Leonard P. Gianessi Cressida S. Silvers Sujatha Sankula Janet E. Carpenter

Transcription

1 Plant Biotechnology: Current and Potential Impact For Improving Pest Management In U.S. Agriculture An Analysis of 40 Case Studies June 2002 Bacterial Resistant Apple Leonard P. Gianessi Cressida S. Silvers Sujatha Sankula Janet E. Carpenter National Center for Food and Agricultural Policy 1616 P Street, NW Washington, DC Phone: (202) Fax: (202) ncfap@ncfap.org Website: Financial Support for this study was provided by the Rockefeller Foundation, Monsanto, The Biotechnology Industry Organization, The Council for Biotechnology Information, The Grocery Manufacturers of America and CropLife America.

2 22. Apple Bacterial Resistant Production Fifteen states account for 94% of U.S. apple production. These states are listed in Table 22.1 along with estimates of apple acreage, production volumes and values for There are two dramatic trends taking place in the U.S. apple industry. The first is a pronounced trend toward variety diversification from red delicious strains. Figure 22.1 charts U.S. production of Red Delicious and Fuji/Gala apples from 1987 to The second dramatic trend taking place is the utilization of more intensive plantings. Since intensively planted orchards have more trees per acre, a size-controlling rootstock is used to limit tree size. Rootstock appropriate for high-density orchards are M9 and M26. A major advantage of higher density plantings is earlier production in the lifetime of the orchard. Increased labor efficiency in the mature orchard is another significant advantage. The M26 and M9 rootstocks, in addition to reducing tree size, promote flowering by the second leaf and continue to bloom heavily each year. Fire Blight Fire blight is the most devastating bacterial disease affecting pome fruits in the U.S. and worldwide [1]. It has eliminated commercial pear production in the eastern United States, where the industry was once centered [2, 3], and continues to cause serious economic damage to western pear production and apple production throughout the country. Fire blight was first described in New York in the late 1700s, and moved west with settlers, becoming established throughout North American apple and pear production areas by the early 1900 s. Currently fire blight is found in New Zealand, England, and throughout Europe, the Mediterranean and in Egypt [1, 2]. Countries in which fire blight 2

3 has not been detected have strict quarantine programs to prevent entry of plant material that may harbor the bacterial disease. In New York it is estimated that fire blight infects 15% of the apple acres annually [17]. While fire blight has always been a concern in eastern apple production, such as in New York and Pennsylvania, severe outbreaks in the west in recent years have caused growers there to adopt more consistent and vigorous monitoring and management programs as well [4]. In Washington state, severe outbreaks occurred in 5% of Washington s apple orchards in 1993, 1997 and 1998, the latter two causing an estimated $68 million loss in trees and production [4, 5, 6, 30]. In 1998, an estimated $40 million was lost in Washington state apples due to fire blight infections. California apple and pear growers suffered a severe outbreak in 2000 [7]. In 1992, Michigan apple growers lost an estimated $3.8 million to fire blight [8]. In 2000, southwest Michigan was hit by a fire blight outbreak the severity of which had never been seen before leaving a deep and long term impact on the state s apple industry [36]. An estimated 400,000 trees on approximately 2000 acres will be lost, representing an investment of over $99 million. Regional apple yields were reduced by 35% with localized losses of 100% in some orchards [37]. Economic losses from the 2000 outbreak are estimated at $10 million for the season, and projected to be $42 million over the subsequent three to five years when tree removal, replacement and accompanying production losses are factored in [9]. Factors contributing to the severity of the 2000 outbreak include perfect environmental conditions for fire blight, the high proportion of acreage planted to varieties with little fire blight tolerance, and the spreading occurrence of antibiotic resistant fire blight strains [37]. Fireblight is caused by the bacterial organism Erwinia amylovora, which grows readily and utilizes sugars and acids as food sources. Fire blight bacteria are microscopic laid side by side would not measure more than an inch. It can affect all parts of the tree, including blossoms and fruit, twigs and leaves, trunk and rootstock [1]. An infected tree may die within a few months of infection, or may survive with reduced yield for a few years, or until the grower pulls it out [2, 10]. Severity and symptoms may vary with the 3

4 timing of infection and the host variety, but the major factor in the severity of fire blight from season to season is the weather. Moderate temperatures in the early spring (65 to 86 degrees F) accompanied by high humidity or rain during the day are ideal conditions for an outbreak [3]. Blossom infection requires open blossoms, bacterial contamination, 2 to 4 days of warm weather, and wet blossoms. Without water to move the bacterial colony into the nectary, blossom infection cannot occur. Fire blight was so named because plant parts it infects look as though they have been burned, with infected tissue becoming progressively darker until it turns black. Blighted blossoms and young fruits remain attached to branches but look scorched and wilted, and blighted young shoots wilt into a characteristic shepherd s crook shape. In a few days, infections can move 6-12 inches or more into the shoot. The bacteria may live for long periods as a resident in or on apparently healthy apple tissue. Each bacterial cell is completely independent and multiplies by dividing at a phenomenal rate, reaching 10 billion in 72 hours. As the bacterial cells multiply, they advance en masse through the tissue, giving rise to typical symptoms [1]. In addition to the scorched appearance, tissue infected with fire blight will exude droplets of sticky ooze, particularly under humid conditions, that contain fresh inoculum [1, 3]. Favorable conditions lead to rapid multiplication of the bacteria, so rapid that the bacteria are forced through the diseased plant tissue, forming drops on its surface. The ooze may be clear, milky or reddish brown. Infected fruits may exude copious amounts of ooze. Fire blight produces lesions on infected wood. When the bacteria enters an inactive, overwintering phase and lesion expansion slows, lesion margins become sunken and cracked, forming a canker. The bacteria overwinter in the canker edges, and ooze out again in the spring. Primary infection from this fresh, inoculum-filled ooze exuding from cankers is spread to other plant tissue and other hosts by insects, wind and rain. During a fire blight epidemic, many insect species are attracted to the bacterial ooze on infected trees and help spread the pathogen. Insects are very effective inoculating agents, carrying 4

5 up to 100,000 cells of the bacteria per insect. The bacteria also produce an aerosol that floats through the air like a fog and infects blossoms of nearby trees. New fire blight infections enter through existing openings in plant tissue. In the early spring, primary infections start in blossoms. In the blossoms the bacteria multiply rapidly and produce toxins, which penetrate cells and kill them. Sugars in invaded plant cells are used by the bacteria for growth and the process is continued until the whole blossom is killed and the bacteria move on. Fire blight inoculum in ooze from blossom infections is the source of secondary infection, and is spread by insects, rain and wind to other plant parts and hosts, often entering plants through the natural openings on the surfaces of young leaves. Older leaves that have hardened off are less susceptible. Wounds created by mechanical damage or insect feeding are also vulnerable entry points for fire blight bacteria. Fire blight outbreaks often follow heavy rain and hail storms, which damage plant tissue, carry inoculum on high winds, and bring high humidity. Fire blight symptoms may be localized to areas surrounding infection sights, and subsequent removal of these sights during dormant pruning may limit or delay the spread of symptoms to the rest of the tree and to neighboring trees. However, scion infections may spread internally to the roots, often resulting in the tree s rapid death [11]. Fire blight can kill an apple tree in as little as 30 days. Such systemic spread may happen regardless of scion susceptibility or expression of disease symptoms. Fire blight infections in the scion reduce production by killing blossoms, leaves and the water and nutrient conducting tissue of trunks and branches. If infection occurs after fruit development, fruit can be marred with red and black spots, making it unmarketable. Rootstock infections interfere with the uptake of water and nutrients, killing the tree. Rootstock infections can not be pruned out. 5

6 Management Fire blight can be difficult to predict and therefore to manage. In order for it to cause serious damage to an orchard, there must be a coincidence of inoculum source (ooze), susceptible host (e.g. bloom, young foliage, or wounds), and weather conducive to fire blight proliferation (warm and humid). Despite being difficult to predict, there are several practices that can help reduce the severity of fire blight, and as many as is feasible should be implemented. They include heavy pruning of cankers and infected branches in order to prevent fatal spread of infection to the rootstock, and to remove sources of inoculum for further disease spread; control of sucking insects whose feeding wounds serve as bacterial entry sights and which may spread the bacteria; pesticide applications; and planting of less susceptible cultivars [3]. Once fire blight infection reaches the point of producing ooze, it is very difficult to control its spread. Fire blight management therefore focuses on preventing initial infections and preventing infections from advancing to ooze production [12]. Copper sprays have been used in commercial orchards for fire blight control since the 1930 s [13]. Copper applied pre-bloom when green shoots are emerging may reduce inoculum on leaves, although insufficient efficacy against fire blight and potential to russet fruit currently limits its usefulness [14]. Little progress was made in the control of fire blight until the 1950 s when antibiotics first developed for human treatment were used as a means of control. Use of streptomycin and oxytetracycline showed very high efficacy as compared to copper products [13, 14]. Although oxytetracycline was introduced in order to help delay development of streptomycin-resistance, its higher cost and lack of efficacy limited its use [15]. Streptomycin has been the effective treatment of choice since, applied two or three times during bloom or following rain and hail storms [1, 3, 16, 17]. Organic apple growers are allowed the use of streptomycin and copper for fire blight control [34]. Antibiotic sprays, however, are only effective for partial prevention of blossom infections. After an infection occurs, the sprays are not effective in reducing the spread 6

7 of blight. Sometimes sprays are not applied at the right time and infections and yield losses occur. Some losses are incurred every year on treated and untreated acreage [20]. Because of their limited systemic and corrective action, timing of antibiotic applications is important in maximizing efficacy. In recent years, streptomycin-resistant fire blight has been detected in orchards in California, Washington, Oregon, Missouri and Michigan [13, 8], with extensive resistance in the northwest. Eighty eight percent of the fire blight strains recovered from orchards in Washington were resistant to streptomycin but none were resistant to oxytetracycline. Where streptomycin-resistant fire blight strains occur, growers only treatment options are oxytetracycline (which must be granted FIFRA section 18 special needs registration annually), and copper products, neither of which ensure significant fire blight control. The states of Washington and Michigan requested emergency registrations for oxytetracycline for nine consecutive years through Table 22.2 displays estimates of antibiotic use and cost in apple orchards by state in Because of resistance development in the target organism, E. amylovora, and fears of possible resistance development in non-target organisms pathogenic to humans, antibiotic use to control fire blight has come under scrutiny of public health agencies. If, despite preventative applications of copper and/or antibiotics, fire blight infestation occurs, there is no cure for it and no way to eliminate it from orchards. Therefore the best way to protect orchard trees from the disease is to plant cultivars with reduced susceptibility to it [1]. Although no apple cultivars are immune to fire blight, some scion cultivars are more susceptible to infection than others. Orchards of Red Delicious, Mcintosh, and Stayman apples seldom become infected unless they are planted next to a highly susceptible cultivar [1]. Very susceptible apple cultivars include Braeburn, Granny Smith, Nittany, Jonathan, Idared, Rome Beauty, Gala, and Fuji. The planting of cultivars and rootstock highly susceptible to fire blight infections is causing an increase in the use of antibiotics for fire blight control. Prior to the 1990 s fire blight was not a 7

8 significant problem in apples in the northwest because the vast majority of acreage was planted with the blight-resistant Red Delicious variety. The shift to high-density plantings on dwarf rootstocks has also contributed to increased disease presence. Closely-planted trees increase disease pressure because spread from tree to tree is easier over a shorter distance. Additionally, the highest performing, and therefore most widely planted, dwarf rootstocks (M9, M26) are also very susceptible to fire blight [18, 19]. Rootstock susceptibility makes even minor infections lethal, regardless of the scion used [36]. Researchers at Cornell calculate that one episode of 10% rootstock infection could result in losses of up to $3,500 per acre [11]. One of the primary goals of apple breeding programs has been to develop fire blight resistant rootstocks as well as scions [11, 19]. Transgenic Resistance Traditional breeding of apples, and tree fruit in general, is a long process and, so far, has been unable to produce apple cultivars that marry horticultural fruit traits desired by marketers and consumers with production traits desired by growers. Fire blight resistance exists in the apple genome, but the difficulty lies in incorporating that resistance into a variety without losing other desirable traits. The promise of traditional breeding programs may be limited to rootstock development since rootstock fruit quality traits are irrelevant. Genetic engineering expedites the development of disease resistant apple scion varieties as well as rootstocks. In addition to reducing varietal development time, techniques of genetic engineering can introduce single traits into familiar market apple varieties in order to enhance production without modifying horticultural quality. Lytic proteins are naturally occurring molecules that damage or inhibit formation of bacterial cell membranes, thus preventing the bacteria from spreading. Several lytic proteins have been identified which show activity against the bacterium which causes fire blight [20]. These include attacin E, an inducible protein found in pupae of giant 8

9 silkworm moths [21], and lysozymes from a T4 bacteriophage and hen egg white [22, 23]. Researchers at Cornell University, with financial support from the university, a local commodity group and USDA, followed up earlier work on the genetic transformation of apple tissue done in England, to investigate the potential for using lytic proteins in the development of fire blight resistant apple cultivars. Optimal protocols for gene transfer to apple leaf tissue using Agrobacterium were investigated, as were optimal plant regeneration techniques [24]. Tissue from the rootstock variety M.26 was transformed with genes for the lytic proteins attacin E and T4 lysozyme, both separately and in combination, and the resulting plants are being tested for fire blight resistance. The same was done with Galaxy [22]. Preliminary results from these projects indicated the attacin protein most enhanced fire blight resistance. Transgenic lines of Royal Gala, a popular commercial cultivar, were also produced to compare relative fire blight resistance activity of the lyctic proteins attacin E and T4 lysozymes, as well as two synthetic cecropin analogs and hen egg white lysozymes [20, 23]. Development of trees was sped up by collaborating with a California nursery. Buds from transgenic seedlings produced in New York were shipped to California in early spring and there grafted onto plants. After taking advantage of California s long growing season, the grafted seedlings were shipped back to New York for spring planting in field plots, speeding up development by a full season. In field tests of two to four year old trees inoculated with shoot blight, several transgenic lines showed fire blight resistance that was significantly greater than the parent line, with lines containing the attacin protein showing the most resistance [20, 23]. One attacinexpressing line had only 5% shoot blight compared with 60% in the nontransformed parent line. Field trials were repeated the following year, with the same lines showing continued fire blight resistance. In quantitative studies of horticultural qualities, fruit from the transgenic Royal Gala lines are indistinguishable from fruit of nontransformed lines. 9

10 Simultaneous research is underway investigating other mechanisms for fire blight resistance using genes derived from plants and from the fire blight bacterium [20]. Rather than directly affecting fire blight, the products of these genes either induce or enhance natural mechanisms already present in plants for defense against invading pathogens. One such protein is harpin. Derived from fire blight bacteria, harpin has been shown to induce host resistance in plants. It is commercially available as a foliar application, but with moderate efficacy against fire blight. Insertion of a harpin gene into apples may provide improved and more consistent fire blight resistance than foliar applications. A harpin gene has been inserted into M.26 rootstock [25] and the resulting transgenic plantlets proved very resistant to fire blight in preliminary trials [26]. While a fire blight resistant apple scion would improve marketable fruit production in infected orchards, rootstock infections would still threaten tree vitality. A rootstock with resistance would reduce losses to tree death but fruit production would still be at risk from blossom and shoot infections. A combination of the two, on the other hand, could eliminate the threat of fire blight altogether. Since apples with lytic genes will be classified by EPA as plant pesticides, they will have to undergo the same extensive regulatory process as do pesticides in order to be registered for use. Currently, Cornell University and the company licensing the genes are not willing to pursue registration due to the potential costs [26]. Estimated Impacts It is estimated that a transgenic apple that resists fire blight would be planted on the acreage currently planted to highly susceptible cultivars (204,175). The planting of the transgenics would eliminate the need to spray antibiotics in U.S. apple orchards (21,800 lbs/yr.) and would save U.S. apple growers $2.8 million/yr.which is currently spent on antibiotic sprays. 10

11 Approximately 50% of U.S. apple production is produced by cultivars highly susceptible to fire blight infections [35]. It is assumed that this percentage applies to each apple producing state. It is further assumed that current losses to fire blight are 5% of total production of the highly susceptible cultivars. These assumptions imply that current losses to fire blight total $35.6 million per year with an associated loss of 251 million pounds of apples. Table 22.3 delineates these losses by state. The transgenic apple would be expected to eliminate current losses to fire blight. 11

12 TABLE 22.1: Apple Production (1999) Acres Production (million lbs) Value (million $) California 35, Idaho 5, Maryland 2, Massachusetts 5, Michigan 52,500 1, New Jersey 3, Missouri 3, New York 55,000 1, North Carolina 9, Ohio 7, Oregon 8, Pennsylvania 23, Virginia 17, Washington 172,000 5, West Virginia 8, Total 408,350 10,017 1,425 % of U.S. 88% 94% 92% Source: [33] 12

13 Table Apples: Antibiotic Usage, 1999 % Acres Treated LBS AI Total (000) Total $ (000) per A/yr. Streptomycin California Idaho Maryland Massachusetts Michigan Missouri New Jersey New York North Carolina Ohio Oregon Pennsylvania Virginia Washington West Virginia Total 18.4 $2,483 Oxytetracycline Oregon Washington Idaho Michigan Total 3.4 $311 Total 21.8 $2,794 Source: [28], [29], [36] Calculated at $93/lb AI for oxytetracycline and $135/lb AI for streptomycin [31]. 13

14 TABLE 22.3: Apple Losses to Fire Blight (1999) Production (million lbs) Value (million $) California Idaho Maryland Massachusetts Michigan Missouri New Jersey New York North Carolina Ohio Oregon Pennsylvania Virginia Washington West Virginia Total ) Calculated as 5% of susceptible cultivar production, which is assumed to be 50% of production in each state (see Table 22.1). 14

15 Figure 22.1 U.S. Apple Production by Variety billion lbs/yr Red Delicious Fuji/Gala 15

16 References 1. Jones, A.L. and H.S. Aldwinkle, eds. Compendium of Apple and Pear Diseases, APS Press, Slape, C. Dampening Fire Blight, The Grower, August, Jones, A.L. and Sutton T.B. Diseases of Tree Fruits in the East, Michigan State University Extension Publication NCR 45, Steward, P. Washington Growers Monitor Orchards for Fire Blight, Capitol Press, May 5, Smith, T.J A Fire Blight Year in Washington State, Proceedings of the 89 th Annual Meeting, Washington State Horticultural Association. 6. Smith, T.J Fire Blight Woes in Apples and What to look Forward to in the 1999 Season, Proceedings of the 94 th Annual Meeting, Washington State Horticultural Association. 7. Souza, C. Fire Blight Disease Flares Up in Pear and Apple Orchards, AgAlert, July 19, Moses, L. Fire Blight Burns Southwest Michigan, Fruit Grower, January, Dean, L. Fire Blight Attacks Southwest Michigan; Disaster Aid Sought, The Fruit Growers News, August, Extinguishing the Fire, Futures, Fall Norelli, J., et al. Fire Blight of Apple Rootstocks, New York Fruit Quarterly 8(1):5-8, van der Zwet, T. and S.S. Miller. Controlling Fire Blight, Fruit Grower, March Moller, W.J., et al. The Scenario of Fire Blight and Streptomycin Resistance, Plant Disease 65(7): , Breth, D.I., et al. Successful Fire Blight Control is in the Details, New York Fruit Quarterly 8(1):10-16, Jones, A.L. Apple Disease Control, 126 th Annual Report, Michigan State Horticultural Society,

17 16. Vidaver, A.K. Antibiotic Usage in Plant Agriculture, Phytopathology News 27(1):6-7, USDA. Crop Profile for Apples in New York, available on the internet at Gardner, R.G., et al. Fire Blight Resistance in the Geneva Apple Rootstock Breeding Program, Journal of the American Society of Horticultural Science, 105(6): , Cummins, J. New Rootstocks Resistant to Fire Blight, Fruit Grower, January, Aldwinkle, H., et al. Genetic Engineering of Apple for Resistance to Fire Blight, New York Fruit Quarterly 8(1):24-26, Ko, K. et al. Isolation of Attacin E Protein from an Escherichia coli Expression Vector and Production of its Antibody for Use in Immunoassays, Proceedings of the 8 th International Workshop on Fire Blight, Acta Horticultura 489: , Ko, K., et al. Effect of Multiple Transgenes on Resistance to Fire Blight of Galaxy Apple, Proceedings of the 8 th International Workshop on Fire Blight, Acta Horticultura 489:257, Norelli, J.L., et al. Genetic Transformation for Fire Blight Resistance in Apple, Proceedings of the 8 th International Workshop on Fire Blight, Acta Horticultura 489: , Borejsza-Wysocka, E.E., et al. Transformation of Authentic M.26 Apple Rootstock for Enhanced Resistance to Fire Blight, Proceedings of the 8 th International Workshop on Fire Blight, Acta Horticultura 489: , Abdul-Kader, A.M., et al. Evaluation of the hrpn Gene for Increasing Resistance to Fire Blight in Transgenic Apple, Proceedings of the 8 th International Workshop on Fire Blight, Acta Horticultura 489: , Aldwinkle, H.S. Department of Plant Pathology, Cornell University. Personal Communication, May Hinman, H., et al. Estimated Capital Requirements and Profitability of Establishing and Producing a High density Fuji Apple Orchard in Eastern Washington, Washington State University, EB1878, November, USDA. Agricultural Chemical Usage:1999 Fruit and Nut Summary, National Agricultural Statistics Service, July

18 29. Gianessi, L. P. and M. B. Marcelli. Pesticide Use in US Crop Production:1997, National Center for Food and Agricultural Policy, November 2000, available at Smith, T. S. Principles of Fire Blight Control in the Pacific Northwest 1998 Update, Washington State University. 31. Gianessi, L. P. and M.B. Marcelli. Prices of Pesticide Active Ingredients(1996), National Center for Food and Agricultural Policy, October Overall Growers Won t Get Burned, Packer, September 18, USDA. Noncitrus Fruits and Nuts 1999 Summary, National Agricultural Statistics Service, July Swezey, S. L., et al. Organic Apple Production Manual, University of California, Publication 3403, U.S. Apple Production and Utilization Analysis, US Apple Association, Jones, Alan, Michigan State University, personal communication 37. Longstroth, Mark, The Fireblight Epidemic in Southwest Michigan, Michigan State University Extension Service, Van Buren County, available at msue.msu.edu/vanburen/fb2000.htm, July 19,