Alternativas de control biorracionales sobre Phytophthora infestans, fitopatógeno causante de la gota en papa / Biorational control alternatives on Phytophthora infestans, phytopathogen causing gout in potatoes

Resumen La gota de la papa o tizón tardío es una de las enfermedades más agresivas que atacan los cultivos de papa y en poco tiempo los destruye, ocasionando enormes pérdidas económicas, es producida por el fitopatógeno Phytophthora infestans, oomyceto que ha tomado gran importancia debido a sus efectos devastadores y las dificultades para lograr su erradicación. Los fungicidas de naturaleza química representan un problema debido al uso inadecuado, lo que hace muy difícil eliminar la enfermedad por la aparición de nuevas especies resistentes. Existen nuevas alternativas para su control, basadas en el uso de sustancias de naturaleza vegetal, y la aplicación de nuevas herramientas capaces de realizar edición de genes, reprogramar o eliminar secuencias de ADN/ARN, favoreciendo así, la obtención de cultivos libres de sustancias tóxicas. En esta revisión, se presentan los métodos existentes de biocontrol: como aceites esenciales, metabolitos microbianos, herramientas moleculares y el uso de sustancias biodegradables que favorecen el manejo y prevención de plagas, que ayudan a mitigar la problemática ambiental generada por el uso de fungicidas de naturaleza química.

Abstract The drop of the potato or late blight is one of the most aggressive diseases that attack the potato crops and in a short time destroys them, causing great economic losses, it is produced by the phytopathogen Phytophthora infestans, oomyceto that has taken great importance due to its devastating effects and difficulties in achieving its eradication. Fungicides of a chemical nature represent a problem due to the affected use, which makes it very difficult to eliminate the disease due to the appearance of new resistant species. There are new alternatives for its control, based on the use of substances of the plant nature, and the application of new specific tools to perform gene editing, reprogram or eliminate DNA / RNA sequences, thus favoring the obtaining of cultures free of toxic substances . In this review, specific biocontrol methods are presented, such as essential oils, microbial metabolites, molecular tools and the use of biodegradable substances that favor the management and prevention of pests, which help mitigate the environmental problems generated by the use of fungicides from chemical nature.

Characterization of glycolipid biosurfactant from Pseudomonas aeruginosa PA 1 and its efficacy against Phytophtora infestans

Aim: The aim of the present study was to identify biosurfactant produced by Pseudomonas aeruginosa and to determine the effectiveness of biosurfactants (rhamnolipid) against P. infestans causing late blight of potato. Methodology: Pseudomonas aeruginosa strains were isolated from soil samples and the potential strain PA 1, selected because of its antagonistic ability, was used to optimize anti-metabolite production and its characterization using HPLC-Mass spectrometry. Rhamnolipid based formulation was developed and its efficacy was tested against late blight disease. Results: The results revealed that four rhamnolipids congeners were identified, among them three were mono-rhamno-di-lipidic congeners and one was di-rhamno-di-lipdic congeners, abundantly present in the crude biosurfactant obtained from P. aeruginosa PA1. The mass spectra of mono-rhamno-di-lipidic Rha-C12-C14 peak value (m/z 584), Rha-C12.1-C10.CH3 peak value (m/z 545), Rha-C12-C-12-CH3 peak value (m/z 575) and di-rhamno-di-lipidic. Rha-Rha-C10-C10 peak value (m/z 651) were also detected. Rhamnolipid-based formulation was developed and evaluated at different concentration ranging from 0.012 and 0.3% in detached leaf test. Significant reduction in lesion area was recorded at 0.2% concentration (lesion area 0.06 cm2 as against 9.8 cm2 on 5th day of inoculation). Interpretation: Microbial produced rhamnolipid based formulation at 0.2% concentration was found effective against late blight of potato in detached leaf test. Further, it could be used in field study as green chemical which would help in replacing application of chemicals in agriculture.

Expresión de efectores RXLR en el linaje clonal EC-1 de Phytophthora infestans en Perú / Expression of RXLR effectors in the EC-1 clonal lineage of Phytophthora infestans in Peru

La papa (Solanum tuberosum L.) es en nuestros días uno de los cultivos alimenticios más importantes. Esta es propensa a la enfermedad de Tizón Tardío, causada por el oomiceto patógeno Phytophthora infestans, el cual secreta cientos de efectores que actúan como factores de virulencia. Poco se conoce sobre la diversidad de genes de virulencia de las cepas pertenecientes al linaje de reproducción clonal EC-1. En el presente estudio, mediante el secuenciamiento del transcriptoma de la interacción de la papa y P. infestans durante los primeros días después de la infección en las hojas de papa, se identificó la expresión diferencial de genes efectores tipo RXLR en dos cepas de P. infestans EC-1, siendo confirmados por qRT-PCR. Estas cepas, aisladas de papas cultivadas en el centro de los Andes peruanos, tienen diferentes patrones de virulencia. Los genes efectores, fueron silenciados en una cepa, para Avr-vnt1 en POX109 y para el homólogo Avh9.1 en POX067, pero expresados en la otra. Los resultados de transcriptoma fueron comparados con tres cepas adicionales del linaje EC-1. La información del repertorio de los efectores del patógeno y su expresión podrían ser informativos para el mejoramiento genético de la resistencia. El descubrimiento de efectores silenciados en las poblaciones del patógeno pueden guiar al uso de genes R específicos en los programas de mejoramiento genético. Por ejemplo, en el contexto de los Andes, donde el linaje clonal EC-1 predomina, el gen Rpi-vnt1 podría no ser recomendado.

Potato (Solanum tuberosum L.) is nowadays one of the most important food crops. It is prone to the disease known Late blight caused by the oomycete pathogen Phytophthora infestans, which secrete a hundreds of effectors that act as virulence factors. Little is known of the diversity of virulence genes of the strains that belong to a clonally reproducing lineage EC-1. In this paper, through the transcriptome sequencing of potato and P. infestans interaction, we identified differentially expressed RXLR type effector genes in two P. infestans isolates EC-1, being confirmed by qRT-PCR. The isolates, originate from cultivated potato in the central Peruvian Andes, have different virulence patterns. Effector genes, were silenced in one isolate, such as Avr-vnt1 in POX 109 and for Avh9.1 homolog in POX 067, but expressed in the other. The transcriptomics results were compared with three additional isolates from the EC-1 lineage. The information on the pathogen effector repertoire and its expression should be informative for resistance breeding. Discovery of silenced effectors in the pathogen populations can guide the use of specific R genes in the breeding programs. For example in the Andean setting where EC-1 lineage dominates the Rpi-vnt1 would not be recommended.

Controle da requeima e pinta preta da batata por fungicidas e seu reflexo sobre a produtividade e a qualidade de tubérculos / Control of potato late blight and early blight by fungicides and its effects on yield and quality of tubers

A requeima (Phytophthora infestans) e a pinta preta (Alternaria solani) estão entre as doenças mais frequentes e destrutivas da cultura da batata. Com o objetivo de avaliar a ação de diferentes grupos fungicidas no controle dessas doenças, foram realizados dois experimentos em cultivo comercial de batata (cultivares Agata e Monalisa), localizados em Pilar do Sul, São Paulo, nas safras 2008 e 2009. O delineamento experimental utilizado foi o de blocos ao acaso, com 4 repetições, sendo cada parcela de 20 m2. As aplicações foram realizadas com um pulverizador costal, munido de barra de aplicação e pressão constante de 3 Bar. O volume de aplicação variou de 300 a 500 L.ha-1 em função do desenvolvimento da cultura. As variáveis avaliadas para as duas doenças foram: severidade em folhas, área abaixo da curva de progresso da doença (AACPD), produtividade total e comercial, e classificação de tubérculos. Os menores níveis de doença e aumentos significativos na produtividade comercial e qualidade de tubérculos foram observados nas parcelas tratadas com fluopicolide + propamocarbe, dimetomorfe + ametoctradina, mandipropamida + clorotalonil, mandipropamida, fenamidona + propamocarbe, bentiavalicarbe + fluazinam, seguidos de dimetomorfe + clorotalonil, mefenoxam + clorotalonil e famoxadona + cimoxanil + mancozebe para requeima, e azoxistrobina + difenoconazol, picoxistrobina, piraclostrobina + metconazol, trifloxistrobina + tebuconazol, azoxistrobina, boscalida + piraclostrobina, iprodiona + pirimetanil e ciprodinil para pinta preta.(AU)

Late blight (Phytophthora infestans) and early blight (Alternaria solani) are among the most current and destructive diseases of potato. With the aim of evaluating the efficiency of different fungicides in the control of both diseases, two experiments were carried out in commercial potato crops (cultivars Agata and Monalisa) in Pilar do Sul, São Paulo State, Brazil, during 2008 and 2009 cropping season. Randomized block designs were used, with 4 replications and each parcel of 20 m2. Applications were carried out using coastal sprayer with spray-bar under constant pressure of 3 Bar. The application volume varied from 300 to 500 L per hectare according to the crop development. The evaluated variables for both diseases were: severity on leaves, area under disease progress curve (AUDPC), total and commercial yield, and classification of tubers. For late blight, the lower severity levels and significant increases in commercial yield and quality tubers were observed on the rows treated with fluopicolide + propamocarb, dimetomorph + ametoctradin, mandipropamid + chlorothalonil, mandipropamid, fenamidone + propamocarb, benthiavalicarb + fluazinam, followed by dimetomorph + chlorothalonil, mefenoxam + chlorothalonil e famoxadone + cymoxanil + mancozeb and, for early blight, azoxystrobin + difenoconazole, picoxystrobin, pyraclostrobin +metconazole, trifloxystrobin + tebuconazole, azoxystrobin, boscalid + pyraclostrobin, iprodione + pyrimethanil and cyprodinil.(AU)

Ametoctradin: a new fungicide for potato late blight control / Ametoctradina: um novo fungicida para controle da requeima da batata

Late blight (Phytophthora infestans ) is among the most important and destructive diseases in potato cultivation. Aiming to evaluate the efficacy of the new fungicide ametoctradin, mixed with dimethomorph and metiram, an experiment was carried out in commercial potato crops (Ágata cultivar) in Pilar do Sul, São Paulo state, Brazil, during the growing season in 2013. A randomized block design was used, with 4 replications, on plots of 15 m2. Applications were carried out using a backpack sprayer with a spray-bar under 3 bar of constant pressure. The application volume varied from 300 L to 600 L.ha-1 based on crop development. The variables evaluated were leaf severity (0 to 100%), area under the disease progress curve, and yield. Ametoctradin + dimethomorph (1.25 L.ha-1) provided significant control of late blight, exceeding benthiavalicarb + fluazinam, dimethomorph + metiram, dimethomorph + pyraclostrobin, cymoxanil + mancozeb, metalaxyl-M + mancozeb, ametoctradin + metiram, and pyraclostrobin + metiram, although similar to ametoctradin + dimethomorph (1.00 L.ha-1), fluopicolide + propamocarb, and fenamidone + propamocarb. Ametoctradin + metiram resulted in moderate control, which was always similar to the standard. Ametoctradin and its associations represent a new alternative for the management of potato late blight.(AU)

A requeima (Phytophthora infestans) é uma das mais importantes e destrutivas doenças da cultura da batata. Com o objetivo de avaliar a ação do novo fungicida ametoctradina em mistura com dimetomorfe e metiram, foi realizado um experimento em cultivo comercial de batata (cultivar Ágata), localizado em Pilar do Sul, São Paulo, na safra 2013. O delineamento experimental utilizado foi o de blocos ao acaso, com 4 repetições, sendo cada parcela de 15 m2. As aplicações foram realizadas com um pulverizador costal, munido de barra de aplicação e pressão constante de 3 Bar. O volume de aplicação variou de 300 a 600 L.ha-1 em função do desenvolvimento da cultura. As variáveis avaliadas foram: severidade em folhas (0 a 100%), área abaixo da curva de progresso da doença e produtividade. Ametoctradina + dimetomorfe (1,25 L.ha-1) proporcionou controle significativo da requeima, sendo superior a bentiavalicarbe + fluazinam, dimetomorfe + metiram, dimetomorfe + piraclostrobina, cimoxanil + mancozebe, metalaxil-M + mancozebe, ametoctradina + metiram, piraclostrobina + metiram e semelhante a ametoctradina + dimetomorfe (1,00 L.ha-1), fluopicolide + propamocarbe e fenamidona + propamocarbe. Ametoctradina + metiram apresentou comportamento intermediário, sendo sempre similar aos padrões. Ametoctradina e suas associações representam uma nova alternativa para o manejo da requeima na cultura da batata.(AU)

Resistencia a Phytophthora infestans linaje clonal EC-1 en Solanum tuberosum mediante la introducción del gen RB

Una de las opciones para el control de la enfermedad del tizón tardío de la papa es el desarrollo de variedades resistentes a Phytophthora infestans mediante la transferencia directa de genes de resistencia (R) por ingeniería genética. En el siguiente trabajo de investigación, se usó el gen RB de Solanum bulbocastanum, el cual otorga un amplio espectro de resistencia a razas de P. infestans. Para dicho fin, se transformó genéticamente vía Agrobacterium la variedad susceptible de papa Desiree (Solanum tuberosum) con el vector binario pCIP68 que contiene el gen RB. Como resultado, se obtuvieron 19 plantas transformadas con el gen RB, confirmadas por la prueba de resistencia a kanamicina y por la prueba de reacción en cadena de la polimerasa (PCR). Las 19 plantas transgénicas fueron sometidas a infección en invernadero bajo condiciones de bioseguridad con el aislamiento POX067 de P. infestans perteneciente al linaje clonal EC-1 que es dominante en el Perú. Tres de las 19 plantas ([RB]54, [RB]56 y [RB]70) presentaron un alto nivel de resistencia al aislamiento POX067 de P. infestans.

One of the most efficient options for the control of late blight disease in potato (Solanum tuberosum) is the development of resistant varieties to Phytophthora infestans mediated by the direct transfer of resistance (R) genes through genetic engineering. In the present work, we used Solanum bulbocastanum RB gene to confers broad spectrum resistance to P. infestans races. To that end, Agrobacterium - mediated genetic transformation was used to transform a susceptible potato variety, Desiree, with the binary vector pCIP68 harboring the RB gene. As a result, 19 transformed plants containing the RB gene were obtained. kanamycin resistance test and polymerase chain reaction (PCR) assays confirmed the integration of the T-DNA in the potato genome. The 19 transformed plants, also called transgenic events were subjected to infection under biosafety greenhouse conditions. Phytophthora infestans isolate POX067 of the EC-1 clonal lineage, commonly find in Peru, was used for the infection. Three of the 19 plants ([RB]54, [RB]56 and [RB]70) show high resistance levels to isolate POX067 of P. infestans.

Agrotransformación y evaluación de la resistencia a Phytophthora infestans en Solanum tuberosum L. variedad Désirée

El Oomiceto Phytophthora infestans (Mont.) de Bary, agente causal de la enfermedad denominada tizón tardío, es el principal responsable del déficit en rendimiento y producción en el cultivo de papa a nivel mundial; una de las alternativas a considerar en la lucha contra este patógeno es la integración de secuencias completas de genes R en el genoma de la papa a través de Agrotransformación. El gen Rpi-blb2 (gen R) de la especie silvestre Solanum bulbocastanum Dunal, presenta una amplia resistencia a los aislamientos de P. infestans, haciéndolo un importante candidato en los estudios de mejoramiento genético en plantas. En el presente trabajo se describe la introducción del gen Rpi-blb2 por Agrobacterium tumefaciens en el genoma de la papa variedad Désirée, la caracterización molecular de 29 eventos transformados e infección de plantas completas con el aislamiento POX067 de P. infestans obtenido en el Perú. Los eventos Désirée [Rpi-blb2] 4 y Désirée [ Rpi-blb2] 30, presentaron una resistencia considerable frente a la infección de P. infestans, comprobando de esta manera la transferencia del gen Rpi-blb2 de una especie silvestre a una cultivada mediante transformación genética.

The Oomycete Phytophthora infestans (Mont.) de Bary, the causal agent of the disease known as late blight, is primarily responsible for the decreased in production performance and potato crops worldwide. The integration of the complete R genes sequences in the potato genome using Agro-transformation appears an alternative to be considered in the fight against this pathogen. The Rpi-blb2 gene (R gene) from the wild species Solanum bulbocastanum Dunal shows a broad resistance to isolates of P. infestans, making it an important candidate for plant breeding studies. This paper reports the integration of the Rpi-blb2 gene into potato var. Désirée genome by Agrobacterium tumefaciens - mediated transformation system, the molecular characterization of 29 events transformed and whole plant infection with isolate POX67 of P. infestans from Peru. Désirée events [Rpi-blb2] 4 and Désirée [Rpi-blb2] 30, showed a substantial resistance to P. infestans infection confirming complete transfer of the Rpi-blb2 gene from a wild species to a cultivated species by genetic transformation.

Profiling carbohydrate composition, biohydrogen capacity, and disease resistance in potato

Background: Potato (Solanum tuberosum) is one of the most important sources of carbohydrates in human diet. Because of its high carbohydrate levels it recently has also received attention in biohydrogen production. To exploit the natural variation of potato with respect to resistance to major diseases, carbohydrate levels and composition, and capacity for biohydrogen production we analyzed tubers of native, improved, and genetically modified potatoes, and two other tuberous species for their glucose, fructose, sucrose, and starch content. Results: High-starch potato varieties were evaluated for their potential for Caldicellulosiruptor saccharolyticus-mediated biohydrogen production with Desirée and Rosita varieties delivering the highest biohydrogen amounts. Native line Vega1 and improved line Yagana were both immune to two isolates (A291, A287) of Phytophthora infestans. Conclusions: Our data demonstrate that native potato varieties might have great potential for further improving the multifaceted use of potato in worldwide food and biohydrogen production.

IDENTIFICATION OF KEY MOLECULAR COMPONENTS OF THE RESISTANCE OF CHERRY TOMATO AGAINSTPhytophthora infestans / Identificación de los principales componentes moleculares de la resistencia de tomate cherry contra Phytophthora infestans

Cherry tomato Solanum lycopersicum var cerasiforme cv Matt's wild cherry is a very resistant cultivar to most Phytophthora infestans isolates. Two isolates were identified, US940480 and US970001 that cause an incompatible and a compatible interaction respectively. US970001 is one of the few isolates producing a compatible interaction with this cultivar. To identify genes with a differential gene expression between compatible and incompatible interactions, gene expression patterns were analyzed with tomato cDNA microarrays including 12,899 independent tomato cDNA clones at different time points after inoculation. A diverse set of statistical tools were used to identify key components of the plant response to the pathogen. Forty-three genes were up-regulated during the incompatible reaction at time point 36 hours, 15 globally at all time points and twelve were found both in globally and at 36 hours. Northern blots analysis was performed to confirm differential expression showed by microarray analysis and to study the differential expression of more plant resistance genes (PR) genes between compatible and incompatible interactions for this interaction.

El tomate cherry Solanum lycopersicum var cerasiforme cv Matt's es bastante resistente a la gran parte de aislamientos de Phytophthora infestans. Se han identificado dos aislamientos, US940480 y US970001 que causan interacción incompatible y compatible respectivamente. US970001 es uno de los pocos aislamientos causantes de interacción compatible con este cultivo. Con el fin de identificar genes con expresión diferencial en interacciones compatible e incompatible, analizamos DNA copia de 12899 clones independientes en tres tiempos posteriores a la inoculación del patógeno. Se aplicaron diversas herramientas estadísticas para identificar componentes moleculares claves de la respuesta de la planta al patógeno. Cuarenta y tres genes fueron detectados como activados durante la interacción incompatible a las 36 horas posinoculación, 15 genes se detectaron como activados globalmente tomando en conjunto los 3 tiempos analizados y 12 genes tanto globalmente como a las 36 horas. Análisis de Northern blot permitieron confirmar la expresión diferencial detectada con los análisis de microarreglos y estudiar la expresión diferencial de otros genes de resistencia en plantas (PR) en in teracciones compatible e incompatible en esta interacción.

Phytophthora infestans POPULATION STRUCTURE: A WORLDWIDE SCALE / Estructura poblacional de Phytophthora infestans: una escala global

Phytophthora infestans, the causal agent of late blight disease in potato and other members of the Solanaceae family, is responsible for causing the Irish potato famine and, even today, it causes enormous economic losses all over the world. For the establishment of an adequate pest management strategy, the determination of the pathogen's population structure is required. To characterize P. infestans populations worldwide two allozymes, Gpi (Glucose-6-phospate isomerase) and Pep ( Pep tidase), the RG57 DNA RFLP fingerprinting probe, as well as resistance to the fungicide metalaxyl and mating type, have been used as markers. P. infestans populations in Mexico have been one of the main focuses of research in the population biology of this pathogen because this country has been considered as one of the possible centers of origin of this oomycete. In this review we present the population structure of P. infestans in Mexico, Europe, Africa, Asia, North America, and South America, expanding it on the present situation of P. infestans in Colombia. Finally, we will discuss different lines of research that are being carried out today with respect to P. infestans in Colombia, which have shown the importance of continuing the study of this devastating plant pathogen in our country.

Phytophthora infestans, el agente causal del tizón tardío de la papa y otros miembros de la familia de las Solanáceas, es el responsable de la gran hambruna irlandesa y aún hoy sigue causando grandes pérdidas económicas alrededor del planeta. Para establecer estrategias de control adecuadas contra este patógeno se requiere comprender la estructura poblacional del mismo. Mundialmente se han utilizado como marcadores las aloenzimas, Gpi (Glucosa-6-fosfato isomerasa) y Pep (Peptidasa) y la sonda de fingerprinting de RFLP (Polimorfismos de la Longitud de los Fragmentos de Restricción), RG57. De igual forma, la resistencia al fungicida metalaxyl y el tipo de apareamiento, han sido empleados para caracterizar las poblaciones de P. infestans. Las poblaciones de P. infestans en México han sido uno de los focos principales de investigación en la biología poblacional de este patógeno debido a que este país ha sido considerado como uno de los posibles centros de origen de este oomiceto. En esta revisión se presentará la estructura poblacional de P. infestans en México, Europa, África, Asia, Norte América y Sur América, profundizando en la situación actual de P. infestans en Colombia. Finalmente, se discutirá las diferentes líneas de investigación que se llevan a cabo hoy respecto a P. infestans en Colombia, las cuales han mostrado la importancia de continuar con el estudio de este devastador patógeno de plantas en nuestro país.

Evaluación de marcadores moleculares asociados con resistencia a gota (Phytophthora infestans L) en papas diploides y tetraploides / Evaluation of molecular markers associated with resistance to late blight (Phytophthora infestans L) in diploid and tetraploid potatoes

La papa, cultivo de importancia a nivel mundial es gravemente afectado por gota, enfermedad ocasionada por el oomycete Phytophthora infestans. Actualmente la forma más efectiva para combatir la enfermedad es mediante el desarrollo de cultivares resistentes al patógeno. Para esto, una estrategia es identificar genes que confieran resistencia al patógeno, para lo cual se buscan marcadores asociados con el carácter de resistencia. En este estudio se evaluaron marcadores moleculares tipo SCAR (Sequence Characterized Amplified Region): CosA, GP179, BA47f2 y Prp1 asociados con resistencia a P. infestans y el gen de resistencia R1, en 22 cultivares tetraploides pertenecientes a la subespecie andigena y cinco especies silvestres. Se evaluó el polimorfismo y se determinó si los alelos polimórficos permitían diferenciar genotipos resistentes de susceptibles. Se comparó el tamaño de los fragmentos obtenidos con los fragmentos esperados asociados con resistencia de acuerdo a reportes. El análisis se realizó considerando presencia/ausencia de los fragmentos: CosA210, CosA250, R11400, R11800, BA47f2500, GP179570, Prp1300, Prp1600, y Prp1900. Los resultados indicaron que en los cultivares tetraploides y silvestres, se presentaron polimorfismos en todos los marcadores evaluados, con excepción del marcador GP179. No se encontró correlación entre el rasgo de resistencia y los alelos. Los resultados de este estudio muestran que hay repuesta diferencial a los marcadores entre las subsp. tuberosum y subsp. Andigena.

Potato is an important worldwide crop seriously affected by late blight disease caused by the oomycete Phytophthora infestans. Currently, the most effective way to control the disease is developing resistant cultivars to the pathogen by identifying genes that confer resistance to the pathogen. For this purpose it is important to find molecular markers associated with the trait. In this study, the SCAR (Sequence Characterized Amplified Region) markers: CosA, GP179, BA47f2 y Prp1, associated with late blight and the resistant gen R1 were evaluated in 22 tetraploid cultivars from subspecie andigena and five wild potato species. Polymorphism was evaluated and it was evaluated if polymorphic alleles allow differentiating resistant from susceptible genotypes. The fragment length for each marker was compared to the allele size reported associated to resistance. The analysis considered the presence/absence of the fragments: CosA210, CosA250, R11400, R11800, BA47f2500, GP179570, Prp1300, Prp1600 and Prp1900. The results indicated that both, tetraploid cultivars and wild potatoes, showed polymorphisms with all these markers, except with the GP179 marker. It was not found correlation between resistance and the presence of specific alleles. Evidence found in this study indicates that results obtained with molecular markers differed between subsp. tuberosum and subsp. andigena.

Induction of systemic resistance in different varieties of Solanum tuberosum by pure and crude elicitor treatment.

A 10 kD elicitor protein (infestin) produced by Phytopthora infestans was purified and its efficacy for induction of systemic resistance in resistant and susceptible varieties of Solanum tuberosum was studied. Culture filtrates from P. infestans with and without purified elicitor (infestin) were used as elicitors to understand the effect of purified elicitor (infestin) on development of systemic resistance. Culture filtrate and purified elicitor (infestin) were found to induce hypersensitive reaction on the leaves of resistant varieties, but not on susceptible varieties after 48 h. Culture filtrate devoid of purified elicitor (infestin) did not induce any necrotic spots even on resistant variety. Purified elicitor (infestin) was found to induce glucose oxidase, NADPH oxidase, superoxide dismutase, glutathione reductase, catalase and peroxidase enzymes in resistant S. tuberosum plants, however the induction of these enzymes was low in susceptible varieties. The oxidative enzymes were found to induce earlier than antioxidative enzymes and there was negative correlation between these two groups of enzymes. Levels of salicylic acid, phenylalanine ammonia lyase (PAL), -1, 3 glucanase and chitinase activities were also found higher in resistant than in susceptible varieties. It was observed that purified elicitor (infestin) was superior to crude culture filtrate, but was not capable of inducing systemic resistance in susceptible varieties.

Sistema de previsão de ocorrência de requeima em clones de batata suscetíveis e resistentes / Forecasting system of late blight occurrence in susceptible and resistant potato clones

Sistemas de previsão e cultivares resistentes à requeima são importantes ferramentas para reduzir a quantidade de fungicidas utilizados e os custos de produção da batata. O objetivo deste trabalho foi avaliar a utilização do sistema de previsão Blitecast e de clones suscetíveis e resistentes no manejo da requeima da cultura da batata na região produtora de Santa Maria, Rio Grande do Sul (RS). Os experimentos foram conduzidos na Universidade Federal de Santa Maria, na primavera de 2006 e no outono de 2007, sendo os dados meteorológicos medidos continuamente acima do dossel das plantas. Foram utilizados 10 tratamentos arranjados no delineamento inteiramente casualizado, com quatro repetições. Os tratamentos foram diferenciados pelos valores de severidade acumulados, calculados pelo sistema Blitecast, e pelos clones SMIJ461-1 e SMINIA793101-3, caracterizados como resistentes à requeima, e Macaca (suscetível). Verificou-se que o sistema Blitecast não foi eficiente para prever o momento de aplicação de fungicida no controle da requeima. Portanto, este deve sofrer ajustes para ser utilizado em clones suscetíveis. Nos clones considerados resistentes, a aplicação de fungicidas com base na utilização do sistema Blitecast não tem efeito sobre a severidade da requeima e a produtividade da cultura da batata.

Forecasting systems and late blight resistant cultivars are important tools to reduce the amount of fungicides and the production cost of a potato farm. The objective of this study was to evaluate the Blitecast forecasting system for late blight occurrence and susceptible and resistant potato clones for managing late blight in Santa Maria, RS, Brazil. Experiments were conducted at the Federal University of Santa Maria during the Spring 2006 and Autumn 2007. Meteorological data were measured continuously above the crop canopy. Ten treatments were used in a completely randomized design, with four replications. Treatments were different values of accumulated severity, calculated by the Blitecast forecasting system and by the potato clones SMIJ461-1 and SMINIA793101-3, characterized as resistant, and the clone Macaca as susceptible to late blight. The Blitecast forecasting system was not effective for predicting the time of fungicide spraying for the control of late blight and, therefore, to be used in susceptible clones it has to be adjusted. For resistant clones, the fungicide spraying based on the Blitecast system has no effect on late blight occurrence and potato productivity.

Resistance Induction and Enhanced Tuber Production by Pre-inoculation with Bacterial Strains in Potato Plants against Phytophthora infestans

Efficacy of resistance induction by the bacterial isolates Pseudomonas putida (TRL2-3), Micrococcus luteus (TRK2-2) and Flexibacteraceae bacterium (MRL412), which were isolated from the rhizosphere of plants growing in Jeju Mountain, were tested in a greenhouse. The disease severity caused by Phytophthora infestans was effectively reduced in the potato plants pre-inoculated with bacterial isolates compared with those of the untreated control plants growing in a greenhouse. In order to estimate the level of protection by the bacterial isolates, Mancozeb WP (Diesen M(R), Kyong nong) and DL-3-amino butyric acid (BABA) were pre-treated, whereas Dimethomorph WP (Forum(R), Kyong nong) and phosphonic acid (H3PO3) were post-treated the challenge inoculation with the pathogen. Disease severities of chemical pre-treated as well as post-treated plants were reduced compare to those of the untreated. The disease reduction in the plants pre-treated with Mancozeb WP was the highest, whereas that of post-treated with Dimethomorph WP was the lowest. The yields of plants pre-inoculated with three bacterial isolates were greatly increased than those of control plants. These results suggest that biological control by bacterial isolates might be an alternative strategy against late blight disease in potato plants growing in greenhouse.