Enhanced governmental funding is needed to upgrade and strengthen the National Clonal Germplasm Repository (NCGR) system. The Davis and Geneva centers need to lead and direct efforts on grape germplasm characterization, acquisition, maintenance and distribution. Grape is the most valuable horticultural crop in the world and the US, yet its germplasm resources are only modestly supported. Because permanent and consistent support is required for the preservation and maintenance of a collection of such high importance, it is essential that this responsibility be borne at the federal level by the US Department of Agriculture. The Grape Crop Germplasm Committee has met to consider the grape germplasm vulnerability and needs, and how to ensure that the repositories are protected, strengthened and better utilized. The following recommendations will protect both Germplasm Repositories, greatly enhance the utility of the current collections, and promote germplasm research to correct deficiencies.
National and International Grape Germplasm Organizations: Background and Statistics
Grapes are one of the most widely planted and economically successful crops in the United States with vineyards and wineries in most of the 50 States. California is the most important producer of grapes and wine in the nation with almost 900,000 acres in production. Washington, New York, Michigan, Pennsylvania and Oregon are the next five states with a combined acreage of about 117,000 acres. Given the importance and different needs of grape production in the various states it is not surprising that there are two National Clonal Germplasm Repositories (NCGR), one in Geneva, NY and the other in Davis, CA, and two USDA grape breeding programs (Geneva, NY and Parlier, CA). In addition to these national efforts, there are public grape breeding and genetics/genomics programs at the University of California, Davis; Cornell University, Geneva; the University of Minnesota; the University of Arkansas, Fayetteville; University of Georgia, Tifton; and Florida Agricultural and Mechanical University, Tallahassee. Many other publicly supported grape breeding programs have been discontinued including those in: Florida, Illinois, Maryland, Missouri, Virginia, and British Columbia. At least four private grape breeding programs emphasizing development of fresh market grapes operate in California. In addition to these efforts, there are grape genomics programs at Southwest Missouri State University; University of Nevada, Reno; University of British Columbia; and University of
Guelph. Several other private corporations are utilizing genetic engineering and other tissue culture approaches to develop improved grape cultivars. There are also numerous viticulture research programs across the country focused on germplasm evaluation, cultivation, and pest control.
There are a variety of public advisory and regulatory organizations that affect grape germplasm. The Grape Crop Germplasm Committee is made up of public and private grape breeders, geneticists, pathologists, entomologists and viticulturists and was established to advise the National Plant Germplasm System. The North American Grape Breeders group is composed of breeders and geneticists, both public and private, from across the country and has direct input into the CGC. At a national level, the Alcohol and Tobacco Tax and Trade Bureau (TTB) regulates the sale of wine and naming of wine grape cultivars. Across the country, state agencies are in charge of regulating their industries. Within California there are two agencies with grape responsibilities. The California Department of Food and Agriculture (CDFA) regulates the grape certification program, the nursery industry, and growers with responsibilities directed at pest control and the sale of grapes. The Foundation Plant Service (FPS) is a service branch of the University of California, Davis responsible for providing certified plant material (disease tested and true to variety) to the grape nurseries. FPS is also the site of the National Grape Importation Program (NGIP), a program sanctioned by the USDA Animal and Plant Health Inspection Service (APHIS) to import grape germplasm. Whereas APHIS regulates importation of germplasm from overseas, the Dept. of Agriculture in each state regulates interstate movement of grapevines. However, there is not a facility for importing grape germplasm that is not of immediate potential commercialization at a cost that is compatible with the volume of accessions and the funding level of collection proposals.
There are international organizations that have interest in cataloging and preserving the world’s grape collections. The International Plant Genetic Resources Institute (IPGRI) has addressed grape germplasm issues in the past and voiced its concern for the conservation and documentation of grape species and collections, and their coordinated description (http://www.ipgri.cgiar.org/). The Office International de la Vigne et du Vin (OIV) is an international body that oversees wine and grape issues. Its primary focus is on international trade, including trade in germplasm. A major contribution to the world’s grape germplasm was made by Alleweldt and Dettweiler who compiled world collections and grape authorities in “The Genetic Resources of Vitis”, which documents the genetic and geographic origin of grape cultivar names and synonyms (http://www.genres.de/vitis/vitis.htm). This document was a monumental undertaking and points to the continued need to identify and document not only cultivar names, but also places where grape germplasm is maintained.
Most important cultivated grape cultivars are Vitis vinifera. They make up not only the majority of U.S. plantings, but are also the dominant cultivars in the world. Vitis vinifera cultivars are widely regarded as having the highest quality for fresh and dried fruit and wine production. The world’s grape acreage was listed at 7,518,111 acres in 2003 (FAO Statistical Service); about 98% of these acres are V. vinifera cultivars. However, these cultivars possess few of the resistance genes needed to defend against a host of biotic and abiotic stresses that confront viticulture around the world. Fungicides and pesticides effectively control many of these problems, but environmental, safety and economic concerns are beginning to limit the utilization of these products. Resistance from other species will have to be utilized. Solutions to environmental stresses such as cold, air pollution and soil problems will depend on utilization of other germplasm.
The recent introduction of the glassy-winged sharpshooter into California, and its potential to dramatically expand and intensify Pierce’s Disease (PD) in this State (see http://www.cdfa.ca.gov/gwss/) dramatically highlights the importance of the Nation’s grape repositories. This bacterial disease is native to southern portions of North America and scattered spots across northern South America. Breeders in these areas have been developing new selections and cultivars for many years in efforts to combat PD. Many resistant species and breeder selections exist at the Davis Repository and are being utilized by the University of California, Davis, USDA Parlier and Florida AMU - Tallahassee grape breeding programs. These sources of resistance are critical to breeding efforts focused on cultivar development and identification of resistance genes.
The Davis Repository also houses one of the world’s most extensive collections of V. vinifera cultivars, all of which are susceptible to PD. Given the tremendous importance of grape to the economy of California, and the key role of the Davis Repository in maintaining a world-renown V. vinifera collection, it is essential that the construction of screenhouses at the Davis Repository to protect this collection before the inevitable spread of the glassy-winged sharpshooter continue. Pierce’s Disease is limited by cold winter temperatures, as is the cultivation of V. vinifera. However, V. vinifera survives lower temperatures than does PD. Research into the range of PD needs to be encouraged and evaluated in the event that the Davis Repository needs to be relocated to a colder region of the State.
A collaborative research project on crown gall disease has been underway for a number of years at the Geneva Repository. This bacterial disease, caused by Agrobacterium vitis, results in galls capable of girdling trunks and killing vines. The disease cycle is initiated as tumorigenic genes from the bacteria’s plasmid are incorporated into grape cells. Galling is induced after trunks are damaged by cold weather, severe pruning or equipment. Because the bacterium is systemic in grape and easily transmitted by herbaceous and woody cuttings, this disease is often nascent until some form of tissue damage occurs. The Geneva Repository collection has been surveyed and resistance to this disease has been identified in accessions of V. amurensis, V. riparia, and various interspecific hybrids. Examinations of the breadth of resistance and efforts to characterize the inheritance of resistance and the genes involved continue.
The soil-borne pests that attack grape, including the root aphid phylloxera and a range of nematodes, are controlled with resistant rootstocks. However, pest populations change and the choice of resistant rootstocks with resistance to multiple pests is limited. Fortunately, there are many sources of disease and pest resistance among the Vitis species. Some of these resistant species and traits have been utilized for over 100 years while the resistance of other species is known, but has not been exploited. Perhaps as many as 60 grape species exist and relatively few have been utilized in grape breeding. This germplasm represents tremendous genetic diversity and in many cases is threatened by habitat loss.
The main charge of the Grape CGC is to advise and assist the NCGR curators. However, this group also plays an important role in the National Plant Germplasm System given their expertise in grape germplasm, its utility, and its vulnerability. It is this latter area that this document addresses.
Grapevine Species: Important Traits and Vulnerability to Loss
Vitis vinifera is by far the most important grape species world wide, although it could be argued that the species used in rootstocks are at least as important, and without these, V. vinifera culture would be extremely restricted. Vitis vinifera originated in the Middle East and spread with the aid of birds and human migration across northern Africa and eastern and central Europe to northern Europe. Vitis vinifera has one subspecies, V. vinifera spp. sylvestris, that is found in north Africa, and in widely scattered regions from Germany to Spain and across to Eastern Europe. However, these populations are very rare and have been declining due to introduced foliar diseases such as downy and powdery mildew, and to the introduced grape phylloxera. It is often difficult to separate the remaining populations of V. sylvestris from feral vines or local land races; however, true V. sylvestris and land races both are likely sources of important genes. Among these are better cold hardiness in northerly accessions, shortened growth cycle in accessions from higher elevations, and other climatically conditioned traits.
The world’s native grape habitat is threatened in all areas of its range. Expanding populations and agriculture have eliminated large expanses of habitat, and political instability and economic decisions have limited both habitat and critical germplasm collections. A key example of such potential loss was the collapse of the Soviet Union and the inability of local governments to continue to fund some of the most important collections of grape and other perennial fruits. These collections were founded by Vavilov, the source of the key grape germplasm collections in Crimea and Turkmenistan. There are many other important collections of grape cultivars around the world with the primary ones located in Montpellier and Pont-de-la-Maye, France; Geilweilerhof, Germany; Bet Dagan, Israel; Bari, Italy; and Merbein, Sunraysia-Irymple and Victoria, Australia.
The collection of Vitis vinifera from its Middle Eastern center of origin is of extreme importance given the tremendous genetic diversity still present. Among the V. vinifera grapes from the Middle East are regional cultivars, distinctive clones, and land races found nowhere else. Although this region is not known for its wine grapes, it is a center for table and raisin grape production. Worldwide table grape production is a major horticultural industry. In California there are about 83,000 acres (33,600 hectares) of table grapes producing crop valued at about $1 billion. The vast majority of California table grapes are seedless and the seedlessness in these cultivars originates from a very narrow genetic base; primarily Thompson Seedless (Sultanina or Kishmish in the Middle East, and Sultana in Australia), an ancient Middle Eastern grape. Collections from this region are likely to have other alleles for seedlessness that might reside in genetic backgrounds with larger berries, different phenological traits, skin color, and flesh texture – all traits growers and breeders desire.
Cultivars from this region may also have resistance or tolerance to a number of diseases, pests and environmental conditions. Fanleaf degeneration is the world’s most serious grape viral disease. Fanleaf is caused by grapevine fanleaf virus (GFLV) and spreads through the soil by the feeding of the dagger nematode, Xiphinema index. This disease causes a slow vine decline, but is considered serious because GFLV interrupts normal berry set and can eliminate fruit harvests. Fanleaf degeneration originated in the Middle East and therefore, sources of resistance to GFLV and perhaps its nematode vector should be found here. The origin of other grape viruses is less well understood; however, it is likely that others also co-evolved with grape in the Middle East, and resistance to these may also be found there.
Middle Eastern V. vinifera cultivars may also possess other desirable traits, drought and salinity tolerance being key among these. This species is regarded as one of the most drought tolerant, having evolved in a very arid region. Drought tolerance is becoming an increasingly important trait in rootstocks. The world’s population pressures will likely force viticulture into more xeric areas and require rootstocks to have better forms of drought tolerance. The form of drought tolerance that currently exists in rootstocks is adaptive — these rootstocks survive because of their very large foraging root systems. When soils are fertile or water supply is adequate such rootstocks promote excessive vigor in scions. Middle Eastern V. vinifera may possess actual drought tolerance whereby the roots are capable of surviving very dry soil without producing a huge root system.
Asia is another center of origin for Vitis species. However, there is little known about Asian grape species because most of the literature is in Chinese and is largely unavailable outside of Asia. Accounts of the number of Asiatic species range from about 10 to more than 50. They inhabit many areas of China from the dry west, the foothills of the northern and southern side of the Himalayas, the very cold northeast near Korea and the hot and humid southeast. Chinese cultivars based on V. amurensis are grown in the northeast of China. These cultivars have relatively large berries, very good cold tolerance and some disease resistance. This species has been utilized in the former Soviet Union as well as Eastern Europe in crosses with V. vinifera to produce numerous hybrid series, widely known for their good cold tolerance and Plasmopara resistance. These hybrids were produced in an attempt to extend the northern range of viticulture, and have also been utilized for breeding in Minnesota, Canada, and Germany. Such cultivars do not offer the same wine quality as V. vinifera, but they are much more cold hardy and could be improved further.
Perhaps the most important attribute of Chinese grape germplasm is its potential to have very strong resistance to fungal diseases. Grape species from the very humid subtropical area should be challenged by many fungi and may possess strong resistance. Specific information on resistance of Chinese species is limited: if relevant studies have been conducted they are not available in English. Access to Chinese grape germplasm is limited and these species represent the most poorly collected of all Vitis. The Chinese government is very hesitant to release grape germplasm, and our importation laws preclude easy acquisition of these grapes. However, there are increasing numbers of contacts with Chinese scientists and controlled crosses and seed populations may provide the avenue for collection of these grapes. The funding of proposals to translate or review Chinese research on the genetics, disease and pest resistance, and taxonomy of Chinese grape species should be encouraged and would greatly benefit US researchers.
An expedition to collect wild grapevine germplasm in Taiwan is planned for 2005. This exploration is supported by a grant from the Plant Exploration Office. Although the island of Taiwan does not have as many native species of grapes as mainland China, it does have several tropical and subtropical grape species that are represented poorly or not at all in germplasm repositories in the United States, especially V. thunbergii, V. flexuosa, and V. kelungensis. The government in Taiwan has been very supportive and cooperative of germplasm exploration and exchange.
The lack of documentation, study and concern about grape germplasm is not limited to the Middle East and Asia. The third center of origin of Vitis exists in North America, and this region is also beset by relatively poor documentation of its grape species, in terms of taxonomy, characterization and availability.
North American grape species are divided into two taxa; either as sub-genera or as separate genera (Vitis and Muscadinia). This determination is unclear due to conflicting taxonomies. Species from these two taxa are found throughout North America from southern Canada to northern South America. There are about 20 species in North America, although that number may be as high as 40 by some accounts. All the species within Vitis are interfertile and they freely hybridize where they are sympatric and their bloom dates overlap. Such opportunities make the occurrence of natural hybrids and hybrid zones common and can lead to confusing taxonomic delineations.
Almost all North American grape species grow near a permanent source of water – a stream, river or spring. All but one are vines and grow supported on trees and fences to various heights. Most of these species are primary successors and they tend to die out as forest canopies produce enough shade to limit their growth. Some of the species are plentiful and are commonly found throughout their range, while others are quite rare and survive in endangered habitats. Vitis rupestris was once found in gravelly and sandy creek beds from Tennessee to Texas. This species is shrubby in nature and has been grazed to near extinction across much of its range since the opening of the south central US to agriculture and cattle. It is only relatively common in southern Missouri. Vitis rupestris has a deep penetrating root system to hold itself in rapidly flowing, highly erosive streambeds. It also propagates very readily from dormant cuttings and resists the root aphid phylloxera. It has been widely used in rootstock development and is a likely parent in future rootstock breeding. A recent survey of this species by Lamboy and Pavek (Am. J. Enol. Vitic. 49:356) and Pavek et al. (HortScience 36:232-235) found it scattered, but rare across its range where it occupies habitat that is threatened by grazing, development and flooding. Some of these areas have now been developed into in situ germplasm conservation zones (Genetic Resources and Crop Evolution 50:165-173).
Other Vitis species that are threatened include V. acerifolia, V. aestivalis, V. monticola, V. palmata, V. shuttleworthii and two natural hybrids V. champinii and V. doaniana. Vitis acerifolia grows in southern Kansas and Oklahoma into north Texas and New Mexico. It is relatively uncommon and its habitat suggests that it should have strong drought tolerance. It roots well from dormant cuttings and some accessions have been shown to resist root-knot nematodes (Olmo, Walker).
Vitis aestivalis is found across the eastern US from Texas to Florida and north to New England. Perhaps the most valuable form of this diverse species is V. aestivalis var. glauca. This form of V. aestivalis has good fruit quality, large berries and good resistance to foliar diseases such as powdery and downy mildew, and Pierce’s disease (PD). Its resistance to PD is of particular importance. Vitis aestivalis var. glauca has been used to produce fruiting hybrids (the Munson hybrids) as it lacks the strong fruit flavors of the grape cultivars based on V. labrusca, while possessing valuable disease resistance. Urbanization and agriculture also threaten this species.
Vitis monticola is found across the central and northern parts of the Edwards Plateau in Texas, although it is not abundant. This weak-growing species is usually found in extremely droughty areas on juniper or mesquite and without an obvious source of permanent water. Although it roots poorly, it may be an excellent choice for drought tolerant rootstock breeding because its progeny might tolerate drought while possessing a smaller, less vigor promoting root system. It should also be an outstanding source of lime tolerance since it is often found growing on limestone deposits.
Vitis palmata is a relatively rare species that inhabits the south central United States and is found in swampy conditions. Although virtually all grape species are associated with permanent water, their root crowns are rarely found in standing water. Vitis palmata is one of the few species that appears to tolerate these low oxygen swampy conditions. Phytophthora root rot is a fungal disease of grape most often found in overly wet soils. Resistance to this disease may be more related to how well a given rootstock tolerates wet, low oxygen soils. If so, V. palmata would be a useful parent in the breeding of such rootstocks. This species is not common and its habitat is becoming more restricted with the growth of agriculture, spread of cities, and draining of wetlands.
Vitis shuttleworthii is native to central and southern Florida, where it is facing extinction as a result of rampant land development. This species is closely related to V. mustangensis (V. candicans), which is found from Texas across to the southeast. Vitis shuttleworthii has relatively large berries and high levels of resistance to Pierce’s disease and a host of damaging foliar fungal diseases, as well as moderate resistance to dagger nematodes. It has been used to produce fruiting hybrids for the southeastern US in the past (Fennell), and remains valuable.
Two relatively rare Vitis species are natural hybrids with restricted ranges due to human population expansion and limited opportunity to reform these hybrids. Vitis champinii is found in central Texas on the Edwards Plateau where it formed through hybridization of V. mustangensis X V. rupestris. Vitis rupestris is now very rare in Texas and the opportunity for this natural hybrid to reform is restricted. True V. champinii is already rare and there are few populations to maintain the species. There are other natural hybrids between V. candicans and V. monticola and with V. cinerea var. helleri, (V. berlandieri), which resemble V. champinii, but they may not possess the excellent and broad nematode resistance of V. champinii. Vitis doaniana is a second natural hybrid with V. mustangensis as one of its parents and V. acerifolia as the other. This species is found from northern Texas to southern Oklahoma. It grows in very dry areas, should have good adaptation to drought (with a deep root system), and may possess good nematode resistance. Both of these natural hybrid species are in need of taxonomic revision and both have value as rootstock parents.
Although grape species in the US are relatively well characterized, confusion as to which are valid taxa remains. This confusion results from conflicting taxonomic descriptions and from the tendency of these species to form hybrid zones where they are sympatric. There have been several relatively recent efforts to delineate and describe Vitis in the south and east (SIDA 19:123-131, SIDA 14:339-367; SIDA 12:279-286), and Moore completed the treatment of Vitis prior to his untimely death for inclusion in an upcoming volume of the Flora of North America. The grapes from south of the US border to northern South America are very poorly characterized and several new species have been described (SIDA 12:273-277). Some of these species are native to tropical areas and should contain high levels of resistance to Pierce’s disease. Much of the resistance to PD comes from Vitis rotundifolia, a species with peculiar fruit and horticultural characters, and genetically incompatible with most Vitis species. Additional forms of PD resistance from bunch grapes species native to the southeastern U.S. would greatly benefit breeders.
Recent discoveries by Walker at UC Davis have determined that V. arizonica has exceptional resistance to PD and to the dagger nematode. This species is part of a very poorly described group that exists in the western and southwestern North America. The taxon V. arizonica seems to contain at least three different species and hybrids among them. A clear understanding of the taxonomy of this group is needed so that better choices can be made about the need for collections and the use of these taxa in breeding. Walker has acquired new accessions, and contacts have been established in northern Mexico to complete these collections. Efforts to increase the number of Mexican accessions were made by Bernard Prins, Vitis horticulturist at the Davis repository, and Peter Cousins, USDA grape rootstock breeder at Geneva, in 2003 while collecting grape germplasm in central Mexico on an expedition supported by the Plant Exploration Office. They observed, documented, and collected herbarium sheets and seeds of V. blancoii, V. nesbittiana, V. popenoei, V. jaegeriana, and V. tiliifolia, in addition to observing and collecting wild grapes of unclear taxonomic status. Further taxonomic work will be needed to conclusively identify all of the material. These collections have not yet been released from Mexico, but they are expected to be available by the end of 2004.
Grape breeders acquire germplasm to enable their breeding efforts. These collections are held at the breeder’s station and are relatively unavailable to others because of poor centralized documentation and limited funds for distribution. The greatest danger such collections face is retirement. In the past 40 years, grape breeding programs have been eliminated at Southwest Missouri State University (Mountain Grove), University of Missouri, Rutgers University, Virginia Polytechnic Institute, North Carolina State University, University of Florida, Clemson University, University of South Dakota, Oklahoma State University, and USDA programs in Illinois, Mississippi, and Beltsville, Maryland. Much of the germplasm developed in these collections has been lost. Ron Lane retired in 1997 from the University of Georgia. He was a muscadine grape breeder and had acquired an excellent collection of this unusual and highly disease and insect resistant grape. When he retired his position was not replaced and this collection is now endangered due to uncertain future funding. John Mortensen retired in 1993 from the University of Florida. He spent most of his career developing bunch grape cultivars. As in the case of Dr. Lane, his position was not replaced, and the collection of germplasm he developed also faces an uncertain future. The recent death of Herb Barrett is an additional example. He collected and bred a large collection of disease resistant, high fruit quality species and hybrids. Herb generously distributed materials to other breeders, but the full extent of his collection is yet to be determined. All of these collections contain resistance to a wide range of fungal and bacterial diseases. In addition, very strong resistance to phylloxera and nematodes is also present. They contain germplasm that may be irreproducible and would greatly benefit grape breeders in the US and around the world. A collection of 20 selections from the private breeding program of Elmer Swenson of Osceola, WI was obtained in 2004 by PGRU, Geneva, NY. Mr. Swenson has had an association with the University of Minnesota grape breeding program, however he recently turned 90 yrs old and can no longer maintain his program. These selections have high levels of cold hardiness along with well-characterized horticultural traits.
Other unique and valuable germplasm from private breeding programs is in danger of being lost. Fennel developed some very disease resistant germplasm from V. tiliifolia;‘Tamiami’ being one example of a cultivar with high levels of resistance to PD and fungal diseases, with large fruit clusters and good fruit quality. Dunstan developed a number of Vitis x Muscadinia hybrids that he backcrossed to interspecific Vitis hybrids. The offspring from these difficult to accomplish crosses have many characteristics of both parents and restored fertility (often lost in Vitis x Muscadinia hybrids).
The above collections primarily contain breeder selections from various hybrid progeny. There are also collections of species germplasm that need to be preserved. In addition to a large private germplasm repository of North American Vitis species accessions, Barry Comeaux has amassed the world’s largest collection of North American Vitis herbarium sheets during his collection trips over the past 20 years. His collections of species from across North America have been sent to both Repositories and need to be encouraged with funding and maintenance. His collection material is well documented with detailed collection data and accurate taxonomic descriptions, something often missing from the USDA Repository collections, which contain limited passport data.
The imperiled nature of grape germplasm collections is not limited to the United States. The collection of wine grape cultivars at the Agriculture Canada Research Station in Summerland, British Columbia, and the collection at the Certification and Importation Center in Saanichton, British Columbia were relocated to a consortium of private nurseries in Canada. This Summerland collection was unique in its focus on cold hardy V. vinifera cultivars, and hybrid materials from Eastern Europe. They have been preserved, but a large collection of germplasm with limited direct economic value may not be safe in private hands.
Germplasm Needs
There are a wide variety of research activities and funding efforts needed to improve the grape germplasm status of the US. A primary goal of the NCGR sites should be to fully document and characterize their collections. These efforts should include complete, as far as possible, passport information, evaluation of critical traits such as sex expression, fruit characteristics, vine morphology, and molecular descriptors. This information should be documented in the Germplasm Resource Information Network (GRIN). Much of this work is underway, and efforts are now shifting towards additional characterization through DNA analysis (Genome 44:432-438).
There is a strong need for complete taxonomic description and revision within grape. This includes not only the obvious areas where information is lacking such as Asia and Central America, but also the United States. These efforts should also focus on documenting diversity within and distribution of the various grape species, preliminary analysis of their vulnerability to habitat loss, and the development of plans to complete NCGR collections. Most importantly, these studies should promote increased efforts to characterize the resistance and horticultural traits of these species.
New collections of grape species are badly needed. These should focus on areas where grape species are endangered and the many under-collected and under-documented areas of the world such as Mexico, Central America, Asia, and the Middle East. Many of these species may be adequately represented in collections around the world, but information regarding these collections is rarely accessible. Efforts to document and catalog international collections are critical. To do this, NCGR personnel should actively cooperate in international grape characterization efforts.
One of the greatest limitations to collection efforts is the grape importation quarantine. This restriction prevents ready collection of germplasm making it difficult to respond to breeder needs or to acquire endangered collections and species. This situation has improved with the institution of a Research Evaluation Quarantine at the USDA Plant Genetic Resources Unit in Geneva, New York, but other such systems should be encouraged in California and at public institutions across the country. The Geneva facility has worked smoothly, while safeguarding the industry from potential pathogens from overseas. Quarantined vines are now fruiting and available to breeders for evaluation and use in hybridization.
Vulnerability of Germplasm Collections and Access to Herbaria Specimens
Grape breeders are the primary holders of grape germplasm. They not only amass genotypes of immediate interest to the specific goals of their breeding program, they also acquire almost anything. Much of this acquired germplasm has no immediate or even future use in these programs, but it might be very valuable in other programs. However, these collections are poorly documented and catalogued. A database detailing what is available and where it exists would be very valuable to both NCGR programs in terms of acquisition and assistance with distribution. Collections also exist at many public universities and colleges such as those mentioned above in relation to breeder retirements and at such places as Grayson County College in Denison, Texas where many of T.V. Munson’s hybrids are assembled. Databases of these collections should become subsets of the NCGR collections to facilitate the use of this germplasm. Germplasm in these collections also needs to tested and treated for the important grape viruses so that restrictions to movement and utility are eliminated.
Preservation of germplasm collections is also critical. The germplasm of retired breeders is frequently at risk and once such collections are cataloged, they should be examined to preserve what may be of value in the future. Funding the acquisition of valuable material and its establishment at NCGR sites is very important. Availability of space and funding for maintenance are always important issues surrounding germplasm maintenance. Efforts towards cryopreservation and storage of in vitro plants need to be intensified, with documentation that these forms of germplasm maintenance will serve the user community. Research in this area is being coordinated by the National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, CO. Funding should also be made available to preserve grape habitat for in situ germplasm maintenance, although given the role of grape species as a primary successor species these habitats will have to be managed. Typical grape habitat could also be maintained and stocked with germplasm, as an alternative to preserving in situ collections. Both forms of conservation might help alleviate the concerns of space availability and maintenance costs at the NCGR sites.
There is also need for research on the preservation of genetic reserves through seed and or pollen collections. Research has been initiated in this area at NCGRP in Fort Collins, CO. Grape seed and pollen lose their viability in relatively short periods of time. If viability could be extended and collections and distribution of these grape germplasm sources facilitated it would be very beneficial. It is relatively easy to amass collections of grape seed and pollen, and in so doing preserve a region’s genetic diversity. Importation restrictions on these materials are relatively uncomplicated making acquisition of genetic diversity from international sources possible and convenient.
Finally, grape herbaria resources need to be catalogued. These herbarium sheets record the existence of grape species and hybrids over time. Changes can be observed and genetic change measured through DNA analysis. However, the existence of these resources is poorly documented and a centralized organizational structure is needed. The NCGR sites could catalog collections and provide information on their location, species composition and availability, and make these databases available on GRIN. These nationwide and hopefully international resources would greatly benefit the knowledge of Vitaceae and help direct where resources for germplasm acquisition should be spent.
Vulnerability to External Threats
Grape is vegetatively propagated and is grown in blocks of single cultivars, and select clones of these cultivars. The size of commercial vineyards varies greatly from two acres to the largest contiguous planting of 7,500 acres in California. Although many different grape cultivars are grown in the United States, more than 95% of these are cultivars of Vitis vinifera, and most of the area is planted to only a few cultivars. In the United States, the top ten grape varieties (by acres planted) accounted for about 71% of total vineyard area (2003 National Agricultural Statistics Service). In California, seven varieties make up 76% of the 767,000 vineyard acres currently listed; ‘Thompson Seedless’ occupies 34% of that acreage (2003 California Grape Acreage Report). The juice grape industry (over 40,000 acres) is primarily planted with a single variety V. X. labruscana ‘Concord’; ‘Niagara’, a seedling of ‘Concord’ is also commonly planted. Thus, we have almost 1 million acres of grapes in the US that contain very few cultivars virtually all of which are V. vinifera. There is more diversity east of the Mississippi River where the acreage includes V. aestivalis, V. labrusca, V. rotundifolia, V. vinifera and many interspecific hybrids of these species. There are grown because disease pressure and climate prevent cultivation of V. vinifera cultivars. Not only is the genetic base of the fruiting scion cultivars very narrow, the rootstocks upon which they are planted also have a very narrow genetic base. The vast majority of rootstocks were derived from three species and six rootstocks account for at least 90% of the usage.
The varieties of V. vinifera have all been imported or derived from European and Middle Eastern sources. They are uniformly and highly susceptible to a wide range of pests and diseases and in fact many of these are North American in origin and were imported to Europe and Asia in the 1800s. The most important diseases are:
Downy mildew (Plasmopara viticola)
Powdery mildew (Uncinula necator)
Eutypa dieback (Eutypa lata)
Fanleaf degeneration (grapevine fanleaf virus)
Leafroll (grapevine leafroll associated virus)
Pierce’s disease (Xylella fastidiosa)
Powdery and downy mildew are effectively controlled by a number of fungicides, but new strains with resistance to these materials are a threat to viticulture. Eutypa lata enters through pruning wounds and is primarily controlled by pruning during periods of low spore incidence. The viral diseases are controlled prophylactically with clean stock programs and cause chronic loses of fruit quality and quantity. Pierces’ disease is limited to regions with relatively mild winters, but has the potential with more effective vectors (like the introduced glassy winged sharpshooter) to cause much greater loss.
There are a large number of insect and nematode pests of grapevine. Most of these are controlled with insecticides and are generally confined to local or regional outbreaks. The most important and widespread of these pests attach the roots of grape:
Phylloxera (Daktulosphaira vitifoliae)
Dagger nematodes (Xiphinema index and X. americanum)
Root-knot nematodes (Meloidogyne spp.)
Phylloxera, the grape root aphid, was the impetus to the development of grape rootstocks after its importation from the US to Europe in the mid 1800s. These rootstocks have been durably resistant for over 100 years, but recent work on genetically and behaviorally distinct phylloxera strains might have an impact on their continued use. The dagger nematodes spread serious viral diseases and continued research on resisting these pests is needed. The root-knot nematodes are very common on agricultural soils and are controlled with several resistant rootstocks. However, this resistance is strain specific and continued breeding to incorporate broader and more durable resistance is needed.
In addition to these diseases and pests, there are a number of others that threaten US viticulture if they are introduced. Many of these are limited by climate such as bacterial blight (Xanthamonas ampelina) and grape rust (Physopella ampelopsidis), but they would cause severe damage. Flavescence dorée is caused by a mycoplasm-like organism and spread by xylem-feeding leafhoppers. There are many parallels between flavescence dorée and Pierce’s disease; both kill grapevines relatively quickly and are spread by similar vectors. There are many strains of grape viruses that are not present in the US, some would be very damaging if they were imported. Foremost among them are types of nepoviruses that are common in Europe, but not yet found in the US. These viruses include: tomato black ring; arabis mosaic; raspberry ringspot; strawberry latent ringspot; grapevine chrome mosaic; Bulgarian latent; and artichoke Italian latent. The effect of these viruses is similar to grapevine fanleaf and tomato ringspot (commonly found in the US) and they can dramatically reduce yields. Many of them do not have identified vectors, but the Longidorid nematodes (also common in the US) and movement through weeds and weed seeds have been documented. Effective quarantines are key to limiting the introduction of these diseases and pests.