First report of impatiens necrotic spot virus infecting Oncidium in Italy

Oncidium is a large genus of orchids that includes over 600 species. The quality of Ligurian Oncidium plant pots and cut flowers is highly appreciated in the Italian floral auction market, and the number of producers have increased in Sanremo area in the last decade. During the 2008 Spring season, Impatiens necrotic spot virus (INSV) was found by DAS-ELISA infecting greenhouse-grown Oncidium orchids displaying leaf symptoms ranging from necrotic concentric rings to necrotic lesions 1-2 cm in diam. Subsequently, symptomatic leaves exhibited yellowing and necrosis along the veins; no flower symptoms were observed. Oncidium plants were growing adjacent to Ranunculus hybrids infected by this tospovirus. To confirm the presence of INSV, total RNA was extracted from symptomatic Oncidium leaves and used for RT-PCR amplification of the nonstructural protein gene of INSV. The resulting primers directed the amplification of a PCR product of approximately 1300 nucleotides. To verify that the amplified products were derived from INSV RNA, the PCR fragment was cloned and 2 independent clones were sequenced in both directions. Sequence analyses of the cloned PCR product showed 98.6% nucleotide sequence identity, and 98.2 and 99.2% amino acid identity and similarity, respectively with a previously published INSV-NSs sequence (Gene Bank Accession no. NC_003624). Methods for reducing the risk of this disease include using uninfected plant material, removing weeds which act as hosts of the insect vector (Frankliniella occidentalis) or using insecticides to prevent virus transmissions. This is thought to be the first report of INSV infecting Oncidium in Italy.