Fusarium Basal Plate Rot of Onion and Garlic

Michael Celetti, Plant Pathologist – Horticulture Program Lead, Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph

The pathogen, Fusarium oxysporum f.sp. cepae, is not new to Ontario. It is a persistent soil-borne organism that can also contaminate onion sets and transplants or cloves of garlic used for seed. In fact it is most likely introduced into non-contaminated fields on infested garlic cloves or onion sets. The disease tends to occur more frequently in garlic than in onions and is more often a problem on Spanish onions varieties than on yellow cooking onion varieties.

Figure 1. Orange to salmon coloured spore masses develop around the rotted basal plate of onions infected with F. oxysporum f.sp. cepae.

Symptoms of this disease are often seen as early senescence of the infected plants. The tips of leaves of infected plants turn yellow then brown as symptoms progresses downward towards the bulb. Occasionally a reddish discolouration may appear on bulb sheathes of severely infected garlic plants early in the season. During very hot and dry conditions infected plants wilt and bulbs appear watery and brown. Often the roots rot off of the basal plate (Figure 1). Severely infected plants are easily removed from the soil when pulled, leaving the rotted basal plate and roots behind. On onions, a white mould is sometimes observed growing on the basal plate and frequently orange to salmon coloured spore masses appear around the rotted basal plate (Figure 1). Bulbs that appear to be free of symptoms at harvest but are infected can decay in storage, however, there is no evidence that the disease spreads from bulb to bulb during storage.

Figure 2. Symptoms of Fusarium basal plate rot (left) in garlic look very similar to damage caused by bulb and stem nematode (right).

The pathogen infects when soils become very warm. Interestingly, even in heavily contaminated fields the disease rarely occurs when soil temperatures are below 15oC. However as the soil temperatures warms up and approach 25-28oC together with hot conditions like what was experienced in many regions of Ontario during 2012, the spores of the pathogen in soil germinate, infect developing bulbs and the disease becomes more prevalent and severe. Because this disease thrives under high soil temperatures this diseases usually shows up in mid to late summer.

The pathogen can infect onion or garlic bulbs directly at any stage of plant growth (even healthy plants!); however, a higher incidence of infected plants tends to occur when roots, bulbs or the basal plate are wounded by insects, nematodes or other pathogens. In garlic, the disease looks a lot like and is often associated with bulb and stem nematode injury (Figure 2) where as in onions it is sometimes associated with onion maggot damage.

The disease is managed effectively by crop rotation with non-host crops for 4 years and through planting vigorously growing onion and garlic varieties that are resistant to this disease.

6 thoughts on “Fusarium Basal Plate Rot of Onion and Garlic”

  1. Bonjour, jaimerais savoir si ce fusarium peut infecter d’autres plantes maraicheres tel que tomate et concombre

    merci

    1. Les maladies causées par Fusarium affectent la plupart des cultures maraîchères. Voici quelques liens qui vous donneront plus d’information sur Fusarium dans les tomates et les cucurbitacées.
      http://www.omafra.gov.on.ca/IPM/french/cucurbits/diseases-and-disorders/fusarium-wilt.html
      http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/FusariumWatermelon.aspx – disponible en anglais seulement
      http://www.omafra.gov.on.ca/french/crops/facts/01-082.htm
      http://ohioline.osu.edu/hyg-fact/3000/3122.html – disponible en anglais seulement
      http://ipm.illinois.edu/diseases/rpds/929.pdf – disponible en anglais seulement

      Merci d’avoir écrit avec votre question.

    1. Hi John,

      Avoid other Allium crops. Soybeans, corn or cover crops such as red clover would be good rotation partners that would decrease the Fusarium spore load over time. Spring wheat has been suggested in past research but other studies have identified cereals to be a susceptible host. Remember to avoid saving and seeding cloves with sunken lesions or imperfections as these cloves could be infected with Fusarium. Be aware that Fusarium basal rot symptoms can easily be mistaken as bulb and stem nematode as they both cause rotting in the basal plate. To be sure the symptom is not bulb and stem nematode, plants can be submitted to a pest diagnostic lab for a nematode extraction. Be sure to deliver the sample to the lab within two days of taking the sample.

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