First report of bacterial wilt caused by Ralstonia solanacearum on eucalypts in South Africa

Ralstonia solanacearum, the causal agent of bacterial wilt, has one of the widest host ranges of all phytopathogenic bacteria. This pathogen was first reported on Eucalyptus spp. in the late 1980s in Brazil. Since then, there have been reports of its occurrence on this host in Australia, China and V enezuela. Early in 1997, an 18-month-old clonally propagated Eucalyptus gra ndis x Eucalyptus camaldulensis (GC) hybrid in Zululand, KwaZulu/Natal, sho wed signs of wilting. The vascular tissue of infected trees was dicoloured and bacterial exudation was produced from cut surfaces. The bacterium was c onsistently isolated from diseased tissue, purified and identified as R. so lanacearum biovar 3 race 1, using the BioLog bacterial identification syste m. Inoculation trials were conducted on three E. grandis x E. camaldulensis clones (GC515, GC550 and GC505). Clone GC550 displayed wilting after 3 day s and all cuttings subsequently died. Clones GC515 and GC505 appeared to be less susceptible with cuttings not showing signs of disease until 7 days a fter inoculation. After 14 days, 90 and 80%, respectively, of cuttings of t hese two clones had died. This is the first report of bacterial wilt on Euc alyptus in South Africa.