Photosynthetic performance of Hevea brasiliensis affected by South American Leaf Blight under field conditions

South American Leaf Blight (SALB), caused by the fungus Pseudocercospora ulei, is the principal rubber crop disease in Latin America. Several studies have focused on the genetics of resistance and the epidemiology of this disease, but few have analyzed the physiological alterations caused by SALB in Hevea brasiliensis. In addition, changes under field conditions are poorly understood. The present study aimed to analyze changes in gas exchange and chlorophyll a fluorescence traits in leaflets with different leaf stages and SALB severity levels from two H. brasiliensis clones with distinct susceptibility to disease in juvenile plants grown under field conditions (clonal garden). The photosynthetic performance was strongly limited in the high susceptibility clone (FX 3864), mainly in the young leaflets with maximum SALB severity (‘3’ and ‘4’), as compared to the low susceptibility clone (FX 4098). The principal alterations included a reduction in the photosynthetic rate (>?79%), stomatal conductance (>?85%), extrinsic water use efficiency (>?85%), and ability to capture, use and dissipate light energy in photosystem II, as compared to healthy leaflets. The damage was less intense in mature leaflets from both rubber tree clones. The favorable performance observed in clone FX 4098 means it is a potential candidate for commercial scale use under non-SALB escape conditions in the Amazon region.