Leaf abaxial and adaxial surfaces differentially affect plant-fungal pathogen interactions

Eudicot plant species have bifacial leaves with each surface varying in a diversity of components, resulting in potentially different microhabitats for pathogens. We tested how Botrytis cinerea, a necrotroph fungal pathogen, interacts with the two different leaf surfaces across 16 crop species and 20 Arabidopsis genotypes. This showed that the abaxial surface is generally more susceptible to the pathogen than the adaxial surface. In Arabidopsis, the differential lesion area between leaf surfaces was associated to jasmonic acid (JA) and salicylic acid (SA) signaling and differential induction of defense chemistry. When infecting the adaxial surface, leaves mounted stronger defenses by producing more glucosinolates and camalexin defense compounds, partially explaining the differential susceptibility across surfaces. Testing a collection of 96 B. cinerea strains showed genetic heterogeneity of growth patterns, with a few strains preferring the adaxial surface while most are more virulent on the abaxial surface. Overall, we show that leaf-Botrytis interactions are complex with host-specific, surface-specific, and strain-specific behaviors. Within Arabidopsis, this mechanistically links to potential variation in JA/SA signaling across the two surfaces. ### Competing Interest Statement The authors have declared no competing interest.