In October 2018, soybean plants displaying elongated black to reddish-brown lesions on stems were observed in a field planted to the cv. BRS Serena in the locality of Puerto López (Meta, Colombia), with 20% incidence of diseased plants. Symptomatic stems were collected from five plants, and small pieces (∼5 mm2) were surface sterilized, plated on potato dextrose agar (PDA) and incubated for 2 weeks at 25°C in darkness. Three fungal isolates with similar morphology were obtained, i.e., by subculturing single hyphal tips, and their colonies on PDA were grayish-white, fluffy, with aerial mycelium, dark colored substrate mycelium, and produced circular black stroma. Pycnidia were globose, black, occurred as clusters, embedded in tissue, erumpent at maturity, with an elongated neck, and often had yellowish conidial cirrus extruding from the ostiole. Alpha conidia were observed for all isolates after 30 days growth on sterile soybean stem pieces (5 cm) on water agar, under 25ºC and 12 h light/12h darkness photoperiod. Alpha conidia (n = 50) measured 6.0 – 7.0 µm (6.4 ± 0.4 µm) × 2.0 – 3.0 µm (2.5± 0.4 µm), were aseptate, hyaline, smooth, ellipsoidal, often biguttulate, with subtruncate base. Beta conidia were not observed. Observed morphological characteristics of these isolates were similar to those reported in Diaporthe spp. by Udayanga et al. (2015). DNA from each fungal isolate was used to sequence the internal transcribed spacer region (ITS), and the translation elongation factor 1-α (TEF1) gene, using the primer pairs ITS5/ITS4 (White et al. 1990) and EF1-728F/EF1- 986R (Carbone & Kohn, 1999), respectively. Results from an NCBI-BLASTn, revealed that the ITS sequences of the three isolates (GenBank accessions MW566593 to MW566595) had 98% (581/584 bp) identity with D. miriciae strain BRIP 54736j (NR_147535.1), whereas the TEF1 sequences (GenBank accessions MW597410 to MW597412) had 97 to 100% (330-339/339 bp) identity with D. ueckerae strain FAU656 (KJ590747). The species Diaporthe miriciae R.G. Shivas, S.M. Thomps. & Y.P. Tan, and Diaporthe ueckerae Udayanga & Castl. are synonymous, with the latter taking the nomenclature priority (Gao et al. 2016). According to a multilocus phylogenetic analysis, by maximum likelihood, the three isolates clustered together in a clade with reference type strains of D. ueckerae (Udayanga et al. 2015). Soybean plants cv. BRS Serena (growth stages V3 to V4) were used to verify the pathogenicity of each isolate using a toothpick inoculation method (Mena et al. 2020). A single toothpick colonized by D. ueckerae was inserted directly into the stem of each plant (10 plants per isolate) approximately 1 cm below the first trifoliate node. Noncolonized sterile toothpicks, inserted in 10 soybean plants served as the non-inoculated control. Plants were arbitrarily distributed inside a glasshouse, and incubated at high relative humidity (>90% HR). After 15 days, inoculated plants showed elongated reddish-brown necrosis at the inoculated sites, that were similar to symptoms observed in the field. Non-inoculated control plants were asymptomatic. Fungal cultures recovered from symptomatic stems were morphologically identical to the original isolates. This is the first report of soybean stem canker caused by D. ueckerae in Colombia. Due to the economic importance of this disease elsewhere (Backman et al. 1985; Mena et al. 2020), further research on disease management strategies to mitigate potential crop losses is warranted.
La antracnosis (Colletotrichum acutatum) reduce considerablemente el rendimiento de los cítricos. Los síntomas de la enfermedad se caracterizan por necrosis de los pétalos, caída prematura de los frutos y formación de cálices persistentes. Con el fin de determinar el efecto del patrón y de condiciones ambientales como la precipitación, la humedad relativa y la temperatura en el desarrollo de la antracnosis, se seleccionaron al azar plantas de lima ácida Tahití injertadas en seis portainjertos: Citrumelo, Sunky x English, Carrizo, Volkameriano, Kryder 15-3 y Cleopatra, establecidos en un huerto experimental en el Centro de Investigación La Libertad de la Corporación Colombiana Agropecuaria AGROSAVIA en Villavicencio, Meta. El experimento se llevó a cabo durante tres estaciones de floración, cada una con condiciones climáticas diferentes. Se evaluó la incidencia de la enfermedad y el porcentaje de cálices persistentes. Los resultados no evidenciaron diferencias significativas en la incidencia de la enfermedad y el número de cálices persistentes entre los patrones evaluados. Sin embargo, el efecto en la caída de los frutos, expresado en cálices persistentes, dependió de las condiciones climáticas que favorecieron el desarrollo del patógeno, siendo los meses lluviosos, la humedad relativa elevada y las temperaturas bajas factores predisponentes de la pérdida considerable de frutos a causa de la enfermedad en la lima ácida Tahití cultivada en el piedemonte llanero de Colombia.
La melina (Gmelina arborea Roxb) es una especie de amplia distribución mundial y de elevado valor comercial por su crecimiento rápido y las excelentes propiedades físicas y mecánicas de su madera; sin embargo, constantemente se ve amenazada por diversos factores físicos, químicos y biológicos, siendo los hongos y las bacterias los microorganismos que más pueden afectar su producción. El presente estudio tuvo como objetivo aislar e identificar hongos y bacterias asociados con fustes enfermos de G. arborea en plantaciones ubicadas en el departamento del Tolima (Colombia). La caracterización morfológica de las colonias fúngicas se realizó en el medio Papa-Dextrosa-Agar (PDA) con posterior identificación microscópica, después de inducir la producción de las estructuras reproductivas. El aislamiento de las bacterias se realizó en Agar Nutritivo (AN), con posterior caracterización bioquímica. La identificación molecular fue realizada mediante la amplificación de la región ITS para hongos y 16S para bacterias. Se identificaron los hongos Lasiodiplodia theobromae, Coniothyrium aleuritis, Curvularia geniculata, Chaetomium globosum, Phomopsis columnaris, Diaporthe sp y un aislamiento perteneciente a la clase Dothideomycetes. Las bacterias correspondieron a Bacillus cereus, Pseudomonas alcaligenes y Pantoea dispersa. Mediante pruebas de patogenicidad se determinó que los microorganismos causantes de la pudrición del tejido vascular en fustes jóvenes de melina fueron L. theobromae y C. geniculata. © 2018. Acad. Colomb. Cienc. Ex. Fis. Nat.
Reporte de caso Reporte de pérdidas en el rendimiento de la soja causadas por la mancha anillada (Corynespora cassiicola Berk. & Curt.) en la Orinoquia colombiana Report of soybean yield losses caused by target spot (Corynespora cassiicola Berk. & Curt) in the Colombian Orinoquia
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