Risk assessment of apple scab occurrence to global warming

Abstract

　Apple scab (Venturia inaequalis (Cooke) Winter) is one of the most devastating diseases of Apple (Malus pumila var. domestica) cultivation. This study focused on the impact of global warming on the occurrence of apple scab and investigated a possible future risk at Aomori Prefecture, Japan. We applied a large-ensemble climate change dataset to the Pear Disease Occurrence Forecast Model and evaluated the infection risk of apple scab. The severe infection risk in the present-climate data was high in spring and after a slight reduction in summer, rose again in autumn, consistent with the priority control period from April to June. Moreover, the probability of severe risk during the priority control period only slightly reduced in future experiment, corresponding to 2090s of a high-end scenario. The risk appearance date defined as the 100-year return period was March 29 in the future, 16 days earlier than in the present climate. The hypothetical experiment revealed that the results can be explained mainly by a temperature increase almost by 5 K from 1980 to 2090. Furthermore, since warmer temperatures exceeded the growth threshold for Venturia inaequalis, the infection risk significantly reduced to the level of 100-year return period in summer in future.