Relación entre la precipitación registrada en estados reproductivos de la soja y la severidad de Septoria glycines y Cercospora kikuchii

71-78From 2003 to 2008, late season disease severity (LSDsev) values (Brown spot and Cercospora leaf blight) were recorded at the R7 growth stage at several sites in Santa Fe and Córdoba Provinces. The annual LSDsev records (N=15) were grouped into two epidemic categories based on a threshold value (median of observed disease data) : severe (LSDsev less than 36 percent) and moderate to light (LSDsev more or equal to 36 percent). Variations in epidemic levels were studied in relation to precipitation-based variables, processed in a time window limited by R3 and R5 growth stages. The variables were expressed as frequency (days) and total accumulation (mm) of daily precipitations greater than the thresholds 1, 5, 7 and 10 mm. The variables PrF7 (number of days with precipitations less than 7 mm) and AcPr7 (total accumulation of daily precipitations less than 7 mm) and the interaction (product) between them (It7) were the most strongly correlated, according to Kendall tau-b coefficients (rK=0.74, 0.60 and 0.71 respectively).Logistic regression model including AcPr7 correctly estimated the probability of occurrence of epidemic categories in 12 cases (out of 15). Logistic models integrating PrF7 or the interaction effect (It7) presented prediction accuracies of 93.3 percent. These results could be useful for prediction and chemical control of LSD

Uso de mezclas de azoxistrobina y triazoles para controlar enfermedades de fin de ciclo de la soja

134-139Widely spread in Argentina, late season diseases (LSD), cause yield losses and seed quality changes. Leaf application of fungicides is an effective procedure to manage LSD under the current cropping conditions (monocrop and no-till system). The aims of the present study were 1) to determine causal agents of LSD, 2) to evaluate yield reduction caused by LSD and 3) to evaluate the efficiency of mixtures containing triazoles and strobirulins, sprayed during R3 or R5 reproductive stages to control LSD. Four experiments were carried out in a randomized complete block design, with four replicates in Armstrong, Santa Fe, Argentina, in a soybean cultivation area in the Pampeana Region. Two assays were performed in 2004/2005, and the remaining ones in 2005/2006 growing seasons. Two azoxystrobin mixtures, one with cyproconazole and the other with difenoconazole, and a mixture of the latter two were tested. The following pathogens were detected: Cercospora kikuchii, Colletotrichum truncatum, Septoria glycines, Glomerella glycines y Phomopsis sojae. All treatments presented higher yield than control, with 5 percent of statistic significance. It can be concluded that, under the present experimental conditions, characterized by frequent rains between R1 and R5.5, the tested mixtures efficiently controlled LSD

Aislamiento, identificación y daños asociados al síndrome de la muerte súbita en el cultivo de soja en Argentina

358-362The main objectives of this work were to isolate and identify the causal agents of sudden death syndrome (SDS) from samples collected in different Argentinean localities, to quantify its incidence, and to estimate yield losses. Two hundred and ffteen roots from plants with typical SDS foliar symptoms were analyzed. In order to perform pathogenicity tests, two bioassays were conducted in the greenhouse. Yield losses were estimated in a feld trial located in Pergamino by quantifcation and comparison of yield of paired samples. Thirty-six percent of total roots (78 roots) presented signs of Fusarium, compatible with signs caused by SDS. Morphological studies allowed the identifcation of 35 isolates as F. tucumaniae and 18 as F. virguliforme. Other eight isolates could not be identifed. All isolates that were inoculated reproduced typical SDS foliar symptoms. Signifcant differences were observed between healthy and diseased plants for 1000-grain weight and between potential and real yield (p less than 0.05). Average yield loss was 1514 kg/ha (range 192-3770 kg/ha). These results corroborated the distribution and predominance of F. tucumaniae and F. viguliforme in the area under study and its destructive potential

Draft genome sequence data of Cercospora kikuchii, a causal agent of Cercospora leaf blight and purple seed stain of soybeans

Cercospora kikuchii (Tak. Matsumoto & Tomoy.) M.W. Gardner 1927 is an ascomycete fungal pathogen that causes Cercospora leaf blight and purple seed stain on soybean. Here, we report the first draft genome sequence and assembly of this pathogen. The C. kikuchii strain ARG_18_001 was isolated from soybean purple seed collected from San Pedro, Buenos Aires, Argentina, during the 2018 harvest. The genome was sequenced using a 2 × 150 bp paired-end method by Illumina NovaSeq 6000. The C. kikuchii protein-coding genes were predicted using FunGAP (Fungal Genome Annotation Pipeline). The draft genome assembly was 33.1 Mb in size with a GC-content of 53%. The gene prediction resulted in 14,856 gene models/14,721 protein coding genes. Genomic data of C. kikuchii presented here will be a useful resource for future studies of this pathosystem. The data can be accessed at GenBank under the accession number VTAY00000000 https://www.ncbi.nlm.nih.gov/nuccore/VTAY00000000.Fil: Sautua, Francisco José. Universidad de Buenos Aires (UBA). Facultad de Agronomía. Catedra de Fitopatología; Argentina.Fil: González, Sergio A. Instituto Nacional de Tecnología Agropecuaria (INTA). Investigación en Ciencias Veterinarias y Agronómicas (CICVYA). Instituto De Investigación Biotecnología; Argentina.Fil: González, Sergio A. Instituto Nacional de Tecnología Agropecuaria (INTA) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto de Agrobiotecnología y Biología Molecular (IABIMO); ArgentinaFil: Doyle, Vinson P. Louisiana State University Agricultural Center (LSU AgCenter). Department of Plant Pathology and Crop Physiology; United States.Fil: Berretta, Marcelo F. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Berretta, Marcelo F. Instituto Nacional de Tecnología Agropecuaria (INTA). Investigación en Ciencias Veterinarias y Agronómicas (CICVYA). Instituto de Microbiología y Zoología Agrícola (IMyZA); Argentina.Fil: Gordó, Manuela. Laboratorio Agrícola Río Paraná; Argentina.Fil: Scandiani, María Mercedes. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Centro de Referencia de Micología (CEREMIC); Argentina.Fil: Rivarola, Máximo L. Instituto Nacional de Tecnología Agropecuaria (INTA). Investigación en Ciencias Veterinarias y Agronómicas (CICVYA). Instituto De Investigación Biotecnología; Argentina.Fil: Rivarola, Máximo L. Instituto Nacional de Tecnología Agropecuaria (INTA) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto de Agrobiotecnología y Biología Molecular (IABIMO); Argentina.Fil: Rivarola, Máximo L. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Fernández, Paula. Instituto Nacional de Tecnología Agropecuaria (INTA). Investigación en Ciencias Veterinarias y Agronómicas (CICVYA). Instituto De Investigación Biotecnología; Argentina.Fil: Fernández, Paula. Instituto Nacional de Tecnología Agropecuaria (INTA) - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto de Agrobiotecnología y Biología Molecular (IABIMO); Argentina.Fil: Fernández, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); Argentina.Fil: Fernández, Paula. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; Argentina.Fil: Carmona, Marcelo Aníbal. Universidad de Buenos Aires (UBA). Facultad de Agronomía. Catedra de Fitopatología; Argentina

Pseudomonas fluorescens showing antifungal activity against macrophomina phaseolina, a severe pathogenic fungus of soybean, produces phenazine as the main active metabolite

Pseudomonas fluorescens 9 and Bacillus subtilis 54, proposed as biofungicides to control Macrophomina phaseolina, a dangerous pathogen of soybean and other crops, were grown in vitro to evaluate their ability to produce metabolites with antifungal activity. The aim of the manuscript was to identify the natural compounds responsible for their antifungal activity. Only the culture filtrates of P. fluorescens 9 showed strong antifungal activity against M. phaseolina. Its organic extract contained phenazine and mesaconic acid (1 and 2), whose antifungal activity was tested against M. phaseolina, as well as Cercospora nicotianae and Colletotrichum truncatum, other pathogens of soybean; however, only compound 1 exhibited activity. The antifungal activity of compound 1 was compared to phenazine-1-carboxylic acid (PCA, 3), 2-hydroxyphenazine (2-OH P, 4), and various semisynthetic phenazine nitro derivatives in order to perform a structure–activity relationship (SAR) study. PCA and phenazine exhibited the same percentage of growth inhibition in M. phaseolina and C. truncatum, whereas PCA (3) showed lower activity against C. nicotianae than phenazine. 2-Hydrox-yphenazine (4) showed no antifungal activity against M. phaseolina. The results of the SAR study showed that electron attractor (COOH and NO2) or repulsor (OH) groups significantly affect the antifungal growth, as well as their α-or β-location on the phenazine ring. Both PCA and phenazine could be proposed as biopesticides to control the soybean pathogens M. phaseolina, C. nicotianae, and C. truncatum, and these results should prompt an investigation of their large-scale production and their suitable formulation for greenhouse and field applications