Erwinia amylovora is a relatively homogeneous species with low genetic diversity at the nucleotide level. However, phenotypic differences and genomic structural variations among E. amylovora strains have been documented. In this study, we identified 10 large chromosomal inversion (LCI) types in the Spiraeoideae-infecting (SI) E. amylovora strains by combining whole genome sequencing and PCR-based molecular markers. It was found that LCIs were mainly caused by homologous recombination events among seven rRNA operons (rrns) in SI E. amylovora strains. Although ribotyping results identified inter- and intra-variations in the internal transcribed spacer (ITS1 and ITS2) regions among rrns, LCIs tend to occur between rrns transcribed in the opposite directions and with the same tRNA content (tRNA-Glu or tRNA-Ile/Ala) in ITS1. Based on the LCI types, physical/estimated replichore imbalance (PRI/ERI) was examined and calculated. Among the 117 SI strains evaluated, the LCI types of Ea1189, CFBP1430, and Ea273 were the most common, with ERI values at 1.31, 7.87, and 4.47°, respectively. These three LCI types had worldwide distribution, whereas the remaining seven LCI types were restricted to North America (or certain regions of the United States). Our results indicated ongoing chromosomal recombination events in the SI E. amylovora population and showed that LCI events are mostly symmetrical, keeping the ERI less than 15°. These findings provide initial evidence about the prevalence of certain LCI types in E. amylovora strains, how LCI occurs, and its potential evolutionary advantage and history, which might help track the movement of the pathogen.

Pantoea vagans C9-1 (C9-1) is a biological control bacterium that is applied to apple and pear trees during bloom for suppression of fire blight, caused by Erwinia amylovora. Strain C9-1 has three megaplasmids: pPag1, pPag2, and pPag3. Prior bioinformatic studies predicted these megaplasmids have a role in environmental fitness and/or biocontrol efficacy. Plasmid pPag3 is part of the large Pantoea plasmid (LPP-1) group that is present in all Pantoea spp. and has been hypothesized to contribute to environmental colonization and persistence, while pPag2 is less common. We assessed fitness of C9-1 derivatives cured of pPag2 and/or pPag3 on pear and apple flowers and fruit in experimental orchards. We also assessed the ability of a C9-1 derivative lacking pPag3 to reduce populations of E. amylovora on flowers and disease incidence. Previously, we determined that tolerance to stresses imposed in vitro was compromised in derivatives of C9-1 lacking pPag2 and/or pPag3; however, in this study, the loss of pPag2 and/or pPag3 did not consistently reduce the fitness of C9-1 on flowers in orchards. Over the summer, pPag3 contributed to survival of C9-1 on developing apple and pear fruit in two of five trials, whereas loss of pPag2 did not significantly affect survival of C9-1. We also found that loss of pPag3 did not affect C9-1's ability to reduce E. amylovora populations or fire blight incidence on apple flowers. Our findings partially support prior hypotheses that LPP-1 in Pantoea species contributes to persistence on plant surfaces but questions whether LPP-1 facilitates host colonization.

Fire blight, caused by Erwinia amylovora, is a devastating disease of apple. Blossom Protect, a product that contains Aureobasidium pullulans as the active ingredient, is one of the most effective biological controls of fire blight. It has been postulated that the mode of action of A. pullulans is to compete against and antagonize epiphytic growth of E. amylovora on flowers, but recent studies have found that flowers treated with Blossom Protect harbored similar to or only slightly reduced E. amylovora populations compared with nontreated flowers. In this study, we tested the hypothesis that A. pullulans-mediated biocontrol of fire blight is the result of induced host resistance. We found that PR genes in the systemic acquired resistance pathway, but not genes in the induced systemic resistance pathway, were induced in hypanthial tissue of apple flowers after the Blossom Protect treatment. Additionally, the induction of PR gene expression was coupled with an increase of plant-derived salicylic acid in this tissue. After inoculation with E. amylovora, PR gene expression was suppressed in nontreated flowers, but in flowers pretreated with Blossom Protect, the heightened PR expression offset the immune repression caused by E. amylovora, and prevented infection. Temporal and spatial analysis of PR gene induction showed that induction of PR genes occurred 2 days after the Blossom Protect treatment, and required direct flower–yeast contact. Finally, we observed deterioration of the epidermal layer of the hypanthium in some of the Blossom Protect-treated flowers, suggesting that PR gene induction in flowers may be a result of pathogenesis by A. pullulans.

The stability of the fire blight control material, oxytetracycline, in water is strongly affected by pH, increasing with increasing acidity. From 2017 to 2021, pear and apple orchard trials were conducted to evaluate if acidic amendments to oxytetracycline sprays improve fire blight control. Compared with the water-treated control, infection suppression after two bloom applications of an acidified commercial oxytetracycline formulation averaged 85.9 ± 0.4% compared with 72.2 ± 1.7% without an acidifier, but individual trials frequently had insufficient statistical power to separate among acidified and non-acidified antibiotic treatments. Across trials, a significant linear relationship was observed for regression of relative infection suppression from oxytetracycline (hydrochloride formulation) on spray tank pH. Similar relationships were observed for oxytetracycline (calcium complex formulation) and kasugamycin (P values were 0.055 and 0.069, respectively). Also based on regression, acidified oxytetracycline and kasugamycin suppressed epiphytic populations of Erwinia amylovora on flowers to a greater degree than the antibiotic only. As spray suspensions, commercial oxytetracycline formulations at label rate and amended with citric acid (1.2 g/liter) in well water had pH values near 3.4, but after spraying, the pH of flowers washed in deionized water (1 ml/flower) measured in a range of 5.2 to 5.5 compared with a pH range of 5.8 to 6.0 after a treatment of oxytetracycline only. In pear fruit finish trials, sprays acidified with citric acid-based materials had negligible effects on fruit russeting. Based on a serological assay, the detectable residual of oxytetracycline on apple foliage was increased by co-application with citric acid compared with a non-acidified control.

Aureobasidium pullulans , formulated commercially as Blossom Protect, has become a highly successful biological material for fire blight suppression in apple and pear. This material, which is composed of viable spores of two strains of A. pullulans , attained this status with minimal prior knowledge that yeasts could be used effectively for this purpose. In early orchard trials, it was observed that mixing A. pullulans in spray tanks with a low pH buffer enhanced disease suppression from very good to outstanding. Prevention of fire blight by Blossom Protect requires that A. pullulans colonizes most of the flowers on a tree with populations that exceed 1 × 10 4 CFU/flower. A. pullulans colonizes floral stigmas similar to bacteria used to suppress fire blight biologically; however, unlike these bacteria, the yeast also colonizes the hypanthial surface within the floral cup, which is where the fire blight pathogen Erwinia amylovora infects the host. In combination with the buffer, colonization activity by A. pullulans on the hypanthium reduces pH of the floral cup and strongly induces host defense genes in hypanthial tissue. A specific risk from use of A. pullulans for fire blight control is a potential to contribute to ‘russeting’ of developing fruitlets. Russeting risk from use of Blossom Protect has been lessened by reformulation of the companion buffer and by use of conventional or organically-approved fungicides in late and post-bloom periods. In large-scale apple production, particularly organic orchards, the use of Blossom Protect requires integration with other sprays that are required for managing crop load and suppression of fungal diseases such as apple scab.

Fire blight, caused by Erwinia amylovora, is an economically important disease in apples and pears worldwide. This pathogen relies on the type III secretion system (T3SS) to cause disease. Compounds that inhibit the function of the T3SS (T3SS inhibitors) have emerged as alternative strategies for bacterial plant disease management, as they block bacterial virulence without affecting growth, unlike traditional antibiotics. In this study, we investigated the mode of action of a T3SS inhibitor named TS108, a plant phenolic acid derivative, in E. amylovora. We showed that adding TS108 to an in vitro culture of E. amylovora repressed the expression of several T3SS regulon genes, including the master regulator gene hrpL. Further studies demonstrated that TS108 negatively regulates CsrB, a global regulatory small RNA, at the posttranscriptional level, resulting in a repression of hrpS, which encodes a key activator of hrpL. Additionally, TS108 has no impact on the expression of T3SS in Dickeya dadantii or Pseudomonas aeruginosa, suggesting that its inhibition of the E. amylovora T3SS is likely species specific. To better evaluate the performance of T3SS inhibitors in fire blight management, we conducted five independent field experiments in four states (Michigan, New York, Oregon, and Connecticut) from 2015 to 2022 and observed reductions in blossom blight incidence as high as 96.7% compared with untreated trees. In summary, the T3SS inhibitors exhibited good efficacy against fire blight.

Fire blight-susceptible, certified organic pome fruit is produced on 9,000 ha in the Pacific Northwest region of the United States with acreage continuing to expand despite a 2014 prohibition on antibiotics as allowable materials for infection suppression. Nonantibiotic practices for fire blight pathogen suppression mirror conventional management, but the full-bloom-to-petal-fall period when antibiotics are typically sprayed for fire blight control continues to receive research scrutiny owing to drawbacks and weaknesses of alternative materials. As solitary treatments, effective nonantibiotic materials (e.g., a yeast biocontrol, soluble coppers, and potassium aluminum sulfate) raise the risk of a crop-value-reducing, phytotoxic response termed "fruit russeting." Conversely, materials with less russeting risk (e.g., Bacillus-based biorationals) are less effective for fire blight control. Spray programs using a sequence of materials applied from midbloom to petal fall have the potential to provide high levels of protection with reduced russeting risk. In orchard trials, the effects of nonantibiotic spray programs on the epiphytic population size of Erwinia amylovora in flowers, yeast biocontrol population size, floral pH, infection suppression, and fruit russeting revealed strategies for sequencing sprays of nonantibiotic materials. The yeast biocontrol, Blossom Protect (Aureobasidium pullulans), sprayed at 70% bloom, was an important contributor to fire blight pathogen suppression as was the soluble copper material, Previsto, when applied at full bloom. Choice of material for the petal-fall spray timing was important to fruit russeting risk but apparently less important to overall infection incidence. Consequently, treatment programs of Blossom Protect at 70% bloom, a soluble copper at full bloom, and a Bacillus-based biorational at petal fall, best balance the quality of infection suppression with the risk of fruit russeting.

Winter squash (Cucurbita maxima cultivar Golden Delicious) produced in Oregon's Willamette Valley for edible seed production has experienced significant yield losses because of a soilborne disease. The symptoms associated with this disease problem include root rot, crown rot, and vascular discoloration in the stems, leading to a severe late season wilt and plant collapse. Through field surveys, Fusarium oxysporum, F. solani, F. culmorum-like fungi, Plectosphaerella cucumerina, and Setophoma terrestris were identified to be associated with diseased tissues, and each produced symptoms of root rot, crown rot, or stem discoloration in preliminary pathogenicity trials. In this study, 219 isolates of these species were characterized by molecular identity analyses using BLAST of the internal transcribed spacer and translation elongation factor 1 alpha genomic regions and by pathogenicity testing in outdoor, large-container trials. Molecular identity analyses confirmed the identity of isolates at 99 to 100% similarity to reference isolates in the database. In pathogenicity experiments, F. solani produced the most severe symptoms, followed by F. culmorum-like fungi, F. oxysporum, P. cucumerina, and S. terrestris. Some treatments of mixed-species inoculum produced symptom severity greater than what was expected from individual species. In particular, the mixture of F. culmorum-like fungi, F. oxysporum, and P. cucumerina and the mixture of F. culmorum-like fungi, F. solani, and S. terrestris had symptom ratings as high as that of F. solani by itself. Results indicate that this soilborne disease is caused primarily by Fusarium solani, but interactions between the complex of F. solani, F. culmorum-like fungi, F. oxysporum, and P. cucumerina can exacerbate disease severity.

Winter squash (Cucurbita maxima) is produced in Oregon’s Willamette Valley for edible seeds, processing, and fresh markets. Recently, prominent cultivar Golden Delicious has experienced significant yield losses due to a soilborne disease. Symptoms include stunting, root and crown rot, vascular discoloration, and late-season vine collapse. To identify potential causal pathogens, 64 fields were surveyed during 2014 to 2016 to characterize the fungal community associated with surface-disinfested root, crown, and stem tissue of diseased and healthy squash. Over 10,000 fungal isolates were identified morphologically, and 1,783 isolates were identified to species by sequencing of internal transcribed spacer and translation elongation factor 1 alpha genomic regions. Fungal communities were analyzed for association with the presence or absence of field symptoms using multivariate community analyses (indicator species analysis, multiresponse permutation procedure, and nonmetric multidimensional scaling). Although no fungal species were consistently associated with disease, five species were consistently isolated from plants regardless of the presence of symptoms and were capable of causing disease in a greenhouse pathogenicity trial: Fusarium oxysporum, F. solani, F. culmorum, Plectosphaerella cucumerina, and Setophoma terrestris. Results from community analyses confirmed that some fungi were more common in specific tissues (e.g., P. cucumerina in stems and crown, F. solani in roots and crown). Symptom severity tended to be greater in fields with a prior history of squash production, although a few fields with no prior history of squash had above average symptom ratings. The results from this study suggest that the five most common fungi may take on greater disease significance when they co-occur in a host.

Aureobasidium pullulans is used as a biocontrol agent for fire blight protection in organic apple and pear production. We assessed colonization of pome flowers by A. pullulans in orchards located near Corvallis, OR and Wenatchee, WA. Blossom Protect, a mix of A. pullulans strains CF10 and CF40, and its citrate-based companion, Buffer Protect, were sprayed at 70% bloom. Later in bloom, the population size of putative A. pullulans on flowers was estimated by dilution plating; plate scrapings of putative A. pullulans were then sampled and subjected to a PCR analysis. Sequenced PCR amplicons of the internal transcribed spacer region and the elongase gene confirmed the presence of A. pullulans, whereas a multiplex PCR with primers specific to CF10 and CF40 was used to determine the presence of the introduced strains. At Corvallis, a wet spring environment, A. pullulans, was recovered from most (>90%) Bartlett pear and Golden Delicious apple flowers sampled from experimental trees, regardless of whether the trees were treated with Blossom Protect. Nevertheless, population size estimates of A. pullulans on the flowers were correlated with the number of times Blossom Protect was sprayed on the trees. At Wenatchee, an arid spring environment, A. pullulans was detected on most flowers from trees treated with Blossom Protect, but only on a minority of flowers from nontreated controls. In both locations, the combined incidence of strains CF10 and CF40 on flowers averaged 89% on Blossom Protect-treated trees, but only 27% on adjacent, nontreated trees. During subsequent trials, the efficacy of Blossom Protect for fire blight control was compared with alternative yeast isolates, with each applied with Buffer Protect; local isolates of A. pullulans and Cryptococcus neoformans and a postharvest biocontrol strain of Cystofilobasidium infirmominiatum were used All yeast strains suppressed fire blight to a degree; however, in each of four trials, the level of suppression was highest with Blossom Protect, and it was significantly superior (P ≤ 0.05) to other yeast isolates in two of the trials. Because A. pullulans strains CF10 and CF40 were detected primarily on flowers on trees treated with Blossom Protect, and because they were detected much less frequently on nearby nontreated tress, we recommend treating every tree row with Blossom Protect at least once for organic fire blight suppression.

HomePlant DiseaseVol. 102, No. 12First Report of Fusarium culmorum Causing Fruit Rot of Winter Squash (Cucurbita maxima) in Oregon PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fusarium culmorum Causing Fruit Rot of Winter Squash (Cucurbita maxima) in OregonH. M. Rivedal, A. G. Stone, and K. B. JohnsonH. M. Rivedal†Corresponding author: H. M. Rivedal; E-mail: E-mail Address: rivedalh@oregonstate.eduhttp://orcid.org/0000-0002-2114-8827Search for more papers by this author, A. G. StoneSearch for more papers by this author, and K. B. JohnsonSearch for more papers by this authorAffiliationsAuthors and Affiliations H. M. Rivedal † , Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331 A. G. Stone , Department of Horticulture, Oregon State University, Corvallis, 97331 K. B. Johnson , Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331. Published Online:23 Oct 2018https://doi.org/10.1094/PDIS-06-18-0922-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Winter squash (Cucurbita maxima) are grown for fall and winter fresh markets in Oregon’s Willamette Valley. Since 2014, aggressive storage rots occurring within 4 months of harvest have been observed, causing significant losses of up to 70% for some cultivars including ‘Sunshine’, which has discouraged growers from storing winter squash. In November 2017, 17 fruits from a closed barn bay storage in Corvallis, OR, were sampled to isolate storage rot pathogens. Symptomatic fruits were covered with 1 to 25% surface rot, generally associated with the calyx end. A sporulating, white-salmon mycelium was present on fruit skin, and beneath the rotted flesh exhibited a dry, grayish-pink discoloration. In some cases, fungal growth expanded to the seed cavity and colonized the seeds with white to pink sporulation. Fungi were isolated by cutting 1 to 3 mm3 tissue pieces from lesion margins. Pieces were soaked in 20% commercial bleach solution for 2 min, followed by a 1 min rinse in sterile distilled water, blotted dry, and placed on one-eighth strength potato dextrose agar amended with 20 μg/ml of chlortetracycline and 50 μg/ml of streptomycin. After 7 days of incubation at 22°C on a 10/14 h light/dark cycle, pink colonies with cottony mycelium typical of a Fusarium species were obtained consistently. Single-spore colonies of three isolates (FR3, FR7, and FR113) from three rotted fruits were obtained on Spezieller Nährstoffarmer agar (SNA). Macroconidia were 25 to 30 μm (10 macroconidia measured per isolate) with blunt apical cells, notched foot cells, three to five septations, producing chlamydospores, with absent microconidia. These morphological traits matched the description of Fusarium culmorum (W.G. Smith) Sacc. (Leslie and Summerell 2006). DNA of the isolates was extracted with InstaGene Matrix (BioRad, Berkeley, CA). Three primer sets were used: EF1/EF2 (O’Donnell et al. 1998) to amplify the translation elongation factor 1α region, and F. culmorum-specific Fc01F/Fc01R and OTP18F470/OTP18R470 (Baturo-Ciesniewska and Suchorzynska 2011). Polymerase chain reaction products were sequenced at the Oregon State University Center for Genome Research and Biocomputing. A NCBI BLASTn search of all products found 99 to 100% DNA similarity to F. culmorum. Each of the F. culmorum isolates was inoculated into three healthy winter squash (C. maxima) fruits from the 2017 growing season. A 1-cm-diameter cork borer was used to make a 0.5-cm deep wound in the winter squash. Plugs of each fungal isolate on SNA were cut with a 0.8-cm cork borer and placed in the wound, mycelium side down, and sealed with petroleum jelly. Control fruits (11 total) were mock-inoculated with a plug of sterile SNA. Fruits were incubated at 22°C on a 10/14 h light/dark cycle at 35% humidity for 2 weeks and then evaluated for rot symptoms. Rot lesions of 3.5 to 7.5 cm diameter and 2 to 12.5 cm depth occurred on all three inoculated fruits for each isolate. No rot was detected on the control fruits. Rot was white-pink on the skin and gray-pink on inner flesh with sporulation in the seed cavity. F. culmorum was reisolated as above and identified molecularly, fulfilling Koch’s postulates. F. culmorum has been identified as a winter squash fruit rot pathogen in New Zealand (Hawthorne 1988) and as a fruit rot pathogen of winter squash and cucumber in Maine (Lewis 1913), but it is most commonly associated with foot and head blights of cereals (Leslie and Summerell 2006). To our knowledge, this is the first report of F. culmorum causing fruit rot of winter squash in Oregon.References:Baturo-Ciesniewska, M., and Suchorzynska, M. 2011. Int. J. Food Microbiol. 148:168. ISI, Google ScholarHawthorne, B. T. 1988. N. Z. J. Exp. Agric. 16:151. ISI, Google ScholarLeslie, J. F., and Summerell, B. A., eds. 2006. The Fusarium Laboratory Manual. Blackwell, Ames, IA. https://doi.org/10.1002/9780470278376 Crossref, Google ScholarLewis, C. E. 1913. Maine AES Bull. 209:203. Google ScholarO’Donnell, K., et al. 1998. Proc. Natl. Acad. Sci. 95:2044. https://doi.org/10.1073/pnas.95.5.2044 Crossref, ISI, Google ScholarFunding: Funding was provided by Western SARE (grant no. GW18-157).DetailsFiguresLiterature CitedRelated Vol. 102, No. 12 December 2018SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 20 Nov 2018Published: 23 Oct 2018Accepted: 20 Jul 2018 Page: 2659 Information© 2018 The American Phytopathological SocietyFundingWestern SAREGrant/Award Number: GW18-157Cited byMorphology, Molecular Identification, and Pathogenicity of Two Novel Fusarium Species Associated with Postharvest Fruit Rot of Cucurbits in Northern Thailand27 October 2022 | Journal of Fungi, Vol. 8, No. 11Identity and Pathogenicity of Fungi Associated with Root, Crown, and Vascular Symptoms Related to Winter Squash Yield DeclineHannah M. Rivedal, Javier F. Tabima, Alexandra G. Stone, and Kenneth B. Johnson3 May 2022 | Plant Disease, Vol. 106, No. 6First report of Fusarium sambucinum causing postharvest fruit rot of winter squash (Cucurbita maxima)7 February 2022 | Journal of General Plant Pathology, Vol. 88, No. 3Fusarium culmorum (culm rot: cereals)CABI Compendium, Vol. CABI CompendiumCharacterization of the Fungal Community Associated with Root, Crown, and Vascular Symptoms in an Undiagnosed Yield Decline of Winter SquashHannah M. Rivedal, Alexandra G. Stone, Paul M. Severns, and Kenneth B. Johnson14 January 2020 | Phytobiomes Journal, Vol. 4, No. 2Full Issue PDF18 May 2020 | Phytobiomes Journal, Vol. 4, No. 2

HomePlant DiseaseVol. 102, No. 12First Report of Setophoma terrestris Causing Pink Root Rot of Winter Squash (Cucurbita maxima) in Oregon PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Setophoma terrestris Causing Pink Root Rot of Winter Squash (Cucurbita maxima) in OregonH. M. Rivedal, A. G. Stone, and K. B. JohnsonH. M. Rivedal†Corresponding author: H. M. Rivedal; E-mail: E-mail Address: [email protected]http://orcid.org/0000-0002-2114-8827Search for more papers by this author, A. G. StoneSearch for more papers by this author, and K. B. JohnsonSearch for more papers by this authorAffiliationsAuthors and Affiliations H. M. Rivedal † , Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331 A. G. Stone , Department of Horticulture, Oregon State University, Corvallis, 97331 K. B. Johnson , Department of Botany and Plant Pathology, Oregon State University, Corvallis, 97331. Published Online:23 Oct 2018https://doi.org/10.1094/PDIS-06-18-0921-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Winter squash (Cucurbita maxima ‘Golden Delicious’) grown for edible seed in the Willamette Valley has shown reduced yields owing to a soilborne disease. Surveys of fields with wilt symptoms found 18 plants in 2014 and 11 plants in 2015 with a bright pink root rot. Symptomatic plants collected during summer months were distributed in aggregated foci. Secondary and tertiary roots were pink, and in severe cases the pink discoloration extended into crown tissues. Fungal isolation was performed by cutting 1- to 3-mm tissue pieces from lesion margins. Pieces were disinfested in 15% commercial bleach (2 min), rinsed in sterile distilled water (1 min), blotted dry, and placed onto one-eighth-strength potato dextrose agar amended with 20 μg/ml of chlortetracycline and 50 μg/ml of streptomycin. After 7 days incubation at 22°C with a 12-h light/dark cycle, dense brown-pink colonies were obtained. Single-spore isolates were obtained by placing dilutions of conidia on water agar followed by collection of individual germinated spores with the aid of a microscope. Single-spore isolates I332 and I677 were pink on carnation leaf agar and were olive to dark brown on oatmeal agar, where they produced numerous aggregated or solitary chlamydospores (12 × 10 μm); conidia were ellipsoid (5 × 2 μm) with multiple lipid deposits and borne on elongated conidiogenous cells; pycnidia were not readily apparent (Ikeda et al. 2012). DNA was extracted with InstaGene Matrix (BioRad, Berkeley, CA), and polymerase chain reaction (PCR) was performed with three primer sets: ITS1/ITS4 for the internal transcribed spacer (ITS) region, EF1-1018F/EF1-1620R (Yang et al. 2017) for elongation factor 1α gene, and T1/β-Sandy-R (Yang et al. 2017) for β-tubulin gene. PCR products were sequenced at an Oregon State University biological services center (GenBank accessions MH657015 to MH657020). A BLAST search found DNA from all isolates and gene regions showed 99% similarity to Setophoma terrestris (H.N. Hansen) Gruyter, Aveskamp & Verkley (accessions KY561336, KY561338, and KY561340). Pathogenicity was evaluated on 3-week-old, greenhouse-grown Golden Delicious plants. Isolates were grown in potato dextrose broth (PDB) (with antibiotic amendments as above) for 7 days at 25°C, shaken at 400 rpm, and then blended for 30 s and strained through cheese cloth, which achieved an inoculum concentration of 104 to 105 CFU/liter. Three plants for each isolate were uprooted, washed, roots trimmed to 2.5 cm, and set in the inoculum suspension for 3 min (Punja and Parker 2000). Three control plants were dipped in noninoculated PDB. Plants were repotted into 3.8-liter containers and grown for 8 weeks. Washed roots of all inoculated plants exhibited a pink root rot that advanced into crown tissue; control plants were symptomless. S. terrestris was reisolated from inoculated plants and reidentified based on ITS sequences. An additional experiment addressed if S. terrestris could infect without wounding. Liquid cultures of S. terrestris (prepared as above) were mixed into potting medium. Squash seeds were sown into inoculated potting medium, and after 12 weeks all plants exhibited pink root rot symptoms from which S. terrestris was reisolated. S. terrestris has been reported as a root pathogen of squash (C. moschata) in Japan (Ikeda et al. 2012) and on melons and summer squash (Bruton et al. 1997) but has not been described on C. maxima. To our knowledge, this is the first report of S. terrestris causing pink root rot of C. maxima in the United States.References:Bruton, B. D., et al. 1997. Subtrop. Plant Sci. 49:34. Google ScholarIkeda, K., et al. 2012. J. Gen. Plant Pathol. 78:372. https://doi.org/10.1007/s10327-012-0398-2 Crossref, ISI, Google ScholarPunja, Z. K., and Parker, M. 2000. Can. J. Plant Pathol. 22:349. https://doi.org/10.1080/07060660009500453 Crossref, ISI, Google ScholarYang, Y., et al. 2017. Can. J. Plant Pathol. 39:354. https://doi.org/10.1080/07060661.2017.1355849 Crossref, ISI, Google ScholarFunding: Funding was provided by Western SARE (grant no. SW15-021).DetailsFiguresLiterature CitedRelated Vol. 102, No. 12 December 2018SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 20 Nov 2018Published: 23 Oct 2018First Look: 2 Aug 2018Accepted: 30 Jul 2018 Pages: 2661-2661 Information© 2018 The American Phytopathological SocietyFundingWestern SAREGrant/Award Number: SW15-021Cited byScreening for broad-spectrum antimicrobial endophytes from Rosa roxburghii and multi-omic analyses of biosynthetic capacity16 November 2022 | Frontiers in Plant Science, Vol. 13Identity and Pathogenicity of Fungi Associated with Root, Crown, and Vascular Symptoms Related to Winter Squash Yield DeclineHannah M. Rivedal, Javier F. Tabima, Alexandra G. Stone, and Kenneth B. Johnson3 May 2022 | Plant Disease, Vol. 106, No. 6Characterization of the Fungal Community Associated with Root, Crown, and Vascular Symptoms in an Undiagnosed Yield Decline of Winter SquashHannah M. Rivedal, Alexandra G. Stone, Paul M. Severns, and Kenneth B. Johnson14 January 2020 | Phytobiomes Journal, Vol. 4, No. 2Full Issue PDF18 May 2020 | Phytobiomes Journal, Vol. 4, No. 2

Suppression of bacterial canker disease of sweet cherry caused by Pseudomonas syringae pv. syringae (Pss), utilizing resistant scion and rootstock varieties holds promise as a cost-effective management strategy. However, a reproducible and rapid method for screening large breeding populations for resistance to Pss poses a challenge. Sweet cherry cultivars Bing, Sweetheart, Regina, Moreau, Emperor Francis and Rainier were used to examine the effects of Pss isolate, inoculum concentration (1 x 10(2) to 1 x 10(8) cfu/ml), leaf age (collected from the tip, middle or base of the shoot) and inoculation assay method (attached versus detached leaf) on disease development. Disease severity was influenced significantly (P <= 0.05) by inoculum concentration and the virulence of the Pss isolate. An inoculum concentration of 1 x 10(8) cfu/ml provided the best disease response in both leaf assays and is recommended for disease screening. Also, a significant Pss isolate x cultivar effect was observed suggesting that proper selection of Pss isolate for disease screening is critical. Disease severity was significantly (P <= 0.05) greater for newly expanding leaves in detached assays than for leaves classified as young or old. Disease response among cultivars for attached and detached leaf assays was significantly correlated (r = 0.53, P = 0.002), but the detached leaf assay provided better separation in disease severity among cultivars. We conclude that the genotypic variation in disease response among sweet cherry germplasm can be differentiated based on a detached assay using new leaves, a highly virulent Pss isolate, and an inoculum concentration of 1 x 10(8) cfu/ml.

Integration of alleles for bacterial canker resistance into new sweet cherry cultivars requires information on the sources of resistance in the germplasm. Five market-leading sweet cherry cultivars, 'Rainier', 'Sweetheart', 'Bing', 'Regina' and 'Chelan', advanced selections 'AA', 'BB', 'CC', 'DD', 'EE', 'GG', and 'PMR-1' used as breeding parents in the Washington State University's Sweet Cherry Breeding Program were evaluated. Comparative genotypic disease severity was obtained with three methods of inoculation (leaf wounding with carborundum, cut wounds in leaf mid-rib and shoot tip) on whole plants. Additionally, genotypic data on susceptibility of detached leaves versus fruit and an assessment of the movement of Pseudomonas syringae pv. syringae (Pss) population in inoculated shoots were obtained. Genotype susceptibility was significantly (P ≤ 0.05) influenced by inoculation method, with shoot inoculation providing the best separation of resistance levels among genotypes. A low correlation (r = 0.26, P = 0.21) was observed between disease responses measured on detached leaf versus fruit, while a moderately high correlation (r = 0.50, P = 0.10) was found among bacterial populations in the tissues and in the degree of symptoms expressed. By all comparative methods, the advanced selections, as well as, 'PMR-1', were less susceptible than the market-leading cultivars. Also, movement of Pss from shoot tip inoculation points to the shoot base was not detected for advanced selections 'AA', 'BB', 'DD', and 'EE'. This study reveals that the advanced selections could be potential sources of resistance alleles to bacterial canker. This is the first evaluation of the advanced selections for bacterial canker disease.

Induction of systemic acquired resistance as a therapeutic aid to restoration of tree health was evaluated in 3- to 14-year-old pear and apple trees diseased with fire blight. Acibenzolar-S-methyl (ASM) was applied to diseased trees in late spring near the time of removal of primary fire blight cankers, which had originated from floral infection. Suspensions of ASM (7.5 to 22.5 g of active ingredient per liter plus silicone surfactant) were painted onto a 30- to 45-cm length of branch tissue immediately below primary pruning cuts or sprayed onto an 80- to 100-cm length of central trunk. In some experiments, a second ASM treatment was made in late June to early July in conjunction with secondary pruning of redeveloped cankers. After pruning primary cankers, effects of ASM were measured by assessing weight and length of secondary cankers that were the result of fire blight redevelopment. Over 5 years of field experiments, trees that received an ASM treatments yielded 62% less diseased wood at the time of secondary and tertiary canker removal compared with non-ASM-treated trees. Moreover, tree mortality and proportion of pruning cuts where fire blight redeveloped were reduced by ASM. Induction of systemic acquired resistance could prove practical as an aid to pruning therapy in young, fire-blight-susceptible pear and apple trees where, after canker removal, disease symptoms frequently redevelop owing to residual cells of the pathogen distributed within symptomless portions of the tree.