Modeling disease progression of camellia twig blight using a recurrent event model.

Authors: Thomson, Jessica; Copes, Warren

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2008
Publication Date: 4/4/2009
Citation: Thomson, J.L., Copes, W.E. 2009. Modeling disease progression of camellia twig blight using a recurrent event model. Phytopathology. 99(4):378-384.

Interpretive Summary: Camellia twig blight is a disease common to the southern United States. To better understand when symptoms appear; mild, moderate, and severe disease stages were studied over time using survival analysis for multiple events. Camellia twigs were purposely infected in all four seasons of the year. Twigs of smaller diameter had a greater risk of showing disease symptoms than did twigs of larger diameter. Additionally, disease progression was influenced by temperature with higher risks associated with both longer hours temperatures between 15 and 30ºC, and warmer seasons. Symptoms of twig blight appeared between 2 (moderate and severe) to 3 (mild) times faster in the spring, summer, and fall seasons than in the winter season. This information will be combined with knowledge concerning fungal spore production to select the time(s) of the year when pruning of infectious twigs will result in optimal disease control. The information will benefit research and extension scientists who develop disease control information for ornamental plant producers and consumers.

Technical Abstract: To improve control of camellia twig blight (CTB) using sanitation methods, a more complete epidemiologic understanding of this disease is necessary. Three CTB disease stages were modeled using recurrent event analysis. Wound inoculated stems were observed at regular intervals for appearance of disease symptoms. Survival times for the three disease stages were regressed against stem diameter, monthly mean hours/day within a specified temperature range, and season. For all three CTB disease stages, stem diameter had a protective effect on survival times, while monthly mean hours/day in the specified temperature range and warmer seasons were risk factors. Based upon median ratios, the rate of mild disease stage occurrence was 2 to 3 times faster in spring, summer, and fall rather than in winter. For moderate and severe disease stages, rates varied from 2 to 2.5 times faster. Seasonal differences in rate of stage development were much smaller among fall, spring, and summer, varying from 1 to 1.6 times faster.Recurrent event modeling of CTB progression provides knowledge concerning developmental expression of this disease, information necessary for creating a comprehensive, integrated disease management program.