Transmission of ‘Candidatus Phytoplasma aurantifolia’ to Bakraee (Citrus reticulata Hybrid) by Feral Hishimonus phycitis Leafhoppers in Iran

Abstract

Witches'-broom disease of lime (WBDL) caused by ‘Candidatus Phytoplasma aurantifolia’ is a devastating disease in the Sultanate of Oman, United Arab Emirates, and southern Iran. The disease primarily affects lime (Citrus aurantifolia), but in Iran, it is also found in bakraee, a natural C. reticulata hybrid. The disease has been experimentally transmitted from lime to several citrus cultivars by grafting and to a number of herbaceous hosts by dodder. However, the natural vector of ‘Ca. P. aurantifolia’ has not been determined. The most common phloem-feeding insect associated with lime trees in the area is the leafhopper Hishimonus phycitis. The WBDL phytoplasma has been detected in the body of this leafhopper by ELISA and PCR (1), but previous attempts to establish its vector status have failed. It was recently reported that the leafhopper can release the phytoplasma into a sugar solution by feeding through a Parafilm membrane (4). Here we report successful transmission of WBDL phytoplasma to bakraee seedlings by H. phycitis. The leafhopper nymphs and adults were collected in a WBDL-infected lime orchard in Minab (Hormozgan Province) in May of 2006. Of more than 100 leafhopper samples tested, at least 70% were positive for the phytoplasma by PCR using P1/P7 primer pair (3). Additional field-collected leafhoppers were caged (five per plant) on bakraee seedlings at the two-leaf stage in pots in the greenhouse in Zarghan (Fars Province). After 8 weeks, the remaining leafhoppers were killed with an insecticide. Six months after inoculation, 3 of 10 inoculated plants showed typical symptoms of WBDL, including bud proliferation, general chlorosis, and stunting. Symptomatic plants were strongly positive in PCR assays using primer pair P1/P7. No amplification was obtained with healthy control lime or nonsymptomatic bakraee seedlings. Amplified P1/P7 primed PCR products (1,800 bp) from experimentally vector-challenged bakraee seedlings, captured H. phycitis, and a naturally infected lime tree from Minab were subjected to restriction fragment length polymorphism (RFLP) analysis using AluI, HhaI, HpaII, RsaI, and TaqI enzymes. RFLP patterns from these sources were identical and similar to those reported earlier (2). These analyses verified the identity of WBDL phytoplasma in experimentally infected bakraee seedlings. To our knowledge, this is the first report of natural transmission of ‘Ca. P. aurantifolia’ by H. phycitis. References: (1) J. M. Bové et al. Proc. Conf. IOCV 12:342. 1993. (2) A. J. Khan et al. Phytopathology 92:1038, 2002. (3) B. Schneider et al. Pages 369–380 in: Molecular and Diagnostic Procedures in Mycoplasmology. Vol. 2. S. Razin and J. G. Tully, eds. Academic Press, New York, 1995. (4) M. Siampour et al. Iran. J. Plant Pathol. 41:139 (Farsi) and 35 (English), 2006.

Expression of phytoplasma‐induced witches’ broom disease symptoms in acid lime (Citrus aurantifolia) trees is affected by climatic conditions

“…The leafhopper Hishimonus phycitis has been reported as a potential vector of 'Ca. Phytoplasma aurantifolia' (Salehi et al, 2007). Phytoplasmas can also be transmitted by other means, including grafting and vegetative propagation .…”

Pest categorisation of Witches' broom disease of lime (Citrus aurantifolia) phytoplasma

“…The WBDL phytoplasma is transmitted to lime in a persistent and propagative manner by the leafhopper H. phycitis, as infected field collected individuals successfully transmitted the disease to Citrus reticulata hybrids (Salehi et al, 2007). According to the available databases of Fauna Europaea and EPPO Global Database, the known vector is not present in the EU, although a species from the same genus (Hishimonus hamatus) has been reported in Slovenia (Seljak, 2013) and, in 2014 However, the ability of H. hamatus to transmit WBDL is unknown.…”

Invasive mutualisms between a plant pathogen and insect vectors in the Middle East and Brazil

“…Hishimonus phycitis is also of concern as there is some evidence that it can vector the phytoplasma ‘ Ca . Phytoplasma aurantifolia’, the etiological agent of Witches' Broom Disease of Lime (WBDL) [17,18]. WBDL is a devastating disease, which has spread across the Middle East and resulted in the destruction of more than 50% of the cultivated lime area and 75% loss in production [19,20].…”