Reaction assessment of a number of citrus hybrids to 'Candidatus Phytoplasma aurantifolia'

South citrus growing belt of Iran including Hormozgan, Sistan-Baluchestan, Bushehr, Fars and Kerman provinces, has a long history of cultivation of acid lime (Mexican lime) [Citrus aurantifolia (Chritm.) Swing.]. In two recent decades due to witches' broom disease of lime (WBDL), caused by 'Candidatus Phytoplasma aurantifolia', thousands of acid lime trees have been killed in the south of Iran. Using resistant or tolerant varieties is one of the important strategies for controlling WBDL . The aim of this study was producing new acid citrus hybrids resistant to the WBDL disease. Four types of crosses were carried out. The female parent was ‘Eurekaʼ lemon [C. limon (L.) Burm. F.] and the male parents were ‘Yuzuʼ [C. junos Sieb. ex Tan.], ‘Cleopatraʼ mandarin [C. reshni Hort. ex Tan.], ‘Kusaieʼ lime (C. limonia Osb.) and ʻHamlinʼ orange [C. sinensis (L.) Osb.]. From the above parents, 79 hybrid plants were successfully inoculated with the 'Ca. P. aurantifolia' by inverted T-budding. Appearance of disease symptoms and nested-PCR assay were used to assess inoculated hybrids for resistance. Two years post-inoculation 63 hybrids remained symptomless. Among symptomless hybrids, 35 and 28 hybrids were negative and positive for presence of WBDL phytoplasma, respectively. Symptomless hybrids negative for WBDL phytoplasma are under more phenotypic evaluation and may be promising as new acid citrus resistant to WBDL.