Construction of pathogenic, biologic and genetic bases of the Colombian populations of Rhizoctonia solani AG-3 necessary for the development of management strategies of stem canker and black scurf diseases of potato

Rhizoctonia solani AG-3 Kühn (teleomorph: Thanatephorus cucumeris (Frank) Donk) es un patógeno del suelo importante en cultivos de papa a nivel mundial. Aunque este patógeno es importante en Colombia actualmente no existe información acerca del patógeno y la enfermedad. Esta investigación se realizo utilizando pruebas moleculares y biológicas con el fin de conocer los Grupos de Anastomosis (GA) asociados a síntomas en las principales regiones productoras de papa en Colombia. Adicionalmente la variabilidad genética y su distribución geográfica, así como la respuesta del patógeno a dos temperaturas, a un fungicida y su agresividad sobre plantas de papa fueron evaluadas. Las muestras fueron colectadas en tallos de plantas sintomáticas de papa en campos naturalmente infestados, posteriormente fueron procesadas en el laboratorio y los aislamientos obtenidos se sometieron a diferentes análisis. El GA-3 de R. solani fue el comúnmente asociado a los síntomas en campo. Los aislamientos colectados en diferentes regiones geográficas fueron variables y la variabilidad no está asociada a regiones geográficas, las poblaciones son genéticamente similares mostrando el efecto del flujo de genes en la estructura genética de la población. La evaluación de la respuesta del patógeno a dos temperaturas, la sensibilidad al fungicida thifluzamide y la agresividad en diferentes órganos de las plantas de papa mostraron que los aislamientos de todas las localidades geográficas varían en la respuesta los factores evaluados. Los niveles de costra negra y de chancros variaron entre aislamientos sobre el cultivar de papa evaluado. / Abstract. Rhizoctonia solani AG-3 Kühn (teleomorph: Thanatephorus cucumeris (Frank) Donk) is a main soil-borne pathogen on potato crops around the world. Actually this pathogen is recognized as important in Colombia; however there is no information about the pathogen and the disease. This research was conducted using biological and molecular tests to know the Anastomosis Groups (AG) associated with symptoms in the main producing potato areas in Colombia. Additionally the genetic variability of the isolates and the distribution of variability along the main potato producing areas in Colombia as well as the response of the pathogen to temperatures and fungicides and its aggressiveness on potato plants were tested. The samples were collected from symptomatic stems of potato on naturally infested fields and then were processed in laboratory. The isolates were subject of different analysis. The AG-3 of R. solani was the most common associated to symptoms in fields. The isolates from different geographical populations were highly variable and the variability was not structured geographically. All the populations are genetically similar showing the effect of gene flow in the genetic structure of the populations. The evaluation of the response of the pathogen to two temperatures, the sensitivity to the fungicide thifluzamide and the aggressiveness on different organs of the potato plants showed that the isolates of all the geographical localities vary in the response to the factors evaluated. The levels of black scurf and cankers were low and variable among isolates in the cultivar of potato evaluated.Doctorad

Efecto de dos cepas de Trichoderma en el control de Botrytis cinerea y la calidad del fruto en fresa (Fragaria sp.)

El moho gris en fresa causado por Botrytis cinerea es una enfermedad limitante ya que disminuye la calidad y el valor comercial de los frutos. El manejo de esta enfermedad se basa en el empleo de fungicidas químicos aplicados al fruto. Por esta razón, el uso de organismos biocontroladores es una alternativa para el control de esta patología ya que permite disminuir los residuos de pesticidas en el ambiente. Se evaluaron dos cultivares comerciales de fresa (Camino Real y Ventana), en un diseño completamente al azar con 4 tratamientos, Trichoderma harzianum y T. lignorum, iprodione en dosis comercial y un tratamiento testigo, cada uno con tres repeticiones, para un total de doce unidades experimentales (UE), cada UE compuesta por cinco plantas. La incidencia de la enfermedad en el tratamiento testigo fue del 60%, mientras que para los tratamientos con T. harzianum y T. lignorum solo alcanzó un 33%, lo que indica un control mayor de los antagonistas en comparación con el químico sobre la enfermedad. En cuanto a la severidad, los tratamientos con T. harzianum y T. lignorum redujeron significativamente en un 32% el desarrollo del patógeno en la planta. La masa fresca de frutos mostró diferencias significativas cuando se aplicó T. lignorum, ya que este tratamiento obtuvo los frutos más grandes y con mayor tonalidad roja. La aplicación de Trichoderma sp. presentó frutos con mayor firmeza en las dos variedades, con valores promedio de 9,1 N, lo que indica que estos frutos soportan mejor la manipulación poscosecha y el almacenamiento

Rhizoctonia solani GA-3PT es el principal patógeno asociado con el chancro del tallo y la sarna negra de la papa en Colombia

Stem canker and black scurf diseases of potatoes are caused by the basidiomycetous fungus Tanatephorus cucumeris (ana-morphic species complex Rhizoctonia solani). Tese diseases have worldwide distribution wherever potato is grown but their etiology varies depending on the predominance of distinct R. solani anastomosis groups (AGs) in a particular area. Within the species complex, several AGs have been associated with stem canker or black scurf diseases, including AG-1, AG-2-1, AG-2-2, AG-3, AG-4, AG-5 and AG-9. Tis article reports on the most comprehensive population-based study, providing evidence on the distribution of R. solani AGs in Colombian potato fields. A total of 433 isolates were sampled from the main potato cropping areas in Colombia from 2005 to 2009. Isolates were assigned to AGs by conventional PCR assays using specific primers for AG-3, sequencing of the ITS-rDNA and hyphal interactions. Most of the isolates evaluated were assigned to AG-3PT (88.45%), and a few to AG-2-1 (2.54%). Te remaining isolates were binucleate Rhizoctonia (AG-A, E, and I). Pathogenicity tests on the stems and roots of different plant species, including the potato, showed that AG-3PT affects the stems of solanaceous plants. In other plant species, damage was severe in the roots, but not the stems. AG-2-1 caused stem canker of Solanum tuberosum cv. Capiro and in R. raphanistrum and B. campestris subsp. Rapa plantlets and root rot in other plants. Te results of our study indicated that R. solani AG-3PT was the principal pathogen associated with potato stem canker and black scurf diseases of potatoes in Colombia

Rhizoctonia solani AG-3PT is the major pathogen associated with potato stem canker and black scurf in Colombia

Stem canker and black scurf diseases of potatoes are caused by the basidiomycetous fungus Tanatephorus cucumeris (ana-morphic species complex Rhizoctonia solani). Tese diseases have worldwide distribution wherever potato is grown but their etiology varies depending on the predominance of distinct R. solani anastomosis groups (AGs) in a particular area. Within the species complex, several AGs have been associated with stem canker or black scurf diseases, including AG-1, AG-2-1, AG-2-2, AG-3, AG-4, AG-5 and AG-9. Tis article reports on the most comprehensive population-based study, providing evidence on the distribution of R. solani AGs in Colombian potato fields. A total of 433 isolates were sampled from the main potato cropping areas in Colombia from 2005 to 2009. Isolates were assigned to AGs by conventional PCR assays using specific primers for AG-3, sequencing of the ITS-rDNA and hyphal interactions. Most of the isolates evaluated were assigned to AG-3PT (88.45%), and a few to AG-2-1 (2.54%). Te remaining isolates were binucleate Rhizoctonia (AG-A, E, and I). Pathogenicity tests on the stems and roots of different plant species, including the potato, showed that AG-3PT affects the stems of solanaceous plants. In other plant species, damage was severe in the roots, but not the stems. AG-2-1 caused stem canker of Solanum tuberosum cv. Capiro and in R. raphanistrum and B. campestris subsp. Rapa plantlets and root rot in other plants. Te results of our study indicated that R. solani AG-3PT was the principal pathogen associated with potato stem canker and black scurf diseases of potatoes in Colombia