Host range, purification and some properties of two carlaviruses from hop (Humulus lupulus): hop latent and American hop latent

Abstract

SUMMARYHop latent virus (HLV) occurs in virtually all commercial hop plants in England, without causing apparent symptoms. It was transmitted between hop plants in a non‐persistent manner by the aphid Phorodon humuli, but was not seed‐borne in hop. The virus infected six species in four families out of 40 in 13 families which were inoculated, but infection was systemic only in Dianthus deltoides and hop. Only Phaseolus vulgaris and Chenopodium murale developed symptoms. Purification of HLV from hop extracts was hampered by aggregation of virus particles but this was minimised either by resuspending pellets in phosphate‐buffered saline containing Tween 20 or by avoiding ultra‐centrifugation. Virus was purified from extracts treated with Triton X‐100 by precipitation with polyethylene glycol (PEG) followed either by centrifugation through sucrose density gradients or by exclusion chromatography through columns of Sephadex G‐25 and Sepharose 4B. Purified preparations contained filamentous particles c. 675 × 14 nm composed of c. 6% single stranded RNA of mol. wt c. 2.9 × 106 and a single protein species of mol. wt c 33 000. Immunosorbent electron microscopy (IEM) decoration tests suggested that HLV was serologically related to carnation latent, Helenium virus S, lily symptomless and Nerine latent viruses.American hop latent virus (AHLV) was found in two introductions to England from Corvallis, USA in 1975 and 1976. It was transmitted between hop plants in the non‐persistent manner by P. humuli. The virus infected 17 species in seven families out of 41 species in 13 families which were mechanically inoculated and was systemic in nine species. It did not cause symptoms in any of five English hop cultivars. C. quinoa was a convenient propagation host and countable local necrotic lesions and ringspots occurred in leaves of Datura stramonium. AHLV was purified by PEG precipitation and centrifugation in sucrose density gradients. Preparations contained filamentous particles c. 680 × 15 nm composed of c. 6% single‐stranded RNA of mol. wt c. 3.0 × 106 and a single protein species of mol. wt c. 33 000. In IEM decoration tests AHLV was serologically related to Nerine latent virus but did not react with antisera to 14 other carlaviruses.