The potential for Fusarium oxysporum f. sp. fragariae, cause of Fusarium wilt of strawberry, to colonize organic matter in soil and persist through anaerobic soil disinfestation

Authors: Henry, Peter; HAUGLAND, M - University Of California; LOPEZ, L - University Of California; MUNJI, M - University Of California; WATSON, D - University Of California; GORDON, THOMAS - University Of California

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2020
Publication Date: 6/2/2020
Citation: Henry, P.M., Haugland, M., Lopez, L., Munji, M., Watson, D.C., Gordon, T.R. 2020. The potential for Fusarium oxysporum f. sp. fragariae, cause of Fusarium wilt of strawberry, to colonize organic matter in soil and persist through anaerobic soil disinfestation. Plant Pathology. https://doi.org/10.1111/ppa.13225.
DOI: https://doi.org/10.1111/ppa.13225

Interpretive Summary: Fusarium wilt is a disease of strawberry that leads to severe economic losses for growers in multiple countries. This disease is caused by a fungus called “Fusarium oxysporum f. sp. fragariae” that lives in the soil and infects plant roots. There are strategies meant to control this disease that involve incorporating plant debris into the soil. The plant debris is consumed by microorganisms, and the growth of these organisms can sometimes suppress the activity of soilborne plant pathogens. To conduct a popular technique called “anaerobic soil disinfestation” (ASD), the soil is also watered and covered with a tarp to retain moisture. When the soil microorganisms consume the plant debris, the soil becomes anaerobic and in this process the pathogen can die. However, we show that F. oxysporum f. sp. fragariae can compete with other soil microbes and consume plant debris added to soil. Specifically, the soil population of this pathogen increased during ASD treatment when the soil did not become sufficiently anaerobic. Furthermore, the pathogen could colonize the leaves of lettuce, raspberry, broccoli, and strawberry in soil. Therefore, incorporating plant debris could lead to increases in the soil population of F. oxysporum f. sp. fragariae.

Technical Abstract: Fusarium wilt of strawberry, caused by Fusarium oxysporum f. sp. fragariae, is a disease of primary concern for strawberry production in multiple countries. Crop rotation and anaerobic soil disinfestation (ASD) have gained recent interest for their potential to contribute to management of this disease. Both techniques involve incorporation of organic matter into soil, which may be utilized by strains of Fusarium that are competitive saprophytes. We show that Fusarium oxysporum f. sp. fragariae can colonize strawberry, lettuce, raspberry, and broccoli leaf tissues, which are sources of organic matter generated during crop rotation. This pathogen increased in soil population density after organic amendments (used for ASD) are added. However, significant population decreases were observed after ASD treatment when a threshold of 100,000 mV/hours was exceeded in a 14-day experiment. Post-ASD abundance of F. oxysporum f. sp. fragariae in soil was negatively correlated with cumulative reduced mV/hours. The treatment that led to the greatest disinfestation was exposed to a maximum temperature of 22ºC, which indicates there is potential for developing effective ASD treatments in cool climates where strawberries are grown. Awareness that F. oxysporum f. sp. fragariae can colonize commonly used organic amendments should inform management decisions, especially where sufficiently anaerobic soil conditions cannot be guaranteed.