Spatiotemporal Dynamics of Zucchini Squash Lethal Chlorosis and its Relationship with the Frankliniella zucchini Population

Abstract

Lethal chlorosis of cucurbits, caused by the tospovirus Zucchini lethal chlorosis virus (ZLCV), is an important disease in the Brazilian zucchini squash crop. The virus is transmitted by the thrips Frankliniella zucchini. Progress of the disease in time and space was studied in zucchini squash experimental fields to better understand disease epidemiology. Nine independent experiments were carried out between December 2006 and September 2010. The effects of the disease were assessed every 2–7 days, depending on the experiment. The thrips population was monitored in five of these experiments. For disease progress over time, four models (exponential, monomolecular, logistic and Gompertz) were tested. Disease progress in space analysis included both the index of dispersion and Taylor’s power law. The monomolecular model was the best fit to the disease incidence data, and spatial analysis indicated aggregated diseased plants at the end of the season in most experiments. A correlation was detected between the number of collected thrips and the incidence of zucchini squash lethal chlorosis. The results indicate that the thrips population significantly contributed to the primary spread of disease incidence. We propose that disease management should focus mainly on the elimination of the source of the inoculum.