Springer Acta Medica Okayama 0168-8162 30 1-3 2003 Orchid Fleck Virus: Brevipalpus californicus Mite Transmission, Biological Properties and Genome Structure 215 223 EN Hideki Kondo Research Institute for Bioresources, Okayama University Takanori Maeda Research Institute for Bioresources, Okayama University Tetsuo Tamada Research Institute for Bioresources, Okayama University Orchid fleck virus (OFV) causes necrotic or chlorotic ring spots and fleck symptoms in many orchid species world-wide. The virus has non-enveloped, bacilliform particles of about 40 nm �~ 100–150 nm and is sap-transmissible to several plant species. OFV is transmitted by the mite Brevipalpus californicus (Banks) in a persistent manner and efficiently transmitted by both adults and nymphs, but not by larvae. Viruliferous mites retain their infectivity for 3 weeks on a virus-immune host. The genome of OFV consists of two molecules of 6431 (RNA1) and 6001 nucleotides (RNA2). The RNAs have conserved and complementary terminal sequences. RNA1 contains five open reading frames (ORF), and RNA2 encodes a single ORF. Although some of the encoded proteins of OFV have sequences similar to those of proteins of plant rhabdoviruses, OFV differs from viruses in the family Rhabdoviridae in having a bipartite genome. No potential conflict of interest relevant to this article was reported.