Induction of systemic disease resistance and pathogen defence responses in Asparagus officinalis inoculated with nonpathogenic strains of Fusarium oxysporum

The ability of nonpathogenic isolates of Fusarium oxysporum (npFo) to induce systemic resistance and defence responses against subsequent challenge with a pathogenic strain of F oxysporum f. sp. asparagi (Foa) was examined in Asparagus officinalis. In a split-root experiment, roots inoculated with npFo exhibited a hypersensitive response and those subsequently inoculated with Foa displayed resistance. Induction of systemic resistance in npFo-treated plants led to significantly fewer necrotic lesions (P = 0.05) and reduced Foa disease severity compared with plants not treated with npFo. In hyphal-sandwich root inoculation experiments, activities of peroxidase and phenylalanine ammonia-lyase and lignin content were higher in npFo-treated plants and increased more rapidly than in npFo-untreated plants after Foa inoculation. Antifungal activity (inhibition of fungal spore germination and germ-tube growth) from exudates of roots inoculated with Foa were observed for npFo-treated plants but not for npFo-untreated plants. Thus, isolates of npFo may function as inducers of systemic acquired resistance (SAR) and defence responses against Foa invasion in A. officinalis.