natural regeneration were present. Although nearly all of the trees showed DNB symptoms, less than 50% of their needles were affected by the disease. In this stand, needles showing typical DNB symptoms were randomly taken from four pines and mixed together to form a single sample for analysis. Total DNA was extracted from symptomatic needle pieces. The presence of D. pini was confirmed by a specific multiplex real-time PCR analysis using the D. pini-specific primers/probe combination DPtef-F1-/R1/-P1 (3), and by sequencing a D. pini-specific amplicon generated by another conventional PCR (3) using DPtef-F/DPtef-R primers (GenBank Accession KC853059) (3). D. septosporum was not detected in the sample. To our knowledge, this is the first report worldwide of D. pini on P. radiata, a pine species largely planted in Spain and in the Southern Hemisphere. This is also the first report of this pathogen on a non-European pine species. The original native range and the host range of D. pini remain unknown and there is currently no data about host preferences or aggressiveness on different pine species.

Decline in vitality of propagules of Phytophthora pluvialis and Phytophthora kernoviae and their inability to contaminate or colonise bark and sapwood in Pinus radiata export log simulation studies

BackgroundPhytophthora pluvialis Reeser, W.L. Sutton & E.M. Hansen is the cause of a newly described disease, red needle cast, in certain stands of Pinus radiata D. Don in New Zealand that experience periodic foliage browning, while Phytophthora kernoviae Brasier, Beales & Kirk is also infrequently isolated from symptomatic needles.MethodsStudies were undertaken to test the possibility that these species may be transported on pine logs either as superficial contaminants or as colonists of bark or wood.ResultsPine-needle baiting found no evidence of Phytophthora species in bark samples or aqueous bark washes from stems of 603 symptomatic trees in 17 affected stands implying that survival after natural deposition of sporangia or zoospores is low or absent. The persistence of zoospores or oospores was evaluated at intervals after applying them at artificially high surface densities to the bark on log segments and incubating at five temperatures between 15°C and 35°C in the laboratory. The ability to re-isolate Phytophthora kernoviae decreased with time and increasing temperature, but this species was still obtained at low frequencies after 4 weeks at 15°C and 20°C following treatment with oospores of Phytophthora kernoviae. Phytophthora pluvialis could not be isolated under any conditions of time or temperature tested. Percentage vitality of oospores of both species as determined using tetrazolium bromide vital staining also decreased with time, although some oospores of both species remained alive after 4 weeks at all temperatures tested. In a further study to test potential log colonisation, Phytophthora spp. were not isolated from bark or xylem at or near points where zoospores, oospores or mycelium of either species were applied to the bark or sapwood of pine segments and incubated for 6 weeks under ambient or humid conditions at 17°C.ConclusionThe results of these studies suggest that occurrence of Phytophthora kernoviae or Phytophthora pluvialis on export logs from affected stands is negligible. In addition, although some remained alive, the substantial decline in vitality among artificially applied oospores implies that the survival of any few that may be naturally present on logs is likely to be slight. Based on the evidence from this work there appears to be little risk of transporting these Phytophthora species on New Zealand radiata pine logs.

Pathogenicity of Phytophthora pluvialis to Pinus radiata and its relation with red needle cast disease in New Zealand

Background Red needle cast, a new foliage disease of Pinus radiata in New Zealand is described. The disease has been variable in incidence and severity both regionally and in different years. The early symptoms of discrete olive coloured lesions, often with a narrow dark resinous mark or band, were first recognised in winter of 2008 in plantation forests on the eastern coast of the North Island. These lesions develop further to result in rapid needle senescence and premature defoliation. The disease has been termed red needle cast in New Zealand as affected trees have a reddish appearance prior to the casting of the needles. The subsequent four years of monitoring have confirmed that, depending on location, symptoms are first observed in late autumn through late winter. Newly developing spring and summer foliage is seldom affected. Isolation from needles using a Phytophthora-selective medium frequently yielded an unknown species of Phytophthora which was subsequently found to be identical to Phytophthora pluvialis, a species described from Oregon, USA in 2013 where it is not associated with disease. Infection appears to be limited to the needles with no recoveries of Phytophthora pluvialis having been made from the roots, stems or branches. Occasionally a second species of Phytophthora, P. kernoviae, was also recovered from needles with the same symptoms.

Management of red needle cast caused by <i>Phytophthora pluvialis</i> a new disease of radiata pine in New Zealand

Ten years ago there were no known foliar diseases caused by Phytophthora on pine trees worldwide Since then two significant Phytophthora diseases have emerged on radiata pine one of which is only known in New Zealand Red needle cast is a disease caused by the pathogen Phytophthora pluvialis which is thought to have originated from northwestern USA This paper reviews the challenges the New Zealand forestry industry faces when dealing with this disease and evaluates the management options such as chemical control biological control and breeding programmes being investigated to minimise its effect on forest productivity The distribution of the pathogen in New Zealand and research that shows bark logs and wood are free of the pathogen therefore unlikely to pose biosecurity threats through trade in these products are also outlined

Incorporating climate change into pest risk models for forest pathogens: a role for cold stress in an era of global warming?

Climate change may alter the distribution and activity of native and alien pathogens that infect trees and, in severe cases, cause tree death. In this study, potential future changes in climate suitability are investigated for three forest pathogens that occur in western North America: the native Arceuthobium tsugense subsp tsugense, hemlock dwarf mistletoe, and two alien invasive species, Dothistroma septosporum, the cause of red band needle blight or Dothistroma needle blight, and Phytophthora ramorum, the cause of sudden oak death or ramorum blight. Specifically, the software CLIMEX is used to calculate Cold-Stress, Heat-Stress, and Dry-Stress indices for each pathogen in 98,224 grid cells in North America. Downscaled climate projections from the general circulation models CGCM1, CSIROMk2, and HadCM3 drive forecasts for 2020, 2050 and 2080. These climate projections are then analyzed to forecast shifts in the geographic extent of abiotic stresses that are severe enough to directly kill pathogen propagules and prevent year-round establishment of these pathogens. Cold stress currently has a major impact on climate suitability for all three pathogens; heat stress is likely to become more significant in the future. I forecast that the geographic extent of cold stress will decline from its current levels by a constant 5% (± 1%) of all grid cells in each 30-yr projection horizon for all three pathogens. Forecasts suggest the extent of heat stress will increase concurrently by 4% (± 1%) in each 30-yr projection horizon. Drought stress shows no consistent trend over time. No disproportionate effect of climate change on the two alien invasive pathogens over the native is forecasted. These results suggest that forecasts of future climate suitability for pathogens based on historical climate normals are accurate for less than 30 yrs. Adaptive management strategies in forestry will be needed to respond as these changes unfold.

Solvent-dependent conformational polymorphism in the crystal structure of mercuric bromide adduct of 1,1′-bis(diphenylphosphino)ferrocene

Two polymorphs of dinuclear mercury–iron complexes, [HgBr2(dppf)] (1) where dppf is 1,1′-bis(diphenylphosphino)ferrocene, are prepared and crystal structures are determined by X-ray crystallography. The reaction of mercury(II) bromide with dppf in methanol–dichloromethane led to orange block polymorph. After crystallization of this complex in DMSO, a red needle polymorph was obtained.