Fusarium spp. associated with asparagus crowns and the influence of the preplant fumigant metam-sodium in Michigan crown nurseries

Fusarium crown and root rot (FCRR) of asparagus caused by Fusarium spp., results in plant stunting, wilting, vascular discoloration, and root rot reducing the longevity and productivity of this perennial vegetable. Metam-sodium is a broad-spectrum pre-plant fumigant commonly used in Michigan asparagus nurseries to mitigate FCRR by reducing disease presence in 1-year-old crowns that are used for establishing production fields. The objective of the current study was to compare the diversity of Fusarium species associated with nursery-grown asparagus crowns from soils fumigated preplant with metam-sodium to those from unfumigated nurseries. Based on sequences of the TEF-1α (transcription elongation factor 1-alpha) region, seven Fusarium spp. were identified including F. oxysporum, F. proliferatum, F. solani, F. acuminatum, F. avenaceum, F. graminearum and F. incarnatum-equiseti. Fusarium oxysporum was the most frequently isolated species (92%). No significant differences were noted between Fusarium populations isolated from nurseries that had been fumigated with metam-sodium and those isolated from the nursery that had not been fumigated. Pathogenic isolates of F. oxysporum were recovered from nurseries at a similar rate regardless of fumigation status. These findings indicate that metam-sodium is inadequate as a pre-plant treatment for Fusarium crown and root rot and alternative strategies need to be explored.