Dust accumulation due to anthropogenic impact induces anatomical and photochemical changes in leaves of Centranthus ruber growing on the slope of the Vesuvius volcano.

In Mediterranean ecosystems, some natural areas are exposed to severe anthropogenic impact. Especially in summer, the considerable number of tourists visiting such areas, often with vehicles, causes deposition of dust over the vegetation due to formation of powder clouds, also favoured by wind erosion, high temperature, low precipitation and incoherent soil structure. The main aim of this study was to analyse whether the deposition of dust can induce changes in leaf anatomical functional traits and in the efficiency of photosynthetic apparatus in Centranthus ruber, a species widespread in Mediterranean ecosystems. Leaf morpho-functional traits were quantified in plants growing at sites characterised by high (HD) and low (LD) dust deposition, in periods with high anthropogenic impact. Analyses included quantification of chlorophyll fluorescence emission parameters, photosynthetic pigment concentration as well as stomatal size and frequency, leaf lamina thickness, quantification of intercellular spaces and phenolics in the mesophyll through microscopy. The overall analysis suggested that the different conditions of dust deposition induced different adjustment of morpho-functional traits in leaves of C. ruber. High dust deposition shielded the leaf lamina, protecting the photosynthetic apparatus from excess light and favoured plant photochemical efficiency. Leaves exposed to low dust deposition showed higher accumulation of phenolic compounds, protecting chloroplast membranes and characterised by high thermal dissipation of excess light. Such adaptive phenomena can affect vegetation dynamics due to possible different species-specific plant responses, resulting in different plant competitiveness under the limiting conditions of Mediterranean environments.

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.