Molecular diagnosis of Guignardia citricarpa in asymptomatic sweet orange tissue

Abstract

Citrus black spot, a fungal disease caused by the quarantine fungus Guignardia citricarpa, restricts the exportation of fresh fruit to countries in the European Union. The occurrence of latent infections and the time required for diagnosis using conventional methods have brought about the need to validate fast, efficient and reproducible molecular techniques to detect the pathogen in asymptomatic tissue. As such, this study aims to detect G. citricarpa in the symptomatic fruit and asymptomatic leaf tissue of sweet oranges by conventional and real-time polymerase chain reaction (PCR). Specificity and limit of detection (LOD) were assessed in tissue samples of fruit lesions and asymptomatic leaves. Low concentrations of the fungus were found in asymptomatic leaves. Under these conditions, real-time PCR proved to be viable, reproducible and highly sensitive to detection of the pathogen.