Phylogenomic analyses and comparative genomics of Pseudomonas syringae associated with almond (Prunus dulcis) in California.

We sequenced and comprehensively analysed the genomic architecture of 98 fluorescent pseudomonads isolated from different symptomatic and asymptomatic tissues of almond and a few other Prunus spp. Phylogenomic analyses, genome mining, field pathogenicity tests, and in vitro ice nucleation and antibiotic sensitivity tests were integrated to improve knowledge of the biology and management of bacterial blast and bacterial canker of almond. We identified Pseudomonas syringae pv.

Regional Comparisons of Sensitivities of and Causing Citrus Brown Rot in California to Four New and Two Older Fungicides.

Isolates of the citrus brown rot pathogens and from the Inland Empire (IE) and Ventura Co. (VE) regions of southern California were evaluated for their sensitivity to ethaboxam, fluopicolide, mandipropamid, and oxathiapiprolin, and the previously published baselines that were generated for Central Valley (CV) isolates of California were expanded. Fungicides were generally more toxic to CV isolates of both species for all four fungicides.

Diversity and Clonality in Populations of and Causing Brown Rot of Citrus in California.

and are currently the primary causal organisms of brown rot of citrus fruits in California. To possibly find an explanation for the prevalence of the previously minor species , we determined the population structures of both pathogens in California using next-generation sequencing and population genomics analyses. Whole-genome sequencing and aligning with newly assembled reference genomes identified 972,266 variants in 132 isolates of and 422,208 variants in 154 isolates (including 24 from noncitrus tree crops) of originating from three major growing regions.

Root Absorption and Limited Mobility of Mandipropamid as Compared to Oxathiapiprolin and Mefenoxam After Soil Treatment of Citrus Plants for Managing Phytophthora Root Rot.

Phytophthora root rot can greatly impact citrus production worldwide, especially in newly established orchards by reducing crop yield and increasing the cost of disease management. Mandipropamid is an Oomycota fungicide that is currently registered as a soil treatment for citrus nursery container plants to manage Phytophthora root rot. In this study, we investigated the uptake of mandipropamid into citrus roots and its translocation to stems and leaves after soil application and evaluated its mobility in roots as compared to oxathiapiprolin and mefenoxam using split-root potted plants and trees in the field.

New Preharvest Treatments and Strategies in Managing Phytophthora Brown Rot of Citrus in California.

Brown rot caused by , , , and is an important fruit disease of citrus in California, and the latter two species are quarantine pathogens in some important export markets. The newly registered fungicides oxathiapiprolin (OXA) and mandipropamid (MAN), as well as a premixture of the two (MAN + OXA) were compared with standard fixed copper and potassium phosphite (KPO) treatments (all with different modes of action) under field conditions in two citrus production regions of California. Fruit were sampled periodically over 8 weeks after application in winter or spring seasons, inoculated with zoospores of or , and brown rot incidence was evaluated.

Mutations in Gene Subunits Confer Different Cross-Resistance Patterns to SDHI Fungicides in Causing Alternaria Leaf Spot of Almond in California.

Alternaria leaf spot caused by and . is a common disease of almond in California. Succinate dehydrogenase inhibitors (SDHIs) are widely used for its management; however, we observed reduced performance of SDHI fungicides at some field sites.

Organic Acid Sanitizers for Natamycin and Other Fungicides in Recirculating Application Systems for Citrus Postharvest Decay Management.

Natamycin is a new postharvest biofungicide for citrus and some other fruit crops in the United States that can be effectively used in recycling drench or flooder treatments. These applications necessitate sanitation of the fungicide solution to ensure that it remains free from contamination by bacteria that are potentially human pathogens. During in vitro experiments, heated (48°C) citric acid (1,100 or 2,200 μg/ml) amended with sodium dodecylbenzenesulfonate (SDBS) (60 or 120 μg/ml, respectively) significantly reduced the viability of a nonpathogenic strain of in natamycin solutions by >5 log compared with the control.

Natamycin, a Biofungicide for Managing Major Postharvest Fruit Decays of Citrus.

The antifungal polyene macrolide natamycin was evaluated as a postharvest biopesticide for citrus fruit. Aqueous spray applications with 1,000 µg/ml were moderately to highly effective against green mold incidence after inoculation but did not reduce sporulation of on infected fruit. Treatments with natamycin were significantly more effective against green mold on grapefruit and lemon than on orange and mandarin, with 92.

Baseline Sensitivities of Major Citrus, Pome, and Stone Fruits Postharvest Pathogens to Natamycin and Estimation of the Resistance Potential in .

Natamycin is a biofungicide that was registered in the United States in 2016 and approved in California in 2017 for postharvest use on citrus and stone fruits. It has been used as a food preservative for many decades, with no resistance ever observed to date. The objective of this study was to determine baseline sensitivities for mycelial growth of 43 to 72 isolates of seven postharvest pathogens to natamycin and the resistance potential of .

Mobility of Oxathiapiprolin and Mefenoxam in Citrus Seedlings After Root Application and Implications for Managing Phytophthora Root Rot.

Oxathiapiprolin is highly effective in the management of Phytophthora root rot of citrus; however, its uptake into plants after soil application is not known. This was investigated and compared with mefenoxam using potted citrus seedlings sampled 7, 10, 13, and 16 days after soil treatments. Bioassays and high-performance liquid chromatography tandem mass spectroscopy (HPLC-MS/MS) were used to quantify fungicide amounts in plant extracts.

Resistance to Potassium Phosphite in Species Causing Citrus Brown Rot and Integrated Practices for Management of Resistant Isolates.

, , , and less commonly are causal agents of brown rot of citrus fruit in California. The chronic disease occurs during the winter season, requires annual management, and has limited California citrus exports because of quarantines in some markets. Potassium phosphite (KPO) is registered as a pre- and postharvest fungicide in the United States to manage Phytophthora brown rot.

Epidemiology and Management of Bacterial Spot of Almond Caused by pv. , a New Disease in California.

Bacterial spot caused by pv. was first detected on almond in California in 2013, and it is reported herein as a new disease in California based on fulfilling Koch's postulates and identification of the pathogen using species-specific PCR primers. Infected mummified fruit from the previous growing season and their peduncles were identified as primary overwintering sites of the bacterium on the tree.

New Oomycota Fungicides With Activity Against and Their Potential Use for Managing Avocado Root Rot in California.

Phytophthora root rot (PRR), caused by , is the most destructive disease of avocado worldwide. In the United States, mefenoxam and phosphonate products are currently the only registered fungicides for managing avocado PRR. Four new Oomycota-specific and two registered fungicides, all with different modes of action, were evaluated.

Management of with Pre- and Postharvest Treatments to Overcome Trade Barriers for California Strawberries.

, the causal agent of angular leaf spot (ALS) of strawberry, is a quarantine pathogen in some export markets, causing trade restrictions and economic loss to the California fresh-market strawberry industry. Preharvest chemical management options are limited to copper, and there are no postharvest treatments available that reduce populations of the pathogen if ALS is detected at an export destination. Here, we report high preharvest efficacy for the experimental bactericide amino thiadiazole and the commercial product zinc thiadiazole, alone and in mixtures with low rates of copper or the antibiotic kasugamycin, with average disease incidence reduction of up to 92.

Evaluation of New Oomycota Fungicides for Management of Phytophthora Root Rot of Citrus in California.

Phytophthora root rot, caused by several species of Phytophthora, is an important disease of citrus in California and other growing regions. For chemical management, mefenoxam and potassium phosphite have been available for many years, and resistance in Phytophthora spp. has been reported for both compounds.

Baseline Sensitivities of New Fungicides and Their Toxicity to Selected Life Stages of Phytophthora Species from Citrus in California.

Phytophthora citrophthora, P. syringae, P. nicotianae, and P.

Natamycin, a New Biofungicide for Managing Crown Rot of Strawberry Caused by QoI-Resistant Colletotrichum acutatum.

Anthracnose crown rot of strawberry, caused by Colletotrichum acutatum, is an important disease affecting California nursery and fruit production. Preplant dip treatments of transplants with fludioxonil-cyprodinil or azoxystrobin are industry standards for managing the disease and have been used extensively. Following reports of reduced efficacy of azoxystrobin in the field, high levels of quinone outside inhibitor (QoI) resistance were detected in California isolates of the pathogen.

Phenotypic Characterization of Genetically Distinct Phytophthora cinnamomi Isolates from Avocado.

Phytophthora cinnamomi, the causal agent of Phytophthora root rot (PRR), is the most destructive disease of avocado worldwide. A previous study identified two genetically distinct clades of A2 mating type avocado isolates in California; however, the phenotypic variation among them was not assessed. This study described the phenotype of a subset of isolates from these groups regarding growth rate, growth temperature, virulence, and fungicide sensitivity.

Temporal Occurrence and Niche Preferences of Phytophthora spp. Causing Brown Rot of Citrus in the Central Valley of California.

Brown rot of citrus fruit is caused by several species of Phytophthora and is currently of serious concern for the California citrus industry. Two species, Phytophthora syringae and P. hibernalis, are quarantine pathogens in China, a major export market for California citrus.

Complete Genome Sequence of Xanthomonas arboricola pv. juglandis 417, a Copper-Resistant Strain Isolated from Juglans regia L.

Here, we report the complete genome sequence of Xanthomonas arboricola pv. juglandis 417, a copper-resistant strain isolated from a blighted walnut fruit (Juglans regia L. cv.

Characterization of Streptomycin Resistance in Isolates of Erwinia amylovora in California.

In surveys from 2006 to 2014, streptomycin resistance in Erwinia amylovora from pear-growing areas in California declined from very high incidence in 2006 and 2007 to very low incidence in 2013 and 2014. The majority of resistant strains were designated as moderately resistant-low (MR-L), and were almost exclusively found in Sacramento County, whereas highly resistant (HR) strains were only recovered in Sutter-Yuba and San Joaquin counties. Resistance of HR strains was associated with a mutation in codon 43 of the chromosomal rpsL gene that results in a change from lysine to arginine, the same mutation that was originally reported for resistant strains from California in the mid-1970s.

Pythium brassicum sp. nov.: A Novel Plant Family-Specific Root Pathogen.

Roots of stunted broccoli plants (Brassica oleracea) from the Palo Verde Valley, CA, were observed at various stages of decay. A species of Pythium with large spiny oogonia was microscopically observed and consistently isolated from decayed roots. Isolates produced spherical, intercalary sporangia (average 34.

Propiconazole Sensitivity in Populations of Geotrichum candidum, the Cause of Sour Rot of Peach and Nectarine, in California.

The sour rot pathogen of peach (Prunus persica var. persica) and nectarine (P. persica var.

Temporal and quantitative analyses of stem lesion development and foliar disease progression of peach rust in california.

ABSTRACT The development of rust epidemics caused by Tranzschelia discolor on leaves and stems of cling peach was studied in California orchards. Sporulating stems lesions were only detected from late March until July in 1997 and 1998. When rust was present in the fall, the quadratic equation Y = -82.