Uromyces transversalis

California Pest Rating for

Uromyces transversalis (Thüm.) G. Winter

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

None. The status of Uromyces transversalis in California, is updated and the current rating is reviewed.

History & Status:

Background: Uromyces transversalis is an autoecious rust pathogen that causes rust disease, commonly known as gladiolus rust, only in members of the family Iridaceae, including Gladiolus, Tritonia, Crocosmia, and Watsonia spp. Gladiolus is the major host of the pathogen, while the other hosts are of lesser economic importance. Of six rust pathogens that can infect gladiolus, U. transversalis is the most economically damaging one.

Uromyces transversalis is indigenous to eastern and southern Africa, where it was first detected on leaves of Tritonia securigera in 1876. Almost a century later, the pathogen spread to the Mediterranean region and southern Europe. During the 1960-70s it was reported from France, Italy, and Morocco, and from England by 1996 (USDA APHIS PPQ, 2007).

Gladiolus rust was first detected and confirmed in the United States in April 2006, from a gladiolus production farm in Manatee County, Florida, and later, in another commercial gladiolus farm in Hendry County, Florida (USDA APHIS PPQ, 2007). Then, in May 2006, gladiolus rust was detected on hybrid gladiolus plants in a home garden in San Diego, California. Consequently, an intensive 23 square mile survey was conducted and the rust pathogen was detected at one commercial nursery and two other residential sites (Blomquist et al., 2007). Since 2006, the pathogen has been repeatedly detected in Florida and California. The source of introduction of Uromyces transversalis into the USA is unknown. The pathogen is known to occur in Mexico and has been intercepted in numerous shipments of cut flowers from Mexico dating back to 2004. The initial detection in Florida was the result of trace-back investigations following an interception of rust-infected flowers in Hawaii that originated in Florida. Infected Florida-produced gladiolus flowers were intercepted in Minnesota in 2008, which had, likewise, originated from one of the original infected Florida gladiolus producers (Preston, 2009).

In California, to date, the disease has been detected in over 680 samples submitted to the CDFA Plant Pest Diagnostics Laboratory. Samples have come primarily from landscapes associated with residences, businesses, and municipalities from no fewer than twelve California counties, ranging from Solano County and San Francisco County in the northern region to San Diego County in the southern region where it was originally detected. Samples have come from no fewer than 38 different California cities (CDFA Pest Detection Reports). The wide distribution indicates that Gladiolus Rust is well beyond the possibility of eradication in California, and is, instead, a management issue.

In August 2006, the gladiolus rust pathogen, Uromyces transversalis, was deemed as actionable and reportable by the USDA. In 2007, federal and state action was taken in accordance with the USDA APHIS’ ‘Gladiolus Rust National Eradication and Management Plan’ (USDA, 2007), whenever the pathogen was detected in commercial growing areas, domestic commerce, and residential areas. The decision to go that route was made when the pathogen was still believed to be limited in distribution in Florida and California and eradication was thought to be feasible. However, on May 15, 2015, APHIS revised the domestic response requirements for U. transversalis to no longer take domestic action or require others to take action when gladiolus rust is found in commercial growing areas, domestic commerce, and residential areas. This revision was made because the pathogen has spread to the limit of its natural range, based on its current distribution, known biology, and plant hardiness zones in the United States. However, APHIS will continue to regulate other gladiolus rust pathogens that are known to occur in the United States (USDA, 2015).

Transmission: The primary pathways for introduction of the pathogen are by shipments of infected plants and cut flowers. Interceptions from commercial shipments and passenger baggage at ports-of-entry in Arizona, California, and Texas confirmed that cut flowers are the major pathway of gladiolus rust from other countries (USDA APHIS, 2007). A significant anecdotal observation of the close proximity of residential infections with cemeteries also comes as no surprise, considering the propensity of the public to use gladiolus cut flowers to decorate grave sites. Long distance and local spread is by wind-blown spores. These airborne spores are easily dispersed by lightly brushing a symptomatic plant and can be spread by surface-contaminated clothing, equipment, corms, rhizomes, and flowers (USDA APHIS PPQ, 2007).

Symptoms: Symptoms are typical for a rust disease, with yellowish-brown (uredinia) or blackish-brown (telia) pustules on the leaves, either solitary or aggregated. Uredinia develop first and produce urediniospores, followed by development of the telia, which produce teliospores. Initial symptoms of gladiolus rust are the appearance of small, yellowish spots. Later, the epidermis bursts open exposing pustules full of yellowish- orange spores. Over time, pustules coalesce to form large lesions. Rust pustules normally form on foliage, on both sides, but under heavy disease pressure, can also form on flower spikes. Severely infected plants fail to even flower or produce mature corms. The pustules are formed in lines that run “transversely” across the leaf veins (as opposed to round or amorphous pustules, as is normally the case with most rust fungi on monocots whose sori run longitudinally along the vein of the leaf). These unique transverse pustules are useful for making field identifications of the rust (USDA, 2007; USDA APHIS PPQ, 2007).

Hosts: All hosts belong to the family Iridaceae. The primary/major host is Gladiolus hybrids (sword lily/gladiolus). Minor hosts include, Crocosmia aurea (falling stars), Freesia refracta (common freesia), Tritonia sp. (flame freesia), T. lineata, T. securigera, T. squalida, Watsonia sp. (bugle lily), W. angusta, W. densiflora, W. meriana, and W. borbonica (CABI, 2017; EPPO, 2017; Farr & Rossman, 2017).

Damage Potential: Gladiolus rust is a serious disease in nurseries and, if left uncontrolled, can completely destroy commercial gladiolus crops. Severely damaged plants do not flower and/or their corms do not ripen (USDA APHIS PPQ, 2007). There are efficacious fungicides available that can control the pathogen, however the frequent treatments necessary to protect the product can be costly for producers (Schwartzburg, 2006). Furthermore, gladiolus rust can be controlled with best management practices (USDA, 2015).

The pathogen has only rarely been found in commercial settings in California, possibly because production managers have taken pro-active measures to protect their crops against the pathogen by frequent scouting and preventive fungicide treatments. An example of this is a large gladiolus cut flower producer in Santa Barbara County that is virtually surrounded by infected residences. The nursery staff routinely inspect and fungicide-treats the crop which is grown from new imported corms each year. As further protection, a host-free period at the production grounds follows the harvest of the year’s crop (Scheck, 2012).

Worldwide Distribution: Africa: Kenya, Malawi, Mauritius, South Africa, Tanzania, Uganda, Zambia, Zimbabwe; North America: Mexico, USA (California, Florida); Central America and Caribbean: Costa Rica, Cuba, Martinique; South America: Argentina, Brazil; Europe: France, Italy, Malta, Spain; Oceania: Australia, New Zealand (CABI, 2017; EPPO, 2017; Farr & Rossman, 2017).

Official Control: Uromyces transversalis is on the ‘Harmful Organism Lists’ for the following countries: Australia, Chile, China, Colombia, Ecuador, French Polynesia, India, Israel, Republic of Korea, Madagascar, Nauru, New Caledonia, Peru, Tunisia (USDA PCIT, 2017).

California Distribution: Alameda, Contra Costa, Los Angeles, Orange, San Diego, San Francisco, San Mateo, Santa Barbara, Santa Clara, Santa Cruz, Solano, and Ventura Counties.

California Interceptions: None reported.

The risk Uromyces transversalis would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: The ability for Uromyces transversalis to have suitable hosts and climate in order to establish in California is already illustrated by its state-wide distribution over the past eleven years.

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 3

– 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.

2) Known Pest Host Range: Gladiolus is the only major host for Uromyces transversalis.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Uromyces transversalis has high reproduction and dispersal potential.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 3

– 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.

4) Economic Impact: Gladiolus Rust is known to lower yields, could increase costs due to fungicide treatments for commercial producers, and could result in quarantines by other states or countries.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C

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.

Economic Impact Score: 3

– 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.

5) Environmental Impact: Gladiolus rust could impact home/urban garden plantings.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

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.

Environmental Impact Score: 2

– 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.

Consequences of Introduction to California for Gladiolus Rust:

Add up the total score and include it here. 12

-Low = 5-8 points

-Medium = 9-12 points

-High = 13-15 points

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.

Evaluation is ‘High’. Gladiolus Rust has spread to at least 12 California counties since its first detection in 2006.

Score (-3).

-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.

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 = 9.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the rating for the gladiolus rust pathogen, Uromyces transversalis, is proposed to continue as C.

References:

Blomquist, C. L., S. L. Thomas, J. M. Mckemy, P. A. Nolan, and M. Luque-Williams. 2007. First report of Uromyces transversalis, causal agent of gladiolus rust, in San Diego County, California. Plant Disease, 91: 1202. http://dx.doi.org/10.1094/PDIS-91-9-1202C

CABI. 2017. Uromyces transversalis (gladiolus rust) full datasheet. Crop Protection Compendium. http://www.cabi.org/cpc/datasheet/55868

EPPO. 2017. Uromyces transversalis (UROMTV). PQR database. Paris, France: European and Mediterranean Plant Protection Organization. https://gd.eppo.int/

Farr, D. F., and A. Y. Rossman. Fungal Databases, U.S. National Fungus Collections, ARS, USDA. Retrieved August 1, 2017, from https://nt.ars-grin.gov/fungaldatabases/

Preston, Catherine (2009) USDA Presentation: Gladiolus Rust, Balancing Eradication Efforts and Growers’ Needs through Regulation. http://dpm.ifas.ufl.edu/plant_pest_risk_assessment/ALS6921%20Presentations/PPQ_GR%20presentation.pdf

Scheck, H. 2012. Communication to Timothy Tidwell, Plant Pathologist, CDFA, from Heather Scheck, Plant Pathologist, Santa Barbara County Department of Agriculture (in 2012).

Schwartzburg, K. 2006. NPAG Report Uromyces transversalis (Thüm.) G. Winter 1884: Gladiolus Rust.

USDA, 2007. Gladiolus Rust (Uromyces transversalis): A National Management Plan for Exclusion and Eradication. GR Plan Original, February 28, 2007.

USDA. 2015. APHIS revives response to domestic detections of gladiolus rust caused by Uromyces transversalis. DA-2015-20, dated May 13, 2015 to State and Territory Agricultural Regulatory Officials.

USDA APHIS PPQ. 2007. Pest Alert. Gladiolus rust: a new threat. United States Department of Agriculture Animal and Plant Health Inspection Service Plant Protection and Quarantine. APHIS 81-35-011.

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. August 1, 2017, 4:03:49 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

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.