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Poster: Biology & Disease Mgmt: Mycology


Modelling potential inoculum availability of Mycosphaerella nawae in persimmon leaf litter using Bayesian growth curves
A. VICENT (1), J. Martínez-Minaya (2), A. López-Quílez (3), D. Conesa (3) (1) Instituto Valenciano de Investigaciones Agrarias (IVIA). Moncada 46113, Valencia, Spain., Spain; (2) Instituto Valenciano de Investigaciones Agrarias (IVIA), Moncada 46113, Vale

Circular leaf spot, caused by Mycosphaerella nawae, is a serious disease of persimmon (Diospyros kaki) inducing necrotic lesions on leaves, defoliation and fruit drop. The disease was initially restricted to humid regions in Japan and South Korea and in 2008 it was detected in arid areas in Spain. The fungus forms pseudothecia in leaf litter during winter and ascospores are released in spring infecting susceptible leaves. Persimmon growers are advised to spray with fungicides during the period of inoculum availability, which was defined based on ascospore counts. In order to develop a model of potential inoculum availability, samples of leaf litter were collected weekly in six affected orchards from 2010 to 2015. Leaves were soaked, placed in a wind tunnel, and released ascospores were counted under the microscope. Hierarchical Bayesian methods were used to fit the dynamics of ascospore production in the leaf litter to Gompertz and logistic growth curves, including temperature and rainfall as nonlinear effects. MCMC methods were used to approximate the posterior distribution of the parameters. Results showed that accumulated degree days best described ascospore dynamics with both Gompertz and logistic curves. The predictive ability of the models was evaluated using ascospore data from two orchards not used in model development. The resulting best model was implemented in a disease warning system to schedule fungicide sprays for the control of circular leaf spot.