The occurrence, hosts and properties of lilac chlorotic leafspot virus, a newly recognised virus from Syringa vulgaris

Lilac chlorotic leafspot virus (LCLV), a hitherto undescribed virus, was isolated from three of 65 lilacs (Syringa vulgaris) with chlorotic leafspotting symptoms growing in S.E. England. The virus was transmitted readily by sap-inoculation to 21 of 52 species from eight of 20 families, but it was not seed-borne in four hosts or transmitted in the semi-persistent manner by any of four aphid species. The virus was moderately stable in vitro; sap from Chenopodium quinoa was infective after 10 min at 60 but not 65 ^oC, after 8–16 days at 20 ^oC or 25–30 wk at 2 ^oC, and after dilution to 10^-3 but not 10^-4. Up to 180 mg of purified virus per kg leaf tissue were obtained from C. quinoa by clarification of buffered leaf extracts with 8% (v/v) n-butanol, followed by one cycle of differential centrifugation and molecular permeation chromatography on controlled pore glass beads (700 Å, 120–200 mesh). LCLV has fragile flexuous filamentous particles which, when intact, mostly measured c. 12-5 times 1500–1600 nm; the helical substructure (pitch c. 3–7 nm) was clearly visible on some particles mounted in uranyl acetate. The particles sedimented as a single component (sedimentation coefficient 96 S; buoyant density 1–302 g cm^-3) and contained c. 5% nucleic acid and a single polypeptide of mol. wt 27 times 10³. Although these properties place LCLV in the closterovirus group, the virus showed no serological relationship to any of six closteroviruses (beet yellows, beet yellow stunt, carnation necrotic fleck, apple chlorotic leafspot, apple stem grooving and potato virus T) and differed from other recognised or possible members of this group in host range and/or symptoms induced in indicator species. The infrequent occurrence of LCLV in lilac in S.E. England indicates that the virus could probably be eradicated by selecting only virus-free plant material for propagation.