Digitaria striate virus—a rhabdovirus of grasses transmitted by Sogatella kolophon (Kirk.)

Abstract

A previously undescribed rhabdovirus causing striate symptoms mainly in the Digitaria species D. decumbens (pangola grass) and D. ciliaris (summer grass) was found within a range of 18–28°S, of the Australian east coast. About 10% of individuals of the delphacid leafhopper Sogatella kolophon (Kirk.) transmitted the virus after a 24 h acquisition feed. The time between acquisition and first transmission was 5–8 days with an 8–11 day latent period before symptoms appeared in the plant. Transmission in a persistent manner was demonstrated for males and females and for nymphs and adults and through the moult to adults.The experimental host range was shown to include Avena sativa, Brachiaria miliiformis, Digitaria sanguinalis, Dinebra retroflexa, Eleusine coracana, Eleusine indica, Hordeum vulgare, Lolium multiflorum, Rhynchelytrum repens and Urochloa mosambicensis. Bullet-shaped particles 280 nm by 55 nm were readily found by electron microscopy of negatively stained sap from infected plants. The particles were often in groups and frequently showed crosss-triations, which were at a spacing of 4.2 nm and coincided with the frequency of the surface projections. Thin-section electron microscopy of infected plant tissue showed bacilliform and bullet-shaped particles in groups bounded by cytoplasmic membranes. No particles were seen within the nucleus or perinuclear space, and the particles were almost exclusively within companion cells and phloem parenchyma cells. Rhabdovirus-like particles and tubular structures were located within the brain and salivary glands of proven vector individuals, but not in healthy insects.