A survey in Israel reveals the presence of Xylella fastidiosa in almond trees in the northern part of the country

Xylella fastidiosa is an insect-vectored, Gram-negative bacterial pathogen that until recent years was thought to be geographically restricted to the Americas. There, X. fastidiosa, caused and still causing significant damages particularly to the grapevine and citrus productions in North and South America, respectively. In 2013, X. fastidiosa was first reported outside the Americas, and was found in association with symptomatic olive trees in southern Italy. X. fastidiosa was later proven as the responsible agent for the devastating epidemic in southern Italy’s olive groves leading to the olive quick decline syndrome. Later, X. fastidiosa was also reported from France mainland and Corsica, and from Spain mainland and Mallorca, causing disease in multiple host plants including Polygala myrtifolia, almond, cherry and grapevines. In a survey conducted in Israel during 2017-2018, leaf scotching symptoms were observed in almond trees in the northern part of the country. Upon emergence from winter dormancy trees appear symptomless, although they tend to suffer from visible loss in foliage mass. From May onwards, the infected plants develop typical leaf scotching and curling symptoms. Both molecular and immunological assays showed that X. fastidiosa is associated with these symptoms. Multi-locus sequencing analysis of several Xylella isolates, revealed that the dominant sequence type (ST) found in almond trees in northern Israel is ST1. Suspected olive and grapevine trees, showing scorching symptoms, were also tested and found negative for the presence of Xylella. Grafting experiments with Xylella-infected almond scions and artificial inoculations of healthy almonds, led to the appearance of typical disease symptoms. These results confirm the presence of X. fastidiosa in almond trees in northern Israel. Further studies to understand the breadth of the damage and to search for possible insect vectors are underway