Fusarium wilt and pink rot of palms in the city of Genoa: incidence and attempts of management

Phoenix canariensis is used extensively as a landscape ornamental in coastal areas of Italy. In 2010, symptoms of wilt and dieback were observed on P. canariensis in the city of Genoa (Italy). Leaves of 28 symptomatic and asymptomatic palms from 8 urban sites were sampled. Isolations were attempted from sections of petioles by transferring small pieces of tissue, after flame-sterilization, on standard growth medium and subsequent incubation at 24±2°C for one week. Two different fungal pathogens were isolated: the Fusarium wilt agent Fusarium oxysporum f.sp. canariensis and the pink rot fungus Nalanthamala vermoesenii. Fungi were identified on the basis of their macroscopic and microscopic features using taxonomic guides and standard procedures. Identification of F. oxysporum at the formae specialis level was achieved through a PCR-based assay by using the taxon-specific primers HK66 and HK67. When isolations failed, PCR was conducted on fungal DNA extracted directly from the petiole tissues. Since chlamydospores of F. oxysporum f.sp. canariensis can survive for long periods in the soil, the same PCR assay was used to detect the pathogen directly from soil samples collected around palms. Fusarium oxysporum f.sp. canariensis was isolated from petiole tissues of 9 palms (32% incidence) and in soil samples from 9 palms (5 of them also positive to isolations); N. vermoesenii was isolated from 6 palms (21% incidence). Only one palm was colonized by both pathogens. In a subsample of infected palms, the effectiveness of two fungicides, i.e. thiabendazole and thiophanate-methyl, was tested. The first treatment was applied through trunk-injections using the recently patented BITE, and the second through soil drenches. Preliminary observations suggest thiophanate-methyl soil treatments may be effective in reducing disease severity.