11
Exchange of Genetic Resources: Quarantine

Quarantine is a strategy of control to prevent the spread of pests and diseases. It covers all regulatory actions taken to exclude animal or plant pests or pathogens from a site, area, country, or group of countries. For example, when animal or plant genetic resources are imported from another country or region, there is a risk that they may contain or carry pests or pathogens that could be damaging to agriculture. For this reason, countries use quarantine practices to protect their agriculture and living natural resources from potential damage or destruction.

Quarantine is usually a government responsibility, and the manner in which quarantine is executed differs among nations. National agencies responsible for plant quarantine may have other responsibilities, such as domestic pest control; research; pesticide registration, safety, and residue monitoring; or seed quality and labeling.

Significant among the pest or pathogen introductions into North America that have been damaging to agriculture are chestnut blight (Cryphonectria parasitica,) white pine blister rust (Cronartium ribicola,) Dutch elm disease fungi (Ceratocystis ulmi,) Mediterranean fruit fly, European corn borer (Ostrinia nubilalis,) potato golden nematode, gypsy moth, cotton boll weevil, San Jose scale, field bindweed, Johnson grass (Sorghum halepense,) kudzu (Pueraria lobata,) and witch weed. Cassava bacterial blight (Xanthomonas manihotis) is believed to have been introduced to Africa and Asia from tropical America by way of infected planting stakes (Plucknett and Smith, 1988). Rinderpest, a significant animal health problem for some countries of sub-Saharan



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Managing Global Genetic Resources: Agricultural Crop Issues and Policies 11 Exchange of Genetic Resources: Quarantine Quarantine is a strategy of control to prevent the spread of pests and diseases. It covers all regulatory actions taken to exclude animal or plant pests or pathogens from a site, area, country, or group of countries. For example, when animal or plant genetic resources are imported from another country or region, there is a risk that they may contain or carry pests or pathogens that could be damaging to agriculture. For this reason, countries use quarantine practices to protect their agriculture and living natural resources from potential damage or destruction. Quarantine is usually a government responsibility, and the manner in which quarantine is executed differs among nations. National agencies responsible for plant quarantine may have other responsibilities, such as domestic pest control; research; pesticide registration, safety, and residue monitoring; or seed quality and labeling. Significant among the pest or pathogen introductions into North America that have been damaging to agriculture are chestnut blight (Cryphonectria parasitica,) white pine blister rust (Cronartium ribicola,) Dutch elm disease fungi (Ceratocystis ulmi,) Mediterranean fruit fly, European corn borer (Ostrinia nubilalis,) potato golden nematode, gypsy moth, cotton boll weevil, San Jose scale, field bindweed, Johnson grass (Sorghum halepense,) kudzu (Pueraria lobata,) and witch weed. Cassava bacterial blight (Xanthomonas manihotis) is believed to have been introduced to Africa and Asia from tropical America by way of infected planting stakes (Plucknett and Smith, 1988). Rinderpest, a significant animal health problem for some countries of sub-Saharan

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies Africa, was introduced from Central Asia during the late nineteenth century (Acree, 1989). REDUCING THE RISKS FROM PESTS AND PATHOGENS Quarantine practices in most countries have at least three common functions. The first is exclusion or regulatory actions to prevent or reduce the risk of entry of exotic pathogens, pests, or parasites along artificial pathways. Second is the containment, suppression, or eradication of pests or pathogens that have been recently introduced. Third is the assisting of exporters to meet the quarantine requirements of importing countries. The general concepts and objectives of plant and animal quarantine are similar; but differences in biology, agricultural production, marketing, exporting, and importing necessitate a variety of quarantine procedures. Animal and plant quarantine procedures. Animal and plant quarantine programs are intended to protect agriculture from the threat of entry of exotic hazardous organisms. In some countries this objective may be extended to the protection of natural domestic flora and fauna. Both types of programs regulate the importation of living individuals (for example, animals or plants or plant parts capable of propagation) and various commodities or unprocessed agricultural raw materials. Plants materials subject to restrictions may include seeds, straw, cereal hulls, THE PRINCIPLES OF SUCCESSFUL QUARANTINE Few reports have examined the challenges and opportunities of developing an effective and efficient quarantine program that addresses the needs and constraints posed by the increasing international movement of germplasm. One recent study (Plucknett and Smith, 1988) describes six principles of successful quarantine. They are summarized as follows: Sound scientific and technical principles should form the foundation of a quarantine program. This should include expertise from a diverse array of scientific disciplines, including, for example, virology, mycology, microbiology, nematology, malacology, entomology, taxonomy, pathology, weed science, and genetic resources. Pests and pathogens should be ranked by quarantine services according to the potential danger they pose to crops and the potential for success in excluding them. For example, germplasm from centers of diversity should receive a high priority because of the potential for such accessions to harbor coevolved pests or pathogens.

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies lumber, logs, bark, fruit, vegetables, cut flowers, fibers, gums, and spices. Animal materials of quarantine interest may include live animals, semen, eggs, or embryos; fresh, frozen, processed, or canned meat; milk and milk products; raw hides; and biological reagents or other compounds (protein, hormones, sera) extracted from animals. In many countries, garbage from other nations also is of quarantine interest. Animal and plant quarantine regulations are similar in that they may: Require import permits issued by the quarantine service of the importing country (these may require the exporting country to certify that specified conditions have been met prior to shipment); Specify things that are prohibited from entry; Grant exceptions to the prohibitions for scientific purposes; Require inspection of imported materials upon arrival; Require appropriate treatment, if warranted, as a condition of entry; and Require, after arrival, quarantine or isolation in an approved facility. Plant quarantine is concerned with a far greater number of species than is animal quarantine. Currently more than 240 crops or plant species are prohibited from entry to one or more countries (Kahn, When germplasm must be planted and grown for the purposes of quarantine testing, it should be done in an area geographically and ecologically separated from the major growing areas for that crop, to prevent the establishment of crop-specific pests or pathogens. When germplasm is endangered or the need for particular accessions is particularly urgent, some discretion should be possible on the part of quarantine officials in allowing exceptions for controlled entry, despite existing regulations to the contrary. Decentralized quarantine services are generally more efficient because they enfold a wider range of expertise in germplasm assessment. However, decentralization places a greater burden on the national system to ensure high standards and to promote accurate and efficient information exchange. Because delays in transit can be detrimental for any germplasm accessions, access to good communication and transportation services is essential for quarantine.

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies 1982; Plucknett and Smith, 1988). More than 1,600 pests or pathogens of plants are the objects of quarantine worldwide (Kahn, 1988). In the United States, more than 1,300 pests or pathogens of pests are a significant threat to crops (Mathys, 1977). In addition, a worldwide survey of 124 countries lists more than 8,000 plants as weeds. Some, such as Bermuda grass (Cynodon dactylon) and wild oats, were already significant problems for many nations (Council for Agricultural Science and Technology, 1987; Holm et al., 1977, 1979). Importations of animal germplasm consist primarily of living individuals, embryos, or if admissible, eggs (birds, fowl), all of which are developed through sexual reproduction. In addition, semen may be imported, subject to regulation. Importations of plant propagative material include seeds, plants, various asexually produced propagative units, or the plants developed from them. These include asexually produced seed (nucellar seeds of Citrus species); underground or aerial storage organs such as bulbs, corms, stems, crowns, or roots; rhizomes; rooted and nonrooted cuttings; suckers; various types of grafts; and tissue cultures. Tissue cultures may include cells, protoplasts, embryoids, embryos, undifferentiated tissues, or plantlets produced from tissue culture. Pollen may also be imported, but this is probably done less frequently and with less overall known risk than that from the importation of animal semen. QUARANTINE AND GLOBAL TRANSFER OF PLANT GENETIC RESOURCES The transfer of genetic resources has, at times, resulted in the unintended introduction of serious pests or pathogens (International Board for Plant Genetic Resources, 1988b; Plucknett and Smith, 1988). In the 1940s more than 20 million citrus trees were lost in Argentina and Brazil because of tristeza disease from virus-infected imported nursery stock (Knorr, 1977). As the international transfer of germplasm has increased, so has the potential hazard to crop production around the world (Karpati, 1981, 1983; Plucknett and Smith, 1988). Movement of wheat germplasm into the United States, for example, has been increasingly hampered over the past decade by the spread of Karnal bunt disease (Plucknett and Smith, 1988). The increasing emphasis on germplasm from wild species is a particular problem. Little may be known about the pathogens that may be present. Wild species are frequently from the geographical region where a crop originated or was domesticated and may harbor coevolved pests or pathogens of potential significance (Plucknett and Smith, 1988).

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies Poor-quality maize cobs harvested in Yemen. Credit: Food and Agriculture Organization of the United Nations. Although hundreds of pests and pathogens have been already been introduced along natural and artificial pathways, there are hundreds of other crop pests and pathogens that have not yet been introduced (Holderman, 1986; Kahn, 1979a,b; MacGregor, 1973; Schoulties et al., 1983; Yarwood, 1983; Zimdahl, 1983). Analyses of the life cycles of these exotic pests show that many organisms do not have a natural means of spreading medium to long distances. These organisms, however, could readily and quickly be moved on imported articles. Quarantine services and the enforcement of biologically based regulations are the only means available to reduce the chances that such organisms might enter a country by artificial pathways. The importation of animals and plants for any purpose, including the transfer of germplasm resources, can be identified as a low- to high-risk pathway, depending on the host, various biological factors, and the occurrence of transferrable exotic pests in other countries. When the potential risk is perceived to be low, germplasm resources

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies usually move with minimal delays under the principle of the least drastic action. When the risk is perceived to be high, there may be an adverse impact on genetic resources transfer when more drastic actions are taken to exclude pests. Some countries are willing and able to provide safeguards such as testing , isolation, or treatment that can lower the risk to an acceptable level. In other cases, the safeguard mechanism chosen is to exclude the material from entry. Rubber tree (Hevea brasiliensis) germplasm, for example, must be passed through an intermediate quarantine site outside of the American tropics before transfer to Southeast Asia because of the threat of South American leaf blight (Dothidella ulei) (Turner, 1977). Indonesia excludes any vegetative H. brasiliensis germplasm from entry (Plucknett and Smith, 1988). Quarantine as a Pest Control Strategy Quarantine is often combined with plant protection to include all regulatory activities carried out by local, regional, national, and international government agencies or organizations. Two components of quarantine that affect the exchange of plant genetic resources on a global scale are (1) exclusion of plant parts or taking of regulatory actions that will reduce the chances that pests and pathogens might enter a country along artificial pathways; and (2) phytosanitary certification or providing of assistance to a country's exporters to meet the quarantine requirements of importing countries. Both importers and exporters of plant germplasm are affected by these two functions. Importers are subject to the regulations of their own country, which might not only require that exporting countries meet certain phytosanitary standards but might also place some restrictions on the imported germplasm after entry. Although the quarantine service of the exporting country may assist in meeting the requirements, it is the importing country that sets quarantine standards. Quarantine and Genetic Resources Plant quarantine practices are frequently viewed as an impediment by those working in research, breeding, or genetic resources management. This has been particularly true for germplasm that is transferred in a vegetative form (Chiarappa and Karpati, 1984; International Board for Plant Genetic Resources, 1988b). The timely transfer of some, but not all, species may be adversely affected by quarantine-imposed delays.

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies For example, Prunus germplasm is prohibited from entry into the United States because (1) the plum pox virus (among other exotic viruses) does not occur in the United States; (2) the virus, which is transmitted by several species of aphids (but only within 30 minutes of its acquisition by the aphid), does not move on natural pathways beyond the range of its aphid vector; (3) several species of the vector already occur in the United States; (4) the virus can cause severe economic losses; (5) the virus could become established in U.S. nurseries and, subsequently, in commercial orchards if imported infected bud wood or root stocks were used in nursery stock production; and (6) several U.S. Prunus species and varieties are known to be susceptible. A period of 5 to 10 years or more may be required to test introduced Prunus germplasm for the presence of viruses (National Research Council, 1991a), and a longer period of time may be required to propagate material for release from tested plants. Wheat breeders in many countries may be confronted with prohibitions or postentry safeguards that may limit research or breeding programs if the Karnal bunt fungus (Tilletia indica) is found to be present in germplasm samples. The perception of risk or potential damage from this fungus is highly controversial in some regulatory and plant breeding circles. It is known to occur in Mexico and India as well as a few nearby countries. However, damage in Mexico is considered by many to be extremely minor. In India, in the past, damage has been considered to be minor, but in recent years heavy losses of some susceptible varieties have been reported in limited areas (Lambat et al., 1983; Plucknett and Smith, 1988). Legume seeds (beans, soybeans, cowpeas) from some areas may carry latent bacteria and fungi. Restrictions may require that the seeds be subjected to seed health testing and virus indexing. Some countries may have restrictive policies to prevent the entry of specific pathogens, and testing or indexing may not usually be considered adequate safeguards. Breeders may receive only a portion of the seeds they sought to introduce. Bean breeders at the Centro Internacional de Agricultura Tropical (International Center of Tropical Agriculture) are severely limited in the number of seeds they can draw from the center's germplasm bank because of Colombian national quarantine restrictions (Plucknett and Smith, 1988). Legal Basis of Quarantine The legal foundation that supports national quarantine regulations and actions is usually either legislation passed by national governments as acts, statutes, orders, decrees, or directives or enabling

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies legislation that authorizes a minister or secretary of agriculture to issue regulations. In addition, regulatory actions may be taken based on policy, guidelines, or instructions for quarantine officers (Kahn, 1977). State or provincial governments may enact legislation or promulgate rules and regulations to exclude or reduce the chances for entry of pests. State or provincial quarantine services often assist the national government in quarantine activities such as survey or export certification. The international exchange of plant genetic resources is not usually affected by state quarantines, except insofar as state officials must often be used to obtain phytosanitary certificates for export. Some countries are also bound by quarantine regulations that are promulgated by regional parliaments, such as the European Community or Andean Pact (Kahn, 1989a). In addition, a number of regional plant protection organizations exist to provide member countries with nonbinding regulatory recommendations (Plucknett and Smith, 1988). The International Plant Protection Convention of 1951 provides an international mechanism for harmonizing most international plant quarantine activities. By 1987, 89 countries were signatories to the convention, and many others followed (Plucknett and Smith, 1988). The convention has been important to efforts to standardize quarantine practices among nations. It has encouraged the establishment of regional organizations (Table 11-1). The quarantine services of most importing countries require that plant genetic resources be accompanied by a phytosanitary certificate issued according to the standards set by the Food and Agriculture Organization of the United Nations. The certificate must be addressed to the quarantine service of the importing country and signed by an authorized officer of the quarantine service of the exporting country. The certificate must include the plant's place of origin and botanical name. The certificate must also contain a statement certifying that the plants or plant products have been inspected and found to be free from quarantined pests. Unfortunately, a country's printed regulations may have little to do with actual practice. A phytosanitary certificate does not ensure that the plant material will be able to enter a country. Countries with developed quarantine services usually do not rely on these documents as a sole safeguard, even though they may be required for entry. Biologic Basis of Quarantine The biologic foundation of plant quarantine rests on knowledge about the identity of pests, pathogens, and hosts; their geographic

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies TABLE 11-1 Regional Plant Protection Organizations Organization Number of Member Countries Headquarters Asia and Pacific Plant Protection Commission (APPPC) 23 Bangkok, Thailand Caribbean Plant Protection Commission (CPPC) 18 Port of Spain, Trinidad Comite Tecnico Ad-Hoc en Sanidad Vegetal para el Area Sur (COSAVE) 6 Montevideo, Uruguay Junta del Acuerdo de Cartagena (JUNAC) 5 Lima, Peru Organismo Internacional Regional de Sanidad Agropecuaria (OIRSA) 7 San Salvador, El Salvador Inter-African Phytosanitary Council (IAPSC) 48 Yaounde, Cameroon North American Plant Protection Organization (NAPPO) 2 Washington, D.C. European and Mediterranean Plant Protection Organization (EPPO) 36 Paris, France   SOURCE: Plucknett, D. L., and N. J. H. Smith. 1988. Plant Quarantine and the International Transfer of Germplasm. Study Paper No. 25. Washington, D. C.: Consultative Group on International Agricultural Research, World Bank. Reprinted with permission, ©1988 by The World Bank. distribution; and the life cycles of these organisms as they are influenced by the environment, climate, and farm practices. An understanding of how these factors influence colonization or establishment of exotic pests is important for determining the entry status of imported germplasm. Quarantine is intended to prevent the release of an exotic pest under conditions favorable to its establishment. The nature of the organisms of quarantine interest affect greatly the complexity of quarantine activities. For potatoes, methods of detection for the major bacteria, fungi, and nematodes of quarantine significance existed in 1975, when the Centro Internacional de la Papa (International Potato Center) began distribution of germplasm. Methods were needed, however, for detecting several viruses and a viroid in potato germplasm (Kaniewski and Thomas, 1988). For temperate fruit trees, lack of knowledge about some pathogens means that sophisticated serologic, nucleic acid, or electron microscopic detection methods are unavailable. For these pathogens, grafting to sensitive indicator plants may be the only detection method available and can greatly lengthen quarantine-imposed delays.

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies Geographic Basis of Quarantine The distribution of exotic pests and pathogens in various countries, regions, or continents is the geographic basis for promulgating quarantine rules and regulations. Information about the occurrence of such organisms is found in the scientific, agricultural, and regulatory literature. Reports (Plant Health Division, Agriculture Canada, 1978–1986; Plant Protection and Quarantine, 1980–1986) of pests intercepted at ports of entry provide information about the detection of exotic pests, but the information is useful only if the country of origin is identified. The center of diversity of a crop is also likely to be the center of diversity for many of its pests and pathogens (Kahn, 1977). Plant collectors often import germplasm from areas where pest, pathogen, and host species have evolved. These can make germplasm from these regions a particularly rich source of genes for resistance or tolerance traits, but it can also constrain its importation (Neergaard, 1977, 1984; Plucknett and Smith, 1988). Some crops have been successfully imported without their coevolved pests and pathogens. Their continued productivity, however, depends, in part, on the effectiveness of quarantine in maintaining their isolation. Examples include rubber in Africa and southeastern Asia, which still escapes from South American leaf blight; coffee in Latin America, which escaped coffee rust (Hemileia vastatrix) from Asia and Africa until recently; and banana in Latin America, which avoided the black sigatoka fungus until the 1970s (Plucknett and Smith, 1988). Organisms from outside a center of diversity are not necessarily innocuous. Although potatoes originated in the Andes of South America, the late blight fungal pathogen, Phytophthora infestans, has origins elsewhere (Kahn, 1977). Pests and Pathogens of Quarantine Significance An organism is considered to be of quarantine significance if it does not occur in the country of concern and is known to cause economic damage elsewhere or has a life cycle that suggests that it is capable of causing damage under favorable conditions. It also may be of significance if it does not occur but is not widely distributed; if it is under a national suppression, containment, or eradication program; if there are more virulent strains that do not occur; or if it has the potential to cause economic damage to crops. Finally, an organism may already be a common pest but regulations require that growers

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies plant only pathogen-tested nursery stock. In such cases, the government may take steps to ensure that imported stocks meet domestic standards. Pathways for the Entry of Pests and Pathogens Plant pests and pathogens can move or be moved along natural or artificial pathways (Table 11-2). Some organisms have stages or life forms that enable them survive biologic, chemical, or physical stresses and physiologic, morphologic, or anatomic characteristics that facilitate active or passive dispersal. Some organisms (most nematodes, bacteria, scale insects, mites, and snails) move, or are naturally moved, from plant to plant or from plants in one field to plants in another, but they have no means of natural spread over long distances. Such organisms may dispersed longer distances by the accumulation of a series of short-distance natural spreads over time until a natural barrier, such as the absence of a host, is reached. Some pathogens (certain fungi, viruses, bacteria) are moved much longer distances by their insect or vertebrate animal vectors. Still others travel distances as airborne spores. A few insects, such as locusts and monarch butterflies, are migratory. Many pests and pathogens of quarantine significance have very inefficient means of natural movement or spread or life cycles that are not conducive to natural spread. They may be moved along artificial pathways, however (Table 11-2). Quarantine is most effective when humans, or the activities of humans rather than those of nature, are the prime long-distance movers of pests and pathogens. TABLE 11-2 Natural and Artificial Pathways for the Movement of Plant Pests and Pathogens Natural Pathways Artificial Pathways Winds, storms, jet streams Cargo (agricultural and nonagricultural Air and convection currents   Ocean currents Mail Surface drainage Baggage Natural seed dispersal Common carriers (ships, vehicles, airplanes) Fliers (insects and mites)   Migratory species (locusts) Dunnage, crates, packing materials Self-locomotion (zoospores)   Vectors (insects, nematodes) Smuggling Other carriers (birds and other higher animals) Farm practices (irrigation, used farm equipment)

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies Pests and pathogens have the best chance of surviving along artificial pathways when they are on or in their hosts. They are then protected from adverse environmental stresses such as extremes of temperature and relative humidity, prolonged exposures to sunlight or ultraviolet light, or their own parasites or predators. Some, such as viruses and other obligate parasites, may not be able to survive in the absence of a host. The importation of infected, infested, or contaminated plants or animals presents the greatest opportunity for pest and pathogen survival and entry. The chances of survival of the pest or pathogen usually depend on the survival of the host. Pest Risk Analysis Pest risk analysis is a determination of the entry status of any imported article, including propagative material, based on the known or perceived risk (chances) of inadvertently introducing hazardous pests or pathogens by artificial pathways (Kahn, 1979, 1985). It is based on data about known pests or pathogens of the germplasm and the ease with which they could gain entry, colonize, and become established. Other factors include the effectiveness of inspection methods; the availability and effectiveness of treatments if a pest is found; the existence of the diseases or disorders in the country of origin for which the causal agent is unknown; the availability in the importing country of technical support in the form of pathologists, entomologists, and other specialists; and the ability to monitor pathogens, provide diagnostic services, and apply timely control measures. A risk analysis is an essential precursor to decisions about the importation of germplasm. The risk associated with a particular species may vary with the nature of the material being imported (Figure 11-1). Seeds, for example, generally present a lower risk than living plants do. Risk analysis necessitates access to a wide array of accurate and timely information about crops and their pests and pathogens. If the potential benefits exceed the risks, importation of germplasm is justified. An example is the benefit to agriculture from the importation of germplasm when balanced against the risk (that a pest will escape and become established) coupled with the use of a quarantine station as a safeguard. However, the benefits from the importation of large amounts of the same material for commercial purposes cannot justify either taking the risk of importation nor the expense involved in passing material through quarantine. For example, the importation of potato tubers, which are considered by many countries to

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies FIGURE 11-1 Factors considered in pest risk analysis and the relative degree of the risk they pose. Source: International Board for Plant Genetic Resources (IBPGR) 1988. Conservation and Movement of Vegetatively Propagated Germplasm: In Vitro Culture and Disease Aspects. Report of the IBPGR Advisory Committee on In Vitro Storage. Rome: International Board for Plant Genetic Resources. Reprinted with permission, ©1988 by International Board for Plant Genetic Resources. present a high risk, can only be justified by passing small amounts (a few tubers) through a quarantine station. However, allowing large amounts to enter for commercial planting or consumption may not be as easily justified. Germplasm collected from a site with a higher incidence of pests and pathogens has a higher chance of being infested, infected, or otherwise contaminated. Plants or animals from such locations may present a higher risk. Risk and hazard factors related to various germplasm collection sites are given in Table 11-3. In general, vegetative propagations of genetic resources constitute a higher level of risk than do seeds. Almost all vegetative propagations taken from mother plants that are systemically infected with

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies TABLE 11-3 Some Plant Germplasm Sources Germplasm Source Risk- or Hazard-Related Factors Collected in the wild Pest and pathogen occurrence and incidence is often unknown; no survey or control Tubers, roots, or seeds collected in marketplaces Health of mother plant is unknown; there is no foliage; material is difficult to inspect; even so, pathogens may be latent; country of origin is uncertain Farms On average, pest control activities are relatively low or absent Orchards, plantations Often, a high level of inspection, pest survey and management, or control Experimental fields May have a high level of pest survey and management or control; personnel are often aware of pests, pathogens, symptoms, and signs Experimental plots isolated from commercial plantings or located where pests are not known to occur Risk is lowered by the absence of specified pests or lower inoculum levels; survey and control are practiced; personnel are aware of pests, pathogens, and symptoms Greenhouse with floor-level planting beds Risk is lowered by isolation and improved phytosanitation, but soilborne pests could create sanitary and management problems Commercial greenhouses with raised benches Risk is lowered by plant isolation and high levels of phytosanitation, survey, and control Research greenhouses with raised benches Similar to commercial greenhouses with raised benches; highly trained personnel Plant tissue cultures, aseptic plantlet culture Propagations usually have the same health status as their mother plant, insofar as obligate or fastidious pathogens are concerned, but other pests and pathogens are usually eliminated during processing; isolated from contamination Approved certification Pathogen-tested plants; approved procedures; survey; phytosanitation; precautions against recontamination From certain quarantine stations, third-country quarantine, other high-containment locations Plants grown under the highest levels of pest detection, eradication, phytosanitation, treatment, and isolation; no recontamination NOTE: Germplasm sources are listed in order, with the highest perceived pest risk given first.

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies pathogens (for example, viruses and many bacteria and fungi) are also infected. Few of these pathogens are transmitted in the seed. Thus, seeds are considered to be safer for transfer, although there are important exceptions (Kahn, 1977; Plucknett and Smith, 1988). Even when pathogens are known to be seedborne, frequently not all seeds are infected or contaminated. For seedborne viruses, the percentage of transmission may be as low as 1 infected seed in 50,000 (for example, lettuce mosaic virus in lettuce) to more than 50 infected seeds. Not all germinating seeds known to be infested or contaminated with certain fungi or bacteria produce infected plants. In general, size, age, and volume of propagules of genetic resources can affect the level of risk. High-risk plant genera are imported in the smallest quantity necessary to establish the base material (for example, a few tubers, a small packet of seeds, or a sample of semen). For vegetative propagations and plants, smaller and younger propagules are less likely to harbor pests. For animals, carefully collected and appropriately treated embryos serve a similar purpose (see Chapter 7) (National Research Council, 1993). The absence of signs or symptoms does not necessarily mean the pathogen is absent. Some nematode-transmitted viruses may not produce observable symptoms in infected germplasm (Bos, 1977). Many cassava seeds infected with cassava bacterial blight (Xanthomonas campestris pathovar manilotis) do not exhibit symptoms (Plucknett and Smith, 1988). IMPORTATION OF GENETIC RESOURCES The quarantine regulations of most countries (Plant Protection and Quarantine, 1960–1988) require that plant and animal materials, including genetic resources, enter through named ports or points of entry. If an airplane or ship has several ports of call in the importing country, inspection usually takes place at the first one. The authorized ports must have inspection stations or facilities. Material that arrives by mail may be held at a post office until it has been inspected by the plant quarantine service. The entry of genetic resources that are prohibited except for scientific purposes may take place through either an inspection station or some other facility named in the special permit authorizing entry. There are, however, many ways in which the inspection of germplasm may be unintentionally or intentionally circumvented (Plucknett and Smith, 1988). A range of safeguard options can be used by a quarantine service in issuing special permits for the importation of small amounts of germplasm. The most drastic is to prohibit importation of the host

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies with no exceptions even for scientific purposes. For example, some countries prohibit coconut plants and seeds from anywhere because of diseases of unknown etiology. Others allow entry but require varying degrees of quarantine isolation. Countries without quarantine stations may allow entry of items that are exempted from prohibitions after passage through intermediate or third-country quarantine (Berg, 1977; Kahn, 1983). Under third-country quarantine, a country imports high-risk material from another country but the material first goes through quarantine in a third country. The first two countries are usually in the tropics or subtropics, but the third country is usually in a region with a temperate climate. The third country may accept the risk because the crop is not grown there; the organisms of concern have narrow host ranges and are not likely to attack crops in the third country, or the organisms are not likely to become established because the environment is unfavorable. Several industrial countries have provided intermediate quarantine services in the past for specified tropical cash crops such as coffee, banana, and rubber (Hevea species). Unfortunately, support has declined or been withdrawn for many such efforts, despite urgent needs (Plucknett and Smith, 1988). It has been suggested that renewed support must come from a consortium of donors that includes industrial and developing nations, commodity and consumer groups, and bilateral and multilateral aid organizations (Plucknett and Smith, 1988). RECOMMENDATIONS Quarantine is essential for protecting a nation's agricultural system. However, regulations and practices must continually balance the potential for release of harmful pests or pathogens with the needs of germplasm scientists, research efforts, and breeding programs. Protection of agriculture is not, however, solely the responsibility of quarantine services. Efforts are needed on the part of national and international germplasm programs to reduce the potential for harboring pathogens in the collections they manage. For quarantine, opportunities to improve present efforts exist in the areas of cooperation, information, and technology. Research should be directed toward the development of improved and efficient methods of pathogen detection, germplasm treatment, and safe transfer. Many of the molecular technologies described in Chapter 7 have the potential to provide powerful tools for the detection of pathogens

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies in plant materials. Fundamental research into the biology of pests and pathogens is an essential part of assessing both the risk of inadvertent transfer and potential methods of detection or elimination. There is a particular need for increased studies of viruses and virus like diseases and to address the pests and pathogens of forage species and the wild species related to cultivated crops. Tissue culture has been successfully used to eliminate pathogens from a number of crop species and enable their safe transfer (International Board for Plant Genetic Resources, 1988b). New and emerging molecular technologies promise to provide the capacity for rapid detection of pathogens that may currently be severely restricted in their transfer because of potential quarantine difficulties. Movement of germplasm through quarantine could be made more efficient through increased cooperation between nations and international institutes, and between quarantine officials and the users of germplasm. Many regional quarantine programs already exist, and these should continue to be supported. In many cases, it may be both practical and efficient to establish regional centers for the quarantine testing of particular materials and, thus, share responsibilities, costs, and benefits. A greater effort is needed to establish sites for intermediate (third-party) quarantine sites. It has been suggested that support for such efforts must come from a consortium of donors that would include governments, commodity and consumer groups, and bilateral and multilateral aid organizations. Such facilities provide a relatively safe mechanism for the transfer of germplasm that might otherwise be restricted because of pests or pathogens with which it might be contaminated. As stated above, quarantine services should be flexible in decisions regarding the fate of germplasm that is endangered or of particular value. Germplasm scientists with specific expertise in a crop can, with appropriate safeguards, receive and test germplasm that might otherwise be detained in quarantine or denied entry into a country. For such cooperation to succeed, germplasm scientists and quarantine officials must acknowledge a mutual goal of efficient and safe transfer of germplasm. Quarantine services in developing nations are in particular need of facilities, supplies, and trained personnel (Plucknett and Smith, 1988). International centers and established national programs can cooperate through the provision of appropriate training of germplasm and quarantine scientists and technicians. Investments in equipment,

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies facilities, and training by international centers, existing national programs, and aid agencies will greatly benefit both the receiving nations and the programs or nations with which they exchange germplasm. The potential to introduce exotic pests or pathogens through the distribution of contaminated germplasm from national and international collections must be reduced. Maintenance of germplasm in a national or international collection does not mean that the material is a priori free of pests or disease. This is especially true for material maintained and exchanged in the vegetative state (for example, plants in the field that are exchanged as bud wood or cuttings). Methods exist to free a number of vegetatively propagated crops, such as potato, sweet potato, and citrus of viruses or viroids that might infect them (International Board for Plant Genetic Resources, 1988b). Once tested and shown to be free of disease, such material can often be maintained and exchanged as in vitro cultures, a practice now routine with potato germplasm (International Board for Plant Genetic Resources, 1988b). Germplasm collections should, to the extent possible, be tested for at least the most potentially significant pests or pathogens they may contain. It has been suggested that, for vegetatively propagated germplasm collections, information about whether the plants have been tested for pathogens and the results of those tests should be part of the data available to quarantine officials (International Board for Plant Genetic Resources, 1988b). Such information should be available for seed collections that are likely sources of seedborne pathogens as well. It may not be technically feasible to eliminate easily some pathogens from some accessions. Although this might limit the distribution of those accessions, it should not be cause to remove them from collections. Wild species, for example, might possess potentially serious pathogens, but their potential contribution of new genes may justify their continued maintenance in a collection. The technique of reducing or eliminating pathogens by selection of disease-free plants during growouts should also be applied cautiously. Although this may yield a disease-free sample, in many cases the selection of a few plants as seed sources for a heterogeneous accession could result in significant loss of genetic diversity (Plucknett and Smith, 1988). Quarantine should not be used as a mechanism to further economic or political objectives. Sound quarantine policies and practices should be biologically based and in accordance with known or potential pest risk (an estimation of the chances that a hazardous pest or pathogen will gain

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Managing Global Genetic Resources: Agricultural Crop Issues and Policies entry along artificial pathways). They should be executed through the least drastic actions that will provide the safeguards and reduce the risk to an acceptable level in a timely fashion. Finally, considerations of the costs of accidental release of a harmful pest or disease versus the benefits to be gained from the imported material should be considered. Usually, the benefits to be derived from the importation of genetic resources justify taking the risk, provided that safeguards are in place, whereas the benefits derived from commercial importations may not necessarily support taking the same risk.

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