In November 2007, leaves of 79 Phalaenopsis and two Dendrobium orchid plants in a nursery in Yunnan Province showed large chlorotic/necrotic ringspot symptoms. Eight symptomatic leaves from Phalaenopsis and two from Dendrobium were sampled and tested for Impatiens necrotic spot virus (INSV), Tomato spotted wilt virus (TSWV), Watermelon silver mottle virus (WSMoV), Groundnut bud necrosis virus (GBNV), Tomato chlorotic spot virus (TCSV), and Groundnut ringspot virus (GRSV) with double-antibody sandwich (DAS)-ELISA kits (Agdia Inc., Elkhart, IN). All samples were positive for INSV and negative for TSWV, WSMoV, GBNV, TCSV, and GRSV. Total RNA extracts were prepared from all ELISA-positive samples with the RNeasy extraction kit (Huashun Inc., Shanghai, China). Reverse transcription (RT)-PCR was carried out with specific primers to the INSV N gene (ZI2F, 5′-GTTTAGCCTTACCAAT-3′ and ZI2R, 5′-TACCAACAACCGTGAA-3′), designed from a sequence of GenBank Accession No. AB109100. All ELISA-positive samples yielded an amplification product of the expected 539 bp as observed by gel electrophoresis in 1% agarose. Three clones from each isolate were sequenced and two N gene consensus sequences of the isolates from Phalaenopsis and Dendrobium were determined (GenBank Nos. GU289904 and GU289905, respectively). Nucleotide sequences of these two Chinese orchid isolates were 98 to 99% identical with sequences of isolates from the Netherlands, United States, Italy, and Japan (GenBank Nos. X66972, D00914, DQ425096 and AB109100, respectively). To our knowledge, this is the first report of INSV infecting Phalaenopsis and Dendrobium in Yunnan Province, although INSV has been reported in Oncidium in Yunnan Province previously (2), and the first time that INSV has been detected in Dendrobium. An investigation of the orchid nurseries looking for the thrips vector (1) of INSV was performed and a few thrips were found, suggesting that thrips may not be responsible for the observed prevalence of INSV in these nurseries. The orchids were imported from Taiwan and reproduced by tissue culture and it is possible that INSV found to be infecting orchids in these Yunnan nurseries may be from the infected source plant and was not eradicated completely through tissue culture. To reduce spread of INSV, virus-free tissue culture should be a priority for orchid production.
References: (1). S. T. Koike and D. E. Mayhew. Orchids. Mag. Am. Orchid Soc. 70:746, 2001. (2). Q. Zhang et al. Plant Quarantine. 22:348, 2008.
