LAUSR

Allorhizobium vitis is the primary causal pathogen of grapevine crown gall disease. As this endophytic bacterium can survive as systemic latent (symptomless) infections in grapevine, there is a great importance to detect and monitor its development in planta. In plant-bacteria studies, plate counting is routinely used as a simple and reliable method to evaluate the level of bacterial populations in planta. However, isolation techniques present some disadvantages such as necessity of working on fresh samples, time-consuming and risk of contamination. In this study, we developed a DNA-based real-time PCR assay that can replace the classical method to monitor the development of A. vitis in grapevine plantlets. Primers targeting A. vitis chromosomic genes and the virulent Ti plasmid were validated. The proposed qPCR technique is highly reliable and reproducible to assess A. vitis numeration at the earliest stage of infection until tumor development in grapevine plantlets. Moreover, this is a low-cost technique which provides rapid and robust in planta quantification of the pathogen, suitable for fundamental research to monitor bacterial development over time.