Standardizing Pathogenicity Assays for Fusarium Wilt Pathogens of Ornamental Palms

Standardized protocols for determining pathogenicity of Fusarium oxysporum ff. spp. canariensis and palmarum, the cause of Fusarium wilt of ornamental palms, were developed using small palm plants with a minimum of three to four seedling leaves. For both protocols, a standard amount of inoculum (25 ml of 10⁶ spores/ml) was pipetted onto and between the leaf bases of each plant, with excess material running down onto the roots and collecting in the container. After 3 days, the palm plants were transplanted into 450-ml containers filled with pine bark/sedge peat/sand potting mix. The protocol for F. oxysporum f. sp. canariensis differed from the protocol of F. oxysporum f. sp. palmarum by requiring that the lower 20% of roots be cut prior to inoculation and having the assay run for 6 months versus 3 months. These two assays were used to evaluate pathogenicity of multiple isolates of each pathogen. All 15 isolates of F. oxysporum f. sp. palmarum were pathogenic, whereas only 7 of 13 F. oxysporum f. sp. canariensis isolates were pathogenic. These assays were also used to determine susceptibility of other palm species to these pathogens. Washingtonia filifera, Butia odorata, Phoenix dactylifera, and P. reclinata appeared susceptible to F. oxysporum f. sp. palmarum, at least in the seedling stage. Other inoculation techniques are described that may be useful for evaluating Fusarium wilt disease management methods.