Fusarium Wilt of Canary Island Date Palm
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Figure 1. A Phoenix canariensis leaf with one side exhibiting necrotic leaflets and a brown stripe on the petiole and rachis due to Fusarium wilt. Photo by M. L. Elliott.
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Figure 2. Close-up of Phoenix canariensis leaf with one side exhibiting necrotic leaflets and a brown stripe on the petiole and rachis due to Fusarium wilt. Photo by M. L. Elliott.
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Figure 3. Cross-section of a Phoenix canariensis rachis illustrating the internal discoloration due to Fusarium wilt. Photo by T. K. Broschat.
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Figure 4. Phoenix canariensis in various stages of decline due to Fusarium wilt. Photo courtesy of University of Florida/IFAS.
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Scientific name of pathogen
Fusarium oxysporum f. sp. canariensis: Kingdom Fungi, Phylum Ascomycota
Hosts
The primary host of Fusarium oxysporum f. sp. canariensis is Phoenix canariensis (Canary Island date palm). Phoenix reclinata (Senegal date palm) has been confirmed as a host.
Distribution
Argentina, Australia, the Canary Islands, France, Greece, Italy, Japan, USA (California, Florida, Louisiana, Nevada, South Carolina, Texas)
Symptoms/signs
Initial symptoms normally occur on the lowest (oldest) living leaves in the canopycanopy:
the cluster of leaves borne at the tip of the stem
. For Phoenix canariensis, there will be at least one leaf with leaflets, either all of them or only a portion, on only one side of the rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
that will be discolored, usually a shade of brown due to desiccation or death. The leaflets on the opposite side of the rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
will be a healthy green color (Fig. 1). This very distinctive symptom is often referred to as a “one-sided wilt” or “one-sided death”. A reddish-brown or dark-brown stripe will be observed on the petiolepetiole:
leaf stem
and rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
of the affected frond, on the same side where the first dead leaflets appear (Fig. 2). This streak may run the full length of the petiolepetiole:
leaf stem
and rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
, or just a portion of it. Internal discoloration will be observed in cross-sections of the discolored petiolepetiole:
leaf stem
and rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
(Fig. 3). Eventually the leaflets on the other side of the rachisrachis:
the axis of a leaf beyond the petiole or an extension of the petiole into the leaf blade
will turn brown also, and the entire leaf dies.
The disease symptoms normally begin on the lowest (oldest) leaves and then move up the canopycanopy:
the cluster of leaves borne at the tip of the stem
, progressively killing younger and younger leaves. For some leaves, the leaflets may begin turning brown at the leaf tip and on both sides at once, rather than just on one side. In all situations, the spear leafspear leaf:
the younges emerging leaf that has not yet opened
is the last leaf to die.
Fusarium wilt of Canary Island date palm often progresses at a relatively slow rate, and the palm can survive for as long as two years after initial symptom development. Since the primary method of pathogen transmission between Phoenix canariensis is pruning tools, it is not uncommon to see a landscape of Phoenix canariensis in various stages of disease development (Fig. 4).
May be confused with
Petiole petiole:
leaf stem
(rachis) blight causes the same leaf symptoms in Phoenix canariensis. Laboratory diagnosis is necessary to confirm which pathogen is responsible for the symptoms. It is possible for a Fusarium wilt pathogen and a petiole (rachis) blight pathogen to be present in the same tissue.
Additional comments
Fusarium wilt caused by Fusarium oxysporum f. sp. canariensis has been observed naturally occurring on Washingtonia filifera in limited areas of California and Australia. While this disease has been artificially induced on Phoenix dactylifera, it has not been observed to occur naturally.
Three other Fusarium oxysporum formae speciales occur on palms. Fusarium oxysporum f. sp. albedinis causes Fusarium wilt of Phoenix dactylifera, but is limited to Morocco, Algeria and Mauritiana. Fusarium oxysporum f. sp. elaeidis causes Fusarium wilt of Elaeis guineensis, but is limited to western African and very limited areas within Ecuador and Brazil. Fusarium oxysporum f. sp. palmarum causes Fusarium wilt of Syagrus romanzoffiana and Washingtonia robusta, but is limited to Florida (USA).
