Recent findings of viruses infecting Ranunculus Hybrids in Liguria (Italy)

Ranunculus asiaticus L. an ornamental species grown in many areas of the world ( western Europe, South Africa, California, Israel, Japan) for tuber, potted plants, and cut flowers production. In Italy, the crops of Ranunculus hybrids are located principally in Liguria region, where virus diseases represent a serious problem in cut flower production, even if the impact of virus infections on the crops has not been well studied. For this reason, in 2005-2007, two hundred samples of Ranunculus hybrids collected in Sanremo area (Imperia province) were examined to verify the presence of viruses associated to severe symptoms on leaves (chlorosis, mosaic, “parsely-like” appearance, vein-yellowing, necrotic spots and rings on the lamina; petiol and stem necrosis) and flowers (colour breaking, malformations), stunting and/or prematurely death of plants. By applying virological tests: mechanical inoculations on herbaceous plants, electron microscopy (“leaf-dip”), DAS and PAS-ELISA, IME (“decoration”), and RT-PCR, several virus species of different lengths (from 700 to 800 nm) and sizes (from 30 to 90-100 nm) singly or in mixed infections were detected. Cucumber mosaic virus (CMV) in a few cases alone, much more in combination with Tomato spotted wilt virus (TSWV) infected plants showing leaf mosaic, necrosis, stunting and severe symptoms on flowers. Both TSWV and Impatiens necrotic spots virus (INSV), in some cases with also Potato virus Y-Ranunculus strain (PVY-R), were detected in the foliage characterized by mosaic, stem and petiol necrosis, and “parsely-like” symptoms. Turnip mosaic virus (TuMV) and other unidentified potyvirus-like viruses were found. CMV and all the Potyviruses detected, were much present during Autumn 2006 season as a consequence of the abundance of aphid infestations. Data obtained clearly show not only the high diffusion of different species of viruses in Ranunculus crops in Sanremo area, but also that the correlation between symptom expression and virus presence is very difficult to be explained. Considering the increasing of economic damages to cut flower production recently observed in this area, control measures to prevent virus spreading are required, such as monitoring and virus-testing programs for a rapid removal of inoculum sources and large-scale indexing of propagation materials. In fact, considering that Ranuncuuls is vegetatively propagated, production and distribution of infected tubers can result in an easily virus spread: virus infected tubers rarely show symptoms, and the plantlets obtained usually do not express symptoms until they are rooted. As consequence, Ranunculus viruses (aphid an thrip transmitted) can spread rapidly to other plants before the grower is aware that the pathological problem exists.