Evaluating the Threat Posed by Fungi on the APHIS List of Regulated Plant Pests

Amy Y. Rossman, Systematic Botany & Mycology Laboratory, USDA Agricultural Research Service, Beltsville, MD 20705 and Chair, Federal Interagency Committee on Invasive Terrestrial Animals and Pathogens Subcommittee on Plant Pathogens; Kerry Britton, USDA Forest Service, Arlington, VA 22209; Doug Luster, Foreign Disease-Weed Science Research Unit, USDA Agricultural Research Service, Ft. Detrick, MD 21702; Mary Palm, Systematic Botany & Mycology Laboratory, USDA Animal and Plant Health Inspection Service, Beltsville, MD 20705; Matthew H. Royer, Emergency and Domestic Programs, USDA Animal and Plant Health Inspection Service, Riverdale, MD 20737-1234; and Jim Sherald, US Department of the Interior, National Park Service, Center for Urban Ecology, Washington, DC 20007

Drs. Erica Cline and David Farr recently reviewed the fungi on the APHIS Regulated Plant Pest List, providing an accurate scientific name as well as the disease, plant hosts, and geographic distribution for each species. In presenting these data they remained neutral on which of these fungi pose a threat to U.S. agriculture and forest resources because such an evaluation was beyond the scope of that project. However, the purpose of such a document is so that someone or some organization can do just that — evaluate the threat posed by these fungi. Once the fungi that threaten U.S. agriculture are known, activities can be directed at preventing the entry of those organisms.

An evaluation of the potential threat of fungi on the APHIS Regulated Plant Pest List was conducted by the federal interagency Invasive Terrestrial Arthropods and Pathogens (ITAP) Subcommittee on Plant Pathogens using the data provided in Cline and Farr (1). Each species was evaluated based on the importance of the plant host, geographic distribution, and state of knowledge. Fungi that cause serious diseases of plants of major economic value and forest trees were considered a threat if the fungus does not occur in the United States. Similarly, fungi that cause serious diseases of plants of horticultural importance or of crops of minor economic importance and do not occur in the United States were placed in the second category. The first two categories could be considered comparable in the need to exclude these fungal pathogens. If the species is reported more than once in the United States and these reports are in the literature or backed by voucher specimens, the species is considered to be established in the United States. Some fungal pathogens occur on crops that are not grown in the United States but are important to the U.S. economy. For some fungi not enough is known to make an evaluation; in fact, some species have not been seen since their original description often decades ago. The pathogens are divided into the following groups.

Threat to Major Crop Plants and Forest Trees

Chrysomyxa abietis on Picea; Europe, Asia

Chrysomyxa himalensis on Picea and Rhododendron; Asia

Chrysomyxa rhododendri on Picea and Rhododendron (telial state already in North America); Europe, Asia

Cronartium flaccidum (Peridermium cornui) on Pinus and alternative hosts; Europe, Asia

Elsinoë australis on citrus; South America

Lachnellula willkommii on larch (eradicated from North America); Asia, Europe

Monilinia fructigena on apples, pears, and peaches; Europe, Asia, South America

Peronosclerospora maydis on corn; Asia, Australia, South America

Peronosclerospora sacchari on sugarcane; Asia, Australia, Central America

Peronosclerospora philippinensis on corn and other grasses (select agent), Asia, Africa

Scerophthora rayssiae var. zeae on corn (select agent), Asia

Synchytrium endobioticum on potato (eradicated from US, select agent); Europe, Asia, Africa, North America (Canada)

Thekopsora areolata on spruce and Prunus; Europe, Asia, Caribbean

Urocystis agropyri on wheat (possibly in US); Europe, Asia, Africa, South America, Australia

Threat to Horticultural or Crop Plants of Minor Economic Importance

Aecidium hydrangeae-paniculatae (Puccinia glyceriae) on Hydrangea and Glyceria; Asia [* see Erratum].

Aecidium mori on mulberry; Asia

Elsinoe batatas on sweetpotato; Asia, Australia, Pacific Islands, Caribbean, South America

Phialophora cinerescens on carnation (reports in Canada, OR and CO questionable); Europe, Asia, South America, New Zealand

Pseudocercospora timorensis on sweetpotato; Asia, Australia, South America, Africa

Puccinia gladioli on gladiolus and Valerianella (aecial state in western US); Europe, Asia, Africa (Libya)

Puccinia horiana on chysanthemum (outbreaks in US greenhouses eradicated); Europe, Asia, Australia, South America, Africa

Pucciniastrum actinidiae on kiwi; Asia

Uromyces gladioli on gladiolus and other Iridacaeae; Africa, South America

Uromyces transversalis on gladiolus and other Iridaceae; Africa, Australia, South America, North America (Mexico), New Zealand

Uromycladium tepperianum on acacia

Already Established in the U.S.

Allantophomopsis pseudotsugae (Phacidium coniferarum) on conifers

Ceratocystis fimbriata on diverse crops and trees

Entyloma oryzae on rice

Phytophthora fragariae on strawberry

Rosellinia necatrix on grape, strawberry, apple, etc.

Stigmina deflectans on juniper (Canada, SD and WI)

Urocystis tritici on wheat

Threat to Crops Not Grown in U.S.

Hemileia vastatrix on coffee

Moniliophthora perniciosa on cacao

Moniliophthora roreri on cacao

Oncobasidium theobromae on cacao

Trachysphaera fructigena on cacao

Uredo dioscoreae-alatae on yam

Not Enough Known to Determine Threat

Diaporthe mali on apples

Fusarium fuliginosporum on cedar (known only from the type)

Guignardia pyricola on apples and pears

Gymnosporangium asiatica (Roestelia koreensis) on pear and juniper (in US based on old specimens, possible misidentifications)

Melanomma glumarum on rice

Oospora oryzetorum on rice (not a fungus)

Pestalotiopsis disseminata on banana

Pseudopezicula tracheiphila on grapes

Puccinia mccleanii on gladiolus (known only from type)

Rhacodiella vitis on grape (known only from type)

Septoria melanosa on grape (reported in North America?)

Uredo gladioli-buettneri on gladiolus (known only from type, lost)

Uromyces nyikensis on gladiolus (known only from type)

Xylobolus hiugense on oak (known only from type, not pathogenic)

Two genera of insect-associated fungi, specifically Beauveria spp. and Entomophthora spp. were included on the APHIS list but are not plant pests and thus are not discussed here.

Out of the 52 species listed, 25 of the fungi on the APHIS Regulated Plant Pest List fall into the first two groups, namely species that are a threat to American crop plants and forests or to horticultural plants or crops of minor economic importance. Attention should be paid to preventing the entry of these fungi. Interestingly, almost 60% of these are rust fungi. In synthesizing the geographic distribution of these fungi, all of these species occur in Asia except the two species of Uromyces on Gladiolus. It would appear that Asia serves as a source for pathogens that threaten U.S. agriculture although many occur elsewhere in the world as well especially in Europe where the fungi are more well-known. Many of these pathogens could enter the U.S. on nursery stock particularly those on horticultural crops. A number of these fungi occur on living forest trees. The cause of Karnal bunt, Tilletia indica, on wheat has a restricted distribution in the United States and Mexico as well as Asia and causes limited lost of quality. The fungal species about which not enough is known to determine if they are a threat should be the subject of research.

Literature Cited

1. Cline, E. T. and Farr, D. F. 2006. Synopsis of fungi listed as regulated plant pests by the USDA Animal and Plant Health Inspection Service: Notes on nomenclature, disease, plant hosts, and geographic distribution. Online. Plant Health Progress doi:10.1094/PHP-2006-0505-01-DG.

*Erratum

A correction was made to this line on May 17, 2006. Previously, Glyceria had been misspelled.