A satellite‐like nucleic acid of arabis mosaic virus associated with hop nettlehead disease

SUMMARY An isolate of arabis mosaic virus (AMV) from a hop plant with symptoms of nettlehead disease induced unusually severe symptoms when transmitted to Chenopodium quinoa. This isolate, called AMV‐Ta, yielded particle preparations in which up to 80% of the nucleic acids consisted of a species of low molecular weight (SNA), estimated to be about 75 000 daltons by polyacrylamide gel (PAG) electrophoresis. An isolate free of detectable S‐NA (AMV‐To) was derived from AMV‐Ta by inoculating plants with the two high molecular weight genomic RNA species of AMV (2–8 times 106 and 1–3 times 106 daltons; Murant, 1981) separated from S‐NA by PAG electrophoresis. This isolate induced much milder symptoms in C. quinoa. Hop seedlings inoculated with AMV‐Ta, either mechanically or by nematodes, developed characteristic nettlehead symptoms. Hop seedlings similarly inoculated with AMV‐To remained free of nettlehead symptoms. Two species of S‐NA associated with hop nettlehead isolates of AMV were detected at two sites in Kent, and two West Midlands sites. At both sites in Kent and at one of the West Midlands sites, the occurrence of the S‐NA species was closely correlated with the incidence of nettlehead symptoms. At the other site in the West Midlands, the occurrence of nettlehead symptoms was too erratic to allow positive correlation of SNA with symptom development. Our results show that S‐NA plays an active part in symptom production in experimentally inoculated plants of both hops and C. quinoa. In addition, the close correlation between the occurrence of AMV with additional nucleic acid species, and the incidence of nettlehead symptoms in commercially grown hops, suggests a role for S‐NA in the aetiology of this disease.