Evidence that Xylella fastidiosa is the Causal Agent of Almond Leaf Scorch Disease in Alicante, Mainland Spain (Iberian Peninsula)

In 2017, Xylella fastidiosa, a quarantine plant-pathogenic bacterium in Europe, was detected in almond trees associated with leaf scorch symptoms in Alicante, a Mediterranean area in southeastern mainland Spain. The bacterium was detected by serological and molecular techniques, isolated in axenic culture from diseased almond trees, and identified as X. fastidiosa subsp. multiplex sequence type (ST) 6. Inoculation experiments on almond plants in greenhouse trials with a characterized strain of X. fastidiosa subsp. multiplex ST6 isolated in the outbreak area have proved that it was able to multiply and systemically colonize inoculated plants. Disease symptoms characteristic of leaf scorch like those observed in the field were observed in the inoculated almond trees after 1 year. Furthermore, the pathogen was reisolated and identified by molecular tests. With the fulfillment of Koch's postulates, we have demonstrated that X. fastidiosa is the causal agent of the almond leaf scorch disease in the Alicante outbreak.