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Araujia sericifera New Host of Alfalfa mosaic virus in Italy

Araujia sericifera Brot. (Fam. Apocynaceae) is an evergreen climbing plant native of South America, originally introduced in Europe as an ornamental. In spring 2012, virus-like symptoms including bright yellow mosaic of calico-type and leaf distortion were observed in three A. sericifera plants growing in an abandoned field located in Pomigliano d'Arco (Campania region, Italy). Leaves from the three plants were collected and examined using commercial antisera (Bioreba AG, Reinach, Switzerland) by double antibody sandwich (DAS)-ELISA against Cucumber mosaic virus (CMV), Alfalfa mosaic virus (AMV), and by indirect plate trapped antigen (PTA)-ELISA against potyviruses (Potygroup test). Only AMV was detected serologically in the three A. sericifera samples. The virus was mechanically transmitted from the ELISA-positive samples to four plants each of Chenopodium quinoa, C. amaranticolor, tobacco (Nicotiana tabacum cv. Xanthi nc), cowpea (Vigna unguiculata, cv. Black eyes), basil (Ocimum basilicum, cv. Gigante), and tomato (Solanum lycopersicum cv. San Marzano), using chilled 0.03 M sodium phosphate buffer, containing 0.2% sodium diethyldithiocarbamate, 75 mg/ml of active charcoal, and traces of Carborundum (600 mesh). Inoculated plants were kept in an insect-proof greenhouse with natural illumination and temperatures of 24 and 18°C day/night. Under these conditions, plants showed the following symptoms after 1 to 3 weeks, consistent with symptoms caused by AMV (1): chlorotic local lesions following by mosaic in C. quinoa and C. amaranticolor, reddish local lesions following by mosaic in cowpea, necrotic local lesions followed by systemic necrosis in tomato, bright yellow mosaic (calico type) in basil, and mosaic and strong deformation of the apical leaves in tobacco. The presence of AMV in ELISA-positive A. sericifera and host plants was further confirmed by conventional reverse transcription (RT)-PCR. Total RNAs were extracted with an RNeasy Plant Mini Kit (Qiagen, Hilden, Germany). RT-PCR was performed with the One-Step RT-PCR Kit (Qiagen) using primers for the coat protein gene (CP) previously used for the molecular characterization of AMV isolates (2). An Italian isolate of AMV from Lavandula stoechas (GenBank Accession No. FN667967) and RNA extracted from a healthy A. sericifera plant were used as positive and negative controls, respectively. An amplicon of the correct predicted size (∼750 bp) was obtained from each of the infected plants assayed, and that derived from A. sericifera isolate Ars2 was purified (QIAqick PCR Purification Kit, Qiagen), cloned in pGEMT easy vector (Promega, Fitchburg, WI) and sequenced (HF570950). Sequence analysis of the CP gene, conducted with MEGA5 software, revealed the highest nucleotide identity of 98% (99% amino acid identity) with the AMV isolate Tef-1 (FR854391), an isolate belonging to subgroup I (3). To our knowledge, this is the first report of AMV infecting A. sericifera in Italy. Since A. sericifera is considered an invasive plant, in continuous expansion to new areas in Italy and in other European countries, particular attention should be paid to the possibility that this species may play a role in the epidemiology of aphid-transmitted viruses such as AMV and CMV, representing a threat to susceptible crops growing nearby.

References: (1) G. Marchoux et al. Page 163 in: Virus des Solanacées. Quae éditions, Versailles, 2008. (2) G. Parrella et al. Arch. Virol. 145:2659, 2000. (3) G. Parrella et al. Plant Dis. 96:249, 2012.