Genetic Diversity Analysis of Anisogramma anomala in the Pacific Northwest and New Jersey.

Anisogramma anomala, a biotrophic ascomycete, causes eastern filbert blight (EFB) of hazelnuts (Corylus spp.). EFB is endemic in eastern North America, preventing the commercial production of European hazelnut (C. avellana L.). In contrast, the historic absence of A. anomala in the Pacific Northwest (PNW) supported the development of a robust hazelnut industry. Circa 1960, A. anomala was inadvertently introduced into southwestern Washington causing orchard devastation. Distribution of the pathogen in the PNW has been hypothesized to be the result of a single-point introduction. This study aimed to investigate the single-point introduction hypothesis of A. anomala by comparing the genetic diversity of A. anomala samples from the PNW and New Jersey (NJ). Specimens from the main PNW production region [n=60] and an area within the pathogen's native range, NJ [n=151], were genotyped using 15 simple sequence repeat (SSR) markers. The following were used to assess genetic diversity and population structure: allelic summary statistics, discriminant analysis of principal components, network median-joining tree, analysis of multilocus genotypes, and allelic population diversity analysis. Analyses separated the samples into one cluster containing all the PNW isolates, and five clusters of NJ isolates. The PNW samples were nearly genetically uniform, and the NJ isolates were diverse. These findings support the hypothesis that A. anomala in the PNW was derived from a single-point introduction and corroborate previous studies that have shown A. anomala is very diverse in NJ. This indicates that maintaining restrictions on the movement of Corylus into the PNW is important to prevent the introduction of new populations of A. anomala, thus protecting the PNW hazelnut industry.

Diagnostic and Historical Surveys of Sweet Cherry (Prunus avium) Virus and Virus-Like Diseases in Oregon.

There are over 35 known virus and virus-like diseases of sweet cherry (Prunus avium), some with potential to cause severe economic impact by reducing vegetative growth, vigor, or fruit quality. Oregon is the second-ranked state for sweet cherry production in the United States. Statewide surveys were conducted in Oregon sweet cherry orchards for virus and virus-like diversity and distribution. Orchards in key production regions with suspected virus disease symptoms were sampled. Virus-specific enzyme-linked immunosorbent assay, isothermal amplification, or quantitative real-time PCR were used to test for the presence of common or economically important sweet cherry pathogens, including cherry leaf roll virus (CLRV), little cherry virus 2 (LChV2), prune dwarf virus (PDV), prunus necrotic ringspot virus (PNRSV), tomato ringspot virus (ToRSV), and 'Candidatus Phytoplasma pruni'. CLRV, a new virus of sweet cherry in Oregon, was found associated with enation and dieback symptoms in The Dalles. Some viruses were found in new regions, which included Hood River (PDV, PNRSV, and ToRSV) and the Umpqua Valley (PDV and PNRSV). A subsequent survey was conducted in the Mid-Columbia production region for the presence of little cherry symptoms associated with little cherry and X-Diseases. All symptomatic samples from The Dalles and Mosier, OR, or Dallesport, WA, tested positive for 'Ca. P. pruni' but not LChV2. These findings provide a foundation for the current understanding and management of virus and virus-like diseases of sweet cherry in Oregon and context for further studies into these pathogens and their vectors.

Management of Grape Powdery Mildew with an Intelligent Sprayer and Sulfur.

Wine grapes are an important agricultural commodity in the Pacific Northwest, where grape powdery mildew (GPM) is one of the main disease problems. The efficacy of various sulfur concentrations and output volumes from an air blast sprayer retrofitted with the Intelligent Spray System (ISS) were evaluated for the management of GPM. The ISS consists of a LiDAR sensor, Doppler speed sensor, embedded computer, flow controller, and individual pulse-width-modulation solenoid valves at each nozzle. GPM cluster severity ranged from 55 to 75% across all trials in the study when the ISS was used at its default spray rate of 62.5 ml/m3 with micronized sulfur at 6 g/liter, which was significantly higher than all other fungicide treatments but lower than nontreated controls. Similarly, leaf incidence values were highest on nontreated vines, followed by micronized sulfur at 6 g/liter applied at 62.5 ml/m3, with all other fungicide treatments being significantly lower in all trials. Using the ISS at the 62.5 ml/m3 rate and a rotation of locally systemic fungicides resulted in the lowest observed GPM leaf incidence and average cluster severity of 11% in both 2019 and 2020, the lowest cluster severity of all fungicide treatments tested. GPM control with the ISS and micronized sulfur was equivalent to a constant-rate air blast treatment at 6 g/liter when the spray rate of the ISS was increased to 125 ml/m3 or the concentration of sulfur was increased to 24 g/liter. In those cases, the amount of sulfur applied to vines was at or above the minimum label rate from bloom until the end of the season, or the entire season, respectively. This study has shown that sufficient disease control cannot always be expected when pesticides are mixed at the same rate as would be used for a constant-rate sprayer in a variable rate sprayer, especially when contact fungicides such as sulfur are used. With appropriate adjustments, the variable-rate ISS can be a useful tool to reduce pesticide quantities, water needed for mixing, and as a result labor, because fewer trips to refill for a given spray event are needed.

Occurrence of Mummy Berry Associated with Huckleberry (Vaccinium membranaceum) Caused by Monilinia spp. in Oregon.

In this Short Communication we describe the occurrence of mummy berry associated with huckleberry (Vaccinium membranaceum) caused by Monilinia spp. in Oregon. To our knowledge, this is the first report of a Monilinia spp. associated with mummy berry of huckleberry in Oregon. Sequence data from our specimens reveal the closest identity was Monilinia vaccinii-corymbosi, a pathogen of commercial blueberry (Vaccinium corymbosum). This may be a new species of Monilinia, not previously reported on huckleberry, and further investigation is needed. Of specific importance, the huckleberry holds cultural importance as a sacred First Food of the Confederated Tribes of the Umatilla Indian Reservation and other Pacific Northwest tribes. Although plant pathogen management in natural landscapes presents unique challenges, we will work with tribal authorities to determine whether cultural management techniques may mitigate yield loss due to Monilinia spp.

Progression of Kernel Mold on Hazelnut.

Hazelnut kernel mold, caused by a number of fungal species, has been a chronic problem in Pacific Northwest hazelnut production areas for many years. Two highly susceptible breeding selections and two commercial cultivars were used to investigate kernel mold development over time and possible correlations with rainfall. Nuts were allowed to naturally fall onto orchard soil, regularly collected, cracked open, and evaluated for kernel mold. Disease progress for each selection or cultivar was evaluated each year with both linear and exponential models. The general progression of kernel mold was similar for the two breeding selections and cultivars Ennis and Lewis, where kernel mold increased slowly during the nut dropping period but more rapidly after normal harvest. An exponential model described disease progress better than a linear model for 8 of the 10 significant disease progress curves examined. Although some years had significantly higher estimated rates of disease increase, this parameter was inversely related to the area under the disease progress curve (AUDPC). The incidence of kernel mold did not significantly increase over time for 8 of the 18 disease progress curves examined, including 6 of 8 curves for commercial cultivars. The relationship between initial kernel mold incidence and AUDPC was described well with a simple linear model indicating that initial disease incidence appeared to be a good predictor of AUDPC. The longer nuts remained on the ground, especially after harvest, the higher the incidence of kernel mold. Kernel mold incidence was not significantly correlated with rainfall totals for any period of time from flowering to harvest. Multiple harvests ending shortly after all nuts have fallen should result in lower incidence of kernel mold for growers.

Canopy spray application technology in specialty crops: a slowly evolving landscape.

Many specialty crops are susceptible to insects and diseases, and as such are reliant on regular canopy pesticide applications to achieve quality attributes required for salability. The majority of specialty crop producers continue to use antiquated pesticide application technologies for directed canopy spraying such as the radial air blast sprayer that has been associated with chemical wastage and off-target drift of around 40% and 15% of total applied spray volume, respectively. However, precision sprayers are available that result in remarkable improvements to these parameters. The wide-scale adoption of precision sprayers by specialty crop producers remains low. Reasons for the continued dominance of old technologies include risk averseness of farmers and regulatory bottlenecks. However, as farm labor becomes more expensive, less available, and consumers and regulations favor sustainably produced products, motivations to improve spray application efficiency are increasing. While there are many opportunities and future directions application technology may take, sensor-controlled sprayer technology that applies a proportionate amount of spray will likely be the primary technology of precision sprayers going into the future. © 2020 Society of Chemical Industry.

Predicting Ascospore Release of Monilinia vaccinii-corymbosi of Blueberry with Machine Learning.

Mummy berry, caused by Monilinia vaccinii-corymbosi, causes economic losses of highbush blueberry in the U.S. Pacific Northwest (PNW). Apothecia develop from mummified berries overwintering on soil surfaces and produce ascospores that infect tissue emerging from floral and vegetative buds. Disease control currently relies on fungicides applied on a calendar basis rather than inoculum availability. To establish a prediction model for ascospore release, apothecial development was tracked in three fields, one in western Oregon and two in northwestern Washington in 2015 and 2016. Air and soil temperature, precipitation, soil moisture, leaf wetness, relative humidity and solar radiation were monitored using in-field weather stations and Washington State University's AgWeatherNet stations. Four modeling approaches were compared: logistic regression, multivariate adaptive regression splines, artificial neural networks, and random forest. A supervised learning approach was used to train the models on two data sets: training (70%) and testing (30%). The importance of environmental factors was calculated for each model separately. Soil temperature, soil moisture, and solar radiation were identified as the most important factors influencing ascospore release. Random forest models, with 78% accuracy, showed the best performance compared with the other models. Results of this research helps PNW blueberry growers to optimize fungicide use and reduce production costs.

Population structure of Geosmithia morbida, the causal agent of thousand cankers disease of walnut trees in the United States.

The ascomycete Geosmithia morbida and the walnut twig beetle Pityophthorus juglandis are associated with thousand cankers disease of Juglans (walnut) and Pterocarya (wingnut). The disease was first reported in the western United States (USA) on several Juglans species, but has been found more recently in the eastern USA in the native range of the highly susceptible Juglans nigra. We performed a comprehensive population genetic study of 209 G. morbida isolates collected from Juglans and Pterocarya from 17 geographic regions distributed across 12 U.S. states. The study was based on sequence typing of 27 single nucleotide polymorphisms from three genomic regions and genotyping with ten microsatellite primer pairs. Using multilocus sequence-typing data, 197 G. morbida isolates were placed into one of 57 haplotypes. In some instances, multiple haplotypes were recovered from isolates collected on the same tree. Twenty-four of the haplotypes (42%) were recovered from more than one isolate; the two most frequently occurring haplotypes (H02 and H03) represented 36% of all isolates. These two haplotypes were abundant in California, but were not recovered from Arizona or New Mexico. G. morbida population structure was best explained by four genetically distinct groups that clustered into three geographic regions. Most of the haplotypes isolated from the native range of J. major (Arizona and New Mexico) were found in those states only or present in distinct genetic clusters. There was no evidence of sexual reproduction or genetic recombination in any population. The scattered distribution of the genetic clusters indicated that G. morbida was likely disseminated to different regions at several times and from several sources. The large number of haplotypes observed and the genetic complexity of G. morbida indicate that it evolved in association with at least one Juglans spp. and the walnut twig beetle long before the first reports of the disease.

Genetic differentiation and spatial structure of Geosmithia morbida, the causal agent of thousand cankers disease in black walnut (Juglans nigra).

The main objectives of this study were to evaluate genetic composition of Geosmithia morbida populations in the native range of black walnut and provide a better understanding regarding demography of the pathogen. The fungus G. morbida, and the walnut twig beetle, Pityophthorus juglandis, have been associated with a disease complex of black walnut (Juglans nigra) known as thousand cankers disease (TCD). The disease is manifested as branch dieback and canopy loss, eventually resulting in tree death. In 2010, the disease was detected in black walnut in Tennessee, and subsequently in Virginia and Pennsylvania in 2011 and North Carolina in 2012. These were the first incidences of TCD east of Colorado, where the disease has been established for more than a decade on indigenous walnut species. A genetic diversity and population structure study of 62 G. morbida isolates from Tennessee, Pennsylvania, North Carolina and Oregon was completed using 15 polymorphic microsatellite loci. The results revealed high haploid genetic diversity among seven G. morbida populations with evidence of gene flow, and significant differentiation among two identified genetic clusters. There was a significant correlation between geographic and genetic distance. Understanding the genetic composition and demography of G. morbida can provide valuable insight into recognizing factors affecting the persistence and spread of an invasive pathogen, disease progression, and future infestation predictions. Overall, these data support the hypotheses of two separate, highly diverse pathogen introductions into the native range of black walnut.

Effect of Copper Bactericides on Copper-Resistant and -Sensitive Strains of Pseudomonas syringae pv. syringae.

Fourteen formulations of copper-based bactericides were evaluated for their efficacy in reducing populations of copper-resistant and -sensitive strains of Pseudomonas syringae pv. syringae growing on tissue-cultured lilac and of copper-sensitive strains of this pathogen on field-grown lilac. The amount of free cupric ions (Cu2+) in solution was the only predictor of formulation efficacy, but this variable could not be estimated from the metallic copper content of the product. Relative to nontreated controls, all copper-based bactericides reduced the population size of copper-sensitive strains by 50%, but only cupric hydroxide mixed with mancozeb or ferric chloride reduced the population size of copper-resistant strains by an equivalent amount. Several noncopper bactericides, including streptomycin-sulfate, caused only small reductions in bacterial populations on tissue-cultured or field-grown lilacs. In the field, two applications of cupric hydroxide (wettable powder) when plant growth stages were at dormant (mid-February) and delayed dormant (late February) provided better control than either one or no treatments.

Rapid Evaluation of Pathogenicity in Pseudomonas syringae pv. syringae with a Lilac Tissue Culture Bioassay and Syringomycin DNA Probes.

Losses from diseases caused by Pseudomonas syringae pv. syringae occur on a large number of deciduous woody plants in commercial nurseries in the Pacific Northwest. Bioassays for pathogenicity are one step in the identification of P. syringae pv. syringae and are usually performed on the host of isolation; however, woody plants can take months to develop symptoms. A bioassay with highly susceptible lilac (Syringa vulgaris 'Sensation') tissue culture plantlets evaluated pathogenicity in strains of P. syringae pv. syringae isolated from 25 species of deciduous woody plants. DNA colony hybridization with the syrB probe for a syringomycin synthetase gene and the syrD probe for a syringomycin export gene was also evaluated as a method for identifying pathogens. Of 552 strains provisionally identified as P. syringae pv. syringae, 59% were pathogenic in the bioassay and hybridized with the syr probes, while 19% were non-pathogenic and did not hybridize with the syr probes, giving 78% agreement between the two methods. Nine percent of strains were pathogenic in the bioassay but did not hybridize with the syr probes, and 13% were not pathogenic in the bioassay but did hybridize with the syr probes. These methods detected pathogenic strains of P. syringae pv. syringae isolated from diverse woody plants in 5 to 16 days.