Leaf spectral reflectance of Hevea brasiliensis in response to Pseudocercospora ulei

Abstract

South American Leaf Blight (SALB) is a fungal disease caused by the pathogen Pseudocercospora ulei. It is the main disease affecting rubber trees in Latin America. This study was designed to investigate the changes in the spectral reflectance of rubber leaflets inoculated with P. ulei under controlled conditions. Young leaflets of two clones of Hevea brasiliensis with different degrees of resistance to SALB were tested. The results demonstrated that SALB severity affected the spectral properties of the rubber leaflets, increasing the spectral reflectance in the visible range, decreasing the near-infrared range, and causing variating in the spectral vegetation indices. The changes were more obvious in the most susceptible clone (FX 3864) than in the most resistant one (FX 4098). The SALB severity classes were correlated with the relative chlorophyll content, the leaflet phenology, and the appearance of disease symptoms after the pathogen inoculation. New mathematical models for predicting the SALB severity in the leaflets B (10–18 days old) and C (22–30 days old) in the two rubber tree clones were designed.