Specific boundaries between the causal agents of the soybean stem canker

Pathogens within the Diaporthe complex cause seed decay, stem blight and stem canker on soybean, representing a serious threat for this crop species. We herein utilize worldwide sequence data retrieved from Genbank in order to assess the species boundaries between the soybean stem canker causal agents, and define whether or not they should be regarded as members of the same biological species. These studies were complemented with compatibility tests, in order to validate our findings from a biological standpoint. Species delimitation assays supported the occurrence of a speciation event between D. caulivora and D. phaseolourm var. meridionalis. A speciation hypothesis between D. aspalathi and D. phaseolourm var. meridionalis was also supported, based on three reciprocally monophyletic substitutions at locus EF1-α. Compatibility tests further validated species delimitation assays indicating that D. caulivora has developed barriers to gene exchange with D. phaseolorum var. meridionalis. Clarification of the specific boundaries of the SSC pathogens and related entities will be an important asset to future research in soybean pathology, epidemiology and breeding.Fil: Guillin, Eduardo A.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; ArgentinaFil: Grijalba, Pablo Enrique. Universidad de Buenos Aires. Facultad de Agronomia; ArgentinaFil: Oliveira, Luiz Orlando de. Universidade Federal de Viçosa; BrasilFil: Gottlieb, Alexandra Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Pathogenic diversity of <i>Phytophthora sojae</i> in the southeast of the Province of Buenos Aires

Phytophthora sojae causes root and stem rot of soybeans. In Argentina, this pathogen has shown dramatic shifts in pathotype variability since its first discovery during the 1970s. The aim of this study was to report the presence and distribution of different pathotypes of P. sojae isolates from 2013 to 2015 in the southeast of Buenos Aires Province in Argentina. Isolates were obtained from diseased soybean plants and soil in contact with the infected root. The pathotype evaluation of P. sojae was determined with a set of eight differential soybean lines. One hundred and twenty-four P. sojae isolates were obtained and forty pathotypes were determined, which is a considerable variability for a relatively new and recently infested soybean area.Instituto de Botánica "Dr. Carlos Spegazzini

Genetic entanglement between Cercospora species associating soybean purple seed stain

Soybean purple seed stain (S-PSS) is a destructive, worldwide distributed fungal disease caused by several Cercospora species. This work aims to shed light on the nature of the genealogical and genetic relationships amongst S-PSS causal agents. Fungal isolates were obtained from Argentina and Brazil, which belong to the leading countries in soybean production worldwide. DNA sequences were obtained from eight loci across the collection of isolates. Relationships were evaluated through Bayesian phylogenetic inferences, and distance and character-based network analyses and discriminant analyses. The occurrence of reticulate evolutionary events was tested with recombination tests. The high haplotype diversity (H = 1.0) was arranged in four validated haplogroups. Reticulate network topologies were evident, and 11 recombination events were validated through several tests. Five of these events occurred across species boundaries. Comparison with sequences from 70 Cercospora species indicated that at least five monophyletic groups of S-PSS-causing agents are currently present in South America. The provided evidence supports the hypothesis that interspecific genetic exchange plays a significant role in the evolutionary dynamics of Cercospora species in this region. The occurrence of interspecific recombination has implications for understanding epidemiological threats to soybean production that appear to be more serious than previously anticipated.Fil: Guillin, Eduardo A.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; ArgentinaFil: de Oliveira, Luiz Orlando. Universidade Federal de Viçosa; BrasilFil: Grijalba, Pablo Enrique. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental. Cátedra de Fitopatología; ArgentinaFil: Gottlieb, Alexandra Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Mycotoxigenic potential of fungi isolated from freshly harvested Argentinean blueberries

Alternaria alternata, A. tenuissima, Fusarium graminearum, F. semitectum, F. verticillioides, Aspergillus flavus, and Aspergillus section Nigri strains obtained from blueberries during the 2009 and 2010 harvest season from Entre Ríos, Argentina were analyzed to determine their mycotoxigenic potential. Taxonomy status at the specific level was determined both on morphological and molecular grounds. Alternariol (AOH), alternariol monomethyl ether (AME), aflatoxins (AFs), zearalenone (ZEA), fumonisins (FBs), and ochratoxin A (OTA) were analyzed by HPLC and the trichotecenes deoxynivalenol (DON), nivalenol (NIV), HT-2 toxin (HT-2), T-2 toxin (T-2), fusarenone X (FUS-X), 3-acetyl-deoxynivalenol (3-AcDON), and 15-acetyl-deoxynivalenol (15-AcDON) by GC. Twenty-five out of forty two strains were able to produce some of the mycotoxins analyzed. Fifteen strains of Aspergillus section Nigri were capable of producing Fumonisin B1 (FB1); two of them also produced Fumonisin B2 (FB2) and one Fumonisin B3 (FB3). One of the F. graminearum isolated produced ZEA, HT-2, and T-2 and the other one was capable of producing ZEA and DON. Two A. alternata isolates produced AOH and AME. Four A. tenuissima were capable of producing AOH and three of them produced AME as well. One Aspergillu flavus strain produced aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), and aflatoxin G1 (AFG1). To our knowledge, this is the first report showing mycotoxigenic capacity of fungal species isolated from blueberries that include other fungi than Alternaria spp.Fil: Munitz, Martín Sebastián. Universidad Nacional de Entre Ríos. Facultad de Ciencias de la Alimentación; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Resnik, Silvia Liliana. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pacin, Ana Maria. Fundación de Investigaciones Científicas "Teresa Benedicta de la Cruz"; ArgentinaFil: Salas, Paula M.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química; ArgentinaFil: Gonzalez, Hector Horacio Lucas. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Montti, Maria Isabel Tatiana. Universidad Nacional de Entre Ríos. Facultad de Ciencias de la Alimentación; ArgentinaFil: Drunday, Vanesa. Fundación de Investigaciones Científicas "Teresa Benedicta de la Cruz"; ArgentinaFil: Guillin, Eduardo A.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; Argentin

More Cercospora species infect soybeans across the Americas than meets the eye

Diseases of soybean caused by Cercospora spp. are endemic throughout the world’s soybean production regions. Species diversity in the genus Cercospora has been underestimated due to overdependence on morphological characteristics, symptoms, and host associations. Currently, only two species (Cercospora kikuchii and C. sojina) are recognized to infect soybean; C. kikuchii causes Cercospora leaf blight (CLB) and purple seed stain (PSS), whereas C. sojina causes frogeye leaf spot. To assess cryptic speciation among pathogens causing CLB and PSS, phylogenetic and phylogeographic analyses were performed with isolates from the top three soybean producing countries (USA, Brazil, and Argentina; collectively accounting for ~80% of global production). Eight nuclear genes and one mitochondrial gene were partially sequenced and analyzed. Additionally, amino acid substitutions conferring fungicide resistance were surveyed, and the production of cercosporin (a polyketide toxin produced by many Cercospora spp.) was assessed. From these analyses, the long-held assumption of C. kikuchii as the single causal agent of CLB and PSS was rejected experimentally. Four cercosporin-producing lineages were uncovered with origins (about 1 Mya) predicted to predate agriculture. Some of the Cercospora spp. newly associated with CLB and PSS appear to represent undescribed species; others were not previously reported to infect soybeans. Lineage 1, which contained the ex-type strain of C. kikuchii, was monophyletic and occurred in Argentina and Brazil. In contrast, lineages 2 and 3 were polyphyletic and contained wide-host range species complexes. Lineage 4 was monophyletic, thrived in Argentina and the USA, and included the generalist Cercospora cf. flagellaris. Interlineage recombination was detected, along with a high frequency of mutations linked to fungicide resistance in lineages 2 and 3. These findings point to cryptic Cercospora species as underappreciated global considerations for soybean production and phytosanitary vigilance, and urge a reassessment of host-specificity as a diagnostic tool for Cercospora

Bayesian phylogeny (consensus tree) showing the relationships among causal agents of Cercospora leaf blight and purple seed stain of soybean and other closely related species.

<p>Fungal isolates were obtained from either purple-stained soybean seeds or infected leaves. The dataset was1566 bases long and resulted from the concatenation of five nuclear genes (act, cal, his, ITS, and tef). Branch lengths are drawn to scale; nodal support values are given as posterior probabilities (%) above the branches (when > 85%). Scale bar corresponds to the expected number of substitutions per site. Color in terminals according to the origin of the isolates: blue, Argentina; green, Brazil; red, United States; and black, data from 6]. Color in branches according to lineage: blue, lineage 1; green, lineage 2; orange, lineage 3; and red, lineage 4. Black arrow indicates the ex-type strain of <i>C</i>. <i>kikuchii</i> (CPC_5068). Gene codes: <i>act</i>, actin; <i>cal</i>, calmodulin; <i>his</i>, histone H3; ITS, internal transcribed spacers and intervening 5.8S nrDNA; <i>tef</i>, translation elongation factor 1-alpha.</p

Median-joining network depincting genealogical relationships among mtDNA haplotypes of <i>Cercospora</i> that is associated with purple seed stain in soybeans.

<p>The network was based on a dataset (653 bases long) obtained from the mitochondrial cytochrome b (<i>cyb</i>) gene. Each circle represents a given haplotype (coded with letters); a line linking two haplotypes indicates a single mutation step. Color slices represent the frequencies of that haplotype in each of the four lineages (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133495#pone.0133495.g003" target="_blank">Fig 3</a>). NR, isolates harboring unexpected <i>cfp</i>–<i>tub</i> gene combinations in the nuclear genome. Numbers in parenthesis refer to the number of occurrences of that haplotype in Argentina, Brazil, and USA, respectively. Diamonds indicate haplotypes harboring the mutation A143G, which is known to confer resistance to Qoi inhibitor fungicides. Dashed line indicates network homoplasy owing to multiple, independent origins of mutation A143G.</p

Bayesian phylogeny (consensus tree) showing the relationships among causal agents of Cercospora leaf blight and purple seed stain of soybean.

<p>The dataset was 3615 bases long and resulted from the concatenation of seven nuclear genes (<i>act</i>, <i>cal</i>, <i>his</i>, ITS, <i>tef</i>, <i>cfp</i>, and <i>tub</i>). <i>Cercospora sojina</i> is shown for reference purpose; the tree was rooted in <i>C</i>. <i>beticola</i>. Branch lengths are drawn to scale; nodal support values are given as posterior probabilities (%) above the branches (when ≥85%). Scale bar corresponds to the expected number of substitutions per site. Color in terminals according to the origin of the isolates: blue, Argentina; green, Brazil; red, United States. Color in branches according to lineage: blue, lineage 1; green, lineage 2; orange, lineage 3; and red, lineage 4. Black arrow indicates the ex-type strain of <i>C</i>. <i>kikuchii</i> (CPC_5068). Gene codes: <i>act</i>, actin; <i>cal</i>, calmodulin; <i>his</i>, histone H3; ITS: internal transcribed spacers and intervening 5.8S nrDNA; <i>tef</i>, translation elongation factor 1-alpha; <i>cfp</i>, cercosporin facilitator protein; <i>tub</i>, β-tubulin 1.</p