Teucrium fruticans (shrubby germander), family Lamiaceae, is a hardy shrub. Being drought tolerant, it is widespread in the Mediterranean area. Because it is readily propagated through cuttings, it is also planted in hedges. In 1997 and 2000, respectively, yellow chlorotic areas were observed on the foliage of T. fruticans in Saint Jean Cap Ferrat (France) and San Remo (Italy). These symptoms were distinct from those produced by a rust that frequently affects T. fruticans in these areas. Viruses from both locations were identified as Cucumber mosaic virus (CMV) based on the following: (i) symptoms after mechanical inoculation of Nicotiana tabacum cv. Xanthi nc, N. tabacum cv. Samsum, Chenopodium quinoa, C. amaranticolor, Vigna unguiculata cv. Black, and Cucumis sativus cv. Poinsett; (ii) the morphology of particles observed in electron microscopy of uranyl acetate stained leaf dips from tobacco; and (iii) positive result from leaves of diseased T. fruticans and mechanically inoculated host plants cited above based on enzyme-linked immunosorbent assay (ELISA) using CMV antisera. On tobacco cv. Xanthi nc, the French (F) and Italian (I) isolates first induced essentially necrotic rings on the inoculated leaves followed by the same systemic symptoms as described above. The two isolates were cloned from local lesions after two successive inoculations in V. unguiculata cv. Black, multiplied in tobacco, purified with the citrate-chloroform method, and stabilized with formaldehyde (1). The serotype determination was made by double immunodiffusion in agar gel with the CMV-D and CMV-To strains and homologous antisera (1,2). The formation of spurs and antigen-antibody lines indicated that both isolates belonged to the ToRS serotype (1). Thirty plants of T. fruticans cv. Azureum, first tested negative for CMV using ELISA, were mechanically inoculated with the F isolate (25 plants) and the CMV-D strain (five plants) and cultivated in a hydroponic system. Three months later, plants inoculated with the F isolate were positive for CMV using ELISA and displayed clear symptoms with chlorotic spots, which were sometimes ring-shaped. As plants mature, symptoms tend to disappear on young shoots. For the CMV-D strain, three plants of five were ELISA positive, but did not show any typical symptoms. This report demonstrates the infection of T. fruticans by CMV and the symptom induction by some CMV isolates. In September 2002, two CMV isolates were collected from T. fruticans in public gardens in Menton (France) and Genoa (Italy). These new isolates have the same characteristics as those described in this report.
References: (1) J. C. Devergne and L. Cardin. Ann. Phytopathol. 7:225, 1975. (2) M. H. V. van Regenmortel. Adv. Virus Res. 12:207, 1966.