Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 462
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
PLoS One ; 15(1): e0227250, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31910244

RESUMO

Oomycete plant pathogens are difficult to control and routine genetic research is challenging. A major problem is instability of isolates. Here we characterize >600 field and single zoospore isolates of Phytophthora capsici for inheritance of mating type, sensitivity to mefenoxam, chromosome copy number and heterozygous allele frequencies. The A2 mating type was highly unstable with 26% of 241 A2 isolates remaining A2. The A1 mating type was stable. Isolates intermediately resistant to mefenoxam produced fully resistant single-spore progeny. Sensitive isolates remained fully sensitive. Genome re-sequencing of single zoospore isolates revealed extreme aneuploidy; a phenomenon dubbed Dynamic Extreme Aneuploidy (DEA). DEA is characterized by the asexual inheritance of diverse intra-genomic combinations of chromosomal ploidy ranging from 2N to 3N and heterozygous allele frequencies that do not strictly correspond to ploidy. Isolates sectoring on agar media showed dramatically altered heterozygous allele frequencies. DEA can explain the rapid increase of advantageous alleles (e.g. drug resistance), mating type switches and copy neutral loss of heterozygosity (LOH). Although the mechanisms driving DEA are unknown, it can play an important role in adaptation and evolution and seriously hinders all aspects of P. capsici research.


Assuntos
Aneuploidia , Phytophthora/fisiologia , Doenças das Plantas/microbiologia , Reprodução Assexuada/genética , Verduras/microbiologia , Alelos , Evolução Biológica , Mapeamento Cromossômico , Cucumis sativus/microbiologia , Variação Genética , Genótipo , Perda de Heterozigosidade , Phytophthora/isolamento & purificação , Polimorfismo de Nucleotídeo Único , Análise de Sequência de DNA , Análise de Célula Única , Esporos/genética
2.
Phytopathology ; 110(2): 447-455, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31454304

RESUMO

Phytophthora capsici is a destructive pathogen of cucurbits that causes root, crown, and fruit rot. Winter squash (Cucurbita spp.) production is limited by this pathogen in Michigan and other U.S. growing regions. Age-related resistance (ARR) to P. capsici occurs in C. moschata fruit but is negated by wounding. This study aimed to determine whether structural barriers to infection exist in the intact exocarp of maturing fruit exhibiting ARR. Five C. moschata cultivars were evaluated for resistance to P. capsici 10, 14, 16, 18, and 21 days postpollination (dpp). Scanning electron microscopy imaging of Chieftain butternut fruit exocarp of susceptible fruit at 7 dpp and resistant fruit at 14 and 21 dpp revealed significant increases in cuticle and epidermal thicknesses as fruit aged. P. capsici hyphae penetrated susceptible fruit at 7 dpp directly from the surface or through wounds before 6 h postinoculation (hpi) and completely degraded the fruit cell wall within 48 hpi. Resistant fruit remained unaffected at 14 and 21 dpp. The high correlation between the formation of a thickened cuticle and epidermis in maturing winter squash fruit and resistance to P. capsici indicates the presence of a structural barrier to P. capsici as the fruit matures.


Assuntos
Cucurbita , Resistência à Doença , Frutas , Phytophthora , Cucurbita/parasitologia , Resistência à Doença/fisiologia , Frutas/citologia , Frutas/parasitologia , Phytophthora/fisiologia , Doenças das Plantas/parasitologia
3.
Gene ; 728: 144288, 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-31846710

RESUMO

Phytophthora root rot, caused by the soilborne oomycete pathogen Phytophthora capsici (Leon.), is a devastating disease causing significant losses in pepper production worldwide. To uncover the mechanism of root-mediated resistance to P. capsici we elucidated the dynamic transcriptome of whole pepper roots of the resistant accession CM334 and the susceptible accession NMCA10399 after P. capsici infection at 0, 12 and 36 hpi using RNA-Seq method. We detected that the roots of the resistant CM334 and the susceptible NMCA10399 had different transcriptional responses to P. capsici, suggesting the former activated a response to P. capsici earlier than the latter. KEGG enrichment analysis showed the pathways involved in the synthesis of secondary metabolites were those in which the most DEGs were enriched. Focusing on the gene regulation of phenylpropanoid biosynthesis-related genes, we found genes related to the key enzyme phenylalanine ammonia-lyase (PAL) were activated earlier with greater changes in the resistant accession than in the susceptible one. Moreover, genes related to cinnamoyl-CoA reductase (CCR1) were also upregulated in resistant roots but downregulated with great folder changes in susceptible roots. Briefly, we inferred that the phenylpropanoid biosynthesis pathway, especially cinnamaldehyde and lignin derived from its branches, played significant roles in pepper root resistance to P. capsici. These results provide new insight into root-mediated resistance to P. capsici in pepper.


Assuntos
Capsicum/genética , Resistência à Doença , Fenilpropionatos/metabolismo , Phytophthora/fisiologia , Doenças das Plantas/genética , Proteínas de Plantas/genética , Raízes de Plantas/genética , Transcriptoma , Capsicum/crescimento & desenvolvimento , Capsicum/microbiologia , Regulação da Expressão Gênica de Plantas , Fenilalanina Amônia-Liase/genética , Doenças das Plantas/microbiologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia
4.
Plant Dis ; 103(12): 3154-3160, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31560616

RESUMO

Phytophthora ramorum, the cause of sudden oak death (SOD), kills tanoak (Notholithocarpus densiflorus) trees in southwestern Oregon and California. Two lineages of P. ramorum are now found in wildland forests of Oregon (NA1 and EU1). In addition to the management of SOD in forest ecosystems, disease resistance could be used as a way to mitigate the impact of P. ramorum. The objectives of this study were to (i) characterize the variability in resistance of N. densiflorus among families using lesion length; (ii) determine whether lineage, isolate, family, or their interactions significantly affect variation in lesion length; and (iii) determine whether there are differences among isolates and among families in terms of lesion length. The parameters isolate nested within lineage (isolate[lineage]) and family × isolate(lineage) interaction explained the majority of the variation in lesion length. There was no significant difference between the NA1 and EU1 lineages in terms of mean lesion length; however, there were differences among the six isolates. Lesions on seedlings collected from surviving trees at infested sites were smaller, on average, than lesions of seedlings collected from trees at noninfested sites (P = 0.0064). The results indicate that there is potential to establish a breeding program for tanoak resistance to SOD and that several isolates of P. ramorum should be used in an artificial inoculation assay.


Assuntos
Phytophthora , Quercus , California , Resistência à Doença , Oregon , Phytophthora/classificação , Phytophthora/fisiologia , Doenças das Plantas/parasitologia , Quercus/parasitologia
5.
J Plant Physiol ; 241: 153030, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31493717

RESUMO

Phytophthora cinnamomi (Pc) is a dangerous pathogen that causes root rot (ink disease) and threatens the production of chestnuts worldwide. Despite all the advances recently reported at molecular and physiological level, there are still gaps of knowledge that would help to unveil the defence mechanisms behind plant-Pc interactions. Bearing this in mind we quantified constitutive and Pc-induced stress-related signals (hormones and metabolites) complemented with changes in photosynthetic related parameters by exploring susceptible and resistant Castanea spp.-Pc interactions. In a greenhouse experiment, five days before and nine days after inoculation with Pc, leaves and fine roots from susceptible C. sativa and resistant C. sativa × C. crenata clonal 2-year-old plantlets were sampled (clones Cs14 and 111-1, respectively). In the resistant clone, stomatal conductance (gs) and net photosynthesis (A) decreased significantly and soluble sugars in leaves increased, while in the susceptible clone gs and A remained unchanged and proline levels in leaves increased. In the resistant clone, higher constitutive content of root SA and foliar ABA, JA and JA-Ile as compared to the susceptible clone were observed. Total phenolics and condensed tannins were highest in roots of the susceptible clone. In response to infection, a dynamic hormonal response in the resistant clone was observed, consisting of accumulation of JA, JA-Ile and ABA in roots and depletion of total phenolics in leaves. However, in the susceptible clone only JA diminished in leaves and increased in roots. Constitutive and Pc-induced levels of JA-Ile were only detectable in the resistant clone. From the hormonal profiles obtained in leaves and roots before and after infection, it is concluded that the lack of effective hormonal changes in C. sativa explains the lack of defence responses to Pc of this susceptible species.


Assuntos
Resistência à Doença , Fagaceae/fisiologia , Interações Hospedeiro-Patógeno/fisiologia , Phytophthora , Doenças das Plantas/microbiologia , Reguladores de Crescimento de Planta/fisiologia , Resistência à Doença/fisiologia , Fagaceae/imunologia , Fagaceae/microbiologia , Metaboloma/fisiologia , Phytophthora/fisiologia , Doenças das Plantas/imunologia , Reguladores de Crescimento de Planta/metabolismo , Folhas de Planta/fisiologia , Raízes de Plantas/fisiologia
6.
Int J Mol Sci ; 20(18)2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31540158

RESUMO

The mediator complex is an essential link between transcription factors and RNA polymerase II, and mainly functions in the transduction of diverse signals to genes involved in different pathways. Limited information is available on the role of soybean mediator subunits in growth and development, and their participation in defense response regulation. Here, we performed genome-wide identification of the 95 soybean mediator subunits, which were unevenly localized on the 20 chromosomes and only segmental duplication events were detected. We focused on GmMED16-1, which is highly expressed in the roots, for further functional analysis. Transcription of GmMED16-1 was induced in response to Phytophthora sojae infection. Agrobacterium rhizogenes mediated soybean hairy root transformation was performed for the silencing of the GmMED16-1 gene. Silencing of GmMED16-1 led to an enhanced susceptibility phenotype and increased accumulation of P. sojae biomass in hairy roots of transformants. The transcript levels of NPR1, PR1a, and PR5 in the salicylic acid defense pathway in roots of GmMED16-1-silenced transformants were lower than those of empty-vector transformants. The results provide evidence that GmMED16-1 may participate in the soybean-P. sojae interaction via a salicylic acid-dependent process.


Assuntos
Estudo de Associação Genômica Ampla , Interações Hospedeiro-Parasita/genética , Complexo Mediador/metabolismo , Phytophthora/fisiologia , Soja/genética , Soja/parasitologia , Mapeamento Cromossômico , Cromossomos de Plantas , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Filogenia , Phytophthora/classificação , Doenças das Plantas/genética , Doenças das Plantas/parasitologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Subunidades Proteicas , Transcriptoma
7.
Phytopathology ; 109(11): 1908-1921, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31282283

RESUMO

The emergence of Phytophthora pluvialis as a foliar pathogen of Douglas fir in New Zealand and the Pacific Northwest United States has raised questions about its interaction with the widespread Swiss needle cast (SNC) disease. During Spring 2017, we repeatedly sampled 30 trees along an environmental gradient in each region and 292 additional trees in a longitudinal transect to assess the P. pluvialis epidemic and the association between P. pluvialis and Nothophaeocryptopus gaeumannii, which are causal agents of SNC. Both pathogens were consistently more abundant in the host's exotic environment in New Zealand. In both areas, the two pathogens co-exist in different spatial scales for regions and needles. The relative abundance of both pathogens was negatively correlated in the Pacific Northwest, where both presumably have co-existed for longer. Our findings confirmed the interaction of P. pluvialis and N. gaeumannii as foliar pathogens of Douglas fir and suggest a within-site spatial variation in the Pacific Northwest.


Assuntos
Ascomicetos , Phytophthora , Pseudotsuga , Ascomicetos/fisiologia , Nova Zelândia , Noroeste dos Estados Unidos , Phytophthora/fisiologia , Doenças das Plantas/microbiologia , Pseudotsuga/microbiologia
8.
Planta ; 250(2): 413-425, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31243548

RESUMO

MAIN CONCLUSION: This article provides an overview of the interactions between Phytophthora effectors and plant immune system components, which form a cross-linked complex network that regulates plant pathogen resistance. Pathogens secrete numerous effector proteins into plants to promote infections. Several Phytophthora species (e.g., P. infestans, P. ramorum, P. sojae, P. capsici, P. cinnamomi, and P. parasitica) are notorious pathogens that are extremely damaging to susceptible plants. Analyses of genomic data revealed that Phytophthora species produce a large group of effector proteins, which are critical for pathogenesis. And, the targets and functions of many identified Phytophthora effectors have been investigated. Phytophthora effectors can affect various aspects of plant immune systems, including plant cell proteases, phytohormones, RNAs, the MAPK pathway, catalase, the ubiquitin proteasome pathway, the endoplasmic reticulum, NB-LRR proteins, and the cell membrane. Clarifying the effector-plant interactions is important for unravelling the functions of Phytophthora effectors during pathogenesis. In this article, we review the effectors identified in recent decades and provide an overview of the effector-directed regulatory network in plants following infections by Phytophthora species.


Assuntos
Interações Hospedeiro-Patógeno , Phytophthora/imunologia , Células Vegetais/imunologia , Doenças das Plantas/imunologia , Imunidade Vegetal , Phytophthora/patogenicidade , Phytophthora/fisiologia , Células Vegetais/parasitologia , Doenças das Plantas/parasitologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Virulência
9.
Plant Dis ; 103(8): 1828-1834, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31184971

RESUMO

Red needle cast is a significant foliar disease of commercial stands of Pinus radiata caused by Phytophthora pluvialis in New Zealand. The effect of copper, applied as a foliar spray of cuprous oxide at a range of doses between 0 and 1.72 kg ha-1, was investigated in two controlled trials with potted plants and in an operational trial with mature P. radiata. In all trials, lesions formed on needles after artificial exposure to the infecting propagules (zoospores) of P. pluvialis were used to determine treatment efficacy, with the number and/or length of lesions as the dependent variable. Results across all trials indicated that cuprous oxide was highly effective at reducing infection of P. radiata with P. pluvialis. Application rates equivalent to ≥0.65 kg ha-1 significantly reduced infection levels relative to a control treatment, with foliar surface copper levels as low as 13 to 26 mg kg-1 of needle tissue preventing infection. Greater copper content was associated with a reduction in the proportion of needles with P. pluvialis lesions, with the probability of lesions developing decreasing approximately 1% for every 1 unit (in milligrams per kilogram) increase in copper content. Over a 90-day period, surface copper content declined to 30% of that originally applied, indicating an approximate period of treatment efficacy of 3 months. Our findings highlight the potential of cuprous oxide for the control of red needle cast in P. radiata stands. Further information about the optimal field dose, timing, and the frequency of foliar cuprous oxide application is key to prevent infection and also reduce the build up of inoculum during severe outbreaks of this pathogen.


Assuntos
Cobre , Phytophthora , Pinus , Doenças das Plantas , Antiparasitários/farmacologia , Cobre/análise , Cobre/farmacologia , Nova Zelândia , Phytophthora/efeitos dos fármacos , Phytophthora/fisiologia , Pinus/parasitologia , Doenças das Plantas/parasitologia , Doenças das Plantas/prevenção & controle
10.
Int J Mol Sci ; 20(12)2019 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-31207889

RESUMO

With the improper application of fungicides, Phytophthora sojae begins to develop resistance to fungicides, and biological control is one of the potential ways to control it. We screened two strains of Bacillus; Bacillus amyloliquefaciens JDF3 and Bacillus subtilis RSS-1, which had an efficient inhibitory effect on P. sojae. They could inhibit mycelial growth, the germination of the cysts, and the swimming of the motile zoospores. To elucidate the response of P. sojae under the stress of B. amyloliquefaciens and B. subtilis, and the molecular mechanism of biological control, comparative transcriptome analysis was applied. Transcriptome analysis revealed that the expression gene of P. sojae showed significant changes, and a total of 1616 differentially expressed genes (DEGs) were detected. They participated in two major types of regulation, namely "specificity" regulation and "common" regulation. They might inhibit the growth of P. sojae mainly by inhibiting the activity of ribosome. A pot experiment indicated that B. amyloliquefaciens and B. subtilis enhanced the resistance of soybean to P. sojae, and their control effects of them were 70.7% and 65.5%, respectively. In addition, B. amyloliquefaciens fermentation broth could induce an active oxygen burst, NO production, callose deposition, and lignification. B. subtilis could also stimulate the systemic to develop the resistance of soybean by lignification, and phytoalexin.


Assuntos
Antibiose , Bacillus amyloliquefaciens/fisiologia , Bacillus subtilis/fisiologia , Phytophthora/fisiologia , Imunidade Vegetal , Transcriptoma , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Regulação Fúngica da Expressão Gênica , Glucanos/metabolismo , Lignina/metabolismo , Óxido Nítrico/metabolismo , Phytophthora/metabolismo , Phytophthora/patogenicidade , Espécies Reativas de Oxigênio/metabolismo , Soja/imunologia , Soja/microbiologia
11.
Plant Dis ; 103(8): 2024-2032, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31246147

RESUMO

Phytophthora root rot (PRR), caused by Phytophthora cinnamomi, 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. Seventy-one isolates of P. cinnamomi from avocado in California, most of them collected between 2009 to 2017, were tested for their in vitro sensitivity to the six fungicides. Baseline sensitivity ranges and mean values (in parentheses) of effective concentrations to inhibit mycelial growth by 50% (EC50) for the new fungicides ethaboxam, fluopicolide, mandipropamid, and oxathiapiprolin were 0.017 to 0.069 µg/ml (0.035), 0.046 to 0.330 µg/ml (0.133), 0.003 to 0.011 µg/ml (0.005), and 0.0002 to 0.0007 µg/ml (0.0004), respectively. In comparison, the EC50 value range (mean) was 0.023 to 0.138 µg/ml (0.061) for mefenoxam and 12.9 to 361.2 µg/ml (81.5) for potassium phosphite. Greenhouse soil inoculation trials with 8-month-old Zutano seedlings and 10-month-old Dusa and PS.54 clonal rootstocks were conducted to assess the efficacy of these fungicides for managing PRR. Mefenoxam and potassium phosphite were effective treatments; however, oxathiapiprolin, fluopicolide, and mandipropamid were more effective. Ethaboxam was effective in reducing PRR on the rootstocks evaluated. Oxathiapiprolin reduced PRR incidence and pathogen population size in the soil by >90%, and plant shoot growth and root dry weight were significantly increased compared with the control; thus, oxathiapiprolin was one of the best treatments overall. The high activity and performance of these new fungicides supports their registrations on avocado for use in rotation and mixture programs, including with previously registered compounds, to reduce the risk of development and spread of resistance in pathogen populations.


Assuntos
Fungicidas Industriais , Persea , Phytophthora , California , Fungicidas Industriais/farmacologia , Persea/parasitologia , Phytophthora/efeitos dos fármacos , Phytophthora/fisiologia , Doenças das Plantas/parasitologia , Doenças das Plantas/prevenção & controle
12.
Plant Dis ; 103(8): 1923-1930, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31140922

RESUMO

Phytophthora plurivora is a recently described plant pathogen, formerly recognized as P. citricola. Recent sampling of Pacific Northwest nurseries frequently encountered this pathogen, and it has been shown to be among the most damaging Phytophthora pathogens on ornamentals. We characterized the population structure of P. plurivora in a survey of four Oregon nurseries across three different counties with focus on Rhododendron hosts. Isolates were identified to the species level by Sanger sequencing and/or a PCR-RFLP assay of the internal transcribed spacer (ITS) region. We used genotyping-by-sequencing to determine genetic diversity. Variants were called de novo, resulting in 284 high-quality variants for 61 isolates after stringent filtering. Based on Fst and AMOVA, populations were moderately differentiated among nurseries. Overall, population structure suggested presence of one dominant clonal lineage in all nurseries, as well as isolates of cryptic diversity mostly found in one nursery. Within the clonal lineage, there was a broad range of sensitivity to mefenoxam and phosphorous acid. Sensitivity of the two fungicides was correlated. P. plurivora was previously assumed to spread clonally, and the low genotypic diversity observed within and among isolates corroborated this hypothesis. The broad range of fungicide sensitivity within the P. plurivora population found in PNW nurseries has implications for managing disease caused by this important nursery pathogen. These findings provide the first perspective into P. plurivora population structure and phenotypic plasticity in Pacific Northwest nurseries.


Assuntos
Phytophthora , Rhododendron , DNA Espaçador Ribossômico/genética , Oregon , Phytophthora/classificação , Phytophthora/genética , Phytophthora/fisiologia , Doenças das Plantas/parasitologia , Rhododendron/parasitologia
13.
Plant Dis ; 103(7): 1703-1711, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31106702

RESUMO

During flooding events in nurseries, Phytophthora root rot caused by Phytophthora cinnamomi Rands often causes damage that leads to complete crop loss. In this study, we evaluated the efficacy of fungicides, biofungicides, and host plant defense inducers for preventive and curative control of Phytophthora root rot on flowering dogwood (Cornus florida L.) seedlings exposed to a simulated flood event of 1, 3, or 7 days. In two greenhouse trials, preventive (7 days before flooding) or curative (1 day after flooding) drench treatments were applied to dogwood seedlings artificially inoculated with P. cinnamomi. The plants were flooded by maintaining standing water for 1, 3, or 7 days. After the trials, plant growth data (total plant weight, root weight, plant height, and plant width) were recorded, and root systems were assessed for disease severity using a scale of 0 to 100% of roots affected, and subsamples were plated on PARPH-V8 medium to determine the percent recovery of the Phytophthora pathogen. Plants preventively treated with Subdue MAXX had reduced disease severity relative to the nontreated, inoculated plants (positive control) flooded 1, 3, or 7 days in both trials. Pageant Intrinsic and Segovis treatments also had lower disease severity than the positive control at all flooding durations in trial two, but not trial one. In trial one, preventive and curative treatments of Orkestra Intrinsic had reduced disease severity compared with the positive control at 1 and 3 days of flooding, whereas curative treatments of Empress Intrinsic and Tartan Stressgard also were effective at 1 and 3 days of flooding in trial one. The host plant defense inducers (Aliette 80 WDG, Signature Xtra, and Actigard) were inconsistent and ineffective at reducing disease severity when applied as preventive or curative treatments. Preventive treatments of the biofungicides RootShield Plus+ and MBI-110 had consistently lower disease severity than the positive control at 1 day of flooding but not 3 or 7 days of flooding. Potentially, growers can use information from this study to manage Phytophthora root rot during flooding or in areas of the nursery that often experience high soil moisture levels.


Assuntos
Cornus , Fungicidas Industriais , Phytophthora , Raízes de Plantas , Cornus/parasitologia , Inundações , Fungicidas Industriais/farmacologia , Phytophthora/efeitos dos fármacos , Phytophthora/fisiologia , Raízes de Plantas/parasitologia
14.
Plant Dis ; 103(7): 1651-1656, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31115269

RESUMO

We performed studies using zoospore inoculum combined from nine isolates of Phytophthora ramorum and determined the effect of leaf wetness on infection of whole plants of Rhododendron 'Cunningham's White' and Viburnum tinus. The mean percentage of infected leaves for both host species increased gradually across a dew chamber moisture period of 1 to 6 h, reaching approximately 80% infection by 6 h. We also evaluated the effect of a postinoculation drying period on infectivity of the two host species with zoospore inoculum. With a 30-min postinoculation drying period, Rhododendron 'Cunningham's White' sustained less than 40% infected leaves, whereas V. tinus had an infection rate of almost 75% infected leaves. Disease percentages for both host species declined sharply with drying periods longer than 30 min. Knowledge of infectivity parameters for P. ramorum will provide a better understanding of epidemic development and lead to improved recommendations for control.


Assuntos
Phytophthora , Rhododendron , Viburnum , Água , Phytophthora/fisiologia , Folhas de Planta/parasitologia , Rhododendron/parasitologia , Viburnum/parasitologia , Água/química
15.
Plant Dis ; 103(6): 1148-1155, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30964419

RESUMO

Phytophthora ramorum, cause of sudden oak death and ramorum leaf blight, can persist undetected in infested nurseries. Many conventional fungicides are effective in reducing or delaying symptom expression but some may confound visual detection of infected plants. We tested film-forming polymers (FFPs) and surfactants for their ability to reduce infection and sporulation of P. ramorum on rhododendron. FFPs (Anti-Stress, Moisturin, Nature Shield, Nu-Film, and Vapor Gard) and surfactants (Tergitol, Zonix, and an unregistered AGAE product) were screened in detached-leaf assays. Anti-Stress, Nu-Film, Zonix, and a Nu-Film-Zonix mixture were additionally tested for durability, protection against exposure to infested water, and a reduction in sporulation. FFP effectiveness was retained for at least 3 weeks of exposure to overhead irrigation and rain. Relative to controls, foliar treatments protected rhododendron branches exposed to infested water. No treatments prevented symptom development when applied postinfection but leaves treated with Anti-Stress, Zonix, and the Nu-Film-Zonix mixture produced significantly fewer sporangia relative to controls. Application of FFPs and surfactants to quarantined, potentially infected plants offers a management tool for reducing infection and sporulation but not symptom expression, thereby limiting disease spread without interfering with disease detection.


Assuntos
Fungicidas Industriais , Phytophthora , Polímeros , Rhododendron , Tensoativos , Fungicidas Industriais/química , Fungicidas Industriais/farmacologia , Phytophthora/fisiologia , Polímeros/química , Polímeros/farmacologia , Rhododendron/microbiologia , Tensoativos/química , Tensoativos/farmacologia
16.
Plant Dis ; 103(6): 1363-1373, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30983521

RESUMO

Apple replant disease (ARD) is a biological phenomenon that is encountered when old apple orchards are replanted, resulting in tree growth and yield reductions in young trees. Three ARD orchard trials were conducted, which showed that semiselective chemicals (fenamiphos, metalaxyl, imidacloprid, and phosphonates) used independently, two fumigant formulations (33.3% chloropicrin and 60.8% 1,3-dichloropropene [Pic33-1,3D] and 57.% chloropicrin and 38% 1,3 dichloropropene [Pic57-1,3D]), and semiselective chemicals combined with Pic33-1,3D or Pic57-1,3D all contributed to significant increases in tree growth (trunk diameter and shoot length) relative to the untreated control 3 to 4 years postplanting. The treatments did not differ significantly from each other in improving tree growth. Yield was more indicative of treatment efficacy, but this varied between the three orchards. The Pic33-1,3D fumigant in combination with semiselective chemistries was the most consistent in significantly increasing cumulative yields. The Pic57-1,3D treatment was superior in increasing yields relative to the Pic33-1,3D treatment, because (i) it significantly increased cumulative yields in comparison with the Pic33-1,3D treatment in one orchard and (ii) in another orchard, a significant increase in yield was obtained with Pic57-1,3D relative to the control treatment but not with the Pic33-1,3D treatment. The quantification of ARD causative agents 20 months postplant showed that Phytophthora cactorum contributed to disease development in all three orchards; significant negative correlations existed between the quantity of P. cactorum DNA detected in tree roots and tree growth and less often, yield. In two orchards, only some of the treatments that significantly reduced the quantity of P. cactorum DNA in tree roots relative to the control also resulted in a significant increase in tree growth. Some of the aforementioned trends were also evident for Pratylenchus spp. root densities in two of the orchards. There was a significant positive correlation between P. cactorum root DNA quantities and Pratylenchus spp. root densities. Pythium spp. and "Cylindrocarpon"-like DNA quantities detected in tree roots typically were not indicative of treatment efficacy. However, a significant positive correlation existed between these two pathogen groups, suggesting complex interactions not associated with pathogen quantities per se.


Assuntos
Hidrocarbonetos Clorados , Malus , Doenças das Plantas , Compostos Alílicos/farmacologia , Animais , Antiparasitários/farmacologia , Fumigação , Hidrocarbonetos Clorados/farmacologia , Malus/parasitologia , Phytophthora/efeitos dos fármacos , Phytophthora/fisiologia , Doenças das Plantas/parasitologia , Doenças das Plantas/prevenção & controle , África do Sul
17.
Phytopathology ; 109(8): 1441-1452, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30973309

RESUMO

In containerized (potted) annual nursery and greenhouse crops, set point-controlled irrigation allows adaptation to increasing water insecurity by precisely reducing water inputs. A key factor influencing adoption is lack of information on disease risk. To facilitate adaptive water use, effects of set-point substrate moisture (SM) control on disease risk and water savings in containerized annual production were evaluated using the Phytophthora capsici-tomato pathosystem (a model system for water stress predisposition to pathogen infection), comparing outcomes of imposing midrange SM (15% volumetric water content [VWC]) and low-range SM (10% VWC) with well-watered (20% VWC) plants. Reducing soil moisture to 10% VWC differentially reduced stem water potential (P < 0.05) and enhanced rate of wilt progress (P = 0.006) and root rot severity (P = 0.03) in P. capsici inoculated plants compared with noninoculated plants. Furthermore, incidence of fine root infections in inoculated asymptomatic plants was greater under reduced SM (10% VWC) compared with in well-watered plants (P < 0.05). Mild reductions to 15% VWC did not influence plant performance (root and shoot weights and plant height) or pathogen infection in either inoculated or noninoculated plants compared with well-watered plants and reduced water inputs by 17%, indicating potential for reducing water usage without increasing disease risk. Furthermore, P. capsici inoculated plants had lower shoot biomass and greater root infection incidence when 15% VWC was applied to older compared with younger plants; the inverse was true for root rot severity, although root rot development was minor overall (P < 0.05). These results indicate that water use reductions pose disease risks, but there is potential to reduce water use and effectively manage plant pathogens in containerized production. Overall, this study indicates that physiological indices should not be solely relied on to develop water reduction methods.


Assuntos
Lycopersicon esculentum , Phytophthora , Doenças das Plantas/microbiologia , Produtos Agrícolas , Lycopersicon esculentum/microbiologia , Phytophthora/fisiologia , Água
18.
PLoS Pathog ; 15(4): e1007729, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-31002734

RESUMO

The use of host nutrients to support pathogen growth is central to disease. We addressed the relationship between metabolism and trophic behavior by comparing metabolic gene expression during potato tuber colonization by two oomycetes, the hemibiotroph Phytophthora infestans and the necrotroph Pythium ultimum. Genes for several pathways including amino acid, nucleotide, and cofactor biosynthesis were expressed more by Ph. infestans during its biotrophic stage compared to Py. ultimum. In contrast, Py. ultimum had higher expression of genes for metabolizing compounds that are normally sequestered within plant cells but released to the pathogen upon plant cell lysis, such as starch and triacylglycerides. The transcription pattern of metabolic genes in Ph. infestans during late infection became more like that of Py. ultimum, consistent with the former's transition to necrotrophy. Interspecific variation in metabolic gene content was limited but included the presence of γ-amylase only in Py. ultimum. The pathogens were also found to employ strikingly distinct strategies for using nitrate. Measurements of mRNA, 15N labeling studies, enzyme assays, and immunoblotting indicated that the assimilation pathway in Ph. infestans was nitrate-insensitive but induced during amino acid and ammonium starvation. In contrast, the pathway was nitrate-induced but not amino acid-repressed in Py. ultimum. The lack of amino acid repression in Py. ultimum appears due to the absence of a transcription factor common to fungi and Phytophthora that acts as a nitrogen metabolite repressor. Evidence for functional diversification in nitrate reductase protein was also observed. Its temperature optimum was adapted to each organism's growth range, and its Km was much lower in Py. ultimum. In summary, we observed divergence in patterns of gene expression, gene content, and enzyme function which contribute to the fitness of each species in its niche.


Assuntos
Proteínas Fúngicas/genética , Glucana 1,4-alfa-Glucosidase/metabolismo , Nutrientes/metabolismo , Phytophthora/genética , Doenças das Plantas/parasitologia , Tubérculos/metabolismo , Solanum tuberosum/metabolismo , Adaptação Fisiológica , Evolução Molecular , Proteínas Fúngicas/metabolismo , Perfilação da Expressão Gênica , Regulação Fúngica da Expressão Gênica , Interações Hospedeiro-Parasita/genética , Phytophthora/classificação , Phytophthora/fisiologia , Doenças das Plantas/genética , Tubérculos/crescimento & desenvolvimento , Tubérculos/parasitologia , Solanum tuberosum/crescimento & desenvolvimento , Solanum tuberosum/parasitologia
19.
Plant Dis ; 103(6): 1264-1274, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30932737

RESUMO

Nursery stocks and irrigation water are important sources of Phytophthora spp. In this study, 20 irrigation water reservoirs and 10 avocado nurseries were surveyed in the Canary Islands between 2013 and 2015 to investigate their potential role in disseminating pathogenic species in avocado orchards. Phytophthora multivora was isolated from one of the irrigation reservoirs, whereas, in two surveys conducted in nurseries, Phytophthora cinnamomi, the primary pathogen in avocado, was detected in addition to other Phytophthora species (P. lacustris, P. multivora, P. nicotianae, P. niederhauserii, and P. palmivora) and Phytopythium vexans. The species recovered from nurseries were isolated mostly from propagated plants but also from nursery irrigation water, soil used for substrate preparation, and soil samples collected in orchards that supply seeds for seedling propagation. Species recovered from nurseries correlated with those found in avocado orchards in a previous study, except for P. lacustris, suggesting that nurseries could be involved in their dissemination in avocado orchards. The improved sanitary status of nurseries resulted in reduced incidence in the second survey, indicating the importance of nursery monitoring to reduce infestations.


Assuntos
Persea , Phytophthora , Agricultura/estatística & dados numéricos , Água Doce/parasitologia , Persea/parasitologia , Phytophthora/fisiologia , Doenças das Plantas/parasitologia , Espanha , Inquéritos e Questionários
20.
Plant Dis ; 103(7): 1631-1641, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31033400

RESUMO

Restoration of American chestnut (Castanea dentata) depends on combining resistance to both the chestnut blight fungus (Cryphonectria parasitica) and Phytophthora cinnamomi, which causes Phytophthora root rot, in a diverse population of C. dentata. Over a 14-year period (2004 to 2017), survival and root health of American chestnut backcross seedlings after inoculation with P. cinnamomi were compared among 28 BC3, 66 BC4, and 389 BC3F3 families that descended from two BC1 trees (Clapper and Graves) with different Chinese chestnut grandparents. The 5% most resistant Graves BC3F3 families survived P. cinnamomi infection at rates of 75 to 100% but had mean root health scores that were intermediate between resistant Chinese chestnut and susceptible American chestnut families. Within Graves BC3F3 families, seedling survival was greater than survival of Graves BC3 and BC4 families and was not genetically correlated with chestnut blight canker severity. Only low to intermediate resistance to P. cinnamomi was detected among backcross descendants from the Clapper tree. Results suggest that major-effect resistance alleles were inherited by descendants from the Graves tree, that intercrossing backcross trees enhances progeny resistance to P. cinnamomi, and that alleles for resistance to P. cinnamomi and C. parasitica are not linked. To combine resistance to both C. parasitica and P. cinnamomi, a diverse Graves backcross population will be screened for resistance to P. cinnamomi, survivors bred with trees selected for resistance to C. parasitica, and progeny selected for resistance to both pathogens will be intercrossed.


Assuntos
Ascomicetos , Cruzamento , Resistência à Doença , Fagaceae , Phytophthora , China , Resistência à Doença/genética , Fagaceae/microbiologia , Fagaceae/parasitologia , Phytophthora/fisiologia , Plântula , Árvores/microbiologia , Árvores/parasitologia , Estados Unidos
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA