STRAWBERRY CHLOROTIC FLECK DISEASE MAY BE CAUSED BY A NOVEL CLOSTEROVIRUS

Abstract

Chlorotic fleck (CF) is a graft transmissible disease identified almost 50 years ago. The disease agent can cause significant losses in strawberry and is known to be transmitted by the cotton aphid, an indication of the viral etiology of the disease. While CF was a major disease in the area where it was first identified (Louisiana, U.S.A.), no further steps were taken towards identification of the causal agent, probably because of the mild and inconsistent symptoms the agent caused on indicator plants. The strawberry decline observed in the western coast of North America during the last six years led us to investigate the possibility that novel agents may be involved in the symptomatology with CF being one of them. The known CF plant known to exist in the U.S.A. is maintained at the National Clonal Germplasm Repository in Corvallis, Oregon and was used to isolate the CF agent. Cloning and sequence analysis from dsRNA isolated from the CF plant verified the presence of three viruses, two of them being the criniviruses associated with pallidosis disease (Strawberry pallidosis associated virus and Beet pseudo yellows virus) and the third, a previously unidentified member of the family Closteroviridae. Phylogenetic analysis placed the virus in the Closterovirus genus, the aphid-borne closteroviruses. The genome of the new virus has been obtained and detection protocols developed have verified the presence of the virus in the U.S.A. Experiments are currently underway to determine if any of the major strawberry aphids are vectors of the virus.