Schefflera ringspot virus, a widely distributed mealybug-transmitted badnavirus occurring in schefflera and aralia

A previously undescribed badnavirus, named schefflera ringspot virus (SRV) was found in scheffleras (Brassaia actinophylla, umbrella tree, and Schefflera arboricola, dwarf umbrella tree) and aralias (Pofyscias baifouriana, P. balfouriana 'Marginata', P. fruticosa and P. guilfoylei) in Australia, Barbados, Cuba, Mauritius, Honduras, Taiwan, Thailand and the USA. SRV infection caused leaf mottling and chlorotic and necrotic ringspots in schefflera, and was associated with chlorotic spotting, vein-clearing and reduction of leaf size in aralia. Symptoms occurred sporadically, and appeared to be correlated with changes in environmental conditions. SRV was transmitted by the citrus mealybug (Planococcus citri) from infected schefflera and aralia to healthy schefflera seedlings, but not to Fatsia japonica or Hedera helix, two other Araliaceae. Virions of SRV were similar to those of other badnaviruses, measuring 30 × 150 nm and containing a ds DNA genome. SRV reacted with antisera to several badnaviruses, but was most closely related serologically to sugarcane bacilliform (ScBV), cacao swollen shoot (CSSV) and rice tungro bacilliform (RTBV) viruses. Scheffleras and aralias infected with SRV frequently contained rod-shaped proteinaceous structures 15 nm in width and varying greatly in length. Similar structures have been found in other badnavirus infections, and are usually associated with virus isolates which produce severe symptoms but relatively few extractable intact virions, and which are poorly mealybug-transmitted. SRV appears to be genomically heterogeneous, a property common to many badnaviruses.