Host range, purification and serological properties of heracleum latent virus

Heracleum latent virus (HLV occurs commonly in wild plants of Heracleum sphondylium (hogweed) in Scotland without causing symptoms. It was transmitted manually or by aphids (Cavariella aegopodii, C. pastinacae or C. theobaldi) to 37 of 105 species in 11 of 18 families (especially to members of the Amaranthaceae, Chenopodiaceae, Solanaceae and Umbelliferae), but was not transmitted through seed of four species tested. It has very flexuous filamentous particles c. 730 × 12 nm in phosphotungstate, with obvious cross-banding of pitch 3–8 nm. Leaf extracts lost infectivity after 1–2 days at 22°C, 10 min at 40–50°C and after dilution 10^-4-10^-5. Infectivity in leaf extracts was not stabilised by addition of Mg²⁺, Ca²⁺ or Ni²⁺, but was abolished by EDTA. HLV was purified by bentonite clarification, precipitation with polyethylene glycol (mol. wt 6000), and differential centrifugation. Its properties resemble those of the tentative closterovirus, apple chlorotic leaf spot (ACLSV), but no serological relationship was detected to this or to any of 18 other filamentous viruses, including six definitive closteroviruses. No cross-protection was observed between HLV, ACLSV and apple stem grooving virus.