Jay William Pscheidt

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.

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.

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.

Development of microsatellite loci in Pityophthorus juglandis, a vector of thousand cankers disease in Juglans spp.

Using next-generation sequencing, 18 microsatellite loci were developed and characterized for walnut twig beetle, Pityophthorus juglandis, a vector of thousand cankers disease (TCD) affecting Juglans spp. Although all Juglans species are susceptible to TCD infection, native populations of J. nigra and J. cinerea, which is endangered in Canada, are most susceptible and threatened by habitat loss. Novel primers amplified di-, tri-, and tetra nucleotide repeats and detected 4–14 alleles per locus. Averaged observed and expected heterozygosity was 0.22 and 0.67, respectively. Our results indicate that P. juglandis microsatellite loci can be used to investigate genetic diversity and population structure of this vector across a widespread geography. These markers will be useful tools for evaluating genetic structure of P. juglandis population outbreaks and developing appropriate conservation strategies. Microsatellite loci obtained in this study can also be utilized to determine relationships of P. juglandis to other closely related Pityophthorus spp.

Disease Incidence and Ascospore Dispersal from Cut Hazelnut Branches Colonized by Anisogramma anomala

Hazelnut branches bearing stromata of Anisogramma anomala cut in December (2009 and 2010) were compared with branches cut prior to bud break in March to investigate these sources of inoculum. Branches were placed into brush piles (sources). Spore traps and potted hazelnut trees were placed adjacent to each source, 6.4 m upwind and downwind, and 20 m downwind from each source. Significantly more ascospores were detected near sources of branches cut in March compared with December in 2010 however, no differences were detected between pruning treatments in 2011. Ascospore viability, as assessed by trypan blue stain, averaged 50% for both pruning times each season. Significantly more ascospores were detected 6.4 m downwind compared with 6.4 m upwind or 20 m downwind of a source both years. All potted trees exposed to branches from both pruning treatments within sources became diseased both years. The proportion of potted trees that became infected was greater for the downwind group than the upwind for both years, suggesting that ascospores were dispersed beyond the rain splash dispersal range of sources. Ascospores from diseased branches pruned in December or March remained viable, infectious and were dispersed at least 20 m downwind.

First report of Cherry leaf roll virus on sweet cherry in Oregon

Sweet cherries (Prunus avium) are of economic importance in Oregon, which ranks third in sweet cherry production in the United States after Washington and California. Cherry leaf roll virus (CLRV) causes decline in sweet cherry trees. Cherry leaf roll virus is a species of the genus Nepovirus in the family Secoviridae. In May 2016, decline, rosetting (bunching of leaves due to shortened internodes), and enation symptoms in approximately 7% of trees were observed in adjacent sweet cherry orchards cvs. ‘Royal Anne’ and ‘Bing’ on Mazzard rootstock in The Dalles, Wasco County, Oregon. A symptomatic leaf sample (cv. ‘Royal Anne’) was collected and tested positive via CLRV-specific antisera in a double-antibody sandwich ELISA (DSMZ; Braunschweig, Germany). A second collection of both cultivars was made in September 2016 from the same and neighboring orchard blocks. Of the 16 samples collected, eight symptomatic leaf samples tested positive and eight asymptomatic samples tested negative with the same CLRV-specif...

Monilinia vaccinii-corymbosi Apothecial Development Associated With Mulch Depth and Timing of Application

Pseudosclerotia of Monilinia vaccinii-corymbosi overwinter on the soil surface and develop apothecia in early spring, supplying primary inoculum for mummy berry disease of blueberry. Burial of pseudosclerotia in soil and incubation in the dark have previously been identified as critical factors inhibiting M. vaccinii-corymbosi apothecial development. Mulches of Douglas-fir (Pseudotsuga menziesii) sawdust at 2.5 or 5 cm depths, blueberry leaves (Vaccinium corymbosum cv. Bluetta) at a 2.5 cm depth, and a bare ground (no mulch) control were assessed for an effect on apothecial development in the spring for 2 years. Mulches were applied corresponding to pseudosclerotial overwintering stages. Loss of mulch depth was also assessed throughout the overwintering season. A 5 cm depth of Douglas-fir sawdust was associated with greater apothecial suppression in comparison with bare ground. Douglas-fir sawdust at a 2.5 cm depth varied in effectiveness, while 2.5 cm of blueberry leaves was not more effective at suppressing apothecial development than the bare ground treatment. Application timing did not affect apothecial development, but mulches lost significantly more depth when applied at the beginning of the overwintering season as compared with late winter mulches. Therefore, loss of mulch thickness due to weathering and/or decomposition may also affect apothecial development.

Evaluation of Quinone Outside and Succinate Dehydrogenase Inhibitors for Effectiveness Against Eastern Filbert Blight of Hazelnut

Most of the hazelnut production in Oregon, a value of

Streptomycin Resistance Genes in Pseudomonas Syringae Isolated from Woody Plants

130 million in 2014, was based on eastern filbert blight (EFB) susceptible cultivars. On these cultivars, EFB management involves, among other tactics, fungicide treatment during bud break and early shoot growth. Many active ingredients have been shown to be effective against EFB. This report summarizes the evaluation of quinone outside (QoI, FRAC group 11) and succinate dehydrogenase (SDHI, FRAC group 7) inhibitors alone and in combination with each other or with demethylation-inhibiting (DMI, FRAC group 3) fungicides for management of EFB. Based on a meta-analysis, picoxystrobin, pyraclostrobin, or trifloxystrobin alone resulted in significant control over nontreated trees ranging between 64 and 74%. Fluoxastrobin was not as effective as other QoI fungicides with an average of 44% control and high variability. SDHI fungicides as a group were less useful for management of EFB with boscalid, fluopyram, and penthiopyrad ineffective while fluxapyroxad averaged 83% control against EFB. Prepackaged mixes of QoI materials with either SDHI or DMI fungicides were also significantly effective against EFB. Use of QoI fungicides and the SDHI material fluxapyroxad offers added flexibility and complexity within EFB management programs. Growers can incorporate any of five different modes of action in EFB management programs including FRAC groups M1, M5, 3, 7, and 11.

Copper and streptomycin resistance in strains of Pseudomonas syringae from Pacific Northwest nurseries

Faiiure to controi diseases incited by Pseudomonas syringae with streptomycin (Sm) sprays led to collecting and testing of isolates from 25 different woody plant species in 44 nurseries spread over a 275 km area of Oregon for resistance to this antibiotic. Of the 467 isolates collected, 38% grew on King’s Medium B amended with 100 μg streptomycin sulfate/ml (KBS). Colony hybridization was evaluated as a method to improve the efficiency and accuracy of detection of Sm-resistant strains as spontaneous Smf mutants are common when P. syringae is grown on KBS. The Smr gene probe consisted of a 3.7-kb Pst1 fragment from pPSR1, a piasmid from P. syringae strain A2, recovered from an ornamental pear in Oklahoma. The Smr gene probe is homologous to the strA-strB genes of the broad host-range enterobacterial Plasmid RSF 1010. The probe was labeled with digoxigenin and colony hybridization was conducted under conditions of moderate stringency. There was 94% agreement between growth on KBS and hybridization with the probe. Of the remaining isolates, 2% grew on KBS but did not hybridize with the probe and 4% hybridized with the probe but did not grow on KBS. This is the first report of sirA-strB homologues in indigenous populations of P. syringae in the Pacific Northwest.