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Oomycetes cause devastating diseases on a wide variety of plant species leading to yield losses in agriculture and forestry, and damage to natural ecosystems. Their lifestyles range from necrotrophic with wide host ranges to biotrophic and highly specialized on one or a few hosts. They share a preference for humid environments. They grow as mycelium and produce sporangia and zoospores for dispersal. Pythium is notorious for causing seedling damping-off and seed and root rot. Phytophthora species cause foliar blights and stem and root rot. Well known are the Irish potato famine pathogen Phytophthora infestans and the “sudden oak death” pathogen Phytophthora ramorum but many other Phytophthora species are just as harmful. Similarly, the hundreds of obligate downy mildews that cause primarily foliar blights are extremely damaging. The grape downy mildew epidemics in Europe in the 19th century is just one example of the devastating power of these pathogens.

Foot rot disease caused by Phytophthora capsici is one of the most destructive diseases of black pepper in Vietnam and worldwide. However, other oomycete species such as P. tropicalis and Pythium deliense reported as serious threats to black pepper in India have also been recorded on this plant. The population of oomycetes occurring in black pepper plantations in Vietnam and their pathogenicity have not been investigated in the last decade. To this end, two hundred fifteen oomycete isolates were collected from the root rots and rhizospheric soil of black pepper in the Central Highlands and the Southeast region of Vietnam. Of these, 23 isolates were representatively chosen based on their origin and morphology for DNA sequence analysis of the internal transcribed spacer region, then 11 isolates were further selected for the translation elongation factor 1-alpha and the beta-tubulin gene analyses. Morphology and molecular analyses indicated that P. capsici, P. cinnamomi, P. heveae, P. nicotianae, P. parvispora, P. tropicalis, Phytopythium vexans, and a new species candidate Phytopythium sp. were identified among oomycete isolates. Of these, P. capsici and P. tropicalis could be the prevalent species in black pepper plantations in studied areas. The inoculation tests demonstrated that P. capsici, P. nicotianae and P. tropicalis were pathogenic on both leaves and roots of black pepper. Phytopythium vexans was pathogenic on root only. Meanwhile, P. cinnamomi, P. heveae, P. parvispora and Phytopythium sp. were non-pathogenic.

Ridomil Gold SL (45.3% a.i. mefenoxam) is a widely used chemical fungicide for the control of oomycetes. However, its impact on fungal communities remains unexplored. Therefore, the goal of this study was to examine the effects of mefenoxam on the temporal dynamics of fungal taxonomic and functional diversities during carrot cultivation under four treatment groups: mefenoxam application with and without Pythium inoculation, and untreated control groups with and without Pythium inoculation. Our in vitro sensitivity assay showed that the maximum recommended concentration of mefenoxam, 0.24 ppm, did not suppress the mycelial growth of P. irregulare. At 100 ppm, mycelial growth was only reduced by 11.4%, indicating that the isolate was resistant to mefenoxam. MiSeq sequencing data revealed transient taxonomic variations among treatments 2 weeks post-treatment. Mortierella dominated the fungal community in the mefenoxam-Pythium combination treatment, as confirmed through PCR using our newly designed Mortierella-specific primers. Conversely, mefenoxam-Pythium combination had adverse effects on Penicillium, Trichoderma, and Fusarium, and decrease the overall alpha diversity. However, these compositional changes gradually reverted to those observed in the control by the 12th week. The predicted ecological functions of fungal communities in all Pythium and mefenoxam treatments shifted, leading to a decrease in symbiotrophs and plant pathogen functional groups. Moreover, the community-level physiological profiling approach, utilizing 96-well Biolog FF microplates, showed discernible variations in the utilization of 95 diverse carbon sources among the treatments. Notably, arbutin, L-arabinose, Tween 80, and succinamic acid demonstrated a strong positive association with Mortierella. Our findings demonstrate that a single application of mefenoxam at its recommended rate triggers substantial taxonomic and functional shifts in the soil fungal community. Considering this

Custard apple (Annona cherimola Mill.), originally from the Andean region of Peru and Ecuador, faces a serious threat from root rot, a disease that significantly reduces its yield. In 2015, root damage caused by Dactylonectria macrodidyma was reported in Chile, while Pythium splendens was identified as the root rot culprit in the Annona genus in Australia and Florida. This study aimed to identify the causal agent of custard apple root rot in Peru using PCR. In 2014, twelve ‘Cumbe’ custard apple plants from commercial fields in Ancash and Lima, Peru, displaying symptoms like yellowing leaves and dieback, were examined. The molecular identification was performed through specific rDNA regions (ITS and Cox II) amplification using primers ITS6/ITS4 and FM66/FM58 and revealed the presence of Globisporangium splendens (previously Pythium splendens), which had not previously been recorded as causing this disease in cherimoyas in Peru. Pathogenicity tests confirmed that ‘Cumbe’ custard apple seedlings exhibited consistent symptoms two to three weeks after inoculation, with G. splendens re-isolated from the infected roots. Notably, there were no prior records in Peru of fungal agents causing root rot or quantifying damage in custard apple, marking this as the first report of G. splendens causing the disease in Peru. This research sheds light on a previously unreported threat to custard apple cultivation in the region., La chirimoya (Annona cherimola Mill.) es originaria de la región andina del Perú y Ecuador, donde crece a altitudes de 1500 a 2200 m.s.n.m. El cultivo de esta fruta afronta un grave desafío, la pudrición de raíz, una enfermedad que puede tener un impacto devastador en su rendimiento. En el año 2015 se registraron casos en Chile en los que la chirimoya sufrió daños en sus raíces debido a la presencia de Dactylonectria macrodidyma. Situaciones similares se han reportado en Australia y Florida, donde el género Annona se vio afectado por la pudrición de las raíces causada por Pythium splendens. Ante esta problemática, se planteó como objetivo identificar al agente causal de la pudrición radicular de la chirimoya utilizando técnicas de PCR (Reacción en Cadena de la Polimerasa). En el año 2014 se recolectaron doce plantas de chirimoya del cultivar ‘Cumbe’ en Ancash, Perú, las cuales mostraron síntomas de pudrición de raíces y deterioro general. La identificación se realizó mediante amplificación de regiones específicas de ADNr (ITS y Cox II) utilizando los cebadores ITS6/ITS4 y FM66/FM58 y reveló la presencia de Globisporangium splendens (anteriormente Pythium splendens), que no se había registrado previamente como causante de esta enfermedad en chirimoyas en Perú. Además, se llevaron a cabo pruebas de patogenicidad en plantones de chirimoya ‘Cumbe’, los cuales mostraron síntomas consistentes con la enfermedad en condiciones de campo. G. splendens se volvió a aislar de las raíces inoculadas, confirmando su papel como agente causal. Este estudio representa el primer informe de G. splendens como agente causante de la pudrición de raíz en chirimoya en Perú y resalta la importancia de identificar y comprender las enfermedades que afectan a este cultivo.

The purpose of this research was to collect efficacy data on biological, biochemical, and chemical fungicide seed treatments on hemp (Cannabis sativa L.) to mitigate damping-off and enhance field stand establishment. Seed treatments were evaluated in fields in New York (NY), North Dakota (ND), and Virginia (VA) and at two planting dates in each state in 2020. A single seed lot of a dual-purpose (fiber + grain) cultivar (‘Anka’) was treated using a laboratory-scale rotary pan coater. Five biological, two biochemical, and four chemical seed treatments were tested. A laboratory germination test revealed that seed treatments did not exhibit phytotoxicity when compared to the non-treated control. A laboratory bioassay with naturally infested soil was used to assess the preliminary activity of seed treatments for protection against damping-off. The biochemical seed treatment Ultim® (active ingredient; organic copper) performed as well as the chemical treatments Apron XL® + Maxim® 4FS and Mertect® 340F in preventing damping-off whereas the biological treatments did not differ from the non-treated control in terms of disease incidence. In all field tests, biological seed treatments did not improve plant stands compared to the non-treated control. Biochemical seed treatments Prudent 44® with Nutrol® (active ingredient; phosphite) and Ultim®, along with chemical seed treatments, had acceptable efficacy and improved stand establishment compared to the non-treated control across field locations. Based on efficacy results from laboratory and field trials, the copper seed treatment has potential for both conventional and organic hemp production.

In this study, four recombinant inbred line (RIL) soybean populations were screened for their response to infection by Pythium sylvaticum, Pythium irregulare, Pythium oopapillum, and Pythium torulosum. The parents, PI 424237A, PI 424237B, PI 408097, and PI 408029, had higher levels of resistance to these species in a preliminary screening and were crossed with “Williams,” a susceptible cultivar. A modified seed rot assay was used to evaluate RIL populations for their response to specific Pythium species selected for a particular population based on preliminary screenings. Over 2500 single-nucleotide polymorphism (SNP) markers were used to construct chromosomal maps to identify regions associated with resistance to Pythium species. Several minor and large effect quantitative disease resistance loci (QDRL) were identified including one large effect QDRL on chromosome 8 in the population of PI 408097 × Williams. It was identified by two different disease reaction traits in P. sylvaticum, P. irregulare, and P. torulosum. Another large effect QDRL was identified on chromosome 6 in the population of PI 408029 × Williams, and conferred resistance to P. sylvaticum and P. irregulare. These large effect QDRL will contribute toward the development of improved soybean cultivars with higher levels of resistance to these common soil-borne pathogens.

application/pdf, Microorganisms. 2021, 9 (9), P.1912(1-13)

Pythiosis is characterized most commonly by ulcerative dermatitis, mainly in the limbs of sheep and occasionally of goats. In sheep, Pythium insidiosum is also responsible for necrotizing rhinitis characterized by marked enlargement and deformity of the nasal region, severe respiratory difficulty, and bloody nasal discharge. A third form of pythiosis in sheep affects the digestive tract, involving ulceration of the esophagus, forestomachs, and abomasum. Pythiosis in sheep and goats has been reported only in Brazil where it occurs mainly in the semiarid region of the country, when animals congregate and stay for longer periods of time within or around water reservoirs. However, it has been reported as well in areas of humid environments, such as the Pantanal of Mato Grosso and in the Brazilian Cerrado. The diagnosis of the different presentations of pythiosis is based on gross and microscopic findings, coupled with detection of the agent by immunohistochemical, molecular, and/or culture-based methods.

Pythium diseases are common in the greenhouse production of tobacco transplants and can cause up to 70% seedling loss in hydroponic (float-bed) greenhouses. However, the symptoms and consequences of Pythium diseases are often variable among these greenhouses. A tobacco transplant greenhouse survey was conducted in 2017 in order to investigate the sources of this variability, especially the composition and distribution of Pythium communities within greenhouses. The survey revealed twelve Pythium species. Approximately 80% of the surveyed greenhouses harbored Pythium in at least one of four sites within the greenhouse, including the center walkway, weeds, but especially bay water and tobacco seedlings. Pythium dissotocum, followed by P. myriotylum, were the most common species. Pythium myriotylum, P. coloratum, and P. dissotocum were aggressive pathogens that suppressed seed germination and caused root rot, stunting, foliar chlorosis, and death of tobacco seedlings. Pythium aristosporum, P. porphyrae, P. torulosum, P. inflatum, P. irregulare, P. catenulatum, and a different isolate of P. dissotocum, were weak pathogens, causing root symptoms without affecting the upper part of tobacco seedlings. Pythium adhaerens, P. attrantheridium, and P. pectinolyticum did not affect tobacco seeds or seedlings. The consequences of Pythium infection were more likely to be severe when they occurred during seed germination than at seedling emergence, or after plant stem elongation when seedling roots had started to grow into underlying nutrient solutions, depending on the species of Pythium. High and low variation was observed among isolates of P. dissotocum and P. myriotylum, respectively. Pythium myriotylum co-existed with multiple other Pythium or oomycete species in the same environments within tobacco greenhouses, and significant in vitro and/or in vivo interactions between P. myriotylum and some naturally co-existing species were revealed. Pythium porphyrae may have the potentia

Anaerobic soil disinfestation (ASD) is a promising alternative to chemical fumigation to control soil-borne plant pathogens and weeds. This research focused on evaluating several locally available carbon sources for ASD on weed control, evaluating the performance of brewers' spent grain (a promising carbon source) under field conditions, and evaluating whether yeast addition enhanced the effectiveness of ASD treatments. A series of greenhouse trials were conducted at the Southern Piedmont AREC (Agricultural Research and Extension Center). The greenhouse trials were conducted in PVC tubes, 20 cm tall and 15 cm in diameter. The first set of trials evaluated ASD conducted over 21-day periods of ASD using locally available carbon sources. The carbon sources included brewer`s spent grain, buckwheat (Fagopyrum esculentum), cowpea (Vigna unguiculata), paper mulch, peanut (Arachis hypogaea) shells, rice bran, sorghum-sudangrass (Sorghum drummondii), and waste coffee grounds applied at 4 mg of C/g of soil. The targeted weed species included common chickweed (Stellaria media (L.) Vill.), redroot pigweed (Amaranthus retroflexus L.), white clover (Trifolium repens L.), and yellow nutsedge (Cyperus esculentus L.). All ASD treatments significantly reduced weed viability compared to the non-treated control. The yeast amendments enhanced weed control over ASD without yeast. The second set of greenhouse trials was focused on ASD using brewer`s spent grain, and on evaluating ASD at the half and one-third carbon dose rates. The target pests were the same weed species in the first set of trials, and Pythium irregulare was added as an additional target pest. This set of trials indicated yeast enhanced addition the effect of BSG in ASD on both weeds and P. irregulare, indicating the potential to reduce carbon input necessary for effective ASD. A follow-up, two seasons, open-field trial conducted over two growing seasons at the Hampton Roads AREC focused on understanding the effects of AS

In this study, four recombinant inbred line (RIL) soybean populations were screened for their response to infection by Pythium sylvaticum, Pythium irregulare, Pythium oopapillum, and Pythium torulosum. The parents, PI 424237A, PI 424237B, PI 408097, and PI 408029, had higher levels of resistance to these species in a preliminary screening and were crossed with “Williams,” a susceptible cultivar. A modified seed rot assay was used to evaluate RIL populations for their response to specific Pythium species selected for a particular population based on preliminary screenings. Over 2500 single-nucleotide polymorphism (SNP) markers were used to construct chromosomal maps to identify regions associated with resistance to Pythium species. Several minor and large effect quantitative disease resistance loci (QDRL) were identified including one large effect QDRL on chromosome 8 in the population of PI 408097 × Williams. It was identified by two different disease reaction traits in P. sylvaticum, P. irregulare, and P. torulosum. Another large effect QDRL was identified on chromosome 6 in the population of PI 408029 × Williams, and conferred resistance to P. sylvaticum and P. irregulare. These large effect QDRL will contribute toward the development of improved soybean cultivars with higher levels of resistance to these common soil-borne pathogens.

[Background] Black‐foot and Petri diseases are the main fungal diseases associated with young grapevine decline. Two field experiments were established to evaluate the preventive effect of two potential biocontrol agents (BCAs), that is Streptomyces sp. E1 + R4 and Pythium oligandrum Po37, and three BCA‐commercial products containing Trichoderma atroviride SC1, Trichoderma koningii TK7 and Pseudomonas fluorescens + Bacillus atrophaeus on fungal infection in grafted plants and plant growth parameters. [Results] The effectiveness of some BCA in reducing the incidence and severity of both diseases was dependent on the plant part analyzed and the plant age. No single BCA application was able to control both diseases. Streptomyces sp. E1 + R4 were able to reduce significantly the infection of the most prevalent black‐foot disease fungi while P. oligandrum Po37 and Trichoderma spp. were able to reduce significantly Phaeomoniella chlamydospora and Phaeoacremonium minimum (Petri disease) infection. BCA treatments had no effect on the shoot weight, and root weight was significantly lower in all BCA treatments with respect to the control. [Conclusions] The combination of the disease‐suppressive activity of two or more beneficial microbes in a biocontrol preparation is required to prevent infection by black‐foot and Petri disease fungi in vineyards.

The processing tomato industry in Victoria, Australia, has experienced a yield decline over the last decade, resulting in losses estimated at 10% per annum. The decline was attributed to the necrosis of lateral and feeder rootlets and the collar region resulting in plant stunting and a reduction in fruit production. Therefore, the hypothesis underlying this study was that the decline is caused by the cumulative effects of damage by a complex of soil-borne root and collar rot pathogens. Surveys of processing tomato crops were undertaken over three consecutive growing seasons between 2016 and 2019 to investigate the pathogens, symptoms and diseases associated with yield decline. Soil-borne fungal and oomycete pathogens were the focus but bacterial pathogens, viruses, nematodes and phytoplasmas were also noted. Systematic isolation from diseased roots and the collar region of plants putatively infected by fungal and oomycete pathogens was undertaken. Identification of isolates was based on cultural morphology, ITS sequencing and in some cases commercial qPCR testing. Fusarium oxysporum and Pythium spp. were the most abundant putative pathogens associated with plants exhibiting poor growth. Other putative pathogenic fungi and oomycetes which were less commonly encountered included Alternaria spp., Colletotrichum coccodes, Fusarium solani, Phytophthora nictotianae, Phytophthora cajani, Plectosphaerella spp., Rhizoctonia solani, Sclerotinia minor and S. sclerotiorum. A novel Fusarium collar and root rot disease of processing tomatoes was discovered during the surveys. The disease was characterised by chocolate-brown streaking in the internal collar and tap root tissue, as well as lateral root rot of stunted tomato plants. Morphological characterisation and multi-loci phylogenetics (ITS, ef1a and Pgx4), were used to identify the causal pathogen as Fusarium oxysporum. The disease was initially thought to resemble Fusarium Crown and Root Rot (FCRR) caused by Fusarium oxyspor

Landbouwbodems verschillen sterk in ziektewering, waardoor bodempathogenen niet altijd evenveel schade veroorzaken bij de teelt van een vatbaar gewas. Je zou een parallel met COVID-19 kunnen trekken: niet alle mensen die geïnfecteerd raken worden hier even ziek van. Maar, wat maakt een bodem meer of minder ziektewerend? Zijn er ziektewerende percelen binnen het bedrijvennetwerk? En natuurlijk ook: wat kan een boer doen om het ziektewerend vermogen van zijn grond te verhogen? We delen graag de eerste onderzoeksresultaten die we hebben verkregen met behulp van de gronden van het bedrijvennetwerk.

Tien zeer uiteenlopende organische producten zijn onderzocht op hun vermogen om ziektewering van een bodem te verhogen. In potproeven werd aangetoond dat een aantal van deze producten de ziektewering van zandgrond tegen Rhizoctonia solani en Meloidogyne hapla konden stimuleren. Vervolgens zijn de organische producten onder praktijkomstandigheden in de teelt van aardappel en suikerbiet getoetst. Bij een dosering van de producten conform de bemestingsadviezen waren de opbrengsten van de gewassen vergelijkbaar met een kunstmest bemeste controle en werd afhankelijk van de samenstelling van de producten tot 160, 50 en 200 kg/ha aan N, P en K bemesting bespaard (bij aardappel). De producten hadden onder veldomstandigheden een geringe invloed op de ziektewerende eigenschappen van de grond: Pythium ziektewering was in enkele gevallen verhoogd, maar er was geen meetbare verhoging van ziektewering tegen Rhizoctonia en Meloidogyne. Daarnaast zijn diverse (biologische) bodemparameters bepaald.

Gastrointestinal (GI) pythiosis is a severe and often fatal disease in dogs that traditionally has been poorly responsive to medical treatment. Although aggressive surgical resection with wide margins is the most consistently effective treatment, lesion location and extent often preclude complete resection. Recently, it has been suggested that the addition of anti-inflammatory doses of corticosteroids may improve outcome in dogs with nonresectable GI pythiosis. This report describes 3 dogs with colonic pythiosis in which complete resolution of clinical signs, regression of colonic masses, and progressive decreases in serological titers were observed after treatment with itraconazole, terbinafine, and corticosteroids. This treatment protocol represents a promising treatment for dogs with GI pythiosis in which surgical intervention is not feasible.

Gastrointestinal (GI) pythiosis is a severe and often fatal disease in dogs that traditionally has been poorly responsive to medical treatment. Although aggressive surgical resection with wide margins is the most consistently effective treatment, lesion location and extent often preclude complete resection. Recently, it has been suggested that the addition of anti-inflammatory doses of corticosteroids may improve outcome in dogs with nonresectable GI pythiosis. This report describes 3 dogs with colonic pythiosis in which complete resolution of clinical signs, regression of colonic masses, and progressive decreases in serological titers were observed after treatment with itraconazole, terbinafine, and corticosteroids. This treatment protocol represents a promising treatment for dogs with GI pythiosis in which surgical intervention is not feasible.

Gastrointestinal (GI) pythiosis is a severe and often fatal disease in dogs that traditionally has been poorly responsive to medical treatment. Although aggressive surgical resection with wide margins is the most consistently effective treatment, lesion location and extent often preclude complete resection. Recently, it has been suggested that the addition of anti-inflammatory doses of corticosteroids may improve outcome in dogs with nonresectable GI pythiosis. This report describes 3 dogs with colonic pythiosis in which complete resolution of clinical signs, regression of colonic masses, and progressive decreases in serological titers were observed after treatment with itraconazole, terbinafine, and corticosteroids. This treatment protocol represents a promising treatment for dogs with GI pythiosis in which surgical intervention is not feasible.

El objetivo de esta investigación fue identificar las especies de Peronosporales presentes utilizando métodos moleculares. Se recuperaron muestras de las raíces secundarias y suelo de ocho campos correspondientes a las cuatro principales regiones productoras a lo largo de la costa peruana (Piura, Lambayeque, Lima e Ica). Los Peronosporales se aislaron en medios de cultivo PAR, PARH y V8. La identificación molecular se realizó por amplificación de 730 - 820 pb de la región del espaciador transcrito interno (ITS) y de 563 pb de la región del citocromo oxidasa II (Cox II) del ADNr, usando cebadores ITS6/ITS4 y FM66/FM58 respectivamente. Los fragmentos amplificados se secuenciaron utilizando la metodología de Sanger y la reconstrucción filogenética se realizó con análisis bayesiano, utilizando dos millones de generaciones. Los resultados formaron grupos con las secuencias de especies similares depositadas en el GenBank, incluyendo: Phytophthora nicotianae, Phytopythium cucurbitacearum y Pp. vexans (aislados de raíz y de suelo), Ph. parsiana y Pythium splendens (aislados de raíz), Py. aphanidermatum, Py. ultimun, Py. deliense, Pp. amazonianum (aislados de suelo); además, se identificó una especie afín con Pythium guangxiense (aislado del suelo). Por otra parte, se realizaron las pruebas de patogenicidad cumpliendo con los postulados de Koch para cada uno de los aislamientos obtenidos, resultando patogénicos Ph. nicotianae, Ph. parsiana y Pp. vexans.

El objetivo de esta investigación fue identificar las especies de Peronosporales presentes utilizando métodos moleculares. Se recuperaron muestras de las raíces secundarias y suelo de ocho campos correspondientes a las cuatro principales regiones productoras a lo largo de la costa peruana (Piura, Lambayeque, Lima e Ica). Los Peronosporales se aislaron en medios de cultivo PAR, PARH y V8. La identificación molecular se realizó por amplificación de 730 - 820 pb de la región del espaciador transcrito interno (ITS) y de 563 pb de la región del citocromo oxidasa II (Cox II) del ADNr, usando cebadores ITS6/ITS4 y FM66/FM58 respectivamente. Los fragmentos amplificados se secuenciaron utilizando la metodología de Sanger y la reconstrucción filogenética se realizó con análisis bayesiano, utilizando dos millones de generaciones. Los resultados formaron grupos con las secuencias de especies similares depositadas en el GenBank, incluyendo: Phytophthora nicotianae, Phytopythium cucurbitacearum y Pp. vexans (aislados de raíz y de suelo), Ph. parsiana y Pythium splendens (aislados de raíz), Py. aphanidermatum, Py. ultimun, Py. deliense, Pp. amazonianum (aislados de suelo); además, se identificó una especie afín con Pythium guangxiense (aislado del suelo). Por otra parte, se realizaron las pruebas de patogenicidad cumpliendo con los postulados de Koch para cada uno de los aislamientos obtenidos, resultando patogénicos Ph. nicotianae, Ph. parsiana y Pp. vexans.

In August and September 2014, different avocado orchards (Persea americana Mill. Var. Hass) were sampled in four municipalities (Tancítaro, Uruapan, San Juan Nuevo Parangaricutiro and Peribán) of the “Franja aguacatera” in Michoacan State, Mexico. Samples were collected from avocado trees showing symptoms of the “Tristeza del aguacate” disease. Strains of Pythium sp. were obtained consistently from symptomatic tissue isolated in the selective medium V8®-Agar-PARPH. Morphological identification was made through taxonomic keys, and molecular identification was obtained by sequencing Internal Transcribed Spacer (ITS) gene. Koch's postulates were corroborated by pathogenicity tests carried out on P. americana seedlings with six true leaves, identifying the strain of P. sp. amazonianum as the causal agent of the “Tristeza del aguacate” disease. This is the first report that associates the “Tristeza del aguacate” with P. sp. amazonianum in Michoacan, Mexico., Resumen En los meses de agosto y septiembre del 2014 se muestrearon diferentes huertas de aguacate (Persea americana Mill. Var. Hass) en cuatro municipios (Tancítaro, Uruapan, San Juan Nuevo Parangaricutiro y Peribán) de la “Franja aguacatera” en el estado de Michoacán, México. Las muestras se recolectaron de árboles de aguacate que mostraban síntomas de la enfermedad “Tristeza del aguacate”. Se obtuvieron cepas de Pythium sp. consistentemente de tejido sintomático, aisladas en medio selectivo V8®-Agar-PARPH. La identificación morfológica se realizó mediante claves taxonómicas y la identificación molecular se obtuvo a través de ITS-PCR. Los postulados de Koch se corroboraron mediante pruebas de patogenicidad llevadas a cabo en plántulas de P. americana con seis hojas verdaderas, identificando la cepa de P. sp. amazonianum como agente causal de la “Tristeza del aguacate”. Este es el primer reporte que asocia la “Tristeza del aguacate” con P. sp. amazonianum en Michoacán, México.

El objetivo de esta investigación fue identificar las especies de Peronosporales presentes utilizando métodos moleculares. Se recuperaron muestras de las raíces secundarias y suelo de ocho campos correspondientes a las cuatro principales regiones productoras a lo largo de la costa peruana (Piura, Lambayeque, Lima e Ica). Los Peronosporales se aislaron en medios de cultivo PAR, PARH y V8. La identificación molecular se realizó por amplificación de 730 - 820 pb de la región del espaciador transcrito interno (ITS) y de 563 pb de la región del citocromo oxidasa II (Cox II) del ADNr, usando cebadores ITS6/ITS4 y FM66/FM58 respectivamente. Los fragmentos amplificados se secuenciaron utilizando la metodología de Sanger y la reconstrucción filogenética se realizó con análisis bayesiano, utilizando dos millones de generaciones. Los resultados formaron grupos con las secuencias de especies similares depositadas en el GenBank, incluyendo: Phytophthora nicotianae, Phytopythium cucurbitacearum y Pp. vexans (aislados de raíz y de suelo), Ph. parsiana y Pythium splendens (aislados de raíz), Py. aphanidermatum, Py. ultimun, Py. deliense, Pp. amazonianum (aislados de suelo); además, se identificó una especie afín con Pythium guangxiense (aislado del suelo). Por otra parte, se realizaron las pruebas de patogenicidad cumpliendo con los postulados de Koch para cada uno de los aislamientos obtenidos, resultando patogénicos Ph. nicotianae, Ph. parsiana y Pp. vexans.

In August and September 2014, different avocado orchards (Persea americana Mill. Var. Hass) were sampled in four municipalities (Tancítaro, Uruapan, San Juan Nuevo Parangaricutiro and Peribán) of the “Franja aguacatera” in Michoacan State, Mexico. Samples were collected from avocado trees showing symptoms of the “Tristeza del aguacate” disease. Strains of Pythium sp. were obtained consistently from symptomatic tissue isolated in the selective medium V8®-Agar-PARPH. Morphological identification was made through taxonomic keys, and molecular identification was obtained by sequencing Internal Transcribed Spacer (ITS) gene. Koch's postulates were corroborated by pathogenicity tests carried out on P. americana seedlings with six true leaves, identifying the strain of P. sp. amazonianum as the causal agent of the “Tristeza del aguacate” disease. This is the first report that associates the “Tristeza del aguacate” with P. sp. amazonianum in Michoacan, Mexico., Resumen En los meses de agosto y septiembre del 2014 se muestrearon diferentes huertas de aguacate (Persea americana Mill. Var. Hass) en cuatro municipios (Tancítaro, Uruapan, San Juan Nuevo Parangaricutiro y Peribán) de la “Franja aguacatera” en el estado de Michoacán, México. Las muestras se recolectaron de árboles de aguacate que mostraban síntomas de la enfermedad “Tristeza del aguacate”. Se obtuvieron cepas de Pythium sp. consistentemente de tejido sintomático, aisladas en medio selectivo V8®-Agar-PARPH. La identificación morfológica se realizó mediante claves taxonómicas y la identificación molecular se obtuvo a través de ITS-PCR. Los postulados de Koch se corroboraron mediante pruebas de patogenicidad llevadas a cabo en plántulas de P. americana con seis hojas verdaderas, identificando la cepa de P. sp. amazonianum como agente causal de la “Tristeza del aguacate”. Este es el primer reporte que asocia la “Tristeza del aguacate” con P. sp. amazonianum en Michoacán, México.

El objetivo de esta investigación fue identificar las especies de Peronosporales presentes utilizando métodos moleculares. Se recuperaron muestras de las raíces secundarias y suelo de ocho campos correspondientes a las cuatro principales regiones productoras a lo largo de la costa peruana (Piura, Lambayeque, Lima e Ica). Los Peronosporales se aislaron en medios de cultivo PAR, PARH y V8. La identificación molecular se realizó por amplificación de 730 - 820 pb de la región del espaciador transcrito interno (ITS) y de 563 pb de la región del citocromo oxidasa II (Cox II) del ADNr, usando cebadores ITS6/ITS4 y FM66/FM58 respectivamente. Los fragmentos amplificados se secuenciaron utilizando la metodología de Sanger y la reconstrucción filogenética se realizó con análisis bayesiano, utilizando dos millones de generaciones. Los resultados formaron grupos con las secuencias de especies similares depositadas en el GenBank, incluyendo: Phytophthora nicotianae, Phytopythium cucurbitacearum y Pp. vexans (aislados de raíz y de suelo), Ph. parsiana y Pythium splendens (aislados de raíz), Py. aphanidermatum, Py. ultimun, Py. deliense, Pp. amazonianum (aislados de suelo); además, se identificó una especie afín con Pythium guangxiense (aislado del suelo). Por otra parte, se realizaron las pruebas de patogenicidad cumpliendo con los postulados de Koch para cada uno de los aislamientos obtenidos, resultando patogénicos Ph. nicotianae, Ph. parsiana y Pp. vexans.

El objetivo de esta investigación fue identificar las especies de Peronosporales presentes utilizando métodos moleculares. Se recuperaron muestras de las raíces secundarias y suelo de ocho campos correspondientes a las cuatro principales regiones productoras a lo largo de la costa peruana (Piura, Lambayeque, Lima e Ica). Los Peronosporales se aislaron en medios de cultivo PAR, PARH y V8. La identificación molecular se realizó por amplificación de 730 - 820 pb de la región del espaciador transcrito interno (ITS) y de 563 pb de la región del citocromo oxidasa II (Cox II) del ADNr, usando cebadores ITS6/ITS4 y FM66/FM58 respectivamente. Los fragmentos amplificados se secuenciaron utilizando la metodología de Sanger y la reconstrucción filogenética se realizó con análisis bayesiano, utilizando dos millones de generaciones. Los resultados formaron grupos con las secuencias de especies similares depositadas en el GenBank, incluyendo: Phytophthora nicotianae, Phytopythium cucurbitacearum y Pp. vexans (aislados de raíz y de suelo), Ph. parsiana y Pythium splendens (aislados de raíz), Py. aphanidermatum, Py. ultimun, Py. deliense, Pp. amazonianum (aislados de suelo); además, se identificó una especie afín con Pythium guangxiense (aislado del suelo). Por otra parte, se realizaron las pruebas de patogenicidad cumpliendo con los postulados de Koch para cada uno de los aislamientos obtenidos, resultando patogénicos Ph. nicotianae, Ph. parsiana y Pp. vexans.

Necrosis and ethylene-inducing peptide 1-like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

BackgroundHow pathogen genomes evolve to support distinct lifestyles is not well-understood. The oomycete Phytophthora infestans, the potato blight agent, is a largely biotrophic pathogen that feeds from living host cells, which become necrotic only late in infection. The related oomycete Pythium ultimum grows saprophytically in soil and as a necrotroph in plants, causing massive tissue destruction. To learn what distinguishes their lifestyles, we compared their gene contents and expression patterns in media and a shared host, potato tuber.ResultsGenes related to pathogenesis varied in temporal expression pattern, mRNA level, and family size between the species. A family's aggregate expression during infection was not proportional to size due to transcriptional remodeling and pseudogenization. Ph. infestans had more stage-specific genes, while Py. ultimum tended towards more constitutive expression. Ph. infestans expressed more genes encoding secreted cell wall-degrading enzymes, but other categories such as secreted proteases and ABC transporters had higher transcript levels in Py. ultimum. Species-specific genes were identified including new Pythium genes, perforins, which may disrupt plant membranes. Genome-wide ortholog analyses identified substantial diversified expression, which correlated with sequence divergence. Pseudogenization was associated with gene family expansion, especially in gene clusters.ConclusionThis first large-scale analysis of transcriptional divergence within oomycetes revealed major shifts in genome composition and expression, including subfunctionalization within gene families. Biotrophy and necrotrophy seem determined by species-specific genes and the varied expression of shared pathogenicity factors, which may be useful targets for crop protection.

[ES] La presente investigación se realizó en el Laboratorio de Patología Vegetal de la Escuela Técnica Superior de Ingeniería Agronómica y del Medio Natural en la Universitat Politècnica de Valencia. Se conoce bien que diversas especies de Pythium causan ‘damping off’ durante las primeras semanas de vida de las plantas. Sin embargo, la información acerca de la interacción de Pythium spp. con las raíces de árboles es escasa. El objetivo de este trabajo fue identificar aislados del género Pythium asociados a la rizosfera de árboles con síntomas de decaimiento, pertenecientes a distintas especies. También se determinó su tasa de crecimiento a distintas temperaturas. La identificación molecular se basó en las secuencias de la región ITS (Internal Transcribed Spacer) del ADN ribosomal y la subunidad II de la citocromo c oxidasa (COXII) del ADN mitocondrial. Estas secuencias se amplificaron mediante la técnica PCR (Reacción en Cadena de la Polimerasa) usando parejas de cebadores universales. Los resultados identificaron 14 especies de Pythium en la colección de aislados analizada. Para la caracterización morfológica, se indujo la formación de estructuras de reproducción, incubando discos de cultivos de Pythium en agua destilada y hojas de Lolium perenne. En aquellos casos en que la identificación molecular del aislado no fue definitiva, la observación al microscopio óptico de sus estructuras de reproducción permitió reconocer su especie. Para determinar la tasa de crecimiento de Pythium spp. y las temperaturas mínima y máxima de cada especie, se cultivó una selección de aislados en medio V8 a distintas temperaturas (5 , 10, 15, 20, 25, 30, 35 y 40 °C), realizando dos repeticiones con tres unidades experimentales cada una., [EN] The present research was carried out in the Laboratory of Plant Pathology at the Universitàt Politécnica de Valencia. Several species of Pythium are known to cause damping off during the first weeks of plant life. However, information about the interaction of Pythium spp. with the roots of trees is scarce. The objective of this work was to identify isolates of the genus Pythium associated to the rhizosphere of trees with symptoms of decay, belonging to different species. Their growth rate was also determined at different temperatures. Molecular identification was based on the ITS (Internal Transcribed Spacer) region of ribosomal DNA and the cytochrome c oxidase (COX II) subunit II of mitochondrial DNA. These sequences were amplified by the PCR (Polymerase Chain Reaction) technique using pairs of universal primers. The results identified 14 species ok Pythium in the collection of isolates analyzed. The formation of reproduction structures was induced for the morphological characterization, incubating plugs of Pythium cultures in distilled water and leaves of Lolium perenne. In those cases, in which the molecular identification of the isolate was not definitive, the observation under the optical microscope of its reproduction structures allowed to recognize the species. To determine the growth rate of Pythium spp. and minimum and maximum temperatures of each species, a selection of isolates werw grown on V8 medium at different temperatures (5, 10, 15, 20, 25, 30, 35 an 40 °C), perfoming two replicates with three experimental units each one.

[ES] La presente investigación se realizó en el Laboratorio de Patología Vegetal de la Escuela Técnica Superior de Ingeniería Agronómica y del Medio Natural en la Universitat Politècnica de Valencia. Se conoce bien que diversas especies de Pythium causan ‘damping off’ durante las primeras semanas de vida de las plantas. Sin embargo, la información acerca de la interacción de Pythium spp. con las raíces de árboles es escasa. El objetivo de este trabajo fue identificar aislados del género Pythium asociados a la rizosfera de árboles con síntomas de decaimiento, pertenecientes a distintas especies. También se determinó su tasa de crecimiento a distintas temperaturas. La identificación molecular se basó en las secuencias de la región ITS (Internal Transcribed Spacer) del ADN ribosomal y la subunidad II de la citocromo c oxidasa (COXII) del ADN mitocondrial. Estas secuencias se amplificaron mediante la técnica PCR (Reacción en Cadena de la Polimerasa) usando parejas de cebadores universales. Los resultados identificaron 14 especies de Pythium en la colección de aislados analizada. Para la caracterización morfológica, se indujo la formación de estructuras de reproducción, incubando discos de cultivos de Pythium en agua destilada y hojas de Lolium perenne. En aquellos casos en que la identificación molecular del aislado no fue definitiva, la observación al microscopio óptico de sus estructuras de reproducción permitió reconocer su especie. Para determinar la tasa de crecimiento de Pythium spp. y las temperaturas mínima y máxima de cada especie, se cultivó una selección de aislados en medio V8 a distintas temperaturas (5 , 10, 15, 20, 25, 30, 35 y 40 °C), realizando dos repeticiones con tres unidades experimentales cada una., [EN] The present research was carried out in the Laboratory of Plant Pathology at the Universitàt Politécnica de Valencia. Several species of Pythium are known to cause damping off during the first weeks of plant life. However, information about the interaction of Pythium spp. with the roots of trees is scarce. The objective of this work was to identify isolates of the genus Pythium associated to the rhizosphere of trees with symptoms of decay, belonging to different species. Their growth rate was also determined at different temperatures. Molecular identification was based on the ITS (Internal Transcribed Spacer) region of ribosomal DNA and the cytochrome c oxidase (COX II) subunit II of mitochondrial DNA. These sequences were amplified by the PCR (Polymerase Chain Reaction) technique using pairs of universal primers. The results identified 14 species ok Pythium in the collection of isolates analyzed. The formation of reproduction structures was induced for the morphological characterization, incubating plugs of Pythium cultures in distilled water and leaves of Lolium perenne. In those cases, in which the molecular identification of the isolate was not definitive, the observation under the optical microscope of its reproduction structures allowed to recognize the species. To determine the growth rate of Pythium spp. and minimum and maximum temperatures of each species, a selection of isolates werw grown on V8 medium at different temperatures (5, 10, 15, 20, 25, 30, 35 an 40 °C), perfoming two replicates with three experimental units each one.

[ES] La presente investigación se realizó en el Laboratorio de Patología Vegetal de la Escuela Técnica Superior de Ingeniería Agronómica y del Medio Natural en la Universitat Politècnica de Valencia. Se conoce bien que diversas especies de Pythium causan ‘damping off’ durante las primeras semanas de vida de las plantas. Sin embargo, la información acerca de la interacción de Pythium spp. con las raíces de árboles es escasa. El objetivo de este trabajo fue identificar aislados del género Pythium asociados a la rizosfera de árboles con síntomas de decaimiento, pertenecientes a distintas especies. También se determinó su tasa de crecimiento a distintas temperaturas. La identificación molecular se basó en las secuencias de la región ITS (Internal Transcribed Spacer) del ADN ribosomal y la subunidad II de la citocromo c oxidasa (COXII) del ADN mitocondrial. Estas secuencias se amplificaron mediante la técnica PCR (Reacción en Cadena de la Polimerasa) usando parejas de cebadores universales. Los resultados identificaron 14 especies de Pythium en la colección de aislados analizada. Para la caracterización morfológica, se indujo la formación de estructuras de reproducción, incubando discos de cultivos de Pythium en agua destilada y hojas de Lolium perenne. En aquellos casos en que la identificación molecular del aislado no fue definitiva, la observación al microscopio óptico de sus estructuras de reproducción permitió reconocer su especie. Para determinar la tasa de crecimiento de Pythium spp. y las temperaturas mínima y máxima de cada especie, se cultivó una selección de aislados en medio V8 a distintas temperaturas (5 , 10, 15, 20, 25, 30, 35 y 40 °C), realizando dos repeticiones con tres unidades experimentales cada una., [EN] The present research was carried out in the Laboratory of Plant Pathology at the Universitàt Politécnica de Valencia. Several species of Pythium are known to cause damping off during the first weeks of plant life. However, information about the interaction of Pythium spp. with the roots of trees is scarce. The objective of this work was to identify isolates of the genus Pythium associated to the rhizosphere of trees with symptoms of decay, belonging to different species. Their growth rate was also determined at different temperatures. Molecular identification was based on the ITS (Internal Transcribed Spacer) region of ribosomal DNA and the cytochrome c oxidase (COX II) subunit II of mitochondrial DNA. These sequences were amplified by the PCR (Polymerase Chain Reaction) technique using pairs of universal primers. The results identified 14 species ok Pythium in the collection of isolates analyzed. The formation of reproduction structures was induced for the morphological characterization, incubating plugs of Pythium cultures in distilled water and leaves of Lolium perenne. In those cases, in which the molecular identification of the isolate was not definitive, the observation under the optical microscope of its reproduction structures allowed to recognize the species. To determine the growth rate of Pythium spp. and minimum and maximum temperatures of each species, a selection of isolates werw grown on V8 medium at different temperatures (5, 10, 15, 20, 25, 30, 35 an 40 °C), perfoming two replicates with three experimental units each one.

BackgroundHow pathogen genomes evolve to support distinct lifestyles is not well-understood. The oomycete Phytophthora infestans, the potato blight agent, is a largely biotrophic pathogen that feeds from living host cells, which become necrotic only late in infection. The related oomycete Pythium ultimum grows saprophytically in soil and as a necrotroph in plants, causing massive tissue destruction. To learn what distinguishes their lifestyles, we compared their gene contents and expression patterns in media and a shared host, potato tuber.ResultsGenes related to pathogenesis varied in temporal expression pattern, mRNA level, and family size between the species. A family's aggregate expression during infection was not proportional to size due to transcriptional remodeling and pseudogenization. Ph. infestans had more stage-specific genes, while Py. ultimum tended towards more constitutive expression. Ph. infestans expressed more genes encoding secreted cell wall-degrading enzymes, but other categories such as secreted proteases and ABC transporters had higher transcript levels in Py. ultimum. Species-specific genes were identified including new Pythium genes, perforins, which may disrupt plant membranes. Genome-wide ortholog analyses identified substantial diversified expression, which correlated with sequence divergence. Pseudogenization was associated with gene family expansion, especially in gene clusters.ConclusionThis first large-scale analysis of transcriptional divergence within oomycetes revealed major shifts in genome composition and expression, including subfunctionalization within gene families. Biotrophy and necrotrophy seem determined by species-specific genes and the varied expression of shared pathogenicity factors, which may be useful targets for crop protection.

Necrosis and ethylene-inducing peptide 1-like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

Recycling irrigation water can provide water during periods of drought for horticulture operations and can reduce nonpoint-source pollution, but water recycling increases production costs and can increase risk of disease infestation from waterborne pathogens such as Pythium and Phytophthora. This study of water recycling adoption by horticultural growers in Virginia, Maryland, and Pennsylvania finds that the potential for increased disease infestation would reduce growers’ probability of adopting water recycling. Widespread adoption of recycling irrigation water would require government incentives or coercion or growers’ ability to pass cost increases on to customers.

La enseñanza del método científico se ve facilitada mediante prácticas experimentales sencillas pero rigurosas. Los postulados de Koch representan un avance histórico en el desarrollo del método científico. Éstos constituyen una guía o protocolo a seguir para comprobar empíricamente que un determinado microorganismo es el agente causal de una patología infecciosa en un hospedero susceptible. En el presente trabajo se demuestra que la patología de marchitamiento fúngico (damping-off ) en plántulas de lechuga constituye un modelo didácticoexperimental para la enseñanza y la puesta en acción de dichos postulados. Fue posible la utilización de materiales de bajo costo con una metodología sencilla, reproducible y libre de riesgos para la salud humana, facilitando su aplicabilidad en cualquier centro de enseñanza secundaria o terciaria., The teaching of the scientific method is facilitated by simple but rigorous experimental practices. Koch's postulates represent a historical breakthrough in the development of the scientific method. These postulates are a guide or protocol to follow in order to find empirically that a particular microorganism is the causative agent of an infectious disease in a susceptible organism. The present work shows that the pathology of lettuce seedlings damping-off is an appropriate experimental model to teach these principles. It was possible to use low-cost materials with a simple, reproducible and free risk to human health methodology, with easy applicability in any high school or university classroom.

La enseñanza del método científico se ve facilitada mediante prácticas experimentales sencillas pero rigurosas. Los postulados de Koch representan un avance histórico en el desarrollo del método científico. Éstos constituyen una guía o protocolo a seguir para comprobar empíricamente que un determinado microorganismo es el agente causal de una patología infecciosa en un hospedero susceptible. En el presente trabajo se demuestra que la patología de marchitamiento fúngico (damping-off ) en plántulas de lechuga constituye un modelo didácticoexperimental para la enseñanza y la puesta en acción de dichos postulados. Fue posible la utilización de materiales de bajo costo con una metodología sencilla, reproducible y libre de riesgos para la salud humana, facilitando su aplicabilidad en cualquier centro de enseñanza secundaria o terciaria., The teaching of the scientific method is facilitated by simple but rigorous experimental practices. Koch's postulates represent a historical breakthrough in the development of the scientific method. These postulates are a guide or protocol to follow in order to find empirically that a particular microorganism is the causative agent of an infectious disease in a susceptible organism. The present work shows that the pathology of lettuce seedlings damping-off is an appropriate experimental model to teach these principles. It was possible to use low-cost materials with a simple, reproducible and free risk to human health methodology, with easy applicability in any high school or university classroom.

Recycling irrigation water can provide water during periods of drought for horticulture operations and can reduce nonpoint-source pollution, but water recycling increases production costs and can increase risk of disease infestation from waterborne pathogens such as Pythium and Phytophthora. This study of water recycling adoption by horticultural growers in Virginia, Maryland, and Pennsylvania finds that the potential for increased disease infestation would reduce growers’ probability of adopting water recycling. Widespread adoption of recycling irrigation water would require government incentives or coercion or growers’ ability to pass cost increases on to customers.

El decaimiento de los Quercus sigue siendo uno de los principales problemas de sanidad forestal en España y Portugal. Es difícil cuantificar los ingentes recursos económicos y humanos destinados a la búsqueda de soluciones, sin que se haya podido atajar el avance de la mortalidad en las dehesas. Aunque se señala a Phytophthora cinnamomi como agente causal de los episodios más graves, otros oomicetos han sido identificados como agentes relacionados con estos procesos de mortalidad, o como patógenos oportunistas o acompañantes. La complejidad de los sistemas forestales influye en la diversidad de patógenos de podredumbre radical en el suelo, por lo que se debe tener en cuenta el efecto agregativo de la interacción de dichos organismos en la podredumbre radical. En el presente trabajo se colectaron muestras de suelo en dehesas de Córdoba, Sevilla y Cáceres, en áreas de afección por decaimiento. El daño del arbolado se evaluó mediante una escala asimilada de Ferreti. Las muestras se cultivaron en medio selectivo, y se identificaron morfológicamente 26 especies diferentes de oomicetos. Phytohthora cinnamomi fue el patógeno que mayor número de aislamientos presentó. El número de especies aisladas en función del grado de daños mostró diferencias significativas, siendo los árboles con grado 2 aquellos en los cuales se identificó el mayor número de especies. La presencia de P. cinnamomi no estuvo asociada significativamente con la diversidad de otras especies.

El decaimiento de los Quercus sigue siendo uno de los principales problemas de sanidad forestal en España y Portugal. Es difícil cuantificar los ingentes recursos económicos y humanos destinados a la búsqueda de soluciones, sin que se haya podido atajar el avance de la mortalidad en las dehesas. Aunque se señala a Phytophthora cinnamomi como agente causal de los episodios más graves, otros oomicetos han sido identificados como agentes relacionados con estos procesos de mortalidad, o como patógenos oportunistas o acompañantes. La complejidad de los sistemas forestales influye en la diversidad de patógenos de podredumbre radical en el suelo, por lo que se debe tener en cuenta el efecto agregativo de la interacción de dichos organismos en la podredumbre radical. En el presente trabajo se colectaron muestras de suelo en dehesas de Córdoba, Sevilla y Cáceres, en áreas de afección por decaimiento. El daño del arbolado se evaluó mediante una escala asimilada de Ferreti. Las muestras se cultivaron en medio selectivo, y se identificaron morfológicamente 26 especies diferentes de oomicetos. Phytohthora cinnamomi fue el patógeno que mayor número de aislamientos presentó. El número de especies aisladas en función del grado de daños mostró diferencias significativas, siendo los árboles con grado 2 aquellos en los cuales se identificó el mayor número de especies. La presencia de P. cinnamomi no estuvo asociada significativamente con la diversidad de otras especies.

The main, most important function of roots belonging to horticultural crops is the uptake of water and nutrients. Healthy roots are essential for a healthy plant. After all, if the uptake of water and nutrients is not functioning properly, then other aspects also leave a lot to be desired

Recycling irrigation water can provide water during periods of drought for horticulture operations and can reduce nonpoint-source pollution, but water recycling increases production costs and can increase risk of disease infestation from waterborne pathogens such as Pythium and Phytophthora. This study of water recycling adoption by horticultural growers in Virginia, Maryland, and Pennsylvania finds that the potential for increased disease infestation would reduce growers’ probability of adopting water recycling. Widespread adoption of recycling irrigation water would require government incentives or coercion or growers’ ability to pass cost increases on to customers.

Recycling irrigation water can provide water during periods of drought for horticulture operations and can reduce nonpoint-source pollution, but water recycling increases production costs and can increase risk of disease infestation from waterborne pathogens such as Pythium and Phytophthora. This study of water recycling adoption by horticultural growers in Virginia, Maryland, and Pennsylvania finds that the potential for increased disease infestation would reduce growers’ probability of adopting water recycling. Widespread adoption of recycling irrigation water would require government incentives or coercion or growers’ ability to pass cost increases on to customers.

The main, most important function of roots belonging to horticultural crops is the uptake of water and nutrients. Healthy roots are essential for a healthy plant. After all, if the uptake of water and nutrients is not functioning properly, then other aspects also leave a lot to be desired.

Plant-derived volatile compounds such as terpenes exhibit substantial structural variation and serve multiple ecological functions. Despite their structural diversity, volatile terpenes are generally produced from a small number of core 5- to 20-carbon intermediates. Here, we present unexpected plasticity in volatile terpene biosynthesis by showing that irregular homo/norterpenes can arise from different biosynthetic routes in a tissue specific manner. While Arabidopsis thaliana and other angiosperms are known to produce the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) or its C16-analog (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene by the breakdown of sesquiterpene and diterpene tertiary alcohols in aboveground tissues, we demonstrate that Arabidopsis roots biosynthesize DMNT by the degradation of the C30 triterpene diol, arabidiol. The reaction is catalyzed by the Brassicaceae-specific cytochrome P450 monooxygenase CYP705A1 and is transiently induced in a jasmonate-dependent manner by infection with the root-rot pathogen Pythium irregulare. CYP705A1 clusters with the arabidiol synthase gene ABDS, and both genes are coexpressed constitutively in the root stele and meristematic tissue. We further provide in vitro and in vivo evidence for the role of the DMNT biosynthetic pathway in resistance against P. irregulare. Our results show biosynthetic plasticity in DMNT biosynthesis in land plants via the assembly of triterpene gene clusters and present biochemical and genetic evidence for volatile compound formation via triterpene degradation in plants.

Plant-derived volatile compounds such as terpenes exhibit substantial structural variation and serve multiple ecological functions. Despite their structural diversity, volatile terpenes are generally produced from a small number of core 5- to 20-carbon intermediates. Here, we present unexpected plasticity in volatile terpene biosynthesis by showing that irregular homo/norterpenes can arise from different biosynthetic routes in a tissue specific manner. While Arabidopsis thaliana and other angiosperms are known to produce the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) or its C16-analog (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene by the breakdown of sesquiterpene and diterpene tertiary alcohols in aboveground tissues, we demonstrate that Arabidopsis roots biosynthesize DMNT by the degradation of the C30 triterpene diol, arabidiol. The reaction is catalyzed by the Brassicaceae-specific cytochrome P450 monooxygenase CYP705A1 and is transiently induced in a jasmonate-dependent manner by infection with the root-rot pathogen Pythium irregulare. CYP705A1 clusters with the arabidiol synthase gene ABDS, and both genes are coexpressed constitutively in the root stele and meristematic tissue. We further provide in vitro and in vivo evidence for the role of the DMNT biosynthetic pathway in resistance against P. irregulare. Our results show biosynthetic plasticity in DMNT biosynthesis in land plants via the assembly of triterpene gene clusters and present biochemical and genetic evidence for volatile compound formation via triterpene degradation in plants.

De afgelopen eeuw is er veel onderzoek gedaan aan bloembollen. Praktische problemen werden opgelost. Nu de sector op een keerpunt staat waar het gaat om de collectieve financiering van onderzoek, is het goed om nog eens na te gaan wat het onderzoek de praktijk heeft gebracht. In deze serie staat die vraag centraal. Dit keer: de periode van de bloei tot de oogst.

Is weerbaarheid tegen Pythium en aaltjes bij chrysanten mogelijk met een monocultuur of alleen in wisselteelten?

Natuurlijke bodems zijn vaak weerbaar tegen bodemziektes, bijvoorbeeld door aanwezigheid van andere micro-organismen. Kan door middel van het aanplanten van een combinatie van planten gezonde teeltgrond, gecreëerd worden waarop weerbare planten tegen ziekten en plagen groeien?

Resultaten van diverse maatregelen tegen het wortellesieaaltje Pratylenchus penetrans op duinzandgrond.

Background The genus Phytophthora includes a group of agriculturally important pathogens and they are commonly regarded as water molds. They produce motile zoospores that can move via water currents and on their own locomotion in aquatic environments. However, zoosporic response to dissolved oxygen, an important water quality parameter, is not known. Like other water quality parameters, dissolved oxygen concentration in irrigation reservoirs fluctuates dramatically over time. The aim of this study was to determine whether and how zoospore survival may be affected by elevated and low concentrations of dissolved oxygen in water to better understand the aquatic biology of these pathogens in irrigation reservoirs. Results Zoospores of P. megasperma, P. nicotianae, P. pini and P. tropicalis were assessed for survival in 10% Hoagland’s solution at a range of dissolved concentrations from 0.9 to 20.1-mg-L-1 for up to seven exposure times from 0 to 72-h. Zoospore survival was measured by resultant colony counts per ml. Zoospores of these species survived the best in control Hoagland’s solution at dissolved oxygen concentrations of 5.3 to 5.6-mg-L-1. Zoospore survival rates decreased with increasing and decreasing concentration of dissolved oxygen, depending upon Phytophthora species and exposure time. Overall, P. megasperma and P. pini are less sensitive than P. nicotianae and P. tropicalis to hyperoxia and hypoxia conditions. Conclusion Zoospores in the control solution declined over time and this natural decline process was enhanced under hyperoxia and hypoxia conditions. These findings suggest that dramatic fluctuations of dissolved oxygen in irrigation reservoirs contribute to the population decline of Phytophthora species along the water path in the same reservoirs. These findings advanced our understanding of the aquatic ecology of these pathogens in irrigation reservoirs. They also provided a basis for pathogen risk mitigation by prolonging the turnover time of runof

In een meerjarig, door het PT, TKI en telers gefinancierd project onderzocht Wageningen UR Glastuinbouw hoe de chrysantenteelt minder afhankelijk kan worden van chemische middelen in de strijd tegen grondgebonden ziekten en plagen, zoals Pythium. Vorig jaar beoordeelde de instelling een reeks van alternatieve middelen. Dat traject is nu aangevuld met een model en een snelle, indicatieve testmethode voor de bodemweerbaarheid tegen deze ziekte. Het plaatje is nog niet compleet, maar de voorlopige uitkomsten geven hoop, erkennen telers en DLV.