Incidencia de potyvirus y caracterización molecular de PVY en regiones productoras de papa (Solanum tuberosum L) de Colombia / Incidence of potyvirus and molecular characterization of PVY in potato (Solanum tuberosum L) growing regions of Colombia

Los problemas virales reducen los rendimientos y la calidad del tubérculo semilla en cultivos de papa de todo el mundo. Esta investigación se planteó con el fin de evaluar los niveles de incidencia de potyvirus en diez de las principales regiones cultivadoras de papa de los departamentos de Antioquia, Boyacá, Cundinamarca y Nariño (Colombia), y las características genotípicas del virus Y de la papa (Potato virus Y, PVY), seleccionado por ser el potyvirus más limitante de este cultivo. Para la evaluación de la incidencia se utilizaron pruebas de Elisa con anticuerpos que reconocen epítopes comunes a los potyvirus, mientras que las pruebas moleculares incluyeron el análisis filogenético de secuencias parciales del gen de la cápside viral de 33 aislamientos, así como la secuenciación de una porción de los extremos 5´ y 3´del genoma de dos cepas colombianas de este virus. Los resultados confirmaron la presencia de potyvirus en los cultivos de los cuatro departamentos evaluados, con una incidencia promedio del 72%, siendo este nivel superior al 56% en todas las zonas evaluadas. Los análisis moleculares del PVY, permitieron asociar las cepas colombianas estudiadas con las razas PVYN y la variante PVYNTN, esta última responsable de la enfermedad conocida en el mundo como PTNRD (Potato tuber necrotic ringspot disease).

Potato viruses are responsible for significant reductions in seed quality and crop yields around the world. In this study, we evaluate the levels of incidence of potyvirus in ten potato growing regions of Colombia from the provinces of Antioquia, Boyacá, Cundinamarca and Nariño. As PVY is the most limiting potyvirus in potato farming, a molecular characterization of Colombian PVY strains was also performed. Incidence was evaluated by ELISA using general potyvirus antibodies. Phylogenetic analysis were made on the partial sequence of the capsid gene from 33 isolates. A portion of the 5´ and 3' genome ends was obtained from two Colombian strains. Results confirmed the presence of potyvirus in the four provinces with an average incidence of 72%. The lowest incidence value was 56%. Molecular analysis clustered all Colombian isolates with strains PVYN and PVYNTN, the latter responsible for the disease known as PTNRD (Potato tuber necrotic ringspot disease).

Nitrogenous components in healthy and potato virus Y-infected solanum and pepper leaves

Solanum nigrum var. judaicum and Capsicum annum cv. California wonder plants at the 4-6 and 5-7 leaf stage, respectively, were artificially infected with potato virus Y, then examined at 5, 10, 15, 20 and 40 days postinfection. Considerable differences were observed in the concentration of the various nitrogenous components of the two hosts. Investigations showed that solanum leaves affected by PVY had a higher total nitrogen content than the leaves of the healthy plants as a result of increasing amino acids, ammonia, amide, total soluble nitrogen and total insoluble protein content. PVY lowered total nitrogen content compared with healthy leaves resulting from a drop in all nitrogenous components, but amide and total insoluble proteins increased

Phosphorus distribution in healthy and potato virus Y-infected tomato plants

The influence of Y degree group of the common strain of potato virus Y [PVY] on the amount and distribution of phosphorus in leaves, stems and roots of the susceptible [Lycopersicon esculentum cv. [Money maker]] and resistant [Lycopersicon pimpinellifolium L.] tomato species at 1/2,1, 5,15, 25 and 35 days post infection was studied. During the first days post infection, the infected leaves of the susceptible tomato showed higher organic and total soluble phosphorus content while the inorganic phosphorus remained unchanged. By the end of the experiment, the inorganic and RNA phosphorus contents were lower than in the healthy leaves .PVY infection lowered the DNA-P content during most periods post infection except on the first and fifth day. It also increased the other insoluble and decreased the total insoluble phosphorus contents. During the whole experimental period, the infected stems were low in their soluble phosphorus components and high in the DNA-P whereas the RNA and the other insoluble phosphorus were not affected. Also the virus did not cause any significant change in the soluble fractions of the roots but their RNA and other insoluble phosphorus decreased whereas the DNA and total insoluble phosphorus contents were not affected. In the resistant tomato, the organic and total soluble phosphorus of the inoculated leaves significantly increased but the inorganic phosphorus remained unchanged during the fifth day post inoculation onwards. The RNA-P decreased whereas the DNA, other insoluble and total insoluble phosphorus increased. Infected stems had lower soluble and insoluble phosphorus components except DNA-P that increased. In roots, the soluble phosphorus components increased but the RNA and other insoluble phosphorus components decreased. The distribution of the different phosphorus fractions revealed that PVY infection increased the organic phosphorus and decreased the DNA-P and RNA-P of the leaves of the susceptible tomato plants and also decreased the organic phosphorus and increased the DNA and RNA phosphorus of the stems and roots. In resistant tomato, PVY increased the DNA-P and decreased the organic and RNA phosphorus distribution in leaves while in stems and roots the virus decreased the inorganic and DNA phosphorus and increased die RNA-P

Carbohydrate content of some potato virus Y-diseased solanaceous plants

Different carbohydrate components, viz. total soluble reducing and non reducing sugars and starch were compared in leaves of four solanaceous plants namely Lycopersicon esculentum cv. Money maker [susceptible tomato]; Lycopersicon pimpinellifolium L. [resistant tomato]; Capsicum annuum cv. "California Wonder" [pepper] and Solanum nigrum var. judaicum [Enab El-Deeb] at different intervals after inoculation with an isolate belonging to Y° group of the common strain of potato virus Y [PVY] studies indicate that: i - In susceptible tomato: virus infection lowered significantly the total carbohydrate content and starch content and decreased also the monosaccharide content but increased sucrose concentration. ii- In resistant tomato: virus infection decreased significantly all carbohydrate fractions except only the monosaccharides. iii- In pepper: virus infection lowered the total carbohydrate content as a result of decreased monosaccharides, sucrose and starch components .iv- In Enab El-Deeb: virus infection also decreased the total carbohydrate as well as the starch and total soluble sugars