Chromatographic Characterization and Phytotoxic Activity of Fusarium oxysporum f. sp. albedinis and Saprophytic Strain Toxins

Abstract The bayoud disease, vascular fusariosis of date palm tree (Phoenix dactylifera L.), is caused by the pathogenic fungus Fusarium oxysporum f. sp. albedinis. The characteristic symptoms of the bayoud disease were elicited on detached leaves of F. oxysporum f. sp. albedinis‐susceptible cultivars of date palm trees, which were treated either with the FII (F. oxysporum f. sp. albedinis) fraction purified from the organic extracts of a F. oxysporum f. sp. albedinis liquid culture, or with a solution of fusaric acid. Enniatins, which are secreted by several Fusarium species, were tested at different concentrations and were not capable of inducing symptoms on such detached leaves. The FII (F. oxysporum f. sp. albedinis) fraction was unable to induce necrosis of potato slices, which indicates that it does not contain significant amounts of enniatins. The high‐performance liquid chromatography (HPLC) profiles of the FII (F. oxysporum f. sp. albedinis) fraction showed toxic peaks different from fusaric acid. A fraction, named FII (AZ4), was obtained from culture filtrates of a saprophytic Fusarium strain maintained in the same cultural conditions as for the F. oxysporum f. sp. albedinis. The HPLC profile of the FII (AZ4) fraction did not show the characteristic phytotoxic peaks present in the FII (F. oxysporum f. sp. albedinis) fraction. This finding well agrees with the fact that the FII (AZ4) fraction is not toxic to detached date palm leaves. Moreover, the HPLC profiles of FII fractions obtained from other special forms of F. oxysporum are different the FII (F. oxysporum f. sp. albedinis) profile. The phytotoxic compounds purified from the FII (F. oxysporum f. sp. albedinis) fraction are probably new molecules that may help in understanding the pathogenesis of bayoud disease.