349 research outputs found

    Re-evaluating the taxonomic status of Phaeoisariopsis griseola, the causal agent of angular leaf spot of bean

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    Angular leaf spot of Phaseolus vulgaris is a serious disease caused by Phaeoisariopsis griseola, in which two major gene pools occur, namely Andean and Middle-American. Sequence analysis of the SSU region of nrDNA revealed the genus Phaeoisariopsis to be indistinguishable from other hyphomycete anamorph genera associated with Mycosphaerella, namely Pseudocercospora and Stigmina. A new combination is therefore proposed in the genus Pseudocercospora, a name to be conserved over Phaeoisariopsis and Stigmina. Further comparisons by means of morphology, cultural characteristics, and DNA sequence analysis of the ITS, calmodulin, and actin gene regions delineated two groups within P. griseola, which are recognised as two formae, namely f. griseola and f. mesoamericana

    Short communication: Occurrence of angular leaf spot caused by Pseudocercospora griseola in Phaseolus vulgaris in Asturias, Spain

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    Angular leaf spot (ALS) symptoms were observed in 2015 in common bean fields at four locations in Asturias, NW Spain. This disease is frequent in tropical areas and we have no record of its presence in our region, at least in the last 30 years. However, since its detection its presence in the crops has been increasing. Symptoms were necrotic spots on leaves and reddish-brown to black circular spots on pods, stems, branches and petioles. The damage observed in the mentioned crops was highly variable (between 60% and 100% affected leaves), being most severe in crops where no agrochemical treatment were applied. Three strains were selected and identified based in morphological features as Pseudocercospora griseola. The ITS region was amplified by PCR obtaining a sequence that was identical for the three isolates (Acc. No. LT222499). This sequence showed 99-100% similarity with those deposited in databases corresponding to P. griseola. To fulfill Koch's postulates, a pathogenicity test was carried out in two common bean cultivars (‘Andecha’ and ‘Maruxina’). P. griseola was re-isolated from inoculated plants and not from control plants. In cv. ‘Andecha’, chlorosis was observed in all the inoculated plants, before the appearance of spots. Consequently this is the first confirmed report of this pathogen in our region

    Efecto del extracto de alga Ulva fasciata sobre Pseudocercospora griseola en el cultivo de frijol

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    Angular leaf spot is one of the most common diseases in beans crops in southern Brazil. This research aims to evaluate the effect of the extract from macroalga Ulva fasciata on angular leaf spot severity, foliar pigment content, and yield of common bean genotypes IPR Uirapuru, CF 22, and Mouro graúdo for 2005 and 2006. Plants were sprayed at phenological stages V3, V5, R6, and R7 with the alga extract or fungicide azoxystrobin. Untreated plants served as controls. Disease severity (%) was estimated from the V3 stage, totaling six examinations a year. Severity values were integrated as the area under the disease progress curve (AUDPC). Foliar pigments (chlorophyll a, b, total, and carotenoids) were determined in 2006. Grain yield was evaluated in both years, but the thousand-grain weight in 2005 only. The control exerted by the U. fasciata extract on angular leaf spot depends on the biological interaction between the bean genotype and the environment. The efficiency of U. fasciata extract in controlling angular leaf spot depended on the interaction between bean genotypes and the environment. Besides, the extract did not affect leaf pigment content or grain yield.La mancha angular es una de las enfermedades foliares más comunes del cultivo de frijol en el sur de Brasil. El objetivo del trabajo fue evaluar el efecto del extracto de la macroalga Ulva fasciata en la severidad de la mancha angular, los niveles de pigmentos foliares y la productividad de los genotipos de frijol común IPR Uirapuru, CF 22 y Mouro graúdo, durante los años 2005 y 2006. Las plantas tratadas con el extracto de alga o el fungicida azoxistrobina se pulverizaron en los estados fenológicos V3, V5, R6 e R7. Plantas no tratadas se utilizaron como testigos. La severidad (%) de la enfermedad se estimó a partir del estado V3, para un total de seis evaluaciones cada año. Los valores de la severidad se calcularon como área bajo la curva de progreso de la enfermedad (ABCPE). En el 2006 se determinaron los pigmentos foliares (clorofila a, b, total y carotenoides) y en los dos años se evaluó el rendimiento de granos, aunque en el 2005 solamente se evaluó el peso de mil granos. En conclusión, el control que ejerce el extracto de U. fasciata sobre la mancha angular depende de la interacción biológica entre el genotipo de frijol y el ambiente. Por otro lado, el extracto no afectó el contenido de los pigmentos foliares ni la producción de granos

    Reação de linhagens de feijoeiro de oito ciclos de seleção recorrente visando a resistência à Pseudocercospora griseola a dois isolados do patógeno.

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    A mancha angular incitada pelo fungo Pseudocercospora griseola é um dos principais problemas da cultura do feijoeiro em algumas regiões do Brasil. Visando a obter linhagens resistentes a esse patógeno, um programa de seleção recorrente vem sendo conduzido há alguns anos pela Universidade Federal de Lavras (UFLA) e Embrapa Arroz e Feijão. Esse trabalho visa avaliar o desempenho de linhagens obtidas nos diferentes ciclos seletivos, sob condições de casa de vegetação, com relação a dois isolados de P griseola

    Avaliação de linhagens de feijoeiro de um programa de seleção recorrente quanto à reação a raça 63-31 de Pseudocercospora griseola.

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    O objetivo deste trabalho foi avaliar 35 linhagens de feijoeiro oriundas dos sete primeiros ciclos desse programa de seleção recorrente quanto à reação à raça 63-31 de P. griseola, em condições controladas.CONAFE

    Linkage mapping of the Phg-1 and Co-14 genes for resistance to angular leaf spot and anthracnose in the common bean cultivar AND 277

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    The Andean common bean AND 277 has the Co-14 and the Phg-1 alleles that confer resistance to 21 and eight races, respectively, of the anthracnose (ANT) and angular leaf spot (ALS) pathogens. Because of its broad resistance spectrum, Co-14 is one of the main genes used in ANT resistance breeding. Additionally, Phg-1 is used for resistance to ALS. In this study, we elucidate the inheritance of the resistance of AND 277 to both pathogens using F2 populations from the AND 277 × Rudá and AND 277 × Ouro Negro crosses and F2:3 families from the AND 277 × Ouro Negro cross. Rudá and Ouro Negro are susceptible to all of the above races of both pathogens. Co-segregation analysis revealed that a single dominant gene in AND 277 confers resistance to races 65, 73, and 2047 of the ANT and to race 63-23 of the ALS pathogens. Co-14 and Phg-1 are tightly linked (0.0 cM) on linkage group Pv01. Through synteny mapping between common bean and soybean we also identified two new molecular markers, CV542014450 and TGA1.1570, tagging the Co-14 and Phg-1 loci. These markers are linked at 0.7 and 1.3 cM, respectively, from the Co-14/Phg-1 locus in coupling phase. The analysis of allele segregation in the BAT 93/Jalo EEP558 and California Dark Red Kidney/Yolano recombinant populations revealed that CV542014450 and TGA1.1570 segregated in the expected 1:1 ratio. Due to the physical linkage in cis configuration, Co-14 and Phg-1 are inherited together and can be monitored indirectly with the CV542014450 and TGA1.1570 markers. These results illustrate the rapid discovery of new markers through synteny mapping. These markers will reduce the time and costs associated with the pyramiding of these two disease resistance genes

    Phylogenetic lineages in the Capnodiales

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    The Capnodiales incorporates plant and human pathogens, endophytes, saprobes and epiphytes, with a wide range of nutritional modes. Several species are lichenised, or occur as parasites on fungi, or animals. The aim of the present study was to use DNA sequence data of the nuclear ribosomal small and large subunit RNA genes to test the monophyly of the Capnodiales, and resolve families within the order. We designed primers to allow the amplification and sequencing of almost the complete nuclear ribosomal small and large subunit RNA genes. Other than the Capnodiaceae (sooty moulds), and the Davidiellaceae, which contains saprobes and plant pathogens, the order presently incorporates families of major plant pathological importance such as the Mycosphaerellaceae, Teratosphaeriaceae and Schizothyriaceae. The Piedraiaceae was not supported, but resolves in the Teratosphaeriaceae. The Dissoconiaceae is introduced as a new family to accommodate Dissoconium and Ramichloridium. Lichenisation, as well as the ability to be saprobic or plant pathogenic evolved more than once in several families, though the taxa in the upper clades of the tree lead us to conclude that the strictly plant pathogenic, nectrotrophic families evolved from saprobic ancestors (Capnodiaceae), which is the more primitive state

    Pathogen variability and new sources of resistance to angular leaf spot among bean landraces in Uganda

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    Angular leaf spot (ALS), a fungal disease caused by Pseudocercospora griseola, has a significant impact on bean productivity in Africa, causing up to 80% yield losses. Efforts to breed for ALS resistance are challenged by continuously evolving pathogen races that differ by location. Released bean varieties in Uganda are susceptible to ALS; the few exotic sources of resistance available are not well adapted to local environmental conditions. To overcome these challenges, a study was conducted to understand pathogen variability and identify new sources of ALS resistance for deployment in ALS resistance breeding. Variability in 45 P. griseola pathotypes was elucidated using a set of 12 ALS differential cultivars, random amplified microsatellite markers, and conserved sequences. The differentials and markers defined 12 pathotypes and 30 haplotypes, respectively, which belonged to the Middle American and Andean gene pool groups, each with high variability. Among the 74 bean landraces screened using the 1:6, 17:39, 21:39, and 61:63 P. griseola pathotypes, only U00279 showed consistent resistance to all the four pathotypes. U00297’s resistance to pathotype 17:39 was conferred by a single dominant gene, while digenic epistatic gene interactions were responsible for resistance to other pathotypes. The dominant gene in U00297 was independent of resistance genes harbored by documented resistance sources AND277 and G5686. The results revealed high variability in P. griseola and identified a new source of broad ALS resistance. The divergent inheritance patterns of resistance to the different pathotypes indicate the importance of race specificity of the target host plant in breeding for disease resistance.Keywords: Pseudocercospora griseola, variability, resistance, inheritance, alleli

    Implicações da severidade de mancha angular em experimentos de avaliação de linhagens elite de feijoeiro.

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    Para verificar se a avaliação por meio de uma escala de notas de severidade da mancha angular (Pseudocercospora griseola) contribui para explicar a variação entre linhagens de feijão com relação à produtividade de grãos, foi realizado o presente trabalho
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