Bacterial gall caused by Pseudomonas amygdali pv. loropetali (PAL) is a prevalent problem on Loropetalum chinense shrubs in commercial plant nurseries. A method was developed to reliably detect PAL on the surface of loropetalum twigs. A whole-genome analysis resulted in the identification of a locus encoding an AraC regulator that is specific to PAL. A pair of primers and a TaqMan probe were designed based on a 71-base-pair sequence in this locus. Positive results of PCR amplification were obtained with genomic DNA samples from all PAL strains but not from those of other Pseudomonas species, Agrobacterium tumefaciens, or Burkholderia contaminans. Melting curve analysis demonstrated that all PAL PCR products shared the same melting temperature of 79°C. TaqMan-based quantitative PCR (qPCR) analysis of the serially diluted genomic DNA from PAL strain AAC exhibited a strong linear response for regressed cycle threshold and logarithm copy values (adjusted R2 = 0.9944) with a high amplification efficiency (E = 1.96), whereas the linear response (adjusted R2 = 0.8885) for PAL genomic DNA extracted from serially diluted bacterial cell suspension had a reduction in detection sensitivity. The limits of detection and quantification of PAL from the spiked plant twigs (diameter × length = ∼0.45 × 2.45 cm) were 873 and 14,724 cells, respectively, using a modified Promega Wizard extraction protocol. These limits of the qPCR method, although restrictive, still allow a practical detection of PAL strains associated with plant tissue that can be used in epidemiological studies to develop disease management options.

Bacterial gall of Loropetalum chinense, caused by Pseudomonas amygdali pv. loropetali (PAL), was reported to have become an invasive problem in nurseries due to a lack of proven control methods. We surveyed six nurseries to assess the frequency of loropetalum plants with and without galls and to assess PAL density on and in woody twigs in three vertical strata (base, mid-height, and new growth sections) of plants. Quantitative counts were determined using a quantitative real-time polymerase chain reaction method involving primers and probe specific for PAL. The whole-plant frequency of galled plants within a single cultivar block of loropetalum varied from 8 to 92%, with three nurseries having moderate levels of 27 to 39%. No consistent relationship was observed between gall frequency and PAL abundance across canopy strata. The pattern of the mean DNA copy number of PAL in twigs of the three vertical plant strata varied between nurseries, with the highest copy number occurring more frequently in the base stratum and least frequently in the new stratum. The presence of PAL in the phyllosphere of loropetalum plants indicates a risk for spreading the pathogen on vegetatively propagated stem cuttings.The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2026.

Disinfestants are an important sanitation tool used to eliminate plant pathogens. Disinfestant product labels, as well as university and company literature, provide instructions and guidance for the proper usage of disinfestants, yet recent research reviews have shown that inconsistencies in efficacy occur even when these information sources are followed. The efficacy of hypochlorite, isopropyl alcohol, quaternary ammonium, and peroxygen compounds against Colletotrichum siamense was evaluated relative to substrate porosity, contact time, and disinfestant wettability properties in a series of in vitro studies in which disinfestants were sprayed on six substrates (concrete, galvanized metal, polypropylene ground fabric, polyethylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) commonly found in ornamental plant production systems. Bayesian generalized linear mixed models were used to calculate posterior distributions of the median point estimate and 95% equal-tailed credible intervals representing uncertainty about the means. Control of C. siamense was consistently achieved on the nonporous surfaces with all six disinfestants, but the level of control was variable when treating porous surfaces. The natural duration of evaporatively declining coverage over 1 to 20 min after disinfestants were sprayed on surfaces and the initial coverage from disinfestants that innately spread out or bead up on surfaces were not prominent factors that affected efficacy. Control outcomes were improved on porous substrates by making two sequential applications of a label dose or one application of a high dose, although two applications of a label dose, which does not violate disinfestant product label guidance, more consistently achieved the lowest recovery of C. siamense.The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2025.

The evaporation rate of disinfestants when sprayed on production surfaces is expected to vary under different weather conditions, but it is unknown how that affects efficacy. This study is an initial investigation into how the evaporation rates of water and six commercial disinfestants vary under eight weather condition categories. Additionally, an empirical model was developed on the evaporation rate of water in response to air temperature, relative humidity, solar radiation, vapor pressure deficit and wind speed under the same eight weather condition categories. Isopropyl alcohol (IPA) lost more weight due to evaporation over 4 h (P < 0.0001) than all other disinfestant solutions and no differences (P = 0.05) existed between the other five disinfestant solutions and water. IPA had a mean percent weight loss of 71% under hot and sunny conditions, 43% under cool and cloudy conditions, and 6% under indoor laboratory conditions. Water, hypochlorite, quaternary ammonium and peroxy disinfestant solutions evaporated at a similar rate over four hours, with an approximate mean percent weight loss of 17% under hot and sunny conditions, 6% under cool and cloudy conditions, and 1% under indoor laboratory conditions. The regression model that best explained the influence of weather on evaporation included the variables solar radiation, temperature and wind speed (P < 0.0001, R2 = 0.5603). This information will be used further to model the evaporative rate of disinfestants under the same range of weather conditions when applied to multiple types of substrate materials that represent common horticultural plant production surfaces.

Conventional ultraviolet C at 254 nm (UVC) and Far UVC at 222 nm (Far UVC) were evaluated as alternatives to fungicides for disease control. Conidia of 13 isolates of strawberry anthracnose pathogens (five Colletotrichum species in two complexes: C. acutatum and C. gloeosporioides) were uniformly dispersed onto agar and irradiated with UVC and Far UVC doses ranging from 52 to 1,248 J·m −2 . After 48 h of incubation, a UVC dose of 1,248 J·m −2 and Far UVC doses from 234 to 935 J·m −2 reduced Colletotrichum colony counts to <10 colonies/Petri dish. Cultures exposed to UVC light followed by 4 h of darkness had lower colony counts than cultures incubated under continuous light. This dark incubation period was not required for Far UVC to obtain optimal lethality, indicating Far UVC irradiation can be applied during the day or night and achieve similar fungal lethality. Inoculation of detached leaves of three anthracnose-susceptible strawberry cultivars with conidial suspensions of Colletotrichum spp. revealed that UV irradiation can affect development of anthracnose symptoms. Leaves receiving UVC doses of 312 and 624 J·m −2 or a Far UVC dose of 467 J·m −2 reduced anthracnose infection with little or no plant injury. A UVC dose of 1,248 J·m −2 and Far UVC doses ≥ 467 J·m −2 inflicted varying degrees of plant injury. Disease control intended to reduce the number of fungicidal applications could be developed with moderate doses of UVC and Far UVC irradiation while slowing the evolution of pesticide-resistant strains. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

IntroductionA quantitative review was performed on the effectiveness of peroxygen products that contain hydrogen peroxide (HP), peracetic acid (PAA) and potassium peroxy-monosulfate (PPMS) to eliminate non-fungal plant pathogens in agricultural and horticultural cropping systems.MethodsThis quantitative analysis is a complementary follow-up to a previous study on efficacy of peroxygen against fungal plant pathogens. The meta-analysis evaluated the biocidal activity of peroxygen intervention treatments against 15 different non-fungal plant pathogens in 81 studies compared to independent non-treated controls that were conducted over the last 30 years.ResultsThe overall summary effect size was a Hedges’ g (g¯+) of 1.98 for the random effects model, which indicates that peroxgen treatments caused a moderate to high reduction in viable propagules or disease progression in most cases. The range in efficacy was defined by the 95% prediction intervals (-0.82 to 4.80) and indicated peroxygen applications would range from ineffective to very highly effective in 95% of similar populations. Peroxygen compounds provided similar control (P = 0.5655) against bacteria, oomycetes and viruses, while being more effective against zygomycetes (P = 0.0001) than other organism types. Differences were observed between peroxygen active ingredients (a.i.) (P = 0.0203), where PPMS was more effective than HP + PAA. Differences were also observed when peroxygen compounds were applied on different target materials (P = 0.0004). Peroxygen compounds were moderately effective against non-fungal plant pathogens when applied in solution and on metal surfaces but ineffective when applied on plants under crop production conditions. Differences between target materials explained 50% of the true variances in a meta-regression model with the length of time peroxygens were in contact with target materials (P = 0.0416).DiscussionThese results show that although the current recommended dose and contact time for commercial peroxygen products are expected to result in pathogen inactivation, their efficacy will likely be influenced by the organism and material being treated. This analysis serves as a base reference for considering efficacy performance of peroxygen compounds against non-fungal plant pathogens.

Passalora sequoiae is a foliar pathogen to conifer tree species. In this study, we conducted whole-genome and transcriptome analyses on isolates of P. sequoiae collected from symptomatic Leyland cypress leaves from a Christmas tree farm in Mississippi. The objectives for this research were to elucidate the pathogenicity mechanisms of P. sequoiae by characterizing the genome and transcriptome and possibly identify unique and shared predicted genes in comparison with non-conifer/canker and foliar pathogens in the family Mycosphaerellaceae. P. sequoiae was found to be similar to other foliar Mycosphaerellaceae pathogens and likely represents a hemibiotrophic lifestyle based on comparisons across pathogens. The genome and in planta transcriptome highlighted some unique features of P. sequoiae: the significant presence of chitin synthases and fructose-degrading carbohydrate-degrading enzymes, trans-AT PKS genes, and antibiotic gene clusters that were unique to P. sequoiae compared with the other Mycosphaerellaceae species genomes. Several transcripts that were highly expressed in planta were identified as effectors, yet the functions were not characterized. These targets provide ample resources to continue to characterize pathogen-conifer host interactions in conifer foliar pathogens. Furthermore, this research helps build genomic resources for an important plant pathogen on Leyland cypress that will further our ability to develop novel management practices that could begin with breeding for resistance.

Drying rates of disinfestants commonly applied to horticultural plant production surfaces were evaluated under cool to hot weather and under laboratory conditions to characterize the range of drying times and how this relates to contact times specified on product labels. Drying rates of six disinfestants (isopropyl alcohol [IPA], two quaternary ammonium compounds [QACs], two peroxygen compounds [PXs], and sodium hypochlorite [bleach]) and water were evaluated when applied to six substrate materials (concrete, galvanized metal, polypropylene ground fabric, polyethylene plastic sheet, pressure-treated pine, and twin-wall clear polycarbonate) based on the weather variables of solar radiation, temperature, and relative humidity. Differences were evident at the point of application. Disinfestants with low (IPA, both QACs, and one PX) and high (bleach, one PX, and water) surface tension provided approximately 100 and 60% coverage, respectively, when applied to horizontal, nonporous solid materials. Disinfestants applied to horizontal porous materials (concrete, fabric, and wood) persisted on the surface for a mean of only 9 to 113 s because solutions were actively drawn into the substrates’ internal structure. Disinfestants applied to vertical twin-wall greenhouse material flowed off, while retaining only a maximum beaded wetness coverage of 14%. A Bayesian analysis procedure was used to model drying effects of disinfestants correlated with substrate and weather variables based on posterior marginal and prediction trends. Generally, the fastest drying rate occurred in the first 2.5 min, and approximately 50% of coverage was retained by 5 min. The evaporative process was variable with distinct interactions occurring among the experimental variables. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Quaternary ammonium compounds (QACs) have been used as disinfestants in plant production systems since the late 20th century. In studies on the control of fungal pathogens in agricultural and horticultural crop production systems, the efficacy of QAC disinfestants is variable, ranging from very high to ineffective. A systematic review and meta-analysis were performed to establish and understand how pathogen- and application-related factors influenced product efficacy. The meta-analysis was based on 124 studies involving 14 fungal plant pathogen genera, eight target materials, and four generations of QAC products that contained different mixtures of active ingredients. A significant (P < 0.0001) reduction in either disease intensity or propagule viability resulted following disinfestation using QAC products. Hedges' g standardized mean difference (<(g)over bar>(+)) across the studies was 2.16, indicating that QACs, on average, were highly effective against fungal pathogens. Heterogeneity was significant (P < 0.0001), indicating that effect sizes (g) were not representative of a common mean effect size and supported selection of a random effects model. In all, 78.5% of the observed variance consisted of variance in true effects with a high estimate of between-study variability (tau(2) = 2.15). For fungal genus, subgroup <(g)over bar>(+) for genera Pseudonectria and Calonectria was significantly (P < 0.0038) higher than for all other genus subgroups, except Fusarium. For target materials, subgroup <(g)over bar>(+) for solution, cloth, plant, and metal were significantly (P > 0.0071) higher than for inorganic material or wood. For product generation, subgroup (g) over bar (+) for fifth-generation products was significantly (P > 0.0071) higher than for fourth-, third-, and second-generation products. Dose and time accounted for only 8 and 4%, respectively, of the true variance in effect sizes in the regression model dose, time, and dose-time (P = 0.0004). Genus accounted for 40 and 51% of the true variance in effect sizes in the regression models dose and genus (P = 0.0008) and time and genus (P = 0.0007), respectively. Target material accounted for 18 and 19% of the true variance in effect sizes in the regression models dose and target (P = 0.0001) and time and target (P = 0.0001), respectively. QAC product generation accounted for 24 and 21% of the true variance in effect sizes in the regression models dose and QAC generation (P = 0.0034) and time and QAC generation (P = 0.0189), respectively. These results show that the current recommended rates for dose and contact time are generally expected to result in effective disinfestation for commercial QAC products. However, the efficacy against fungal plant pathogens is likely to be influenced by the fungal genus and target being treated and the generation of the QAC product that is used for disinfestation.

The peroxygen compounds, i.e. hydrogen peroxide, peracetic acid and potassium peroxymonosulfate, have been used as disinfestants in agricultural and horticultural operations for about 30 years. This systematic review was conducted to establish the overall efficacy of peroxygen compounds against fungal plant pathogens under production settings. A meta-analysis was performed to evaluate the biocidal activity of peroxygen intervention treatments compared to non-treated controls against 20 fungal genera of plant pathogens in 95 studies. The overall summary effect was a high Hedges' g value of 3.48 with 95% confidence limits of 3.02–3.93 (P < 0.0001) for the random effects model. This observation indicated that use of peroxygen compounds, in most cases, resulted in a high reduction in viable propagules or disease progression. However, heterogeneity was also high with 88.9% of the total variance accounted for by true variance and a high between-study variance of 3.71. To understand what influences heterogeneity, subgroup analyses were performed on the categorical moderators, i.e. fungal genera, target materials and peroxygen active ingredients (a.i.). In addition, two-variable meta-regression analyses were performed with the continuous moderators of peroxygen dose and/or contact time and the three categorical moderators. Subgroup analyses showed differences between target materials (P = 0.0151) and peroxygen a.i. (P = 0.0101) but not between fungal genera (P = 0.1753). Meta-regression results concurred with subgroup analysis results wherein models with target materials and dose (P = 0.0119) or time (P = 0.0122) accounted for 8 and 9% of the true variance, respectively. Models with peroxygen a.i. and dose (P = 0.0067) or time (P = 0.0093) accounted for 5 and 4% of the true variance, respectively. Thus, heterogeneity was only partly explained by the moderators evaluated and a larger portion of the true variance attributed to factors not available through the systematic review. Additional factors were evident also, such as diversity of research protocol, assessment measurements, sample size and small-study bias. The results support that the current doses and contact times recommended for peroxygen compounds will generally be effective at controlling fungal plant pathogens in agricultural and horticultural production systems. Results also indicate that efficacy of peroxygen compounds against fungi can be affected by the target material being treated and the peroxygen a.i. applied and potentially by fungal genus. This analysis serves as a base reference for considering efficacy performance of peroxygen compounds in these production settings.

This quantitative review and systematic analysis of the effectiveness of quaternary ammonium compounds (QACs) in disinfesting nonfungal plant pathogens in agricultural and horticultural cropping systems is a complementary follow-up to a previous study that evaluated the efficacy of QACs against fungal plant pathogens. In the present study, a meta-analysis involving 67 studies was conducted to assess the overall efficacy of QACs against plant pathogenic bacteria, oomycetes, and viruses and to identify factors associated with observed differences in product efficacy. Across all studies, QACs resulted in a significant (P < 0.0001) reduction in either disease intensity or propagule viability with a mean Hedges' g (g(g(+)) of 1.75, indicating that overall QAC treatments were moderately effective against nonfungal pathogens. Significant differences in product efficacy were observed between organism types (P = 0.0001), with QAC interventions resulting in higher efficacy (P = 0.0002) against oomycetes(g(+ )= 4.20) than against viruses(g(g(+)) = 1.42) and bacteria g(+)= 1.07), which were not different (P = 0.2689) from each other. As a result, bacterium and virus types were combined into a composite set (BacVir). QAC intervention against BacVir resulted in significant differences in efficacy within categorical moderator subgroups for genus (P = 0.0133), target material (P = 0.0001), and QAC product generation (P = 0.0281). QAC intervention against oomycetes resulted in significant differences in efficacy only for genus (P < 0.0001). For the BacVir composite, five random effect (RE) meta-regression models were significant (P = 0.05), where models with dose and time, dose and genus, time and genus, dose and target, and time and target accounted for 62, 61, 52, 83, and 88%, respectively, of the variance in true effect sizes (R-2) associated with(g(g(+)). For oomycetes, three RE meta-regression models were significant (P = 0.05), where models with dose and time, dose and genus, and time and genus accounted for 64, 86, and 90%, respectively, of R-2 associated withg(+). These results show that while QACs are moderately effective against nonfungal plant pathogens, the observed variability in their efficacy due to dose of active ingredient and contact time of these products can be influenced by organism type, genus within organism type, the target being treated, and the generation of QAC products

HomePlant DiseaseVol. 106, No. 9Complete Genome Sequence Resource for Pseudomonas amygdali pv. loropetali Strain AAC Causing Bacterial Gall of Loropetalum chinense PreviousNext RESOURCE ANNOUNCEMENT OPENOpen Access licenseComplete Genome Sequence Resource for Pseudomonas amygdali pv. loropetali Strain AAC Causing Bacterial Gall of Loropetalum chinenseJiayuan Jia, Warren E. Copes, Kate Phillips, and Shi-En LuJiayuan JiaDepartment of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mail Stop 9655, Mississippi State, MS 39762Search for more papers by this author, Warren E. CopesUnited States Department of Agriculture–Agricultural Research Service, Thad Cochran Southern Horticultural Research Laboratory, Poplarville, MS 39740Search for more papers by this author, Kate PhillipsDepartment of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mail Stop 9655, Mississippi State, MS 39762Search for more papers by this author, and Shi-En Lu†Corresponding author: S.-E. Lu; E-mail Address: sl332@msstate.eduhttps://orcid.org/0000-0003-2255-1404Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mail Stop 9655, Mississippi State, MS 39762Search for more papers by this authorAffiliationsAuthors and Affiliations Jiayuan Jia1 Warren E. Copes2 Kate Phillips1 Shi-En Lu1 † 1Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mail Stop 9655, Mississippi State, MS 39762 2United States Department of Agriculture–Agricultural Research Service, Thad Cochran Southern Horticultural Research Laboratory, Poplarville, MS 39740 Published Online:26 Jul 2022https://doi.org/10.1094/PDIS-04-22-0919-AAboutSectionsView articlePDFSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat View articleGenome AnnouncementThe plant-pathogenic Pseudomonas syringae species complex (Pssc) represents a group of closely related bacteria that cause diseases on hundreds of plant species that comprise monocots, herbaceous dicots, and woody dicots (Young 2010). A reclassification revealed that the Pssc group contains 10 species with 60 pathovars, which includes P. amygdali (Gardan et al. 1999; Young 2010). Specifically, several species were classified into P. amygdali, including P. savastanoi, P. ficuserectae, P. meliae, and P. tremae, based on DNA relatedness ribotyping studies, repetitive element sequence-based PCR, and rpoD analyses (Gardan et al. 1999; Marques et al. 2008; Parkinson et al. 2011). Currently, the genomes of the majority of P. amygdali strains were drafted as contigs and scaffolds, and only a few complete genomes are available in GenBank, which include the pathovars tabaci, lachrymans, and morsprunorum. However, no complete genome sequence of the pathovar loropetali is available.Loropetalum chinense, also known as the Chinese fringe flower or loropetalum, is a well-adapted woody ornamental in regions of the southeastern United States that is propagated by cuttings. The bacterial knot disease caused by P. amygdali pv. loropetali on loropetalum cultivars was first reported in 2013 (Conner et al. 2013; Harmon et al. 2018). Disease symptoms include inconspicuous bacterial galls of 0.2 to 1.0 cm in diameter and irregular dark callus formation on limbs or girdled stems, with progressive death of twigs and branches and foliar nutrient deficiency symptoms distal of stem symptoms. This disease has led to a significant problem in commercial plant nurseries and has been given accelerative prevalence in the landscape of the same region. Thus, to further expand the genome information of P. amygdali and understand the genomic basis underlying host–pathogen interaction of pathovar loropetali, we report the complete genome sequence of P. amygdali pv. loropetali strain AAC, which was originally isolated from loropetalum shrubs purchased at a local retail outlet in Forest County, Mississippi, United States (Copes et al. 2019).Bacterial strain AAC from a stock at the Thad Cochran Southern Horticultural Research Laboratory, United States Department of Agriculture–Agricultural Research Service, was streaked onto nutrient broth yeast extract agar medium, then incubated at 28°C (Vidaver 1967). Genomic DNA was extracted from overnight bacterial cultures using Promega Wizard Genomic DNA Purification Kit (Promega Corp.), following the manufacturer’s protocols, with RNase A treatment. DNA quantity and quality were assessed using a NanoDrop 1000 Spectrophotometer (Thermo Fisher Scientific). The library preparation and genome sequencing were conducted at Novogene (Beijing Novogene Corporation, China) by PacBio single-molecule real-time (SMRT) DNA sequencing. To prepare SMRTbell libraries, DNA (5 µg) was fragmented, damage repaired, end repaired, adapter ligated, primers annealed, and polymerase bound. The library was checked with Qubit for quantification and bioanalyzer for size distribution detection (Mardis and McCombie 2017). Quantified libraries were pooled and sequenced on the PacBio Sequel II system. Default parameters were used for all software. In total, 194,745 subreads with an N50 value of 15,678 bp and average read length of 12,468 bp were obtained, which provided approximately 391-fold coverage. Genome assembly was carried out using FALCON (FALCON-kit = 1.8.1) with hierarchical genome assembly process algorithm version 4. Merged contigs were circularized with the software Circlator (1.5.5) (Hunt et al. 2015). All reads and contigs after circularization were polished with Arrow (2.3.3). Based on evolutionarily informed expectations of gene content from near-universal single-copy orthologs, the benchmarking universal single-copy orthologous (BUSCO 4.0.2) analysis was used to verify the completeness of the genome assembly with database Pseudomonadales_odb10 (Simão et al. 2015). The BUSCO analysis showed that 124 complete and single-copy BUSCOs (100.00%) were detected. Clusters of orthologous groups of proteins (COGs) (Galperin et al. 2015) and gene ontology (GO) (Ashburner et al. 2000) were used for functional analysis. The genome was automatically annotated using the NCBI’s Prokaryotic Genome Annotation Pipeline (Tatusova et al. 2016). The Microbial Genomes Atlas (MiGA) webserver was used to establish the taxonomic classification of the strain AAC (Rodriguez-R et al. 2018). To evaluate genetic relatedness between closely related genomes, average nucleotide identity (ANI) was calculated by using the OrthoANIu v0.93 with OrthoANIu algorithm (Yoon et al. 2017). BLAST comparison of genomes was conducted by BRIG (Alikhan et al. 2011).The genome of P. amygdali pv. loropetali AAC comprises one circular chromosome (Fig. 1). The genome features of strain AAC are summarized in Table 1. The chromosome of AAC is 6,241,584 bp in length, with 5,279 protein-encoding genes and 58.20% G+C content, 16 ribosomal RNAs, and 66 transfer RNAs. According to functional protein alignments, 4,318 proteins were assigned to the COGs database, and GO terms were assigned to 3,927 genes. Strain AAC was preliminarily identified as P. amygdali based on the multilocus sequence analysis in a previous study (Copes et al. 2019). In this study, the MiGA analysis revealed that the closest related type strain was P. amygdali CFBP 3205T. In addition, comparisons of the complete genome assemblies of nine close type strains of the genus Pseudomonas demonstrated that strain AAC shares the highest ANI value of 98.78% to the type strain CFBP 3205T of P. amygdali, which is above the benchmark for species demarcation (95 to 96%) as described by Richter and Rosselló-Móra (2009) (Supplementary Table S1). Therefore, strain AAC was further identified as P. amygdali based on the MiGA and ANI results.Fig. 1. Circular representation of the complete genome of Pseudomonas amygdali pv. loropetali AAC compared with eight sequenced P. amygdali complete genomes. Rings from inside to the outside represent (1) Scale (black kilobase-pair-scaled ring), (2) GC content (black ring of segmented domains), (3) GC skew(−) (purple ring of segmented domain); GC skew(+) (green ring of segmented domains), (4) BLAST comparison with P. amygdali 35-1 (lavender ring), (5) BLAST comparison with P. amygdali HS1 (blizzard blue ring), (6) BLAST comparison with P. amygdali pv. morsprunorum 15244 (blue ring), (7) BLAST comparison with P. amygdali pv. tabaci 6605 (cornflower blue ring), (8) BLAST comparison with P. amygdali pv. tabaci ATCC 11528 (yellow ring), (9) BLAST comparison with P. amygdali pv. lachrymans 8 (Caribbean green ring), (10) BLAST comparison with P. amygdali pv. lachrymans M301315 (bud green ring), and (11) BLAST comparison with P. amygdali pv. lachrymans NM002 (red ring).Download as PowerPointTable 1. Genome features of Pseudomonas amygdali pv. loropetali strain AACFeatureAACSequence stateCompleteGenomic typeChromosomeAccession numberCP089282Size (bp)6,241,584Genes5,647Coding sequences5,279Pseudogenes282Ribosomal RNAs16Transfer RNAs66Noncoding RNAs4G+C content (%)58.20Table 1. Genome features of Pseudomonas amygdali pv. loropetali strain AACView as image HTML Blast research of the AAC genome against all available complete genomes of P. amygdali, including P. amygdali 35-1 (CP084212), P. amygdali HS1 (CP079716), P. amygdali pv. morsprunorum 15244 (CP026558), P. amygdali pv. tabaci 6605 (AP024464), P. amygdali pv. tabaci ATCC 11528 (CP042804), P. amygdali pv. lachrymans 8 (CP075686), P. amygdali pv. lachrymans M301315 (CP031225), and P. amygdali pv. lachrymans NM002 (CP020351), revealed noticeable genome diversity and multiple unique gene regions which were only found in the AAC genome (Fig. 1). In addition, the typical virulence factors of Pseudomonas spp. were analyzed in the AAC genome. The type III secretion system (T3SS), which delivers type III secretion effectors (T3SEs) into the host cell, where they act by suppressing the plant immune defenses and promoting virulence by different mechanisms, was found (Green and Mecsas 2016). As expected, two sets of T3SSs and 25 T3SEs were found in the AAC genome. The auxin phytohormone indole-3-acetic acid (IAA) has been described as a pathogenicity or virulence factor in P. savastanoi and P. syringae pathovars (Glickmann et al. 1998). The iaaM, iaaH, iaaL, aldA, and aldB genes that are involved in production of IAA (Aragón et al. 2014; Glickmann et al. 1998; McClerklin et al. 2018) were searched in the AAC genome. According to Glickmann et al. (1998), most of the IAA production pathovars of P. syringae harbor the iaaL gene. The entire iaaMH operon is absent in the AAC genome; however, it harbors part of the iaaL gene and the entire aldA and aldB genes. Thus, the possibility of AAC production of IAA could be attributed to aldehyde dehydrogenase family proteins, which are encoded by the genes aldA and aldB.To the best of our knowledge, this is the first reported complete genome of P. amygdali pv. loropetali. This genome sequence of P. amygdali pv. loropetali AAC will provide a valuable resource for future studies on the Loropetalum bacterial gall pathogen and its interactions with loropetalum.Data AvailabilityThe genome sequence of P. amygdali pv. loropetali AAC has been deposited in GenBank in BioProject accession number PRJNA786935 and the BioSample ID SAMN23753993. The sequence of the chromosome is deposited in GenBank under accession number CP089282.The author(s) declare no conflict of interest.Literature CitedAlikhan, N.-F., Petty, N. K., Ben Zakour, N. L., and Beatson, S. A. 2011. 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Lu.The author(s) declare no conflict of interest.DetailsFiguresLiterature CitedRelated Vol. 106, No. 9 September 2022SubscribeISSN:0191-2917e-ISSN:1943-7692 Download Metrics Article History Issue Date: 30 Aug 2022Published: 26 Jul 2022Accepted: 23 May 2022 Pages: 2502-2505 Information© 2022 The American Phytopathological SocietyFundingNon-Assistance Cooperative Agreement of United States Department of AgricultureGrant/Award Number: 6062-21430-004-00DNational Institute of Food and AgricultureGrant/Award Number: MS-401200Keywordsbacterial gallcomplete genomeLoropetalum chinensePseudomonas amygdaliThe author(s) declare no conflict of interest.PDF download

Hypochlorite is often used as a disinfestant of fungal pathogens in a range of agricultural and horticultural settings. However, reports of its effectiveness are variable across studies and it is unclear what factors could potentially influence the reported estimates of its efficacy. A systematic review and meta-analysis was conducted to assess the efficacy of hypochlorite against fungal pathogens and explore factors that may explain the observed heterogeneity in estimates of efficacy. Standardized mean effect size, Hedges' g, was calculated for each of the 109 selected studies, published from 1972 to 2019, that met the criteria defined for the systematic review. A random-effects model was used to estimate the overall mean effect size ([Formula: see text]) and determine the heterogeneity in g among studies. Hypochlorite resulted in a significant (P < 0.001) reduction in either disease intensity or propagule viability with [Formula: see text]= 2.25, suggesting a large overall effect. However, 95% prediction intervals ranged from -0.18 to 4.68, indicating that hypochlorite could be ineffective against some fungi or when targeting some substrate materials. An estimate of the within-study variability, τ2, was 1.48 and the proportion of heterogeneity in g among studies due to true effects was 71.5%. Inclusion of categorical moderator variables in the random effects model showed that hypochlorite treatments were significantly (P < 0.0062) more effective when used to disinfest spores in an aqueous solution ([Formula: see text]= 4.58) than when used on plastic ([Formula: see text]= 2.13), plant ([Formula: see text]= 2.13), and wood ([Formula: see text]= 0.79). Similarly, hypochlorite treatments were significantly (P < 0.0083) more effective in disinfesting fungal propagules of Thielaviopsis spp. ([Formula: see text]= 2.51) than those of Verticillium spp. ([Formula: see text]= 1.21). A meta-regression indicated that the effect of dose (β = -3.54; P = 0.0398) and contact time (β = -0.05; P = 0.0001) on [Formula: see text] were highly significant. Further, [Formula: see text]was significantly affected by the dose × time interaction (β = -0.017; P = 0.0269). In the meta-regression models, dose and time explained 0 and 16% of the variance in true effects, respectively. In meta-regression models with a continuous variable of dose or time, a categorical variable of target or genus and their interaction term, genus and target explained an additional 7 to 19% of the variance in true effects. These results show that although the current recommended dose and contact time for commercial bleach products are expected to result in effective disinfestation, the target material and genera of the fungal pathogen of interest will likely influence their efficacy.

Bleach products containing hypochlorite are commonly used as disinfectants to eliminate nonfungal plant pathogens from production surfaces, tools, plant surfaces, irrigation water, and produce dump tanks. Although bleach products are useful, their effectiveness has been reported to vary under specific settings. A meta-analysis was conducted of 86 studies to assess the overall efficacy of hypochlorite against plant pathogenic bacteria, oomycetes, and viruses and to identify factors that explain differences in product efficacy. Hypochlorite resulted in a significant (P < 0.0001) reduction in disease intensity or propagule viability, with a mean Hedges’ g standardized difference ([Formula: see text]) of 3.01, indicating that overall, hypochlorite treatments are highly effective. However, heterogeneity in g was significant (P < 0.0001) between studies, wherein 69.8% of the variance observed in g was attributed to true effects. Furthermore, an estimate of between-study variability was moderate (τ2 = 1.46). Random effects (REs) metaregression showed limited effects of moderator variables dosage, contact time, targeted material of treatment, and organism type on product efficacy when all organism types were considered together. Because subgroup [Formula: see text] was significantly higher (P = 0.0070) for oomycetes ([Formula: see text] = 3.30) than for bacteria ([Formula: see text] = 2.19), subsequent metaregressions were performed by organism type. For oomycetes, five RE metaregression models, each containing two moderators and their interaction, resulted in significant (P = 0.05) effects, where models with dosage and time, dosage and genus, time and genus, dosage and target, and time and target accounted for ≤50, 71, 57, 48, and 47%, respectively, of the variance in true effect sizes (R2) associated with [Formula: see text]. For viruses, only the RE metaregression model containing time and target and their interaction resulted in significant (P = 0.0435) effects accounting for 38% of the variance in true effect sizes associated with [Formula: see text]. None of the RE metaregression models for bacteria were significant, although they still accounted for ≤28% of the variance in true effect sizes associated with [Formula: see text]. These results show that although the current recommended rates for dosage and contact time for commercial bleach products are generally expected to result in effective disinfestation, the efficacy against nonfungal plant pathogens is expected to be influenced by the organism type and target being treated with hypochlorite.

Calonectria pseudonaviculata and Pseudonectria foliicola causing the infamous “boxwood blight” and “Volutella blight,” respectively, are a constant threat to the boxwood production and cut boxwood greenery market. Both pathogens cause significant economic loss to all parties (growers, retailer, and customers) in the horticultural chain. The objective of this study was to evaluate efficacy of disinfesting chemicals (quaternary ammonium compound [QAC], peroxy, acid, alcohol, chlorine, and cleaner) in preventing plant-to-plant transfer of C. pseudonaviculata and P. foliicola via cutting tools, as well as reduction of postharvest boxwood blight and Volutella blight disease severity in harvested boxwood greenery. First, an in vitro study was conducted to select products and doses that completely or near-completely inhibited conidial germination of C. pseudonaviculata and P. foliicola. The selected treatments were also tested for their ability to reduce plant-to-plant transfer of C. pseudonaviculata and P. foliicola and manage postharvest boxwood blight and Volutella blight in boxwood cuttings. For the plant-to-plant transfer study, Felco 19 shears were used as a tool for mechanical transfer of fungal conidia. The blades of Felco 19 shears were exposed to a conidial suspension of C. pseudonaviculata or P. foliicola by cutting a 1-cm-diameter cotton roll that had been dipped into a fungal suspension. Disease-free boxwood rooted cuttings (10-cm height) were pruned with the contaminated shears. The Felco 19 shears were equipped with a mounted miniature sprayer connected to a pressurized reservoir of treatment solution that automatically sprayed the blade and plant surface while cutting. The influence of accumulated sap on the shear blade was studied through 1- or 10-cut pruning variable on test plants and screened for the efficacy of treatments. Then, the boxwood rooted cuttings were transplanted and incubated in room conditions (21°C, 60% RH) with 12 h of fluorescent light; data evaluation on disease severity was done weekly for a month. Disease progress (area under disease progress curve [AUDPC]) was calculated. In another study, postharvest dip application treatments were used for the management of postharvest boxwood blight or Volutella blight on boxwood cuttings. The harvested boxwood cuttings were inoculated with a conidial suspension of C. pseudonaviculata or P. foliicola and then dipped into treatment solution 3 days afterward. The treated boxwood cuttings were kept in room conditions, and boxwood blight or Volutella blight disease severity as well as marketability (postharvest shelf life) was assessed every 2 days for 1 week. A significant difference between treatments was observed for reduction of boxwood blight or Volutella blight severity and AUDPC. The treatments [Octyl decyl dimethyl (ODD) + dioctyl dimethyl (DoD) + didecyl dimethyl (DdD) + dimethyl benzyl (DB)] ammonium chloride (AC) (Simple Green D Pro 5), 2-propanol + didecyl dimethyl ammonium chloride (DDAC) (0.12%; KleenGrow), and dimethyl benzyl ammonium chloride (DBAC) + dimethyl ethylbenzyl ammonium chloride (DEAC) (GreenShield) were the most effective in reducing the plant-to-plant transfer of boxwood blight and Volutella blight when pruned with contaminated Felco 19 shears. In addition to the three effective treatments above, acetic acid (2.5%; vinegar), 2-propanol + DDAC (0.06%), sodium hypochlorite (Clorox), and potassium peroxymonosulfate + NaCl (2%; Virkon) were effective in reducing postharvest boxwood blight, whereas DBAC + DBAC (Lysol all-purpose cleaner), ethanol (70% [ethyl alcohol]), and DDAC + DBAC (Simple Green D Pro 3 plus) were effective in reducing Volutella blight disease severity and AUDPC, and they also maintained better quality and longer postharvest shelf life of boxwood cuttings when applied as a dip treatment. The longer postharvest shelf life of boxwood cuttings noted may be attributed to reduced disease severity and AUDPC resulting in healthy boxwood cuttings.

Objective: Passalora sequoiae (family Mycosphaerellaceae) causes a twig blight on Leyland cypress that requires numerous fungicide applications annually to minimize economic losses for ornamental plant nursery and Christmas tree producers. The objective was to generate a high-quality draft assembly of the whole genome of P. sequoiae as a resource for primer development and to investigate genotype diversity. Data description: We report here the genome sequence of P. sequoiae 9LC2 that was isolated from Leyland cypress 'Leighton Green' in 2017 in southern Mississippi, USA. The draft genome was obtained using Pacific Biosciences (PacBio) SMRT and Illumina HiSeq 2500 sequencing. Illumina reads were mapped to PacBio assembled contigs to determine base call consistency. Based on a total of 44 contigs with 722 kilobase (kb) average length (range 9.4 kb to 3.4 Mb), the whole genome size was estimated at 31,768,716 bp. Mapping of Illumina reads to PacBio contigs resulted in a 1000 x coverage and were used to confirm accuracy of the consensus sequences.

Clorox Germicidal Bleach, Cuproxat, Green-Shield II, KleenGrow, Virkon S, and ZeroTol 2.0 were evaluated for their ability to inactivate Pseudomonas amygdali pv. loropetali on stainless steel (SS), pressure-treated wood (PtW), and loropetalum stem sections. Clorox at 11% product and Virkon S at 1.0% product eliminated P. amygdali pv. loropetali on SS surfaces and nearly eliminated it on PtW surfaces. Green-Shield II at 0.5% product and KleenGrow at 0.8% product nearly eliminated the bacterium on SS, while causing a significant reduction without elimination on PtW. Cuproxat and ZeroTol 2.0 were not effective against this bacterium in these applications. Clorox and KleenGrow were evaluated further for their ability to kill P. amygdali pv. loropetali on loropetalum stems, which was used as a preliminary surrogate for vegetative stem cuttings. Only Clorox eliminated bacteria from stem surfaces, but the bacterial inoculum level appeared to affect efficacy. Several disinfestants are commercially available that kill P. amygdali pv. loropetali on production surfaces.