CORESTA Congress, Paris, 2006, PPOST 09

Early diagnosis of Peronospora tabacina Adam in tobacco plant with systemic infection

Biologia e Difesa Fitosanitaria, Scafati, Italy
A disease characterised by the absence of sporulation on leaves and evident necrosis underneath the bark tissues, affected adult tobacco plants during 2005 in South Italy. In the field, diagnosis is based mainly on recognition of symptoms, often non-specific, that could result in the application of useless control strategy. Two current diagnostic methods based on microscopic observations were compared with polymerase chain reaction (PCR) technique. DNA extraction protocol was modified by replacing sonication with a further lysis step at 60 °C and PCR was performed using primers that amplified a specific DNA fragment (230 bp). Microscopy methods were able to detect the pathogen in 50% and 6% of cases, respectively, while PCR was able to detect P. tabacina in all diseased plants. Elimination of sonication in DNA extraction rendered the method easier to perform and avoided the possibility of DNA fragmentation. The results demonstrated that PCR makes the diagnosis fast and reliable while microscopy gives discontinuous results, is time consuming and not applicable for monitoring.