Otimização da técnica de PCR para detecção de Xanthomonas axonopodis pv. phaseoli em sementes de feijão

Abstract

Common blight caused by Xanthomonas axonopodis pv. phaseoli (Xap) is the main bacterial malady in Brazilian beans, being transmitted mainly by seeds. This present work aimed at improving a technique for the detection of Xap in bean seeds, by using different extract preparation methods for detection through via PCR, and the simultaneous detection of Xap and Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) in the extracts by using a Bio-PCR. After inoculating the bean seeds an assessment was made of gross extract obtained directly from the seeds, extract concentrated in Millipore membrane, extract concentrated via centrifugation and plating of seed extracts on a semi-selective agar medium (Bio-PCR). The presence of Xap and Cff in commercial lots of beans from several regions of Brazil by using the same procedures as those for inoculated seeds was also assessed. For the optimization of the PCR technique primers X4c and X4e were used. Neither from the gross extract, the extract concentrated by centrifugation and by Millipore membrane detection of Xap in artificially contaminated bean seeds nor in the 47 commercial lots of bean seeds/grains was the detection of Xap possible. The Bio-PCR technique enabled for the detection of Xap from artificially contaminated bean seed extracts and in 18 of the 47 commercial lots. The technique for the simultaneous detection of Xap and Cff in the same gel was not viable due to the amplification of typical Cff DNA fragments in the control Xap sample. The semi-selective cultivation medium XCP1 without antibiotics can be used for the recovery of Xap colonies.