Tuber necrosis is one of the symptoms associated with potato purple top (PT) disease. In 2005 in Texas, USA, this symptom was named “zebra chip” or striped potato and was associated with the presence of Xyllela fastidiosa. The aim of this research was to detect the bacterium in plants exhibiting symptoms of PT. The three major regions of potato production in the State of Mexico were selected (Toluca, Atlacomulco and Valle de Bravo). Directed sampling was carried out in the spring-summer season of 2006. Polymerase Chain Reaction (PCR) with the specific primers RST31/RST33 was used to detect Xyllela fastidiosa; 25 % of the plants tested positive for the pathogen. Sequences of amplified fragments compared with sequences registered in the GENEBANK were 97 and 99 % homologous. The results suggest that necrosis and the symptoms of PT expressed in the potato plants in the State of Mexico are associated with X. fastidiosa.

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