Biological, Serological and Molecular Techniques to Xanthomonas Axonopodis pv. Citri Asymptomatic Detection

Abstract

Xanthomonas axonopodis pv. citri (Xac) produces citrus canker disease in all citrus commercial species. The bacteria can be disseminated through vegetative propagation material in asymptomatic form. To optimize bacteria detection techniques applicable to asymptomatic citrus plant tissue routine analysis, ELISA, Immunofluorescence, PCR, qRT_PCR and host plant inoculation (bioassay) diagnostic techniques were compared. Tests were made from decimal dilutions between 10⁸ ufc.mL^-1 and 10² ufc.mL^-1 using a pure culture of 49b strain.The detection level obtained was 1.8 x 10² ufc.mL^-1 using Inmunofluorescence; 1.8x10⁴ ufc.mL^-1 with indirect ELISA, 1.8 x 10³ ufc.mL^-1 by means of PCR; 10 ufc.mL^-1 through of qRT_PCR and 230 ufc.mL^-1 in sour orange inoculated plants. The experiment was repeated at least three times for each technique. Considering this result, and taking into account that sensitivity, practicity and cost, are important when a great number of plants need to be tested, the PCR and inoculation in host plants were those that met the best characteristics to be evaluated in asymptomatic plant material.