Climate-driven shifts in suitable areas of Alternaria leaf blotch (Alternaria mali Roberts) on apples: Projections and uncertainty analysis in China

Abstract

Apple production in China faces significant threats from Alternaria leaf blotch (ALB), a disease potentially exacerbated by climate change through shifts in its distribution and severity. However, the impacts of future climate change on ALB distribution remain insufficiently explored. We collected ALB occurrence data from orchard surveys, public databases, and the literature. Using five species distribution models (SDMs), we examined the relationship between environmental variables and ALB occurrence, and assessed its potential distribution under different climate change scenarios. The analysis used five Global Climate Models (GCMs) from the CMIP6 dataset, with a baseline period (1970–2000) and projections for the 2030s, 2050s, 2070s, and 2090s, based on four shared socioeconomic pathways (SSP126, SSP245, SSP370, and SSP585). The SDMs showed high reliability, with average values for the area under the receiver operating characteristic curve exceeding 0.96 and the true skill statistic exceeding 0.86. During the baseline period, ALB-suitable areas were primarily concentrated in the Bohai Bay, Loess Plateau, and Old Course of the Yellow River apple-planting regions. By the 2090s, under the SSP126, these areas were projected to decrease by 8.89 %. In contrast, under the SSP245, SSP370, and SSP585 scenarios, they were expected to increase by 4.89 %, 21.30 %, and 23.22 %, respectively, with a northwestward shift of 137 to 263 kms and an elevation increase of 288 to 680 m. Additionally, our findings indicated that GCMs contribute 42.2 % of the uncertainty in predictions, while SDMs and scenarios contribute 31.5 % and 8.28 %, respectively. This research highlights the importance of using multiple models and scenarios to enhance the accuracy of disease distribution predictions under changing climatic conditions. By identifying potential future hotspots and suitable areas of ALB, the study provides critical insights for safeguarding apple production in China against the impacts of climate change.