In a German vineyard (PRO) between 10 and 13 June 2004, the incidence of grapevine downy mildew ( Plasmopara viticola ) increased abruptly from 0 to 99%. Infected vines bore on average between 45 and 60 lesions each, corresponding to about 220 000 lesions ha -1 in a non-aggregated distribution. A second vineyard (FUT), approximately 50 m distant from PRO, had been inoculated 3 weeks before the abrupt increase in incidence of disease in PRO. Using microsatellites to ascertain the sources of inoculum and likelihood and extent of interplot spread from FUT to PRO, 555 samples were collected and 20 unique genotypes were identified, of which one caused 80% of the sampled lesions in both vineyards. Three genotypes responsible for 95% of the lesions in FUT and PRO were identified as the genotypes originally established through earlier inoculations in FUT. This is the first report of definitive and quantitative evidence of sporangial migration up to 130 m in a single infection event. The utility of molecular tools to address practical epidemiological issues in this pathosystem is illustrated. The results of this study provide an example of how P. viticola was able to rapidly colonize European vineyards after the pathogen was introduced from North America in 1878.
The double setting of two seed tubers is introduced as a new method for research on primary stem blight of potato, Solanum tuberosum L. caused by Phytophthora infestans (Mont.) de Bary). The principal focus of this experimental layout is the planting of a healthy seed tuber adjacent to an inoculated one, termed double setting. The infected tuber serves as a source of inoculum, enabling the disease to spread to the neighboring plant, where stem infections occur. The new method was compared to the common procedure of direct inoculation of tubers. The rate of emergence using double setting was significantly higher compared to direct inoculation. Additionally, stem blight was more intense and generally occurred earlier. Direct inoculation proved to be less suitable for research where the occurrence of higher percentages of stem blight symptoms is necessary. Further more, the double setting method generally permits insight into the spread of the disease from latent infected tubers to healthy ones under the natural conditions within the potato hill.Resumen Se presenta el duplicado de dos tubérculos semilla como nuevo método de investigación en tizón de tallo primario de papa, Solanum tuberosum L., causado por Phytophthora infestans (Mont.) de Bary. El enfoque principal de este planteamiento experimental es la siembra de un tubérculo semilla sano junto a otro inoculado, que le llamamos duplicado. El tubérculo infectado sirve como fuente de inoculo, permitiendo que la enfermedad se disperse a la planta vecina, donde se presenta la infección del tallo. El nuevo método se comparó con el procedimiento común de inoculación directa de los tubérculos. El nivel de emergencia del duplicado fue significativamente mas alto comparado con la inoculación directa. Además, el tizón del tallo fue mas intenso y generalmente se presentó más temprano. Se evidenció que la inoculación directa fue menos deseable para investigación cuando se necesita la incidencia de porcentajes mayores de síntomas de tizón del tallo. Aún más, el método del duplicado generalmente permite discernir sobre la dispersión de la enfermedad de tubérculos con infección latente a los sanos bajo las condiciones naturales al interior del surco.
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