SEVERE OUTBREAK OF FUSARIUM SOLANI ON QUERCUS ILEX VECTORED BY XYLOSANDRUS COMPACTUS

Abstract

The black twig borer Xylosandrus compactus (Eichhoff) (Coleoptera: Scolytinae) causes severe damages to its hosts (Chong et al., 2011) because it also vectors Fusarium solani, which induces wilting of twigs and terminal branches (Ngoan et al., 1976). In two urban parks in Naples and Portici (southern Italy) an evident flagging of the leaves of holm oak (Quercus ilex) was observed, followed by a rapid wilting of shoots and twigs of saplings and mature trees (Garonna et al., 2012). A fungus isolat- ed from the beetle’s reproductive galleries, entry holes and the adjacent black-stained woody tissues, was grown on potato dex- trose agar (PDA) at 25°C, and identified by sequencing the ITS 1-4 region of rDNA. The sequence showed 99% identity with that of Fusarium solani from GenBank (accession No. EU719658.1). In pathogenicity tests, holm oak branches were in- oculated with a 2-mm PDA dish collected from a 7-day-old cul- ture of the F. solani isolate (FS1). Control branches were inocu- lated with plugs of sterile PDA. All branches were incubated at 25±1°C. After five days, symptoms resembling those exhibited by naturally infected plants developed only on the branches inocu- lated with FS1, from whose tissues this fungus was re-isolated, thus proving to be a Q. ilex pathogen. Symptoms recalling those observed in the two sites surveyed are spreading through the holm oak woodlands of Campania (southern Italy), so the geo- graphical distribution of the outbreak may already be consider- able. To the best of our knowledge this represents the first Euro- pean record of a severe outbreak of F. solani on Q. ilex following a massive attack by X. compactus.