Fungi Associated with Garlic During the Cropping Season, with Focus on Fusarium proliferatum and F. oxysporum

Fusarium proliferatum has been reported as the main causal agent of garlic dry rot during the postharvest stage, but information on this fungus during the crop growth stage is lacking. We focused on the cropping season of garlic (Allium sativum L.) in the field, until its harvest, with the aim of clarifying the role of F. proliferatum in bulb infection as well as the impact of crop growing conditions on pathogen-plant interaction. Studies were conducted in Piacenza (northern Italy) for three seasons from 2016 to 2019. Six garlic farms were sampled. A different field was sampled every year. Soil samples were recovered at sowing time for the counting of fungal colony forming units (CFU). Plant samples were collected at three growth stages, from BBCH 15 (fifth leaf visible) to BBCH 49 (ripening), for which disease severity assessment and fungi isolations were performed. Fusarium was the most frequently isolated genus, of which F. proliferatum and F. oxysporum were the dominant species. F. proliferatum registered the highest incidence in all the farms tested, but F. oxysporum was dominant in the first year of the study. F. oxysporum incidence was correlated with dry weather, whereas F. proliferatum was correlated with rainy weather. In conclusion, our result confirms the association of F. proliferatum with garlic bulbs from the crop's early growth stages, suggesting potential seed transmission as a source of this fungal pathogen. Further studies should investigate the link between fusaria occurrence in the field and dry rot outbreaks occurring postharvest and during storage of garlic.