Crude Extracts and Secondary Metabolites of Epichloë bromicola against Phytophthora infestans

Potato late blight caused by Phytophthora infestans is still one of the main factors limiting potato production. Epichloë spp. can provide host plants with various resistances, which makes them show great potential in the biological control of diseases. In this study, we explored the potential biological activity of crude extracts of 20 strains of Epichloë bromicola to control P. infestans. The crude extracts of strains 1 and 8 showed significant antifungal activity with an inhibition rate of 88 % and 81 %, respectively, and showed different effects on the mycelium morphology of P. infestans observed by scanning electron microscopy. Moreover, the two crude extracts demonstrated an interesting therapeutic and protective effect on potato late blight, and none of the extracts had an adverse effect against zebrafish embryos. A total of 13 metabolites were isolated from the crude extract of strain 8, and these tested compounds showed a weak antifungal effect and the inhibition rate was less than 80 %. These findings suggested that strains 1 and 8 have potential for biocontrol of late potato blight.     

Phenotypic markers of Phytophthora infestans

Abstract

Phytophthora infestans is one of the most destructive pathogens of potato and causal agents of notorious disease late blight. Different chemicals are used to control the pathogen of late blight but the most commonly used is metalaxyl; its extensive use of has caused decreased sensitivity in the P. infestans population. The metalaxyl sensitivity of the Pakistani population of P. infestans is investigated in the present study. For this purpose, 178 isolates of P. infestans were obtained from the lesions of diseased potato leaves and stems, and samples were collected from the different potato-growing areas of Pakistan, where late blight is a problem. Sensitivity of the isolates of P. infestans was investigated by metalaxyl sensitivity test and with the help of test isolates were divided into three categories, i.e. sensitive, intermediate and resistant, based on their Co-efficient of mycelial growth inhibition (CMGI) values. During the study, highest percentage (50.17%) of resistant isolates was observed in the population of Punjab (zone 2), whereas the lower percentage (33.33%) was observed in the population of Swat valley (zone 6b). In the present study, it was discovered that P. infestans late blight-causing fungus has adopted more resistance against metalaxyl because of its wide use.     

Screening and Evaluation of Biosurfactant-Producing Strains Isolated from Oilfield Wastewater

The six biosurfactant-producing strains, isolated from oilfield wastewater in Daqing oilfield, were screened. The production of biosurfactant was verified by measuring the diameter of the oil spreading, measuring the surface tension value and emulsifying capacity against xylene, n-pentane, kerosene and crude oil. The experimental result showed three strains (S2, S3, S6) had the better surface activity. Among the three strains, the best results were achieved when using S2 strain. The diameter of the oil spreading of the biosurfactant produced by S2 strain was 14 cm, its critical micelle concentration (CMC) was 21.8 mg/l and the interfacial tension between crude oil and biosurfactant solution produced by S2 strain reduced to 25.7 mN/m. The biosurfactant produced by S2 strain was capable of forming stable emulsions with various hydrocarbons, such as xylene, n-pentane, kerosene and crude oil. After S2 strain treatment, the reduction rate of oil viscosity was 51 % and oil freezing point reduced by 4 °C.     

Effect of orange essential oil and its constitutes on late blight disease of potato plants under field conditions

Late blight caused by Phytophthora infestans is the most important disease attacking potato plants. Four concentrations of essential oils i.e. 0.0, 1.25, 2.5, 5.0 and 7.5 ml/l of Orange, Citral, Methyl antranate (MA), and Terbinol were tested for controlling late blight disease. Results indicate that all treatments except orange oil have an inhibitory effect against the linear growth of P. infestans. Complete reduction in linear growth was obtained with Citral and MA at concentrations of 5.0 and 7.5 ml/l. Other treatments showed moderate effect against P. infestans. In greenhouse experiments, results indicate that all treatments have protective and therapeutic effects against late blight disease except Orange oil which has a protective effect only. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 77.1 and 62.8% when applied as protective and therapeutic treatments respectively. Moderate effect was obtained with orange oil and Citral at concentration of 7.5 ml/l for both treatments which reduced the disease severity by more than 65.7% when applied as protective treatments. Similar results were obtained under field coditions; results indicate that all treatments reduced the late blight severity during two growing seasons. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 80.0%. As for potato yield, results indicate that all treatments increased potato yield during two growing seasons. A high increase was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which increased the potato yield by more than 59.1%. Other treatments showed a moderate increase. It could be suggested that some essential oils of citrus or their constituents might be used for controlling late blight disease potato plants under field conditions.     

Functional analysis of potato genes involved in quantitative resistance to Phytophthora infestans

The most significant threat to potato production worldwide is the late blight disease, which is caused by the oomycete pathogen Phytophthora infestans. Based on previous cDNA microarrays and cDNA-amplified fragment length polymorphism analysis, 63 candidate genes that are expected to contribute to developing a durable resistance to late blight were selected for further functional analysis. We performed virus-induced gene silencing (VIGS) to these candidate genes on both Nicotiana benthamiana and potato, subsequently inoculated detached leaves and assessed the resistance level. Ten genes decreased the resistance to P. infestans after VIGS treatment. Among those, a lipoxygenase (LOX; EC 1.13.11.12) and a suberization-associated anionic peroxidase affected the resistance in both N. benthamiana and potato. Our results identify genes that may play a role in quantitative resistance mechanisms to late blight.     

Sequence variation of intergenic mitochondrial DNA spacers (mtDNA‐IGS) of Phytophthora infestans (Oomycetes) and related species

The potato late‐blight disease is caused by the pseudofungus Phytophthora infestans (Oomycetes). This pathogen was of historical importance as it caused the Irish Potato Famine. There is currently a worldwide resurgence of the disease. Following worldwide migrations as well as being able to discriminate P. infestans from related species are key issues. We present sequence variation of five inter‐genic mitochondrial DNA spacers (mtDNA‐IGS) for P. infestans and four related taxa. Intra and inter‐taxon variation was observed showing potential for both molecular ecology and molecular systematic.     

Reassessment of QTLs for Late Blight Resistance in the Tomato Accession L3708 Using a Restriction Site Associated DNA (RAD) Linkage Map and Highly Aggressive Isolates of Phytophthora infestans

Tomato late blight caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary is a major threat to tomato production in cool and wet environments. Intensified outbreaks of late blight have been observed globally from the 1980s, and are associated with migration of new and more aggressive populations of P. infestans in the field. The objective of this study was to reassess late blight resistance in the wild tomato accession L3708 (Solanum pimpinellifolium L.) against pathogens of different aggressiveness. An F_2:3 genetic mapping population was developed using L3708 as the paternal parent. Two isolates of P. infestans, Pi39A and Pi733, were used for inoculation. Pi733 is a highly aggressive genotype that defeats three known late blight resistance genes, Ph-1, Ph-2, and Ph-5t in tomato. In contrast, Pi39A is a less aggressive genotype that defeats only Ph-1. Restriction site Associated DNA Sequencing (RAD-Seq) technology was used to massively sequence 90 bp nucleotides adjacent to both sides of PstI restriction enzyme cutting sites in the genome for all individuals in the genetic mapping population. The RAD-seq data were used to construct a genetic linkage map containing 440 single nucleotide polymorphism markers. Quantitative trait locus (QTL) analysis identified a new disease-resistant QTL specific to Pi733 on chromosome 2. The Ph-3 gene located on chromosome 9 could be detected whichever isolates were used. This study demonstrated the feasibility and efficiency of RAD-Seq technology for conducting a QTL mapping experiment using an F_2:3 mapping population, which allowed the identification of a new late blight resistant QTL in tomato.     

Biosurfactant Production by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> SNP0614 and its Effect on Biodegradation of Petroleum

An efficient biosurfactant-producing strain was isolated and cultured from Dagang oil field (China) using crude oil as sole source of carbon. Based on partial sequenced 16S rDNA analysis, the isolated strain was identified as Pseudomonas aeruginosa SNP0614. The bacterium P. aeruginosa SNP0614 produced a type of biosurfactant with excessive foam-forming properties. After microbial cultivation at 37°C and 150 rpm for 12 h, the produced biosurfactant was found to reduce the surface tension to 25.4 mN/m with critical micelle concentration (CMC) of 45.0 mg/L. After 20 days of incubation, the biosurfactant exhibited 90% emulsification activity (E₂₄) on crude oil. FTIR spectroscopy of extracted biosurfactant indicated the biosurfactant as lipopeptide. The significant synergistic effect between P. aeruginosa SNP0614 and the mixed oildegrading bacteria resulted in increasing n-alkanes degradation rate by 30%. The strain P. aeruginosa SNP0614 represented as a promising biosurfactant producer and could be applied in a variety of biotechnological and industrial processes, particularly in microbial enhanced oil recovery and the bioremediation of oil pollution.     

泡菜水中产生物表面活性剂酵母菌株的筛选

[背景]由微生物产生的生物表面活性剂(biosurfactant,BS)具有低毒性、高效性、生物可降解性等多种特性,能在一定程度上缓解化学表面活性剂所造成的环境问题,因此筛选高产、安全的BS生产菌株备受研究者的关注.[目的]从泡菜水中筛选能代谢合成药食两用型BS的微生物菌株.[方法]运用滴崩法和排油圈法从传统发酵食品泡...     

Bikaverin and fusaric acid from Fusarium oxysporum show antioomycete activity against Phytophthora infestans

Aims: To isolate and identify antioomycete substances from Fusarium oxysporum EF119 against Phytophthora infestans and to investigate their antimicrobial activities against various plant pathogenic bacteria, oomycetes and true fungi. Methods and Results: Two antioomycete substances were isolated from liquid cultures of F. oxysporum EF119, which shows a potent disease control efficacy against tomato late blight caused by P. infestans. They were identified as bikaverin and fusaric acid by mass and nuclear magnetic resonance spectral analyses. They inhibited the mycelial growth of plant pathogenic oomycetes and fungi. Fusaric acid also effectively suppressed the cell growth of various plant pathogenic bacteria, but bikaverin was virtually inactive. Treatment with bikaverin at 300 μg ml^?1 suppressed the development of tomato late blight by 71%. Fusaric acid provided effective control against tomato late blight and wheat leaf rust over 67% at concentrations more than 100 μg ml^?1. Conclusions: Both bikaverin and fusaric acid showed in vitro and in vivo antioomycete activity against P. infestans. Significance and Impact of the Study: Fusarium oxysporum EF119 producing both bikaverin and fusaric acid may be used as a biocontrol agent against tomato late blight caused by P. infestans.     

A locus conferring effective late blight resistance in potato cultivar Sárpo Mira maps to chromosome XI

Late blight of potato, caused by Phytophthora infestans, is one of the most economically important diseases worldwide, resulting in substantial yield losses when not adequately controlled by fungicides. Late blight was a contributory factor in The Great Irish Famine, and breeding for resistance to the disease began soon after. Several disease-resistant cultivars have subsequently been obtained, and amongst them Sárpo Mira is currently one of the most effective. The aim of this work was to extend the knowledge about the genetic basis of the late blight resistance in Sárpo Mira and to identify molecular markers linked to the resistance locus which would be useful for marker-assisted selection. A tetraploid mapping population from a Sárpo Mira × Maris Piper cross was phenotyped for foliar late blight resistance using detached leaflet tests. A locus with strong effect on late blight resistance was mapped at the end of chromosome XI in the vicinity of the R3 locus. Sárpo Mira’s genetic map of chromosome XI contained 11 markers. Marker 45/XI exhibited the strongest linkage to the resistance locus and accounted for between 55.8 and 67.9 % of variance in the mean resistance scores noted in the detached leaflet assays. This marker was used in molecular marker-facilitated gene pyramiding. Ten breeding lines containing a late blight resistance locus from cultivar Sárpo Mira and the Rpi-phu1 gene originating from the late blight resistant accession of Solanum phureja were obtained. These lines have extended the spectrum of late blight resistance compared with Sárpo Mira and it is expected that resistance in plants containing this gene pyramid will have enhanced durability.     

Systemically Induced Resistance in Potato Cultivars with Different Degree of Resistance to Late Blight caused by Phytophthora infestans (Mont.) de Bary

Systemically induced resistance in potato plants (Solanum tuberosum L.) against late blight Phytophthora infestans was studied macroscopically on three potato cultivars with different degrees of resistance to late blight. The cultivars, were Bintje(2), Elin(3) and Matilda(4). Figures within brackets represent resistance to leaf late blight on a scale from 1 to 5, where 5 denotes the highest level of resistance. In vitro propagated cuttings were used in the experiments, which were, performed under controlled environmental conditions. Disease resistance was induced by a local pre-infection with P. infestans or with the nonpathogen P. cryptogea. Induced resistance was observed on all cultivars. The protection causedby, induced resistance tended to be most intense on cv. Matilda, with 50–60% reduction in lesion formation 4 days after challenge inoculation.     

Novel rhamnolipid biosurfactants produced by a polycyclic aromatic hydrocarbon-degrading bacterium Pseudomonas aeruginosa strain NY3

A novel rhamnolipid biosurfactant-producing and Polycyclic Aromatic Hydrocarbon (PAH)-degrading bacterium Pseudomonas aeruginosa strain NY3 was isolated from petroleum-contaminated soil samples. Strain NY3 was characterized by its extraordinary capacity to produce structurally diverse rhamnolipids. A total of 25 rhamnolipid components and 37 different parent molecular ions, representing various metal ion adducts (Na⁺, 2Na⁺ and K⁺), were detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Among these compounds are ten new rhamnolipids. In addition to its biosurfactant production, strain NY3 was shown to be capable of efficient degradation of PAHs as well as synergistic improvement in the degradation of high molecular weight PAHs by its biosurfactant. These findings have added novel members to the rhamnolipid group and expanded current knowledge regarding the diversity and productive capability of rhamnolipid biosurfactants from a single specific strain with variation of only one carbon source. Additionally, this paper lays the foundation for improvement in the yield of NY3BS and study of the degradation pathway(s) of PAHs in P. aeruginosa strain NY3.     

Control Efficacy of Bacillus velezensis AFB2-2 against Potato Late Blight Caused by Phytophthora infestans in Organic Potato Cultivation

Although late blight is an important disease in ecofriendly potato cultivation in Korea, it is highly dependent on the use of eco-friendly agricultural materials and the development of biological control technology is low. It is a necessary to develop an effective biocontrol agent to inactivate late blight in the field. AFB2-2 strain is a gram-positive with peritrichous flagella. It can utilize 20 types of carbon sources, like L-arabinose, and D-trehalose at 35°C. The optimal growth temperature of the strain is 37°C. It can survive at 20–50°C in tryptic soy broth. The maximum salt concentration tolerated by AFB2-2 strain is 7.5% NaCl. AFB2-2 strain inhibited the mycelial growth of seven plant pathogens by an average inhibitory zone of 10.2 mm or more. Among the concentrations of AFB2-2, 10⁷ cfu/ml showed the highest control value of 85.7% in the greenhouse. Among the three concentrations of AFB2-2, the disease incidence and severity of potato late blight at 10⁷ cfu/ml was lowest at 0.07 and 6.7, respectively. The nucleotide sequences of AFB2-2 strain were searched in the NCBI GenBank; Bacillus siamensis strain KCTC 13613, Bacillus velezensis strain CR-502, and Bacillus amyloliquefaciens strain DSM7 were found to have a genetic similarity of 99.7%, 99.7%, and 99.5%, respectively. The AFB2-2 strain was found to harbor the biosynthetic genes for bacillomycin D, iturin, and surfactin. Obtained data recommended that the B. velezensis AFB2-2 strain could be considered as a promising biocontrol agent for P. infestans in the field.     

Fine mapping of the Ph-3 gene conferring resistance to late blight (Phytophthora infestans) in tomato

Late blight, caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary, is a devastating disease for tomato and potato crops. In the past decades, many late blight resistance (R) genes have been characterized in potato. In contrast, less work has been conducted on tomato. The Ph-3 gene from Solanum pimpinellifolium was introgressed into cultivated tomatoes and conferred broad-spectrum resistance to P. infestans. It was previously assigned to the long arm of chromosome 9. In this study, a high-resolution genetic map covering the Ph-3 locus was constructed using an F₂ population of a cross between Solanum lycopersicum CLN2037B (containing Ph-3) and S. lycopersicum LA4084. Ph-3 was mapped in a 0.5 cM interval between two markers, Indel_3 and P55. Eight putative genes were found in the corresponding 74 kb region of the tomato Heinz1706 reference genome. Four of these genes are resistance gene analogs (RGAs) with a typical nucleotide-binding adaptor shared by APAF-1, R proteins, and CED-4 domain. Each RGA showed high homology to the late blight R gene Rpi-vnt1.1 from Solanum venturii. Transient gene silencing indicated that a member of this RGA family is required for Ph-3-mediated resistance to late blight in tomato. Furthermore, this RGA family was also found in the potato genome, but the number of the RGAs was higher than in tomato.     

Tuber Blight Development in Potato Cultivars in Response to Different Genotypes of Phytophthora infestans

Migrations or introduction of new genotypes of Phytophthora infestans to a specific region imposes a different perspective for potato production. During 2009–2010, a late blight epidemic affected the Northeastern United States, which quickly spread through several states. The epidemic was characterized by the appearance of a new genotype of P. infestans designated US‐22, which was isolated from tomato and potato. Potato tubers are an essential component of late blight epidemics where the pathogen cannot overwinter on Solanaceous plants. Six potato cultivars were inoculated with 12 isolates of P. infestans (five different genotypes), including isolates of the genotype US‐22. Tuber blight development was characterized in terms of tissue darkening expressed as area under the disease progress curve values and lenticel infection. The responses indicated that US‐8 was more aggressive than US‐22, but US‐22 isolates obtained from potato were more aggressive on potato than those acquired from tomato. Tuber periderm responses to infection were limited, yet US‐8 isolates infected the periderm more often than US‐22 isolates. There were significant differences among the cultivars tested but cv. Jacqueline Lee was the most resistant overall. Although isolates of P. infestans genotype US‐22 were less aggressive in comparison with US‐8 isolates, US‐22 isolates still infected potato tubers and were as aggressive us US‐8 isolates on some cultivars. Management of late blight caused by isolates of US‐22 through host resistance may be feasible but imposes a different set of criteria for consideration from those that US‐8 imposed.     

Effect of methyl jasmonate on arachidonic acid-induced resistance of potato to late blight

Methyl ester of jasmonic acid (Me-JA) influences the induced resistance of potato tubers to late blight caused byPhytophthora infestans. Treatment of potato tuber disk surfaces with Me-JA solution or exposure to an atmosphere containing Me-JA vapors (10⁻⁶–10⁻⁵ M) increased the rate of rishitin biosynthesis induced by arachidonic acid orP. infestans. Methyl jasmonate increased the sensitivity of potato tissue to arachidonic acid. As a result, in the presence of Me-JA, the protective properties of arachidonic acid were observed at lower concentrations than in the absence of Me-JA. In addition, Me-JA reduced the adverse effects of lipoxygenase inhibitors (salicylhydroxamic acid and esculetin) on the induced resistance of potato tubers to late blight. Therefore, the synergistic interaction of Me-JA and biogenic elicitors can be regarded as part of a mechanism of potato defense against diseases.     

Monitoring airborne concentrations of sporangia ofPhytophthora infestans in relation to tomato late blight in Emilia Romagna,Italy

Late blight caused byPhytophthora infestans is one of the most important diseases of tomato crops in Emilia Romagna. In total, 7–8 chemical sprays are applied per season to control the disease without taking into account the risk of infection. An integrated warning service for the prediction of tomato late blight was set up in order to define a more rational disease control strategy. As a part of the warning service, a number of sites monitoringPh. infestans airborne sporangia was set up for a timely disease prediction in the regional tomato growing areas. The results of 3 years monitoring ofPh. infestans sporangia are presented. They suggest that concentrations of airborne sporangia rapidly increase 1–2 weeks prior the blight onset in the field.