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ISHS Acta Horticulturae 1218: IX International Symposium on Kiwifruit

The association between vine management wounds and weather risk on the development of kiwifruit bacterial canker in 'Hayward' kiwifruit

Authors:   K.J. Froud, N. Cogger, R.M. Beresford
Keywords:   cross-sectional observational study, weather risk model, multivariable logistic regression, odds ratio
DOI:   10.17660/ActaHortic.2018.1218.31
Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae biovar 3 (Psa), has caused considerable damage in New Zealand to susceptible kiwifruit vines. In 2013, a study of kiwifruit bacterial canker in Actinidia chinensis var. deliciosa 'Hayward'orchards investigated whether commercial vine management activities, undertaken during periods of high weather risk, increased the risk of severe bacterial canker symptoms of shoot wilt and cane dieback in kiwifruit orchard blocks. The approach taken, which is novel to botanical epidemiology but widely used in veterinary and medical epidemiology, used observational data with multivariable modelling. Data were collected from a cross-sectional survey from 223 kiwifruit growers. Our results showed statistically significant associations between pruning activities conducted in high-weather-risk periods in spring and the presence of severe symptoms. These results suggested that a risk-indicator threshold of about 25 from the weather-based Psa risk model may be associated with increased risk of severe disease in kiwifruit orchard blocks. This study provides the first evidence that the Psa risk model can predict infection leading to severe bacterial canker symptoms, in addition to its proven ability to predict leaf spotting. It also indicated that lower risk-indicator values than previously thought are associated with substantial disease risk. The combination of disease predictive models with disease risk-factor statistical models has potential for wider application in plant protection research, particularly in validating the use of predictive models within commercial orchards.

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