Towards an integrated control of peach powdery mildew (Podosphaera pannosa) through the application of molecular tools in epidemiological and genetic resistance studies

La malaltia de l’oïdi o cendrosa del presseguer, causada pel fong ascomicet Podosphaera pannosa, pot arribar a causar pèrdues greus en la producció i en la qualitat del fruit. Actualment, el control de l’oïdi es basa en aplicacions periòdiques de fungicides. Els efectes derivats de l’ús d’aquests productes en la salut humana i en el medi ambient han provocat una gran conscienciació de la societat, tot afavorint el desenvolupament de noves estratègies basades en el maneig integrat de plagues i malalties. Aquestes estratègies han de comptar necessàriament amb un coneixement profund dels agents implicats en la malaltia; és a dir, del patogen, de l’hoste i de les condicions ambientals. En aquesta tesi doctoral s’han estudiat algunes variables ambientals que descriuen el progrés de la malaltia de l’oïdi i s’ha dissenyat una estratègia per a retardar l’inici de l’aplicació dels tractaments fitosanitaris (Capítol 3). En concret, l’inici retardat del programa de protecció, a partir dels 220 graus-dia acumulats després de la floració, ha permès reduir el nombre de tractaments fitosanitaris en un 33%, sense perdre eficàcia en el control de la malaltia. També s’han estudiat aspectes relacionats amb l’inòcul primari de P. pannosa i l’aerobiologia del fong durant l’època infectiva (Capítol 4). Mitjançant tècniques moleculars, s’ha confirmat que l’inòcul primari es troba principalment en forma de miceli hivernant en la superfície dels branquillons afectats. També s’ha pogut quantificar els propàguls de P. pannosa presents en l’aire durant el període infectiu, d’abril a juliol. Una alternativa al control de l’oïdi que requereix més temps en la seva aplicació, però que evitaria el tractament amb fungicides, és el desenvolupament de cultivars resistents de presseguer. En aquesta tesi s’ha caracteritzat el gen de resistència Vr3, procedent de l’ametller (Capítol 5). Ha estat possible localitzar-lo en una regió molt específica del genoma, que inclou 27 gens candidats a conferir la resistència. Mitjançant una anàlisi d’expressió dels gens candidats i l’anàlisi dels polimorfismes de les reseqüències dels parentals, s’ha pogut determinar que el gen de resistència RGA2 podria ser el gen candidat Vr3, a falta d’una futura validació funcional. Finalment, i per tal d’obtenir noves varietats resistents a P. pannosa, s’ha introgressat la resistència Vr3 en cultivars comercials de presseguer (Capítol 6), mitjançant els creuaments d’individus amb una o dues introgressions d’ametller que incloïen el gen Vr3.El oídio del melocotonero, enfermedad debida al hongo ascomiceto Podosphaera pannosa, puede llegar a causar pérdidas graves en la producción y en la calidad del fruto. Actualmente, el control del oídio se basa en aplicaciones periódicas de fungicidas. Los efectos derivados del uso de estos productos en la salud humana y en el medio ambiente han tenido como consecuencia una mayor concienciación social, lo que ha llevado al desarrollo de nuevas estrategias basadas en el control integrado de plagas y enfermedades. Este tipo de estrategias deben contar con un conocimiento profundo de los agentes implicados en la enfermedad; esto es, del patógeno, el huésped y el ambiente. En esta tesis doctoral se han estudiado algunas variables ambientales que describen el progreso de la enfermedad del oídio y se ha diseñado una estrategia para retardar el inicio de las aplicaciones fitosanitarias (Capítulo 3). En concreto, el retardo en el inicio del programa de protección, a partir de los 220 grados-día acumulados después de la floración, ha permitido reducir hasta un 33% el número de tratamientos fitosanitarios sin perder la eficacia en el control de la enfermedad. También se ha estudiado el inóculo primario de P. pannosa y la aerobiología del mismo durante la época infectiva (Capítulo 4). Mediante el uso de técnicas moleculares se ha confirmado que el inóculo primario se encuentra principalmente en forma de micelio latente en la superficie de las ramillas afectadas. También se ha logrado cuantificar los propágulos de P. pannosa presentes en el aire durante el período infectivo, que se extiende principalmente de abril a julio. Una técnica alternativa en el control de la enfermedad, que requiere más tiempo en su aplicación pero que puede evitar el uso de fungicidas, es el desarrollo de cultivares resistentes de melocotonero. En esta tesis se ha caracterizado el gen de resistencia Vr3 procedente del almendro (Capítulo 5). Ha sido posible localizarlo en una región muy específica del genoma, que incluye 27 genes candidatos. Mediante un análisis de expresión de los genes candidatos y un análisis de los polimorfismos de las resecuencias de los parentales, se ha podido determinar que el gen de resistencia RGA2 podría ser el gen candidato Vr3, aunque ello depende de una futura validación funcional. Finalmente, y con el fin de obtener nuevas variedades resistentes a P. pannosa, se ha introgresado la resistencia Vr3 en cultivares comerciales de melocotonero (Capítulo 6), mediante el cruce de individuos con una o dos introgresiones de almendro que incluían dicho gen.Peach powdery mildew (PPM), caused by the ascomycete fungus Podosphaera pannosa, is one of the major diseases of peach, which may cause significant decreases in yield and fruit quality. Powdery mildew is currently managed through calendar-based fungicide applications. Adverse effects resulting from pesticide applications on human health and the environment have raised a great social awareness, which has driven the development of new integrated strategies more respectful to both environment and human health status. These disease management strategies are strongly depending on a deep knowledge of key aspects of the disease, which includes the pathogen and the host, and their relationship with the environment. In this thesis, the influence of some environmental variables on the disease progress of PPM have been studied. Furthermore, a strategy was designed to delay the onset of fungicide applications (Chapter 3). Specifically, the delayed initiation of fungicide programs at 220 accumulated degree-days after flowering reduced the number of fungicide applications by 33% while keeping effectiveness in the disease control. Several traits related to the latency of the pathogen primary inoculum and the aerobiology of the pathogen propagules during the infectious period were also studied (Chapter 4). Thus, by using molecular techniques, it was confirmed that the primary inoculum is mainly present as overwintering mycelium on the surface of the affected twigs. The detection and quantification of airborne P. pannosa propagules during the growing season confirmed that those propagules can be detected from April to July. The development of resistant cultivars is considered an alternative to disease control that is only based on fungicide treatments. In this thesis, the resistance gene Vr3, inherited from almond, was characterized (Chapter 5). We were able to locate it in a very specific region of the genome spanning 27 candidate genes. Through the expression analysis of candidate genes and an analysis of polymorphisms from parental resequences, it was concluded that the RGA2 resistance gene could be the best Vr3 candidate gene, assuming that a future functional validation is still required. Finally, in order to obtain resistant varieties to P. pannosa, the Vr3 resistance is currently being introgressed into high-quality peach varieties (Chapter 6), by crossing individuals with one or two almond introgressions which included the Vr3 gene

Fine mapping and identification of candidate genes for the peach powdery mildew resistance gene Vr3

Powdery mildew is one of the major diseases of peach (Prunus persica), caused by the ascomycete Podosphaera pannosa. Currently, it is controlled through calendar-based fungicide treatments starting at petal fall, but an alternative is to develop resistant peach varieties. Previous studies mapped a resistance gene (Vr3) in interspecific populations between almond (‘Texas’) and peach (‘Earlygold’). To obtain molecular markers highly linked to Vr3 and to reduce the number of candidate genes, we fine-mapped Vr3 to a genomic region of 270 kb with 27 annotated genes. To find evidence supporting one of these positional candidate genes as being responsible of Vr3, we analyzed the polymorphisms of the resequences of both parents and used near-isogenic lines (NILs) for expression analysis of the positional candidate genes in symptomatic or asymptomatic leaves. Genes differentially expressed between resistant and susceptible individuals were annotated as a Disease Resistance Protein RGA2 (Prupe2G111700) or an Eceriferum 1 protein involved in epicuticular wax biosynthesis (Prupe2G112800). Only Prupe2G111700 contained a variant predicted to have a disruptive effect on the encoded protein, and was overexpressed in both heterozygous and homozygous individuals containing the Vr3 almond allele, compared with susceptible individuals. This information was also useful to identify and validate molecular markers tightly linked and flanking Vr3. In addition, the NILs used in this work will facilitate the introgression of this gene into peach elite materials, alone or pyramided with other known resistance genes such as peach powdery mildew resistance gene Vr2.info:eu-repo/semantics/publishedVersio

Effect of humidity on the writing speed and domain wall dynamics of ferroelectric domains

Altres ajuts: the ICN2 was funded by the CERCA programme / Generalitat de Catalunya.The switching dynamics of ferroelectric polarization under electric fields depends on the availability of screening charges in order to stabilize the switched polarization. In ferroelectrics, thin films with exposed surfaces investigated by piezoresponse force microscopy (PFM), the main source of external screening charges is the atmosphere and the water neck, and therefore relative humidity (RH) plays a major role. Here, it is shown how the dynamic writing of domains in BaTiO thin films changes by varying scanning speeds in the range of RH between 2.5% and 60%. The measurements reveal that the critical speed for domain writing, which is defined as the highest speed at which electrical writing of a continuous stripe domain is possible, increases non-monotonically with RH. Additionally, the width of line domains shows a power law dependence on the writing speed, with a growth rate coefficient decreasing with RH. The size of the written domains at a constant speed as well as the creep-factor μ describing the domain wall kinetics follow the behavior of water adsorption represented by the adsorption isotherm, indicating that the screening mechanism dominating the switching dynamics is the thickness and the structure of adsorbed water structure and its associated dielectric constant and ionic mobility

Non-linear nanoscale piezoresponse of single ZnO nanowires affected by piezotronic effect

Zinc oxide (ZnO) nanowires (NWs) as semiconductor piezoelectric nanostructures have emerged as material of interest for applications in energy harvesting, photonics, sensing, biomedical science, actuators or spintronics. The expression for the piezoelectric properties in semiconductor materials is concealed by the screening effect of the available carriers and the piezotronic effect, leading to complex nanoscale piezoresponse signals. Here, we have developed a metal-semiconductor-metal model to simulate the piezoresponse of single ZnO NWs, demonstrating that the apparent non-linearity in the piezoelectric coefficient arises from the asymmetry created by the forward and reversed biased Schottky barriers at the semiconductor-metal junctions. By directly measuring the experimental I-V characteristics of ZnO NWs with conductive atomic force microscope together with the piezoelectric vertical coefficient by piezoresponse force microscopy, and comparing them with the numerical calculations for our model, effective piezoelectric coefficients in the range d 33eff ∼ 8.6 pm V¯¹-12.3 pm V¯¹ have been extracted for ZnO NWs. We have further demonstrated via simulations the dependence between the effective piezoelectric coefficient d 33eff and the geometry and physical dimensions of the NW (radius to length ratio), revealing that the higher d 33eff is obtained for thin and long NWs due to the tensor nature proportionality between electric fields and deformation in NW geometries. Moreover, the non-linearity of the piezoresponse also leads to multiharmonic electromechanical response observed at the second and higher harmonics that indeed is not restricted to piezoelectric semiconductor materials but can be generalized to any type of asymmetric voltage drops on a piezoelectric structure as well as leaky wide band-gap semiconductor ferroelectrics

A Decision Support System Based on Degree-Days to Initiate Fungicide Spray Programs for Peach Powdery Mildew in Catalonia, Spain

The incidence of peach powdery mildew (PPM) on fruit was monitored in commercial peach orchards to i) describe the disease progress in relation to several environmental parameters and ii) establish an operating threshold to initiate a fungicide spray program based on accumulated degree-day (ADD) data. A beta-regression model for disease incidence showed a substantial contribution of the random effects orchard and year, whereas relevant fixed effects corresponded to ADD, wetness duration, and ADD considering vapor pressure deficit and rain. When beta-regression models were fitted for each orchard and year considering only ADD, disease onset was observed at 242 ± 13 ADD and symptoms did not develop further after 484 ± 42 ADD. An operating threshold to initiate fungicide applications was established at 220 ADD, coinciding with a PPM incidence in fruit around 0.05. A validation was further conducted by comparing PPM incidence in i) a standard, calendar-based program, ii) a program with applications initiated at 220 ADD, and iii) a nontreated control. A statistically relevant reduction in disease incidence in fruit was obtained with both fungicide programs, from 0.244 recorded in the control to 0.073 with the 220-ADD alert program, and 0.049 with the standard program. The 220-ADD alert program resulted in 33% reduction in fungicide applications.info:eu-repo/semantics/acceptedVersio

A qPCR-based method for the detection and quantification of the peach powdery mildew (Podosphaera pannosa) in epidemiological studies

A qPCR-based method was developed to detect and quantify Podosphaera pannosa, the main causal agent of peach powdery mildew. A primer pair was designed to target part of the ITS region of the fungal ribosomal DNA, which proved to be highly specific and sensitive. A minimum of 2.81 pg µL− 1 of P. pannosa DNA and 6 conidia mL− 1 in artificially-prepared conidia suspensions were found to be the limit of detection. Moreover, a quantification of conidia placed on plastic tapes commonly used in volumetric air samplers was performed. Regression equations on conidia quantification obtained either from aqueous conidia suspensions or conidia placed on plastic tapes were similar. The protocol was further validated in field conditions by estimating the number of P. pannosa conidia obtained with an air sampler, by both microscopic and molecular quantification. Both techniques detected the peaks of conidia production during a 4-month sampling period, and a significant correlation (r = 0.772) was observed between both quantification methods. Additionally, the molecular method was applied to detect latent fungal inoculum in different plant parts of peach trees. The pathogen was detected mainly on the bark of affected twigs, and to a lesser extent, in foliar buds. The method developed here can be applied in the study of P. pannosa epidemiology and can help in improving the management of this pathogen through its early detection and quantification.info:eu-repo/semantics/acceptedVersio

Tunable Molecular Electrodes for Bistable Polarization Screening

The polar discontinuity at any ferroelectric surface creates a depolarizing field that must be screened for the polarization to be stable. In capacitors, screening is done by the electrodes, while in bare ferroelectric surfaces it is typically accomplished by atmospheric adsorbates. Although chemisorbed species can have even better screening efficiency than conventional electrodes, they are subject to unpredictable environmental fluctuations and, moreover, dominant charged species favor one polarity over the opposite. This paper proposes a new screening concept, namely surface functionalization with resonance-hybrid molecules, which combines the predictability and bipolarity of conventional electrodes with the screening efficiency of adsorbates. Thin films of barium titanate (BaTiO) coated with resonant para-aminobenzoic acid (pABA) display increased coercivity for both signs of ferroelectric polarization irrespective of the molecular layer thickness, thanks to the ability of these molecules to swap between different electronic configurations and adapt their surface charge density to the screening needs of the ferroelectric underneath. Because electron delocalization is only in the vertical direction, unlike conventional metals, chemical electrodes allow writing localized domains of different polarity underneath the same electrode. In addition, hybrid capacitors composed of graphene/pABA/ferroelectric have been made with enhanced coercivity compared to pure graphene-electode capacitors

Ferroelectrics as smart mechanical materials

This is the peer reviewed version of the following article: Cordero, K., Domingo Marimon, Neus, Abdollahi, A., Sort Viñas, Jordi, Catalan, G. Ferroelectrics as smart mechanical materials. "Advanced materials", 21 Juliol 2017, vol. 29, núm. 37, p. 1-6, which has been published in final form at DOI: 10.1002/adma.201702210. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact-resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO3) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains.Peer ReviewedPostprint (author's final draft

Oxidation processes at the surface of BaTiO3 thin films under environmental conditions

Altres ajuts: the ICN2 is funded by the CERCA programme/Generalitat de Catalunya. I. S. acknowledges support of the Secretaria d'Universitats i Recerca - Departament d'Empresa i Coneixement - Generalitat de Catalunya and the European Social Fund (ESF) (FI grant reference 2020 FI_B2 00157).Dissociation and adsorption of water on ferroelectric oxide surfaces play important role in the processes of screening and switching dynamics of ferroelectric polarization, as well as in catalytic processes which can be additionally coupled with light, temperature or vibration stimuli. In this work, we present XPS study of ferroelectric BaTiOthin films and determine the entanglement between surface chemistry, polarization direction and stability, by observing changes upon time exposure to environmental conditions, heating in Oatmosphere and irradiation in vacuum. We devote special attention to Ba 3d spectral region and identify two different oxidation states of O atoms in the compounds of Ba. While this second specie was generally attributed to Ba in surface compounds where it has different oxygen coordination than in the bulk, based on the XPS results of oxygen annealed thin films, we demonstrate that this so far neglected component, corresponds to barium peroxide (BaO) and identify it as important active specie for the study of screening mechanisms closely related with catalytic activity present in this ferroelectric material. Finally, we report on chemically assisted polarization switching in thin films induced by heating in vacuum or exposure to X-Ray radiation due to the formation of positive surface electric field created by oxygen or electron vacancies, respectively