Temporal analysis of white rot (Sclerotium cepivorurum Berk.) in onion (Allium cepa L.) under three pathogen inoculum densities.

摘要

Temporal behavior of white rot disease, caused by the fungus Sclerotium cepivorum, was assessed on three onion plots, located at Rancho Agua Nueva, municipality of Juventino Rosas, Guanajuato, Mexico. The plots had different soil inoculum density (ID) of the pathogen: 0.021, 0.052, and 0.44 sclerotia g-1 soil, classified as low, medium, and high. The first plants with symptoms were observed 30 d after transplanting (dat), and the last diseased plants were recorded 160 dat. At this time, accumulated disease incidence was 51.93, 67.75, and 82.9%, corresponding to low, medium, and high ID. The relationship between disease progress curves and crop phenology showed that at the highest soil ID, maximum disease incidence (ymax) occurs at the earliest phenology stages. Temporal progress of white rot at low and medium ID (0.021 and 0.052 sclerotia g-1 soil) was described by Gompertz growth model, while high ID (0.44 sclerotia g-1 soil) was described by the monomolecular model. The comparison of epidemics was performed taking into account the growth rates homologized to the Gompertz model (Rho) and by the area under the disease progress curve (AUDPC) showing significant differences (p<=0.01). Initial ID of S. cepivorum in soil determines important epidemiological characteristics like disease increase rate (r), form of disease progress curve, phenological stage of maximum incidence (ymax), and final disease incidence (yf), useful for understanding and predicting disease development in field and taking decisions on disease management.