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Autophagy in eukaryotes functions to maintain homeostasis by degradation and recycling of long-lived and unwanted cellular materials. Autophagy plays important roles in pathogenicity of various fungal pathogens, suggesting that autophagy is a novel target for development of antifungal compounds. Here, we describe bioluminescence resonance energy transfer (BRET)-based high-throughput screening (HTS) strategy to identify compounds that inhibit fungal ATG4 cysteine protease-mediated cleavage of ATG8 that is critical for autophagosome formation. We identified ebselen (EB) and its analogs ebselen oxide (EO) and 2-(4-methylphenyl)−1,2-benzisothiazol-3(2H)-one (PT) as inhibitors of fungal pathogens Botrytis cinerea and Magnaporthe oryzae ATG4-mediated ATG8 processing. The EB and its analogs inhibit spore germination, hyphal development, and appressorium formation in Ascomycota pathogens, B. cinerea, M. oryzae, Sclerotinia sclerotiorum and Monilinia fructicola. Treatment with EB and its analogs significantly reduced fungal pathogenicity. Our findings provide molecular insights to develop the next generation of antifungal compounds by targeting autophagy in important fungal pathogens. [ABSTRACT FROM AUTHOR] more...

Summary: Cyst-forming nematodes of the genus Heterodera are highly derived and economically important plant parasites. The Schachtii group of this genus is one of the largest ones with a total of 18 species parasitising dicotyledons. In this study, we provided comprehensive phylogenetic analyses of several hundred COI and ITS rRNA gene sequences of selected species from the Schachtii group, including H. betae , H. cajani , H. ciceri , H. galeopsidis , H. glycines , H. medicaginis , H. mediterranea , H. schachtii , H. sonchophila and H. trifolii , using Bayesian inference, maximum likelihood, and statistical parsimony. One hundred and twenty four new COI , 57 ITS rRNA and eight hsp90 gene sequences from 81 nematode populations collected in 19 countries were obtained in this study. Our study showed that the ITS rRNA gene has limited discrimination power compared to the COI gene. However, our analysis also revealed that partial COI gene sequences were identical for H. trifolii , H. betae and H. galeopsidis. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that the majority of the Schachtii group species originated and diversified in the Mediterranean Basin biodiversity hotspot during the Pleistocene and then dispersed from this region across the world. The Sino-Japanese Floristic Region is likely one of the centres of diversification for the soybean cyst nematode, which showed distinct population structure. The possible role of hybridisation and polyploidisation in the evolution of species of the Schachtii group is discussed. [ABSTRACT FROM AUTHOR] more...

Summary: The Humuli group of the genus Heterodera contains species that parasitise dicotyledons and are characterised by a lemon-shaped cyst having a bifenestrate vulval cone (ambifenestrate for H. fici), long vulval slit and weak underbridge. Presently, the Humuli group includes seven species: H. amaranthusiae , H. fici , H. humuli , H. litoralis , H. ripae , H. turcomanica and H. vallicola. In this study we provided comprehensive phylogenetic analyses of COI and ITS rRNA gene sequences of species from the Humuli group using Bayesian inference, maximum likelihood, and maximum and statistical parsimony. All seven valid species from the Humuli group, one putatively new species belonging to this group and the willow cyst nematode, H. salixophila , sharing a common ancestor with the Humuli group, were analysed. Some 84 COI and 5 ITS rRNA new gene sequences from 37 nematode populations collected from 12 countries were obtained in this study. Our results confirmed that the COI gene is a powerful DNA barcoding marker for identification of populations and species from the Humuli group. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that some species of the Humuli group primarily originated and diversified in Western and Middle Asian regions during the Pleistocene and Holocene periods and then dispersed from this region across the world. Two secondary diversification centres of the Humuli group were likely located in East and Southeast Asia, Russian Far East, and Oceania. [ABSTRACT FROM AUTHOR] more...

Summary: The pigeon pea cyst nematode, Heterodera cajani , is an important nematode pest of pigeon pea that is present in all major growing regions of this crop in India and reported from Pakistan, Egypt and Myanmar. In this study, a new real-time PCR assay for detection of H. cajani using a species-specific primer and a TaqMan probe was developed. The primers and a probe were designed to amplify the COI gene fragment. The specificity of the primer-probe set was tested in singleplex or multiplex reactions against target and non-target nematodes. In multiplex real-time PCR experiments with the specific and universal primer-probe sets, the signals were simultaneously observed for COI and D3 of 28S rRNA target genes. The results showed that the real-time PCR assay with species-specific primer and probe was sensitive enough to detect H. cajani DNA extracted from 0.003 egg or second-stage juvenile. [ABSTRACT FROM AUTHOR] more...

Summary: Globodera presently contains 13 valid and three as yet undescribed species. Three species, G. rostochiensis , G. pallida and G. ellingtonae , the potato cyst nematodes (PCN), cause significant economic losses on potatoes around the world. In our study we provide comprehensive phylogenetic analyses of 455 ITS rRNA, 219 COI and 164 cytb gene sequences of 11 valid and two undescribed species of Globodera using Bayesian inference, maximum likelihood and statistical parsimony. New 205 COI , 116 cytb and 21 ITS rRNA gene sequences were obtained from 148 populations of these species collected from 23 countries. The phylogenetic analysis revealed that Globodera displayed two main clades in the trees: i) Globodera from South and North America parasitising plants from Solanaceae; and ii) Globodera from Africa, Europe, Asia and New Zealand parasitising plants from Asteraceae and other families. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it is hypothesised that Globodera species originated and diversified from several centres of speciation located in mountain regions and then dispersed across the world from these regions during the Pleistocene. High genetic diversity of Bolivian populations of G. rostochiensis was observed for both mtDNA genes. Analysis of phylogenetic relationships of G. pallida and G. rostochiensis populations revealed incongruence in topology between networks inferred from mtDNA genes, which might be an indication of possible recombination and selective introgression events through gene flow between previously isolated populations. This puts some limitations on the use of the mtDNA marker as universal DNA barcoding identifier for PCN. Globodera bravoae syn. n. is proposed as a junior synonym of G. mexicana. [ABSTRACT FROM AUTHOR] more...

Phytophthora ramorum is an invasive and devastating plant pathogen that causes sudden oak death in coastal forests in the western United States and ramorum blight in nursery ornamentals and native plants in various landscapes. As a broad host-range quarantine pest that can be asymptomatic in some hosts, P. ramorum presents significant challenges for regulatory efforts to detect and contain it, particularly in commercial nurseries. As part of a program to develop new detection methods for cryptic infections in nursery stock, we compared volatile emissions of P. ramorum-inoculated and noninoculated Rhododendron plants using three gas chromatography–mass spectrometry methods. The first used a branch enclosure combined with headspace sorptive extraction to measure plant volatiles in situ. Seventy-eight compounds were found in the general Rhododendron profile. The volatile profile of inoculated but asymptomatic plants (121 days post-inoculation) was distinguishable from the profile of the noninoculated controls. Three compounds were less abundant in inoculated Rhododendron plants relative to noninoculated and mock-inoculated control plants. A second method employed stir bar sorptive extraction to measure volatiles in vitro from leaf extractions in methanol; 114 volatiles were found in the overall profile with 30 compounds less abundant and one compound more abundant in inoculated Rhododendron plants relative to mock-inoculated plants. At 128 days post-inoculation, plants were asymptomatic and similar in appearance to the noninoculated controls, but their chemical profiles were different. In a third technique, volatiles from water runoff from the soil of potted healthy and inoculated Rhododendron plants were compared. Runoff from the inoculated plants contained four unique volatile compounds that never appeared in the runoff from mock-inoculated plants. These three volatile detection techniques could lead to innovative approaches that augment detection and diagnosis of P. ramorum and oomycete pathogens in nurseries and other settings.Detection of volatile signatures may aid in discriminating healthy vs. infected but asymptomatic plants in nursery and greenhouse facilities [ABSTRACT FROM AUTHOR] more...

The walnut twig beetle (WTB), Pityophthorus juglandis Blackman (Coleoptera: Curculionidae), vectors a fungus, Geosmithia morbida Kolařík, Freeland, Utley, and Tisserat (Ascomycota: Hypocreales), which colonises and kills the phloem of walnut and butternut trees, Juglans Linnaeus (Juglandaceae). Over the past two decades, this condition, known as thousand cankers disease (TCD), has led to the widespread mortality of Juglans species in the United States of America. Recently the beetle and pathogen were discovered on several Juglans species in northern Italy. Little is known about the extra-generic extent of host acceptability and suitability for the WTB. We report the occurrence of both the WTB and G. morbida in three species of wingnut, Pterocarya fraxinifolia Spach, Pterocarya rhoifolia Siebold and Zuccarini, and Pterocarya stenoptera de Candolle (Juglandaceae) growing in the United States Department of Agriculture-Agricultural Research Service, National Clonal Germplasm Repository collection in northern California (NCGR) and in the Los Angeles County Arboretum and Botanic Garden in southern California, United States of America. In two instances (once in P. stenoptera and once in P. fraxinifolia) teneral (i.e., brood) adult WTB emerged and were collected more than four months after infested branch sections had been collected in the field. Koch’s postulates were satisfied with an isolate of G. morbida from P. stenoptera, confirming this fungus as the causal agent of TCD in this host. A survey of the 37 Pterocarya Kunth accessions at the NCGR revealed that 46% of the trees had WTB attacks and/or symptoms of G. morbida infection. The occurrence of other subcortical Coleoptera associated with Pterocarya and the first occurrence of the polyphagous shot hole borer, a species near Euwallacea fornicatus Eichhoff (Coleoptera: Curculionidae), in Juglans are also documented. [ABSTRACT FROM PUBLISHER] more...

Predisposition results from abiotic stresses occurring prior to infection that affect susceptibility of plants to disease. The environment is seldom optimal for plant growth, and even mild, episodic stresses can predispose plants to inoculum levels they would otherwise resist. Plant responses that are adaptive in the short term may conflict with those for resisting pathogens. Abiotic and biotic stress responses are coordinated by complex signaling networks involving phytohormones and reactive oxygen species (ROS). Abscisic acid (ABA) is a global regulator in stress response networks and an important phytohormone in plant-microbe interactions with systemic effects on resistance and susceptibility. However, extensive cross talk occurs among all the phytohormones during stress events, and the challenge is discerning those interactions that most influence disease. Identifying convergent points in the stress response circuitry is critically important in terms of understanding the fundamental biology that underscores the disease phenotype as well as translating research to improve stress tolerance and disease management in production systems. [ABSTRACT FROM AUTHOR] more...

Phytophthora ramorum attacks many forest and nursery species, primarily causing trunk or stem cankers, foliar blight, and dieback, and in some species root infection has been demonstrated. However, the abiotic and edaphic factors that influence infection and disease development are unresolved. Root infection by P ramorum and the potential for mild abiotic stress in disease predisposition was examined with Rhododendron hybrid Cunningham's White and Viburnum tinus cv. Spring Bouquet. To impose water stress in a uniform and synchronous manner, osmotic stress induced with 0.2 M NaCI was selected. Roots were exposed to NaCI for 16 to 24 h in modified hydroponic culture or standard potting soil, removed from the NaCI, and then inoculated with zoospores. In the hydroponic regime, disease symptoms developed in Rhododendron and V tinus plants within I week after inoculation of salt-stressed roots, whereas symptom development was delayed in nonstressed, inoculated plants. Microscopic examination of roots from both species revealed that their apices were covered with sporangia of P ramoruin. On potted Rhododendron plants inoculated by applying zoospores directly to the soil, stem lesions developed rapidly in salt-stressed plants, with death of the plant occurring within 4 weeks after inoculation. Nonstressed plants survived for 6 to 8 weeks before succumbing to disease, and symptom development in these plants was delayed by I to 2 weeks relative to the inoculated, salt-stressed plants. A postinfection episode of salt stress to inoculated roots in the hydroponic regime resulted in significantly faster development of stem lesions in Rhododendron relative to nonstressed, inoculated plants. [ABSTRACT FROM AUTHOR] more...

Plants respond to changes in the environment with complex signaling networks, often under control of phytohormones that generate positive and negative crosstalk among downstream effectors of the response. Accordingly, brief dehydration stresses such as salinity and water deficit, which induce a rapid and transient systemic increase in levels of abscisic acid (ABA), can influence disease response pathways. ABA has been associated with susceptibility of plants to bacteria, fungi, and oomycetes but relatively little attention has been directed at its role in abiotic stress predisposition to root pathogens. This study examines the impact of brief salinity stress on infection of tomato and chrysanthemum roots by Phytophthora spp. Roots of plants in hydroponic culture exposed to a brief episode of salt (sodium chloride) stress prior to or after inoculation were severely diseased relative to nonstressed plants. Tomato roots remained in a predisposed state up to 24 h following removal from the stress. An increase in root ABA levels in tomato preceded or temporally paralleled the onset of stress-induced susceptibility, with levels declining in roots prior to recovery from the predisposed state. Exogenous ABA could substitute for salt stress and significantly enhanced pathogen colonization and disease development. ABA-deficient tomato mutants lacked the predisposition response, which could be restored by complementation of the mutant with exogenous ABA. In contrast. ethylene, which exacerbates disease symptoms in some host-parasite interactions, did not appear to contribute to the predisposition response. Thus. several lines of evidence support ABA as a critical and dominant factor in the salinity-induced predisposition to Phytophthora spp. infection. [ABSTRACT FROM AUTHOR] more...

A serious concern for nurseries is the potential for Phytophthora ramorum and other Phytophthora species to colonize roots without inducing aboveground symptoms in plants that then serve as cryptic reservoirs of inoculum. Episodic abiotic stresses that reduce plant water potential can compromise the host resistance to trigger disease development from root and crown infections during many Phytophthora- plant interactions. We conducted a series of experiments with root-inoculated Rhododendron plants in a potting soil mix to assess the influence of excess salt or water deficit on ramorum blight development and the potential for these abiotic stresses to affect the efficacy of oomycete-suppressive chemical soil treatments. During growth chamber trials, P. ramorum colonized roots of both nonsalt-treated and salt-treated plants. However, salt treatment offset the benefit realized from soil treatment with mefanoxam (Subdue Maxx) and mandipropamid (Micora), as evidenced by the enhanced pathogen colonization of roots. A 3-week episode of water stress imposed after chemical treatment but before inoculation eliminated protection against P. ramorum root colonization conferred by fosetyl-Al (Aliette). At an outdoor experimental nursery, foliar symptoms were apparent in 23% of root-inoculated plants during two trials and absent during one trial. However, the majority of inoculated plants in all trials had colonized roots with little or no aboveground symptoms. A single application of Subdue Maxx or Aliette reduced root colonization by P. ramorum in Rhododendron plants. Although salt stress did not enhance ramorum blight symptom expression at the nursery, salt partially offset protection from P. ramorum root colonization obtained by Subdue Maxx. more...

Draft genome sequences of 28 strains of Microbacteriaceae from plants infested by plant-parasitic nematodes were obtained using Illumina technology. The sequence data will provide useful baseline information for the development of comparative genomics and systematics of Microbacteriaceae and facilitate understanding of molecular mechanisms involved in interactions between plants and nematode-associated bacterial complexes., (Copyright © 2021 Tarlachkov et al.) more...

In September 2020, several plants of fowl bluegrass, Poa palustris with seed galls were collected on a bank of river in Teton County, Wyoming, USA. Isolated nematodes were identified by both morphological and molecular methods as Anguina agrostis. This is a first report of A. agrostis in Wyoming and its report on fowl bluegrass., (© 2020 Authors.) more...