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Phytophthora nicotianae causes serious black shank disease in tobacco. Syringa oblata essential oil and its main components were evaluated to develop an effective and environmentally friendly biocontrol agent. Eugenol, which exhibited the strongest activity, was intensively investigated in vitro and in vivo . The mycelial growth of P. nicotianae was inhibited by eugenol at a minimum inhibitory concentration of 200 μg mL − 1 , and inhibition occurred in a dose-dependent manner. Extracellular pH and extracellular conductivity results indicated that eugenol increased membrane permeability. Flow cytometry and fluorescent staining results further showed that eugenol disrupted mycelial membranes but did not affect spore membrane integrity. The in vivo results confirmed that treatment of tobacco with various concentrations of eugenol formulations reduced disease incidence and better controlled against the disease. Our results suggested that the ability of eugenol to control tobacco black shank depended on its ability to damage mycelial membranes and that eugenol formulations have potential as an eco-friendly antifungal agent for controlling tobacco blank shank. [ABSTRACT FROM AUTHOR]

The antifungal activity of the entomopathogenic fungi isolates Metarhizium brunneum EAMb 09/01-Su and Beauveria bassiana EABb 09/16-Su against the olive pathogens Verticillium dahliae and Phytophthora megasperma was evaluated. The crude extract and its partial purified fractions obtained from both isolates showed complete inhibition of the mycelial growth of V. dahliae . However, the same fractions obtained from B. bassiana EABb 09/16-Su were less effective against the mycelial growth of P. megasperma . Our results showed that M. brunneum EAMb 09/01-Su had the highest fungicidal activity, inhibiting the mycelial growth of both pathogens. Both fractions IV and VI from M. brunneum EAMb 09/01-Su were evaluated by the progress of the Verticillium wilt of the plant and showed clear antagonism against V. dahliae , reducing the severity of the symptoms between 38.9 and 58.9%. The active metabolite obtained from M. brunneum not only reduced the germination of V. dahliae microsclerotia but also inhibited hyphal formation, decreased the number of reproductive structures, and changed the conformation of the microsclerotial colony, preventing the formation of new microsclerotia. The evaluation of temperature, UV light and pH on the antifungal activity of the dialyzed fraction from M. brunneum showed that the antifungal activity was stable at 60 °C (2 h) and 120 °C (20 min) and to UV light radiation. However, the exposition to the dialyzed fraction at pH 7.5 and 8.5 affected the antifungal activity. The results of this study clearly showed that the entomopathogenic fungus M. brunneum EAMb 09/01-Su produces antifungal compounds that reduce the number of the pathogen propagules in the soil and the severity of Verticillium wilt. Therefore, this resource should be further studied as an alternative for the integrated management of Verticillium wilt and Phytophthora root rot, which is the most severe disease in all traditional olive-growing regions worldwide, and as a reliable and sustainable strategy for a reduced reliance on pesticides. [ABSTRACT FROM AUTHOR]

Simple sequence repeats (SSRs) or microsatellites may be present in coding or non coding regions of prokaryotic and eukaryotic genomes and constitute a small proportion of the genome. We have attempted to understand the abundance of microsatellites in the different regions (supercontigs, genes, upstream 1000 bp, upstream 1000 UTR, downstream 1000 bp and downstream 1000 UTR region) of genomes of different plant pathogenic fungi viz., Phytophthora infestans, Phytophthora parasitica, Collectotrichum graminicola, Fusarium oxysporium, Magnoparthae oryzae, Magnoparthae poae, Puccinia graminis, Puccinia striiformis and Ustilago myadis. No direct correlation was found between the genome size and number of SSRs present in the genomes. The size of Phytophthora infestans genome i.e. 240 Mbp is larger among all other fungi studied but the total number of SSRs were less in comparision to all other genomes. On the other hand, Puccinia graminis, with three times smaller genome than P. infestans had higher number of SSRs. The mononucleotide repeats A/T were found to be more prevalent in the all fungal genomes region except in Collectotrichum graminicola where C/G repeats were dominant over other repeat types. The dinucleotides repeats, AG/CT, were the second most numerous, whereas tri-, tetra-, penta and hexa-nucleotide repeats were in less number in all regions of these fungal genomes. Overall, longest mono-, tri-, tetra- and hexa-nucleotide repeats were found in Magnoparthae oryzae, whereas di- and penta-nucleotide repeats were found in P. infestans and Puccinia gramini. Overall, there was no consistetant pattern of microsatellite organization and abundance among these genomes, and their abundance in genomes is probably being regulated species-specific factors. Such information may be effective in characterizing the phytopathogenic fungal populations, which in turn may be useful in designing the protective strategies for the crop plants. [ABSTRACT FROM AUTHOR]

In previous research, we discovered a favorable quantitative trait locus (QTL) in cigar tobacco cultivar 'Beinhart 1000' designated as Phn15.1, which provides a high level of partial resistance to the black shank disease caused by Phytophthora nicotianae. A very close genetic association was also found between Phn15.1 and the ability to biosynthesize Z-abienol, a labdanoid diterpene exuded by the trichomes onto above-ground plant parts, and that imparts flavor and aroma characteristics to Oriental and some cigar tobacco types. Because accumulation of Z-abienol is considered to be undesirable for cultivars of other tobacco types, we herein describe a series of experiments to gain insight on whether this close association is due to genetic linkage or pleiotropy. First, in an in vitro bioassay, we observed Z-abienol and related diterpenes to inhibit hyphal growth of P. nicotianae at concentrations between 0.01 and 100 ppm. Secondly, we field-tested transgenic versions of Beinhart 1000 carrying RNAi constructs for downregulating NtCPS2 or NtABS, two genes involved in the biosynthesis of Z-abienol. Thirdly, we also field tested a recombinant inbred line population segregating for a truncation mutation in NtCPS2 leading to an interrupted Z-abienol pathway. We observed no correlation between field resistance to P. nicotianae and the ability to accumulate Z-abienol in either the transgenic materials or the mapping population. Results suggest that, although Z-abienol may affect P. nicotianae when applied at high concentrations in in vitro assays, the compound has little effect on black shank disease development under natural field conditions. Thus, it should be possible to disassociate Phn15.1-mediated black shank resistance identified in cigar tobacco cultivar Beinhart 1000 from the ability to accumulate Z-abienol, an undesirable secondary metabolite for burley and flue-cured tobacco cultivars. [ABSTRACT FROM AUTHOR]

Black shank, caused by Phytophthora nicotianae, occurs worldwide and is responsible for significant yield loss in tobacco production in Georgia. Management of the disease has primarily relied on utilization of tobacco cultivars with resistance to race 0 of the pathogen and application of the fungicide mefenoxam. Races of P. nicotianae currently prevalent in tobacco production in Georgia, their sensitivity to mefenoxam, and genetic diversity of the pathogen are largely unknown. To determine population structure and genetic diversity of the pathogen, simple sequence repeat (SSR) markers were used. Three races of P. nicotianae (races 0, 1, and 3) were isolated from infected tobacco plants, with race 3 identified in Georgia for the first time. The majority of isolates were identified as A2 mating type and all isolates were sensitive or intermediately sensitive to mefenoxam at 1 or 10 µg/ml, with effective concentration of mefenoxam for 50% mycelial growth reduction values ranging from <0.01 to 0.12 µg/ml. Bayesian and unweighted pair group method with arithmetic means analyses of 59 isolates using SSR markers grouped the isolates in two major groups. Group I contained 20 isolates, of which 19 isolates were collected from Berrien County. Group II contained 39 isolates collected from Bacon, Cook, Tift, and Toombs Counties as well as one sample from Berrien County. Genetic diversity of the isolates was associated with geographical location of collection, and isolates in group I were primarily (75%) race 1, whereas isolates in group II were primarily (69%) race 0. The presence of a single pathogen mating type at most of the locations implies low probability of sexual recombination that may have contributed to the low genetic diversity at a particular geographical location. Sensitivity of the isolates to mefenoxam indicates that the fungicide remains to be a potent tool for growers to combat the disease. Information generated in the study advances our knowledge about diversity and population structure of P. nicotianae, which facilitates development and implementation of effective disease management programs. [ABSTRACT FROM AUTHOR]

Crown and root rot of tomato and sweet pepper can be caused by Phytophthora parasitica. In this work, 23 P. parasitica isolates from diseased pepper or tomato plants as well as 54 isolates from 23 monocrop tomato soils (from Spain and Chile) and one from a pepper soil were studied for their host-pathogen response. Results show significant host specificity for the isolates from tomato plants and tomato soils (63 of 64 isolates were unable to cause disease in pepper). None of the pepper plant/soil isolates showed pathogenicity on tomato, and only four of 14 reproduced their pathogenicity on pepper. Only one tomato isolate was pathogenic to both Solanaceae species. Two different inoculation protocols were evaluated (substrate irrigation and stem cutting). All isolates which expressed pathogenicity when stem inoculated also did it when root inoculated, but not vice-versa. Therefore, the recommended test protocol for tomato and pepper breeding programmes is that based on root inoculation by irrigation. [ABSTRACT FROM AUTHOR]

Zoospore exudates play important roles in promoting zoospore communication, homing and germination during plant infection by Phytophthora. However, it is not clear whether exudates affect plant immunity. Zoospore-free fluid (ZFF) and zoospores of P. nicotianae were investigated comparatively for effects on resistance of Arabidopsis thaliana Col-0 and mutants that affect signaling mediated by salicylic acid (SA) and jasmonic acid (JA): eds16 (enhanced disease susceptibility16), pad4 (phytoalexin deficient4), and npr1 (nonexpressor of pathogenesis-related genes1). Col-0 attracted more zoospores and had severe tissue damage when flooded with a zoospore suspension in ZFF. Mutants treated with ZFF alone developed disease symptoms similar to those inoculated with zoospores and requirements of EDS16 and PAD4 for plant responses to zoospores and the exudates was apparent. Zoospore and ZFFs also induced expression of the PR1 and PDF1.2 marker genes for defense regulated by SA and JA, respectively. However, ZFF affected more JA defense signaling, down regulating PR1 when SA signaling or synthesis is deficient, which may be responsible for Arabidopsis mutant plants more susceptible to infection by high concentration of P. nicotianae zoospores. These results suggest that zoospore exudates can function as virulence factors and inducers of plant immune responses during plant infection by Phytophthora. [ABSTRACT FROM AUTHOR]

Small RNAs (sRNAs) are important non-coding RNA regulators, playing key roles in developmental regulation, transposon suppression, environmental response, host-pathogen interaction and other diverse biological processes. However, their roles in oomycetes are poorly understood. Here, we performed sRNA sequencing and RNA sequencing of Phytophthora parasitica at stages of vegetative growth and infection of Arabidopsis roots to examine diversity and function of sRNAs in P. parasitica, a model hemibiotrophic oomycete plant pathogen. Our results indicate that there are two distinct types of sRNA-generating loci in P. parasitica genome, giving rise to clusters of 25-26 nt and 21 nt sRNAs, respectively, with no significant strand-biases. The 25-26 nt sRNA loci lie predominantly in gene-sparse and repeat-rich regions, and overlap with over 7000 endogenous gene loci. These overlapped genes are typically P. parasitica species-specific, with no homologies to the sister species P. infestans. They include approximately 40% RXLR effector genes, 50% CRN effector genes and some elicitor genes. The transcripts of most of these genes could not be detected at both the vegetative mycelium and infection stages as revealed by RNA sequencing, indicating that the 25-26 nt sRNAs are associated with efficient silencing of these genes. The 21 nt sRNA loci typically overlap with the exon regions of highly expressed genes, suggesting that the biogenesis of the 21 nt sRNAs may be dependent on the level of gene transcription and that these sRNAs do not mediate efficient silencing of homologous genes. Analyses of the published P. infestans sRNA and mRNA sequencing data consistently show that the 25-26 nt sRNAs, but not the 21 nt sRNAs, may mediate efficient gene silencing in Phytophthora. [ABSTRACT FROM AUTHOR]

Phytophthora parasitica is a notorious oomycete pathogen that causes severe disease in a wide variety of crop species. Infection of plants involves mainly its asexual life stage, including papillate sporangia and biflagellated zoospores, which are the primary dispersal and infection agents of this pathogen. Calcium signaling has been thought as the key regulator for sporangium formation and zoospore differentiation. However, not much is known about the molecular players involved in these processes. In Saccharomyces cerevisiae, mating pheromone-induced death 1 (MID1) encodes a component of a putative calcium channel. Here, we identified and characterized the function of PpMID1, an MID1 homolog from P. parasitica. The expression of PpMID1 was high in sporangia. Gene silencing of PpMID1 resulted in the formation of sporangia that lacked papilla and showed a tendency for direct germination. Notably, in response to cold shock to induce zoospore formation, these sporangia showed no sign of cytoplasmic cleavage and thereby failed to form zoospores. Nonetheless, the addition of CaCl2 or MgCl2 partially recovered the silenced sporangia phenotype, with the formation of papillate sporangia similar to those of the wild type and the release of zoospores upon cold shock. As well, virulence toward Nicotiana benthamiana was reduced in the PpMID1-silenced transformants. These results indicate a role of PpMID1 in the asexual development and virulence of P. parasitica. [ABSTRACT FROM AUTHOR]

The ecological importance of riparian forests is well known. However, these forest habitats have been disturbed by human activities over the past century as a result of the introduction of flow regulations. Mortality of the riparian alder population caused by Phytophthora has become an important issue in Europe in the past two decades. The main objective of this study was to examine the pathogenicity of the Phytophthora alni complex ( P. x alni, P. uniformis and P. xmultiformis) and P. plurivora in Alnus glutinosa seedlings. Phytophthora alni complex has traditionally been identified as the main causal agent of alder decline; however, in this study, P. plurivora was found to cause as much damage in inoculated seedlings as P. alni complex. In fact, Spanish isolates of P. x alni caused mortality rates of ca. 30%, whereas P. plurivora killed ca. 50% of seedlings. Likewise, there were no differences between P. x alni - and P. plurivora-inoculated seedlings in either the length of lesion or biomass allocation. The pathogenicity of the species within P. alni complex did not differ significantly. The findings confirm that P. plurivora, which is one of the most common species of Phytophthora found in European nurseries, is highly pathogenic to alder seedlings. Urgent implementation of measures to prevent the risk of spread of the pathogen from nurseries to natural ecosystems is required. Further studies are required to clarify the role that P. plurivora is playing in alder decline both individually and in combination with P. alni complex. [ABSTRACT FROM AUTHOR]

The understanding of the dynamic of soil-borne diseases is related to the microbial composition of the rhizosphere which is the key to progress in the field of biological control. Trichoderma spp. is commonly used as a biological control agent. The use of next generation sequencing approaches and quantitative PCR are two successful approaches to assess the effect of using compost as substrate fortified with two Trichoderma strains (Trichoderma harzianum or Trichoderma asperellum) on bacterial and fungal communities in pepper rhizosphere infected with Phytophthora nicotianae. The results showed changes in the bacterial rhizosphere community not attributed to the Trichoderma strain, but to the pathogen infection, while, fungi were not affected by pathogen infection and depended on the type of substrate. The Trichoderma asperellum fortified compost was the most effective combination against the pathogen. This could indicate that the effect of fortified composts is greater than compost itself and the biocontrol effect should be attributed to the Trichoderma strains rather than the compost microbiota, although some microorganisms could help with the biocontrol effect. [ABSTRACT FROM AUTHOR]

Buckeye rot disease of tomato which is one of the most devastating diseases of tomato crop is caused by soil born fungus Phytophthora nicotianae var. parasitica. In present study, the pathogen was isolated, morphologically identified and its pathogenicity was proved on susceptible commercial variety Solan Lalima and resistant line EC-251649 of tomato. Isolation of pathogen from the infected tomato fruit was achieved on Corn Meal Agar (CMA) out of two different media viz., Potato Dextrose Agar (PDA) and CMA. Fungal inoculum was prepared on Corn Meal broth. Inoculation with 10 ml of inoculum was found optimum in plant parts namely, stem, leaves and fruits. Parental lines were inoculated to test their disease reaction to buckeye rot. Symptoms of infection appeared on leaves and fruits only. Solan Lalima was found to be highly susceptible to with disease severity of 92 % and 100 % disease incidence, while EC-251649 was found moderately resistant on the basis of 16 % disease severity and 10 % disease incidence to the disease. After confirmation of resistance and susceptibility, the parental lines were surveyed for polymorphism using 42 primers and 32 were recorded to be polymorphic revealing that the differences are present at DNA level also. This is the very first study which evaluated parental lines for buckeye rot disease reaction on morphological as well as molecular basis. These lines will be further used for quantitative trait loci (QTL) analysis/gene tagging for buckeye rot and marker assisted selection to provide improved varieties to the farmers. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae , the causal agent of black shank, is one of the most important soilborne pathogens of tobacco ( Nicotiana tabacum L.). The use of soil applied fungicides has been a significant component of effective black shank management for tobacco growers. Oxathiapiprolin is a new fungicide with a novel mode of action that has shown efficacy against many oomycetes, including P . nicotianae . Studies were conducted in 2012 in fields naturally infested with P . nicotianae to determine the efficacy of different rates, methods, and timing of applications of oxathiapiprolin against black shank. Field trials were conducted in 2013 and 2014 to examine the efficacy of alternating applications of oxathiapiprolin and mefenoxam against black shank. Fungicide treatments were applied to the soil on the day of transplanting tobacco to the field, on the day of first cultivation (14–25 days after transplant), and during last cultivation (46–65 days after transplant). A single application of oxathiapiprolin in the transplant water at 0.07, 0.14, or 0.28 kg a.i./ha significantly decreased area under the disease progress curve (AUDPC) compared to the non-treated control in the 2012 field trials. In addition, treatments with three applications of oxathiapiprolin at all tested rates significantly reduced AUDPC compared to non-treated control. In field trials from 2013 and 2014, alternating applications of oxathiapiprolin at transplant, mefenoxam at first cultivation, and oxathiapiprolin at last cultivation significantly lowered AUDPC compared to the non-treated control. In contrast, the AUDPC after three applications of mefenoxam at transplant, first cultivation, and last cultivation did not differ significantly from the non-treated control. Overall, our results indicate that soil-directed applications of oxathiapiprolin, alone or in alternation with mefenoxam are efficacious for the reduction of black shank of tobacco. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae causes root and crown rot disease in open field paprika pepper crops of Extremadura (western Spain). Sensitivity of the vegetative structures (mycelia and chlamydospores) of P. nicotianae to Brassica carinata pellets (Biofence) was evaluated in vitro at different doses (3, 6, 12 and 24 mg of pellet per plate) and temperatures (15, 20, 25 and 30 °C). The effectiveness of the pellets varied depending on the dose. An inhibition effect that decreased with time, was observed in the mycelial growth and chlamydospores germination in plate. The highest dose of pellets tested (24 mg) was fungitoxic to mycelium regardless of temperature for all the isolates. Moreover, biofumigation was effective to suppres chlamydospores germination when the pellets were incorporated into the soil (1.5 and 3 g L −1 of soil) under different temperature regimes. In bioassays with pepper plants, both rates of B. carinata pellets (1.5 and 3 g L −1 of soil) reduced populations of P. nicotianae below the limits of detection of our bioassay (<2 CFU g −1 of soil) after a 4-week biofumigation treatment and totally controlled the disease. The results suggest that chlamydospores of P. nicotianae in the soil might be suppressed by the commercial rates of B. carinata pellets, although further studies are required in more real soil conditions to form part of integrated pest management program. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae is the principal causal agent of root and crown rot disease of pepper plants in Extremadura (western Spain), a spring-summer crop in this region. Preplant soil treatment by anaerobic soil disinfestation (ASD) may effectively control plant pathogens in many crop production systems, but field conditions and availability of C sources can limit its practical application. A laboratory experiment was conducted to study P. nicotianae control by ASD with low temperatures and several carbon (C) sources: rice bran, rapeseed cake, grape pomace and brewer’s spent grain. Survival and infectivity of pepper by P. nicotianae chlamydospores were reduced with all C sources assayed and redox potential in all ASD treatments indicated that reductive soil conditions were achieved. Rice bran (20 tons ha −1 ); rapeseed cake (20 tons ha −1 ), and grape pomace (40 tons ha −1 ) were also assayed in a field experiment in early spring. Survival and infectivity of P. nicotianae were also reduced with all C sources. An increase of dehydrogenase and urease activities and a strong pH decline were observed with rice bran and rapeseed cake, probably related to an increase of anaerobic bacterial populations in soil. Application of ASD with high C source rates may be effective in control of P. nicotianae under low temperature conditions. [ABSTRACT FROM AUTHOR]

• BC 1 F 3 hybrid seedlings exhibited the largest total growth and incremental height growth. • Seedlings from the BC 3 F 3 generation had intermediate Cryphonectria parasitica resistance. • Phytophthora root rot contributed to mortality in planted chestnut seedlings. • High performing and poor performing BC 3 F 3 families could be identified. • Using larger size seedlings at planting will reduce time needed to obtain desired tree size. The American chestnut (Castanea dentata) is imperiled due primarily to two diseases caused by nonnative pathogens, notably chestnut blight and Phytophthora root rot (PRR) caused by Cryphonectria parasitica and Phytophthora cinnamomi , respectively. Field reintroduction trials are important to test trees bred for blight resistance under forest conditions to quantify survival and field performance in managed stands that represent future restoration sites. We planted 513 pedigreed bare-root (1–0) nursery seedlings into an even-aged regeneration harvest in the Blue Ridge Mountains of eastern Tennessee, USA to test effects of breeding, genetics, and seedling size class on field performance, including survival, total growth, incremental growth (a measure of growth efficiency), and height growth patterns. Mortality was highest in the first two years after planting, and PRR symptoms coupled with soil and root assays that tested positive for P. cinnamomi suggested this disease was a significant contributor to mortality. Chinese chestnut (C. mollissima), known to be resistant to P. cinnamomi and C. parasitica , had the highest survival (96 percent) compared to American chestnut (34 percent) and hybrid generations, including the BC 3 F 3 generation (41 percent). Less advanced hybrid generations, such as the BC 1 F 3 and BC 2 F 3 , had the greatest total height and ground-line diameter (GLD) and height growth efficiencies. BC 3 F 3 generation seedlings were associated with higher-than-expected rates of nominal height growth patterns (i.e., flat growth rates over time or early mortality) compared to Chinese chestnut seedlings. Results, however, indicated the breeding program was successfully integrating desired American chestnut growth traits into the hybrid genome while transferring an intermediate level of resistance from the Chinese chestnut. We identified superior and inferior BC 3 F 3 families that can help inform breeding and restoration efforts. Visually grading seedlings before planting affected survival and growth of generations and genetic families differently, indicating that refinement of nursery production and restoration plantings should consider genetic effects. Across generations, seedling size grading improved total height and GLD growth that would save resources necessary for competition control and animal browsing protection, but large-size seedlings also exhibited lower C. parasitica resistance rankings over time, probably owing to earlier bark fissuring. PRR probably affected outcomes, particularly for hybrid and American chestnut seedlings that have very low levels of P. cinnamomi resistance. Managers could expect advanced breeding generations to perform similarly to American chestnut in growth through the critical stage of early stand development. More durable resistance to C. parasitica and mitigation of PRR through better site selection and/or resistance screening will improve future restoration efforts. [ABSTRACT FROM AUTHOR]

Tobacco black shank (TBS), caused by Phytophthora nicotianae , is one of the most harmful diseases of tobacco. There are many studies have examined the mechanism underlying the induction of disease resistance by arbuscular mycorrhizal fungi (AMF) and β-aminobutyric acid (BABA) alone, but the synergistic effects of AMF and BABA on disease resistance have not yet been studied. This study examined the synergistic effects of BABA application and AMF inoculation on the immune response to TBS in tobacco. The results showed that spraying BABA on leaves could increase the colonization rate of AMF, the disease index of tobacco infected by P.nicotianae treated with AMF and BABA was lower than that of P.nicotianae alone. The control effect of AMF and BABA on tobacco infected by P.nicotianae was higher than that of AMF or BABA and P.nicotianae alone. Joint application of AMF and BABA significantly increased the content of N, P, and K in the leaves and roots, in the joint AMF and BABA treatment than in the sole P. nicotianae treatment. The dry weight of plants treated with AMF and BABA was 22.3% higher than that treated with P.nicotianae alone. In comparison to P. nicotianae alone, the combination treatment with AMF and BABA had increased Pn, Gs, Tr, and root activity, while P. nicotianae alone had reduced Ci, H 2 O 2 content, and MDA levels. SOD, POD, CAT, APX, and Ph activity and expression levels were increased under the combined treatment of AMF and BABA than in P.nicotianae alone. In comparison to the treatment of P.nicotianae alone, the combined use of AMF and BABA increased the accumulation of GSH, proline, total phenols, and flavonoids. Therefore, the joint application of AMF and BABA can enhance the TBS resistance of tobacco plants to a greater degree than the application of either AMF or BABA alone. In summary, the application of defense-related amino acids, combined with inoculation with AMF, significantly promoted immune responses in tobacco. Our findings provide new insights that will aid the development and use of green disease control agents., Competing Interests: Authors BC, SC and YY were employed by Technical Center of Yunnan Zhongyan Industry Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Li, Cai, Chang, Yang, Zi and Liu.)

Severe outbreaks of Phytophthora fruit rot on brinjal, ridge gourd, and tomato have been observed since 2011 in Andhra Pradesh, Karnataka, Telangana, and Tamil Nadu states of India. Therefore, 76 Phytophthora nicotianae isolates, recovered from brinjal (17), ridge gourd (40), and tomato (19) from different localities in these states during the June to December cropping season of 2012 and 2013, were characterized based on phenotypic and genotypic analyses and aggressiveness on brinjal, tomato, and ridge gourd. All brinjal and ridge gourd isolates were A2, while tomato isolates were both A1 (13) and A2 (6). All isolates were metalaxyl sensitive. In addition, isolates were genotyped for three mitochondrial (ribosomal protein L5-small subunit ribosomal RNA [ipl5-ms], small subunit ribosomal RNA-cytochrome c oxidase subunit 2 [ms-cox2], and cox2+spacer) and three nuclear loci (hypothetical protein [hyp], scp-like extracellular protein [.wp], and beta-tubulin [/3-tub]). All regions were polymorphic but nuclear regions were more variable than mitochondrial regions. The network analysis of genotypes using the combined dataset of three nuclear regions revealed a host-specific association. However, the network generated using mitochondrial regions limited such host-specific groupings only to brinjal isolates. P. nicotianae isolates were highly aggressive and produced significantly (P < 0.01) larger lesions on their respective host of origin than on other hosts. The results indicate significant genetic variation in the population of P. nicotianae, leading to identification of host-specific lineages responsible for severe outbreaks on brinjal, ridge gourd, and tomato. [ABSTRACT FROM AUTHOR]

Background: Black shank is a severe plant disease caused by the soil-borne pathogen Phytophthora nicotianae. Two physiological races of P. nicotianae, races 0 and 1, are predominantly observed in cultivated tobacco fields around the world. Race 0 has been reported to be more aggressive, having a shorter incubation period, and causing worse root rot symptoms, while race 1 causes more severe necrosis. The molecular mechanisms underlying the difference in virulence between race 0 and 1 remain elusive. Findings: We assembled and annotated the genomes of P. nicotianae races 0 and 1, which were obtained by a combination of PacBio single-molecular real-time sequencing and second-generation sequencing (both HiSeq and MiSeq platforms). Gene family analysis revealed a highly expanded ATP-binding cassette transporter gene family in P. nicotianae. Specifically, more RxLR effector genes were found in the genome of race 0 than in that of race 1. In addition, RxLR effector genes were found to be mainly distributed in gene-sparse, repeat-rich regions of the P. nicotianae genome. Conclusions: These results provide not only high quality reference genomes of P. nicotianae, but also insights into the infection mechanisms of P. nicotianae and its co-evolution with the host plant. They also reveal insights into the difference in virulence between the two physiological races. [ABSTRACT FROM AUTHOR]

Trunk injection with penicillin has been tested to control citrus huanglongbing (HLB), but side effects and environmental safety must be assured before approval of penicillin injection can be considered. We investigated effects of penicillin injection on densities of Candidatus Liberibacter asiaticus (Las) in leaves, as well as culturable bacterial populations in rhizospheres and petioles of grapefruit trees in field and greenhouse experiments. Trees were injected with penicillin G, and leaf and root concentrations were assessed in bioassays with Bacillus subtilis . Las densities were determined by qPCR, and bacteria were isolated on a low carbon medium from roots plus rhizosphere and surface-sterilized petioles at various times after penicillin injection. Selected bacterial isolates were tested for penicillin resistance (20 μg/mL) and glyphosate resistance (7000 μg/mL), because glyphosate is widely used and cross-resistance against antibiotics had been documented. One month after penicillin injection half of the greenhouse trees were inoculated with Phytophthora nicotianae . Cycle threshold (Ct) values of Las in old and young leaves significantly increased 90 days after trunk injection with penicillin. Bacterial populations in petioles and root-rhizospheres initially increased after penicillin injections, probably due to nutrient release, then returned to control levels after one week. Penicillin resistance was common in isolates from penicillin-injected and control trees (30–94%). Significantly more glyphosate resistant than sensitive isolates were penicillin resistant (81% versus 52%). Phytophthora root rot was not increased after penicillin injection. Thus, side effects of penicillin injection tested here were minimal, while Las titers were reduced after three months. [ABSTRACT FROM AUTHOR]

The genetic diversity of antagonistic bacteria from the tobacco rhizosphere was examined by BOXAIR-PCR, 16S-RFLP, 16S rRNA sequence homology and phylogenetic analysis methods. These studies revealed that 4.01% of the 6652 tested had some inhibitory activity against Phytophthora nicotianae. BOXAIR-PCR analysis revealed 35 distinct amplimers aligning at a 91% similarity level, reflecting a high degree of genotypic diversity among the antagonistic bacteria. A total of 25 16S-RFLP patterns were identified representing over 33 species from 17 different genera. Our results also found a significant amount of bacterial diversity among the antagonistic bacteria compared to other published reports. For the first time; Delftia tsuruhatensis, Stenotrophomonas maltophilia, Advenella incenata, Bacillus altitudinis, Kocuria palustris, Bacillus licheniformis, Agrobacterium tumefaciens and Myroides odoratimimus are reported to display antagonistic activity towards Phytophthora nicotianae. Furthermore, the majority (75%) of the isolates assayed for antagonistic activity were Gram-positives compared to only 25% that were Gram-negative bacteria.

Black shank incited by Phytophthora nicotianae is a devastating disease in the production of tobacco. Fungicides have been commonly used for managing the disease; however, there is only a narrow pool of effective fungicides. A few new fungicides became available in recent years, including fluopicolide, mandipropamid, and oxathiapiprolin, which reduced diseases incited by oomycetes under field conditions. Limited information is available regarding sensitivity of P. nicotianae isolates to these new fungicides. Research was conducted to determine effects of the three new fungicides on P. nicotianae isolates from tobacco in Georgia. Studies with 106 isolates indicated that they did not grow when agar medium was amended with the fungicides at the rate of 1 Îg/ml. Twenty isolates were used for in vitro studies to determine sensitivity to the fungicides. Fluopicolide, mandipropamid, and oxathiapiprolin inhibited mycelial growth of the isolates with mean EC50 values (effective concentrations that provide 50% growth reduction) of 0.09, 0.04, and 0.001 Îg/ml, respectively. EC50 values of fluopicolide, mandipropamid, and oxathiapiprolin for inhibiting sporangial formation were 0.15, 0.03, and 0.0002 Îg/ml, respectively. EC50 values for suppressing zoospore germination averaged 0.16, 0.04, and 0.002 Îg/ml for fluopicolide, mandipropamid, and oxathiapiprolin, respectively. Results from the study indicated that P. nicotianae isolates from tobacco in Georgia were sensitive to the fungicides, with lower EC50 for oxathiapiprolin than for fluopicolide and mandipropamid. The information on effectiveness and baseline sensitivity of fungicides on P. nicotianae will facilitate monitoring of resistance development in the pathogen population. [ABSTRACT FROM AUTHOR]

In all, 231 isolates of Phytophthora nicotianae representing 14 populations from different host genera, including agricultural crops (Citrus, Nicotiana, and Lycopersicon), potted ornamental species in nurseries (Lavandula, Convolvulus, Myrtus, Correa, and Ruta), and other plant genera were characterized using simple-sequence repeat markers. In total, 99 multilocus genotypes (MLG) were identified, revealing a strong association between genetic grouping and host of recovery, with most MLG being associated with a single host genus. Significant differences in the structure of populations were revealed but clonality prevailed in all populations. Isolates from Citrus were found to be genetically related regardless of their geographic origin and were characterized by high genetic uniformity and high inbreeding coefficients. Higher variability was observed for other populations and a significant geographical structuring was determined for isolates from Nicotiana. Detected differences were related to the propagation and cultivation systems of different crops. Isolates obtained from Citrus spp. are more likely to be distributed worldwide with infected plant material whereas Nicotiana and Lycopersicon spp. are propagated by seed, which would not contribute to the spread of the pathogen and result in a greater chance for geographic isolation of lineages. With regard to ornamental species in nurseries, the high genetic variation is likely the result of the admixture of diverse pathogen genotypes through the trade of infected plant material from various geographic origins, the presence of several hosts in the same nursery, and genetic recombination through sexual reproduction of this heterothallic species. [ABSTRACT FROM AUTHOR]

Citrus gummosis, caused by Phytophthora nicotianae, becomes one of the most destructive diseases in citrus production in Tunisia. Thus, the selection of resistant rootstocks is needed to reduce the damage caused by this disease. In the present study, five citrus rootstocks (Citrange carrizo (Citrus sinensis x Poncirus trifoliata), Citrumelo Swingle-4475 (Citrus paradisi x Citrus trifoliata), Citrus volkameriana (Citrus limon x Citrus aurantium), Citrange C-35 (Citrus sinensis 'ruby blood' x Poncirus trifoliata) and Sour orange (Citrus aurantium)) were screened against P. nicotianae by inoculating young citrus seedlings with the freshly zoospores suspension. After three months of inoculation, the disease severity was evaluated based on root damaged, plant height, stem and root weights (fresh and dry) and density of P. nicotianae population in infested roots. The evaluation of the rootstocks response revealed different levels of susceptibility against P. nicotianae. Regarding to all the parameters studied, results showed that the rootstock Citrumelo Swingle-4475 and the rootstock Sour orange are tolerant to P. nicotianae. The rootstock Citrange C-35 was considered as a moderately tolerant, while the two rootstocks Citrange carrizo and Citrus volkameriana were very susceptible. The index severity was ranged from 1 for the tolerant rootstocks to 3.16 for the very susceptible one. The highest percent of the stem growth rate was 75.5 % recorded with the tolerant rootstocks, while it ranged between 18.25 % and 19 %, respectively, for the moderately tolerant and for the susceptible rootstocks. In the case of the other parameters like the fresh and the dry weight of stem and root, the tolerant rootstocks showed the minimum percent of reduction (17.8 %). However, the minimum percent of reduction of the moderately tolerant and of the very susceptible rootstocks was ranged between 38.5 and 30.8, respectively. The lowest number of propagules of P. nicotianae was found in the tolerant rootstocks (4.25), the highest number was found in the very susceptible rootstocks (24.5). However, the number was 12.25 in the case of the moderately tolerant one. It is believed that the rootstock Citrumelo Swingle-4475 should be involved with the resistance of citrus plants to P. nicotianae. [ABSTRACT FROM AUTHOR]

Phytophthora root rot caused by Phytophthora nicotianae is an economically important disease in pepper crops. The use of suppressive composts is a low environmental impact method for its control. Although attempts have been made to reveal the relationship between microbiota and compost suppressiveness, little is known about the microorganisms associated with disease suppression. Here, an Ion Torrent platform was used to assess the microbial composition of composts made of different agro-industrial waste and with different levels of suppressiveness against P. nicotianae. Both bacterial and fungal populations responded differently depending on the chemical heterogeneity of materials used during the composting process. High proportions (67–75%) of vineyard pruning waste were used in the most suppressive composts, COM-A and COM-B. This material may have promoted the presence of higher relative abundance of Ascomycota as well as higher microbial activity, which have proved to be essential for controlling the disease. Although no unique fungi or bacteria have been detected in neither suppressive nor conducive composts, relatively high abundance of Fusarium and Zopfiella were found in compost COM-B and COM-A, respectively. To the best of our knowledge, this is the first work that studies compost metabolome. Surprisingly, composts and peat clustered together in principal component analysis of the metabolic data according to their levels of suppressiveness achieved. This study demonstrated the need for combining the information provided by different techniques, including metagenomics and metametabolomics, to better understand the ability of compost to control plant diseases. [ABSTRACT FROM AUTHOR]

Black shank is a major annual disease threat to all types of tobacco worldwide. It is caused by the fungus Phytophthora parasitica var. nicotianae (PPN). The major tobacco growing areas in US - Kentucky, Tennessee and North Carolina can experience devastating losses, reaching in some fields up to 100%. Thus far, the main approaches to control this disease have been creation of resistant varieties, fungicide treatments, and crop rotation. Some fungicides are reported to have negative effects on the environment. The goal of this work was to test the antifungal activity of several natural products that are synthesized by certain Nicotiana species, and secreted to the leaf surface. We hypothesized that phylloplanin, cis-abienol, labdenediol and sclareol can suppress PPN-race 0- and PPN-race 1-caused disease in Burley tobaccos KY 14 and MS KY 14 × L8LC in the greenhouse. We developed methods for leaf surface extraction, spore preparation and soil drench application of the natural compounds tested. Experiments were performed on 5-8 week-old greenhouse grown seedlings. cis-Abienol showed high inhibitory properties toward the disease. Race 0 infection was completely subdued in KY 14 while race 1 infection was reduced by 70-80%, and delayed by 6-10 days in KY 14 and MS KY14 × L8LC. Sclareol was very effective in inhibiting race 0-caused disease in both tobacco cultivars. In MS KY 14 × L8LC race 1 infection was inhibited while in KY 14 it was reduced by 85% and delayed by 6 days. Labdenediol reduced the disease by half in eight week-old KY 14 plants. Tobacco phylloplanin reduced plant infection by both races by 50-60% and delayed the disease by 6-10 days. Phylloplanin was least suppressive in both tobacco cultivars. We consider sclareol to be the best candidate for future studies due to its antifungal properties and availability. cis-Abienol, despite its good antifungal activity, is not feasible for large-scale use due to the production and stability limitations. [ABSTRACT FROM AUTHOR]

Background: Ipomoea carnea subsp. fistulosa is a plant native to South America, but sparsely distributed in India and Bangladesh. Aphrodisiac, purgative, cathartic and sore curing properties have been attributed to the plant. Although there were several papers on the antifungal and antibacterial activities of on the crude extractives of the plant, the first report on the bioassay monitored isolation and characterization of the chief antifungal compounds as a mixture of E and Z isomers of octadecyl p-coumarates was published from this Institute. Material and Methods: The methanol extractive of Ipomoea carnea subsp. fistulosa exhibited antifungal activity against the mycelial growth of Phytophthora nictotiana by poisoned food technique. This is in addition to the reported activity against Colletotrichum gloeosporioides. Results and Discussion: Octadecyl p-coumarates isolated from the plant by column chromatography followed by HPLC exhibited activity against the mycelial growth of Cercospora capsici. This is in addition to the reported activity of octadecyl p-coumarates against the spore germination of Alternaria alternata, Alternaria porri and Cladosporium cucumerinum. Conclusion: Additional studies conducted with the crude extractive of Ipomoea carnea subsp. fistulosa confirmed its antifungal activity against Phytophthora nicotianae. Identification of octadecyl p-coumarates as antifungal active principles was confirmed by its activity against Cercospora capsici by modified mycelial growth inhibition study. [ABSTRACT FROM AUTHOR]

BACKGROUND Biofumigation with defatted seed meal of Brassicaceae in the form of pellets has several advantages over the incorporation of fresh Brassicaceae crops to control soil-borne diseases. Two field experiments were established to evaluate the effect of biofumigation with brassica pellets on the survival and infectivity of Phytophthora nicotianae Breda de Haan inoculum introduced before treatments. In the spring experiment the incorporation of additional Brassicaceae cover crop ( Brassica nigra L. and Sinapis alba L.) was tested, and in the summer experiment two brassica pellet doses were applied. RESULTS Biofumigation with brassica pellets in spring (3000 kg ha−1 with and without plastic) or in summer (3000 kg ha−1 with or without plastic; 6000 kg ha−1 without plastic) had no significant effect on the survival of P. nicotianae, regardless of the incorporation of additional Brassicaceae cover crop in spring. Reduction in infectivity in spring was related to the application of plastic, especially when combined with brassica pellets and Brassicaceae crop. In summer, soil temperature was the main factor in the inactivation of the inoculum, especially when plastic was applied, and no additional inactivation was achieved with brassica pellets. CONCLUSION In spring and summer, biofumigation with brassica pellets had no effect on the survival of P. nicotianae. Application of plastic in spring may reduce infectivity. Soil temperature is the main factor in the inactivation of inoculum in summer, especially when plastic is applied. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The aim of the study was to learn the influence of culture media on two species of Phytophthora. The development and colony appearance was observed for ten days and the number of spores for ten weeks. In order to achieve this experiment two species of the genus Phytophthora were used Phytophthora infestans de Bary and Phytophthora parasitica Dast. and four culture media PDA, CMA, V8 and TA. In determining the number of spores, 63.63 cm2 of mycelium were collected from the surface of the culture medium and mixed with 250 ml of sterile water. The containers with sterile water and Phytophthora parasitica Dast. and Phytophthora infestans de Bary., were placed in a refrigerator at a temperature of 7° C, to make sure that zoospores are released. The number of spores per milliliter was determined for each of the fungi using the hemocytometer. The highest values were recorded on the dishes with PDA medium, where after calculating the average of nine dishes the colony registered a rate of growth of approximately 1.47 cm. According to these observations we can conclude that the PDA is the most favorable for the development of the Phytophthora infestans de Bary colony. The highest values of the Phytophthora parasitica Dast colony diameter were observed in the plates with V8, where more than half of the plates have reached the edge of the analyzed Petri plates, thus an average diameter of 8.4 cm was registered in the last day of observation. On the TA plates there was also a high growth rate, the diameter of the colony reaching an average value of 5.5 cm at the end of the 10th day of observation. The PDA provided a slower growth rate of the colony diameter, at the end of the observations the colony only measured 3.94 cm, while CMA media composition has provided conditions for development of the average diameter of only 1.67 cm. [ABSTRACT FROM AUTHOR]

Strong statistical evidence was found for differences in tolerance to natural infections of Tobacco streak virus ( TSV) in sunflower hybrids. Data from 470 plots involving 23 different sunflower hybrids tested in multiple trials over 5 years in Australia were analysed. Using a Bayesian Hierarchical Logistic Regression (BHLR) model for analysis provided: (a) a rigorous method for investigating the relative effects of hybrid, seasonal rainfall and proximity to inoculum source on the incidence of severe TSV disease; (b) a natural method for estimating the probability distributions of disease incidence in different hybrids under historical rainfall conditions; and (c) a method for undertaking all pairwise comparisons of disease incidence between hybrids while controlling the familywise error rate without any drastic reduction in statistical power. The tolerance identified in field trials was effective against the main TSV strain associated with disease outbreaks, TSV-parthenium. Glasshouse tests indicate this tolerance to also be effective against the other TSV strain found in central Queensland, TSV-crownbeard. The use of tolerant germplasm is critical to minimise the risk of TSV epidemics in sunflower in this region. We found strong statistical evidence that rainfall during the early growing months of March and April had a negative effect on the incidence of severe infection with greatly reduced disease incidence in years that had high rainfall during this period. [ABSTRACT FROM AUTHOR]

BACKGROUND Currently, real-time polymerase chain reaction ( qPCR) is the technique most often used to quantify pathogen presence. Digital PCR ( dPCR) is a new technique with the potential to have a substantial impact on plant pathology research owing to its reproducibility, sensitivity and low susceptibility to inhibitors. In this study, we evaluated the feasibility of using dPCR and qPCR to quantify Phytophthora nicotianae in several background matrices, including host tissues (stems and roots) and soil samples. RESULTS In spite of the low dynamic range of dPCR (3 logs compared with 7 logs for qPCR), this technique proved to have very high precision applicable at very low copy numbers. The dPCR was able to detect accurately the pathogen in all type of samples in a broad concentration range. Moreover, dPCR seems to be less susceptible to inhibitors than qPCR in plant samples. Linear regression analysis showed a high correlation between the results obtained with the two techniques in soil, stem and root samples, with R2 = 0.873, 0.999 and 0.995 respectively. CONCLUSIONS These results suggest that dPCR is a promising alternative for quantifying soil-borne pathogens in environmental samples, even in early stages of the disease. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Oxathiapiprolin is a new fungicide active against oomycetes. In vitro assays and field studies were conducted to examine the effect of oxathiapiprolin on Phytophthora nicotianae ( Pn ) , the causal agent of black shank. The efficacy of oxathiapiprolin on mycelial growth, sporangia production, zoospore motility, and zoospore germination was assessed with four Pn isolates. EC 50 values were low ranging from 0.0039 to 0.0049 μg a.i./mL for mycelial growth, 0.00052–0.00081 μg a.i./mL for sporangia production, 0.0035–0.0051 μg a.i./mL for encysted zoospore germination, and 0.0055–0.0166 μg a.i./mL for zoospore motility. Sixty six Pn isolates, 60 from tobacco and six from ornamental plants were examined for sensitivity to oxathiapiprolin at 1 μg a.i./mL. Mycelial growth at 1 μg a.i./mL was observed in only one isolate from tobacco whereas the six Pn isolates from ornamental plants five of which were resistant to mefenoxam at 100 μg a.i./mL, were found to be sensitive to oxathiapiprolin. The efficacy of oxathiapiprolin against black shank was assessed in three field studies in North Carolina. Treatments of oxathiapiprolin were equal or superior to mefenoxam against black shank in each field study. Our results suggest that oxathiapiprolin is a highly efficacious fungicide against P . nicotianae , and will be a useful tool in controlling black shank of tobacco. [ABSTRACT FROM AUTHOR]

Phytophthora species that cause root rot, foot rot, gummosis and decline of citrus in India were characterized by morphological and molecular means. P. nicotianae was found to be the predominant species followed by P. palmivora and P. citrophthora in the 28 nurseries and 174 orchards of five major citrus growing states of the country viz. Maharashtra, Madhya Pradesh, Punjab, Andhra Pradesh and Sikkim. Morphological characterization of 100 Phytophthora spp. isolates revealed 12 different types of colony pattern on V8 agar and 9 isolates of P. nicotianae were observed as A2 mating type and rest all the 91 isolates of Phytophthora spp. were of A1 mating type, while no self-fertile isolate was observed. The species P. nicotianae, P. palmivora, and P. citrophthora could all be clearly identified by PCR amplification of the nuclear ribosomal internal transcribed spacer (ITS) region followed by restriction analysis with MspI, AluI and RsaI. Sequencing and phylogenetic analyses of the ITS region, beta tubulin gene, translation Elongation factor 1 alpha and the region containing the mitochondrial cytochrome c oxidase subunit 2 gene fragment also confirmed the identity of these species. The phylogenetic groups did not correlate with geographic origin of the isolates. Additionally, isolates of P. nicotianae and P. palmivora were identified using species-specific PCR primers. The identification tools described in this study accurately detected the species of Phytophthora affecting citrus in nurseries and orchards in India. [ABSTRACT FROM AUTHOR]

This report investigates population structure and genetic variability of Phytophthora spp. isolated from botanically diverse plants in Florida. Internal transcribed spacer-based molecular phylogenetic analyses indicate that Phytophthora isolates recovered from ornamental plants in Florida represent a genetically diverse population and that a majority of the isolates belong to Phytophthora nicotianae (73.2%), P. palmivora (18.7%), P. tropicalis (4.9%), P. katsurae (2.4%), and P. cinnamomi (0.8%). Mating type analyses revealed that most isolates were heterothallic, consisting of both mating type A1 (25.2%) and mating type A2 (39.0%), and suggesting that they could outcross. Fungicide sensitivity assays determined that several isolates were moderate to completely insensitive to mefenoxam. In addition, several isolates were also moderately insensitive to additional fungicides with different modes of action. However, correlation analyses did not reveal occurrence of fungicide cross-resistance. These studies suggest that a genetically diverse Phytophthora population infects ornamental crops and the occurrence of mefenoxam-insensitive Phytophthora populations raises concerns about disease management in ornamentals. Mitigating fungicide resistance will require prudent management strategies, including tank mixes and rotation of chemicals with different modes of actions. [ABSTRACT FROM AUTHOR]

Background: Black shank is a severe plant disease caused by the soil-borne pathogen Phytophthora nicotianae. Two physiological races of, races 0 and 1, are predominantly observed in cultivated tobacco fields around P. nicotianae the world. Race 0 has been reported to be more aggressive, having a shorter incubation period, and causing worse root rot symptoms, while race 1 causes more severe necrosis. The molecular mechanisms underlying the difference in virulence between race 0 and 1 remain elusive. Findings: We assembled and annotated the genomes of P. nicotianae races 0 and 1, which were obtained by a combination of PacBio single-molecular real-time sequencing and second-generation sequencing (both HiSeq and MiSeq platforms). Gene family analysis revealed a highly expanded ATP-binding cassette transporter gene family in P. nicotianae. Specifically, more RxLR effector genes were found in the genome of race 0 than in that of race 1. In addition, RxLR effector genes were found to be mainly distributed in gene-sparse, repeat-rich regions of the P. nicotianae genome. Conclusions: These results provide not only high quality reference genomes of P. nicotianae, but also insights into the infection mechanisms of and its co-evolution with the host plant. They also reveal insights into the P. nicotianae difference in virulence between the two physiological races. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae was first isolated from tobacco at the end of the 19th century. This organism is now considered as one of the most devastating oomycete plant pathogens, with a recognized host range of more than 255 species over five continents and a wide diversity of climates. The economic losses caused by P nicotianae are difficult to estimate, because of the diversity of its hosts and ecological niches. For these reasons, this pathogen represents a continuous challenge to plant disease management programmes, which frequently rely solely on the use of chemicals. Phytophthora nicotianae is better adapted than its competitors to abiotic stresses, especially to climate warming. As a result, its importance is increasing. This review illustrates, with some examples, how P nicotianae currently impacts plant economies worldwide, and how it may constitute more severe threats to agriculture and natural ecosystems in the context of global climate change. [ABSTRACT FROM AUTHOR]