Abstract
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.
Highlights
Citrus black spot (CBS), caused by Guignardia citricarpa (=Phyllosticta citricarpa), is one of the main fungal diseases in citriculture
It was first reported in Australia in 1895 (SUTTON and WATERSTON, 1966) and has since spread to other citrus growing regions, such as southern and central Africa, South America and Asia, becoming a major phytosanitary problem in citrus crops (HINCAPIE et al, 2014; MARTÍNEZ-MINAYA et al, 2015). It was recently identified in the United States, where it is limited to certain areas of Florida (SCHUBERT et al, 2012). Since it is a quarantine disease, CBS limits the exportation of fresh fruit to the European Union (EPPO, 2015)
Since there are no reports of techniques to detect latent G. citricarpa infection, and given the need for efficient and accurate diagnosis of CBR regardless of phenological growth stage, this study aimed to achieve early diagnosis of G. citricarpa in asymptomatic sweet orange leaves using conventional and real-time polymerase chain reaction (PCR)
Summary
Citrus black spot (CBS), caused by Guignardia citricarpa (=Phyllosticta citricarpa), is one of the main fungal diseases in citriculture. All varieties of sweet orange (Citrus sinensis) and species such as C. limon, C. paradisi, C. reticulata and C. deliciosa are susceptible to the pathogen (HU et al, 2014) It was first reported in Australia in 1895 (SUTTON and WATERSTON, 1966) and has since spread to other citrus growing regions, such as southern and central Africa, South America and Asia, becoming a major phytosanitary problem in citrus crops (HINCAPIE et al, 2014; MARTÍNEZ-MINAYA et al, 2015). It was recently identified in the United States, where it is limited to certain areas of Florida (SCHUBERT et al, 2012).
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