California Pest Rating for
Fusarium brachygibbosum Padwick 1945
Pest Rating: C
PEST RATING PROFILE
Initiating Event:
On July 18, 2016, CDFA plant pathologists were notified by Dr. R. Bostock, Professor, Department of Plant Pathology, University of California, Davis, of a fungal pathogen, Fusarium brachygibbosum, detected in cold-stored, bare-root nursery almond trees in California. This detection marked a first report of the pathogen in California. Therefore, a risk analysis of F. brachygibbosum to California agriculture and environment was conducted and a permanent rating is proposed here for the otherwise non-rated pathogen.
History & Status:
Background: In California, Seidle et al. (2016) reported the first detection of Fusarium brachygibbosum from asymptomatic, cold-stored, bare-root propagated almond (Prunus dulcis) trees. Samples had been collected in fall 2013, from a nursery in Sutter County.
In 2011, that same nursery had experienced the re-emergence of a canker disease that occurred in the late 1900s. During the winter of 1997-98, a severe canker disease developed during cold storage of dormant almond trees and other fruit tree species in several nurseries in California. Fusarium acuminatum and F. avenaceum were identified as the primary causal agents of the disease. The predominant symptoms were necrosis of the inner bark, cambium, and sapwood, which in severe cases, resulted in girdling and death of trees. However, in the absence of external symptoms, internal necrosis was not readily evident in dark-bark trees, but detectable in light-bark trees. Notably, the canker phase of Fusarium-infected young trees did not become apparent unless predisposed by some physiological stresses. Consequently, infected trees were distributed to growers and the disease that developed under abiotic stress factors, including desiccation and variable cold storage temperatures, resulted in loss of thousands of trees, newly planted orchards, and millions of dollars (Marek et al., 2013). Fusarium acuminatum and F. avenaceum were also detected along with F. brachygibbosum in the 2013 almond samples reported by Seidle et al. (2016). The ability to detect F. brachygibbosum during the last few years than earlier was likely due to the availability of molecular tools for distinguishing this pathogen from other Fusarium species associated with nursery trees and storage/processing facilities and fields (Personal communication: Dr. R. M. Bostock, Professor, Department of Plant Pathology, University of California, Davis).
Fusarium brachygibbosum has been found on diverse host species within five plant families and reported from few countries in Asia, Africa, and North America (see ‘Worldwide Distribution’).
Hosts: Citrullus lanatus (watermelon; Cucurbitaceae), Euphorbia larica (spurge; Euphorbiaceae), Sorghum vulgare (broom corn; Poaceae), Triticum spp. (wheat; Triticeae), Prunus dulcis (syn. P. amygdalus, almond; Rosaceae) (Al-Mahmooli et al., 2013; Farr & Rossman, 2016; Mirhosseini et al., 2014; Renteria-Martinez et al., 2015; Seidle et al., 2016; Van Coller et al., 2016).
Symptoms: Fusarium brachygibbosum is associated with symptoms of wilting, dieback, and cankers and has often been found infecting plants with a complex of fungi species. Therefore, symptoms particular to the species have only been demonstrated experimentally through pathogenicity tests. In pathogenicity tests using almond branches inoculated with F. brachygibbosum and incubated at 15°C for two weeks, Siedle et al. (2016) found that canker lesions (area: 26.7 mm2 to 83.0 mm2) developed, comparable to those produced by F. acuminatum and F. avenaceum. Additionally, F. brachygibbosum was found in asymptomatic almond rootstock. Experimentally in watermelon, F. brachygibbosum produced variable sized light brown colored lesion at neck and root causing wilting of leaves or whole plants (Renteria-Martinez et al., 2015). The pathogen produced dark brown to black, circular to elliptical leaf spots in oleander (Mirhosseini et al., 2014). In South Africa, F. brachygibbosum was isolated along with several other Fusarium species from kernels of field-grown wheat exhibiting symptoms of Fusarium head blight disease (Van Coller et al., 2013).
Disease cycle: While the disease cycle has not been reported specifically for Fusarium brachygibbosum, it is likely that it is similar to other Fusarium species causing canker and wilt disease. Generally, Fusarium species inhabit soils and plants. They can exist saprophytically, but can also act as opportunistic pathogens. On hosts predisposed by stress, as in cold storage temperatures, or in combination with other pathogens, symptoms may become severe. The pathogen overwinters as mycelium or spores in infested crop residues and seed, or as chlamydospores (thick walled asexual spores) in soil, and produces asexual spores (microconidia and macroconidia) which are dispersed to plants and other plant debris by wind or rain-splash. Generally, under warm and humid conditions, sexual spores are produced which are forcibly discharged into the air and transmitted by wind currents to susceptible plants where infection and further development of the pathogen occur.
Damage Potential: Precise losses due to Fusarium brachygibbosum have not been reported. More than one Fusarium species and/or other fungal species may be present in cold-stored canker diseased nursery stock (Marek et al., 2013). Fusarium brachygibbosum may remain cryptic and asymptomatic within the host, and the canker phase does not become apparent unless young trees are subjected to some physiological stress. Asymptomatic, infected nursery trees may result in the development of the disease and losses in production in the field.
Transmission: Infected plants, roots, stems, leaves, seeds (Van Coller et al., 2016), plant debris, soil, air currents, rainwater splash, and contaminated equipment.
Worldwide Distribution: Asia: India, Iran, Oman; Africa: South Africa; North America: Mexico, USA (California) (Al-Mahmooli et al., 2013; Farr & Rossman, 2016; Mirhosseini et al., 2014; Renteria-Martinez et al., 2015; Seidle et al., 2016; Van Coller et al., 2016).
Official Control: None reported.
California Distribution: Sutter and Stanislaus Counties (Seidle et al., 2016). However, suspected to be widespread in California (R. M. Bostock, Professor, Department of Plant Pathology, University of California, Davis: personal communication).
California Interceptions: None reported.
The risk Fusarium brachygibbosum would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:
– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.
Risk is Medium (2) – In California, Fusarium brachygibbosum was detected in young almond nursery rooting predisposed to cold storage temperatures. It was also isolated from soil under almond production (Seidle et al., 2016), and is suspected to be widespread within California. The disease is likely to establish primarily in nurseries with bare-root propagative almond plants predisposed to abiotic stresses – including temperature variations in cold storage, and in almond production fields within California. Watermelon is a reported host of the pathogen (although not reported from California) and may also be affected by the disease.
2) Known Pest Host Range: Evaluate the host range of the pest. Score:
– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.
Risk is Low (1) – Presently, the known host range of Fusarium brachygibbosum is limited to watermelon, almond, wheat, spurge, and broom corn.
3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:
– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.
Risk is High (3) – Fusarium brachygibbosum has high reproduction and dispersal potential through infected plants, roots, stems, leaves, seeds, soil, plant debris, air currents, rainwater splash, and contaminated equipment.
4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:
A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.
– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.
Risk is High (3) – Quantitative estimates of losses in crop yield have not been reported, however, based on losses caused by the complex of other Fusarium species also detected in cold-stored almond tree seedlings in California (Marek et al., 2013), significant loss in crop production, value and yield is possible. However, development of the pathogen and production of visible disease symptoms in young trees is subject to predisposing physiological stresses.
5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.
A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.
Score the pest for Environmental Impact. Score:
– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.
Risk is Low (1) – The pathogen has not been reported to significantly impact the environment. However, leaf spots caused by the pathogen in infected ornamental oleander have been reported (but not from California).
Consequences of Introduction to California for Fusarium brachygibbosum:
Add up the total score and include it here. (Score)
-Low = 5-8 points
–Medium = 9-12 points
-High = 13-15 points
Total points obtained on evaluation of consequences of introduction of Fusarium brachygibbosum to California = (10).
6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)
-Not established (0) Pest never detected in California, or known only from incursions.
-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.
Evaluation is Medium (-2). Fusarium brachygibbosum has been detected in cold-stored young almond rootings in Sutter and Stanislaus Counties, however, the pathogen is suspected to be widespread in California.
Final Score:
7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)
Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 8
Uncertainty:
The full distribution of Fusarium brachygibbosum in California needs to be confirmed.
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for Fusarium brachygibbosum is C.
References:
CABI. 2016. Fusarium brachygibbosum basic datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/119707.
Farr, D.F., and A. Y. Rossman. 2016. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved January 28, 2016, from http://nt.ars-grin.gov/fungaldatabases/.
Marek, S. M., M. A. Yaghmour, and R. M. Bostock. 2013. Fusarium spp., Cylindrocarpon spp., and environmental stress in the etiology of a canker disease of cold-stored fruit and nut tree seedlings in California. Plant Disease 97: 259-270. http://dx.doi.org/10.1094/PDIS-04-12-0355-RE .
Seidle, A. J., M. A. Yaghmour, S. C. Kirkpatrick, T. R. Gordon, and R. M. Bostock. 2016. First report of Fusarium brachygibbosum causing cankers in cold-stored, bare-root propagated almond trees in California. (Submitted for publication: Plant Disease, shared with J. Chitambar, CDFA, August, 2016).
Van Coller, G. J., A. -L. Boutigny, L. Rose, T. J. Ward, S. C. Lamprecht, and A. Viljoen. 2013. Head blight of wheat in South Africa is associated with numerous Fusarium species and chemotypes. Conference paper: 12th European Fusarium Seminar, at Palais de la Bourse, Bordeaux, France, May 2013. https://www.researchgate.net/publication/269700231_Head_blight_of_wheat_in_South_Africa_is_associated_with_numerous_Fusarium_species_and_chemotypes
Responsible Party:
John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.
Pest Rating: C
Posted by ls
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