Xylella fastidiosa causes leaf scorch of pistachio (Pistacia vera) in Iran

Abstract

Since the early 2010s, pistachio (Pistacia vera L.) leaf scorch symptoms have been observed in orchards in several provinces in Iran. Seventeen of 83 symptomatic leaf samples from pistachio plants from 21 orchards were positive for the presence of Xylella fastidiosa, as detected by DAS-ELISA with X. fastidiosa-specific antibodies and by PCR assays with X. fastidiosa-specific primers. A Gram-negative bacterium similar to X. fastidiosa was isolated into solid media. DAS-ELISA and PCR confirmed the identity of the isolated bacteria as X. fastidiosa. Koch’s postulates were fulfilled by artificially inoculating isolates obtained from pistachio showing leaf scorch to healthy pistachio and Nicotiana tabacum (cv. White Burley). Selected isolates induced leaf scorch symptoms when inoculated on tobacco and pistachio seedlings grown under greenhouse conditions. Early leaf scorch symptoms appeared approx. 2 months after inoculation of tobacco and approx. 3 months for pistachio. Reisolation of X. fastidiosa from inoculated and symptomatic plants and DAS-ELISA and PCR tests confirmed the identity of the re-isolated bacteria to be X. fastidiosa. On the basis of disease symptoms, pathogen isolation, pathogenicity tests and positive diagnosis by DAS-ELISA and PCR, X. fastidiosa is concluded to be the causal agent of pistachio leaf scorch in Iran. This is the first report of isolation and pathogenicity of X. fastidiosa in pistachio worldwide.