UC & Natural Resources California Agriculture

Title Despite benefits, commercialization of transgenic horticultural lags

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Journal California Agriculture, 58(2)

ISSN 0008-0845

Authors Clark, David Klee, Harry Dandekar, Abhaya

Publication Date 2004

Peer reviewed

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RESEARCH ARTICLE

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Despite benefits, commercialization of transgenic horticultural crops lags

David Clark Harry Klee Abhaya Dandekar ing recombinant DNA technology were engineered with resistance ▼ available in the United States: papaya, and tested in field trials but remain sweet corn, squash and a carnation. Ex- uncommercialized. Disease resistance, cept for transgenic papaya, which ac- particularly to viruses, can be devel- counts for approximately 50% of the oped using , and potato The acreage of agronomic crops Hawaiian (HASS 2001), the frac- and papaya engineered for vi- (soybean, cotton, corn and canola) tion of the total horticultural com- rus resistance have been commercial- developed using recombinant DNA modities represented by transgenic ized, but many potential applications technology has expanded varieties is miniscule. are currently underutilized. Improving dramatically since their introduction The absence of significant commer- traits that directly benefit consumers, in 1996, while the commercialization cialization of transgenic varieties in such as nutritional or aesthetic quality, of biotech horticultural crops is not due to lack of poten- is also technically feasible now in many tial products or value (Dandekar and horticultural crops, but only a few (vegetables, , nuts and Gutterson 2000; see sidebar, page 94). products have reached the market. ornamentals) has languished. This is The basic techniques of molecular biol- not due to a lack of both current and ogy have become routine, and consid- Approved traits and technologies potential traits that could be utilized erable research is being conducted on The major technologies that have in horticultural crops, as ongoing horticultural crops. For example, herbi- been approved and widely adopted by research is identifying a diverse array cide resistance has been transferred the industry focus on input traits, or of applications. However, into bentgrass and bluegrass to make those affecting production of the crop in municipal and highly rather than the qualities of the final commercialization is stalled by managed turf environments such as product. Although most approved market reluctance to accept biotech golf courses more efficient. However, genes confer insect resistance and her- products, particularly in the absence they have not been commercialized. bicide tolerance, a range of genetic of clear benefits to consumers. High Similarly, some horticultural crops, in- traits has been approved by the U.S. regulatory costs and restricted access cluding lettuce and tomato, have been regulatory system (table 1). to intellectual property create additional hurdles for specialty crops. These challenges are causing the horticultural industry to forego a Florigene number of current benefits. New products with clear advantages for producers, marketers and consumers may be required before the potential of biotechnology can be realized.

2003, nearly 106 million acres IN of transgenic or genetically en- gineered (GE) crops was planted in the United States, part of 167 million acres of such crops grown worldwide (James 2003). Despite the fact that the first commercialized transgenic food crop was the Flavr Savr tomato, four agronomic crops (corn, soy, cotton and canola) account for virtually all of the current acreage. Last year, only Florigene, of Melbourne, Australia, markets transgenic carnations engineered for blue- four horticultural crops developed us- violet color under the variety name ‘Moonshadow’.

http://CaliforniaAgriculture.ucop.edu • APRIL-JUNE 2004 89 TABLE 1. Approved transgenic traits for U.S. crops

Trait Examples Herbicide tolerance Bromoxynil, glufosinate, glyphosate, sulfonylurea to other damaging diseases, such as Insect resistance Bt kurstaki, Bt tenebrionis those caused by geminiviruses (Gilbertson et al. 1998). Virus resistance Papaya ringspot virus, cucumber mosaic virus, zucchini yellow mosaic virus, watermelon mosaic virus, Flavr Savr tomato. Transgenic horti- potato leaf roll virus, potato virus Y cultural crops providing direct benefits Male sterility Barnase/barstar to the consumer have also been devel- Modified ripening ACC synthase, ACC deaminase, SAM hydrolase, oped. Calgene’s Flavr Savr tomato polygalacturonase silenced the gene encoding polygalac- Modified oils High lauric, myristic, oleic acids turonase, an enzyme implicated in softening. The expectation was that the tomato would soften and spoil more slowly and could be picked at a later Insect resistance. Insect resistance bicide resistance have been commer- stage of maturity. This later harvest, in has been engineered primarily by using cialized, although several have been principle, would permit greater devel- two classes of bacterial genes derived developed and tested. opment of flavor compounds and better from Bacillus thuringiensis (Bt) ssp. Virus resistance. The use of viral taste. This product, first marketed in kurstaki and ssp. tenebrionis (de Maagd coat protein genes to confer resistance 1994, was a success with consumers but et al. 2003). These Bt genes control a has been approved for several virus- failed economically for a variety of rea- broad spectrum of lepidopteran and co- crop combinations (table 1). The most sons (Martineau 2001). This same gene leopteran insects, respectively. The commercially successful has been papa- was also used in a tomato variety pro- genes have been approved for use in yas engineered for resistance to the pa- cessed for paste and marketed by major row crops (feed corn and cotton) paya ringspot virus. This product has Zeneca in the United Kingdom. The and some horticultural crops (sweet revived the Hawaiian papaya industry, trait reduced processing costs and con- corn and potato). Potato and sweet corn which was devastated by the virus in sumers accepted the clearly labeled varieties engineered for resistance to the 1990s (see sidebar, page 92). Small product, until the European uproar Colorado potato beetle and corn ear- acreages of transgenic squash resistant over biotech foods forced it off the su- worm, respectively, were in commer- to mosaic viruses are also grown. permarket shelves. cial production for several years and Virus-resistant potato varieties were U.S. regulatory agencies also ap- were technically and agronomically formerly commercialized but are not proved several other delayed-ripening successful, allowing significant reduc- currently being marketed. Newer tech- tomato varieties based on strategies tar- tions in insecticide use (Shelton et al. nologies, such as RNA interference or geted to block the ethylene biosynthetic 2002). However, the transgenic potato RNA silencing (Waterhouse et al. 2001), pathway (ACC deaminase and varieties were withdrawn from the offer promise for developing resistance antisense/cosuppressed ACC synthase) market after major processors and dis- that is essential for ripening. None of tributors chose not to purchase and these products is currently marketed, market them. Bt sweet corn, while still despite their technical feasibility and available, is not widely grown for the potential consumer benefits. Rather, same reason (Cornell Cooperative Ex- they were preempted by a nonbiotech tension 2003). Courtesy of USDA-ARS approach utilizing the naturally occur- Herbicide tolerance. Several ring rin mutant of tomato that delays herbicide-tolerance genes are registered fruit ripening. Heterozygous for use. The most widely commercial- produce fruits that ripen at a signifi- ized gene is a bacterial enzyme confer- cantly slower rate than normal fruits. ring tolerance to glyphosate, the active ingredient of Roundup herbicide. Transgenes conferring tolerance to bromoxynil (Buctril), glufosinate (Lib- erty) and sulfonylurea (Glean) herbi- cides are also approved for use in a Doug Wilson/USDA-ARS wide variety of crops. In addition, crops tolerant to imidizolinone (Clearfield) and sulfonylurea have been developed through Left, scientists are investigating ways to prevent Pierce’s disease in grapes by genetically nontransgenic methods based on natu- engineering genes from a naturally resistant variety, Muscadinia rotundifolia, into ral or induced mutations. However, no susceptible varieties. In a peer-reviewed study, a parasitoid wasp that controls the horticultural crops engineered for her- diamondback moth, right, a canola pest, was not affected by Bt canola.

90 CALIFORNIA AGRICULTURE, VOLUME 58, NUMBER 2 A nontransgenic approach achieved es- not find a major- sentially the same objective, and aggres- ity negative opin- sive breeding and marketing of the ion about it (see long-shelf-life rin hybrid tomatoes made page 99). Many

Courtesy of UC Biotech Web site the transgenic approach redundant. food companies Lengthening time. are unwilling to Similarly, virtually all bananas mar- risk the conse- keted in the United States are naturally quences of alien- deficient in their ability to initiate ethyl- ating even a small ene synthesis, allowing them to be fraction of their shipped green and ripened by exposure potential market to ethylene gas prior to sale. However, (Gillis 2000). where natural mutants are not avail- Clearly, growers, able, the general approach of manipu- distributors and Biotechnology is contributing to the development of sensitive diagnostic lating ethylene synthesis has great consumers must techniques. Above, samples are placed in wells and subjected to a potential for application in other cli- all see biotech color-based detection system; yellow shows evidence of disease. macteric fruits (whose ripening is me- crops as in their diated by ethylene), particularly best interests for commercialization to cides is currently undertaken for their tropical fruits with short postharvest be successful. Products offering com- control. As for herbicides, it is also dif- lives such as mango, papaya and ba- pelling value could alter the economic ficult to maintain registrations for mi- nana. A higher quality fruit bringing forces influencing producer choices and nor crops grown on smaller acreages, tangible value to the consumer could could create consumer demand to pull which are primarily horticultural. improve the market acceptance of such products through the market- Biotech strategies are being developed biotech crops. place. that could provide broader spectrum Despite their early introduction and Loss of . One factor that disease control and reduced depen- initial market success, and in contrast may significantly alter grower econom- dence upon chemical pesticides (Lin- to what many consumers may believe, ics is the loss of currently registered coln et al. 2002). Resistance to viral the only biotech horticultural com- pesticides due to environmental and diseases would be valuable in many modities currently marketed in the health concerns. For example, methyl horticultural crops, as there are few United States are Hawaiian papayas, a bromide is scheduled to be withdrawn other options for control, and methods small amount of squash and sweet corn, from use in the United States in 2005 for engineering virus resistance are and a few carnation varieties. The com- because it contributes to depletion of well established. monly cited estimate that as much as 70% the ozone layer. Methyl bromide is Tree fruit, nuts and grapes. Re- of food products in U.S. supermarkets widely used in horticultural crops to search is well under-way to build a ro- contain ingredients from GE crops is not control soilborne diseases and weeds bust platform of technologies to utilize attributable to fruits and vegetables, but and to fumigate harvested crops to in the discovery of useful rather to the widespread use of corn, eliminate insects. The majority of this traits for trees (Dandekar et al. 2002). canola and soybean oil, soybean pro- use is in horticultural crops (primarily Transformation technology has been tein, corn starch and related products , tomatoes, peppers, orna- developed and trait evaluation is under in virtually all processed foods. mentals and nurseries, and tree crops) way on apple, almond, peach, citrus, with California and Florida together ac- walnut, pear, plum, grapevine and per- Opportunities for biotechnology counting for 80% of the 35 million simmon. Good progress has been made As global acreage of biotech agro- pounds applied each year for preplant in developing resistance to codling nomic crops sustains its eighth con- fumigation (Economic Research Service moth and fireblight in apple, plum pox secutive year of double-digit growth 2000). Many genes are available that virus in plum/Prunus, crown gall and rates (increasing 15% from 2002 to potentially could be used to enable al- codling moth in walnut, citrus tristeza 2003)(James 2003), it is paradoxical that ternative weed-control strategies. virus (CTV) in citrus and Pierce’s dis- the trend in horticultural crops is ex- Horticultural crops are also limited ease in grapevine. actly the opposite, particularly as many in the numbers of herbicides registered Engineering of resistance to codling of the approved genes fit naturally with for use. Loss of registration for a few moth in apple to reduce the use of the needs of horticultural crops. Fear of key chemicals could markedly limit chemical pesticides has advanced to consumer rejection on the part of both grower options, making crop resistance the point of commercial interest in producers and marketers of horticul- to broad-spectrum herbicides more product development. Work is also un- tural products is a major impediment to critical. Resistance to fungal and bacte- der way to develop productivity and wider utilization of biotechnology, rial diseases would also be desirable, as quality traits such as modified sugar even though many consumer polls do in some areas extensive use of pesti- metabolism and ripening in apple and

http://CaliforniaAgriculture.ucop.edu • APRIL-JUNE 2004 91 Virus-resistant transgenic papaya helps save Hawaiian industry

Dennis Gonsalves

he pivotal year in the history of and established in a THawaii’s papaya industry was field trial in 1992. In May 1992, papaya ringspot vi- Waimanalo on Oahu rus (PRSV) was discovered in Puna on in April 1992. By De- Hawaii Island, where 95% of Hawaii’s cember 1992, it was papaya was being grown. Just one evident that line 55-1 Courtesy of R. Manshardt month earlier, a small field trial to test was resistant under the resistance of a transgenic papaya field conditions. From line had been started on Oahu Island, the 1992 field trial, where papaya production had previ- two cultivars were de- ously been devastated by PRSV. The veloped and desig- timely commercialization of PRSV- nated ‘SunUp’ and resistant transgenic papaya trees has ‘Rainbow’. ‘SunUp’ is revived Hawaii’s papaya industry and homozygous for the provides an example of the challenges coat protein gene and opportunities for horticultural bio- while ‘Rainbow’ is an Two varieties of papaya resistant to papaya ringspot virus technology. Fl hybrid of ‘SunUp’ have been developed using biotechnology: SunUp, left, and Rainbow, right. They have performed well for In 1945, D.D. Jensen made the first and the nontransgenic Hawaiian growers, even under prolonged and heavy report in Hawaii of PRSV, a potyvirus ‘Kapoho’. Unfortu- disease pressure. that is transmitted nonpersistently by nately, by October aphids (Gonsalves 1998). PRSV was 1994, PRSV had spread throughout tion had dropped to only 26 million first discovered on Oahu and caused much of Puna, causing HDOA to aban- pounds as PRSV spread throughout such severe damage that the papaya don rouging efforts to slow the spread the region. Since then, the transgenic industry was relocated to Puna in the of PRSV. The race was on to move the varieties have enabled farmers to re- late 1950s and early 1960s. The papaya transgenic papaya line to commercial- claim infected areas and in 2001, industry expanded and prospered in ization. A 1995 field trial in Puna con- Puna produced 40 million pounds of clusively showed that papaya. The resistance has held up The experience in Hawaii shows ‘SunUp’ and ‘Rainbow’ were remarkably well and remains stable resistant under prolonged after 5 years of extensive plantings. that transgenic virus resistance is and heavy disease pressure. Hawaii also exports papaya to an excellent approach for controlling The U.S. Department of Canada and Japan. The transgenic Agriculture’s Animal Plant papaya was recently deregulated in viral diseases in horticultural crops. Health Inspection Service Canada, which is a relatively small (APHIS) deregulated market for Hawaii. The main chal- Puna, primarily because PRSV was ab- transgenic line 55-1 in November 1996, lenge is deregulation of transgenic sent. However, by the 1970s PRSV was and the U.S. Environmental Protection papaya in Japan, where Hawaii found only about 19 miles away in Agency deregulated it in August 1997. sells about 30% of its papaya. Pres- Hilo, and the Hawaii Department of The consultation process with the U.S. ently, nontransgenic papaya must Agriculture (HDOA) took rouging (the Food and Drug Administration was also be produced in Hawaii to sat- removal of infected trees) and quaran- completed in September 1997. Licenses isfy the Japanese market, but this is tine actions to prevent its spread to to commercialize the transgenic papaya increasingly difficult due to the dis- Puna. In 1986, efforts were initiated to were obtained by the Papaya Adminis- ease pressure. Exporters face added develop a virus-resistant transgenic pa- trative Committee in Hawaii by April expenses to guard against the acci- paya by transforming commercial lines 1998. A celebration was held to mark dental shipment of transgenic pa- of Hawaiian papaya with the coat pro- the debut of the transgenic papaya on paya to Japan. In December 2000, tein gene of PRSV from Hawaii. May 1, 6 years after PRSV was discov- Japan’s Ministry of Agriculture, By 1991, the team of Maureen Fitch, ered in Puna and after the first field Forestry and Fisheries approved Jerry Slightom, Richard Manshardt and trial of line 55-1 was initiated. The line 55-1, and the Ministry of Dennis Gonsalves identified a transgenic fruit is currently sold Health, Labor and Welfare is re- transgenic line (55-1) that showed re- throughout the United States. viewing a recently submitted peti- sistance under inocula- In 1992, Puna produced 53 million tion for deregulation. Anticipated tions. These plants were micropagated pounds of papaya, but by 1998 produc- approval of transgenic papaya in

92 CALIFORNIA AGRICULTURE,AGRICULTURE, VOLUMEVOLUME 5858,, NUMBERNUMBER 22 Simply the diversity of crops utilized in horticulture slows the adoption of new technologies. For example, as many as 60 distinct cultivars of iceberg lettuce alone may be grown throughout the year.

regulation of self-incompatibility in al- for industrial purposes (Lu et al. 2003). mond and other Prunus species. Some Florigene is selling Transgenic Moon

D. Gonsalves and S. Ferreira deployment strategies for transgenic series carnations engineered for dark vio- trees are also being developed, such as let-purple color around the world. The the use of transgenic trees as “trap varieties are developed in Australia and crops” to control insects in conven- flowers are produced primarily in South tional and the use of America for marketing in the United transgenic rootstocks to control dis- States and Japan. eases and pests in nontransgenic Floral scent. Putting the scent back scion varieties (see sidebar, page 96). into flowers that have “lost” this trait The latter approach avoids the task of over years of traditional hybridization transforming many varieties of a par- and selection, or creating new fragrances ticular tree crop and in the future may in plants, has considerable potential and be used to regulate quality and pro- appeal. Research on genes controlling the ductivity traits. different biochemical pathways for vari- Nutrients, consumer qualities. Al- ous floral fragrances Papaya ringspot virus causes small, darkened though more difficult technically and is being conducted on wild plants and on rings on the surface of fruit, as well as foliar therefore not close to market, there are crops such as snapdragon, petunia and damage. many potential opportunities for en- rose (Vainstein et al. 2001). hancing the nutritional value or con- Plant size. Currently, growth- sumer appeal of horticultural products regulating chemicals are applied to Japan will allow Hawaiian growers to through biotechnology. In addition to ornamental plants to inhibit gibberellic expand their transgenic papaya mar- modification of ripening, projects to in- acid (GA) synthesis and reduce plant kets and will eliminate excessive costs crease the content of vitamins, minerals height during crop production. Many associated with segregating trans- or nutraceuticals in horticultural prod- newly introduced ornamental species are genic and nontransgenic fruits. ucts are in progress (Grusak and Della receiving particular attention via conven- The experience in Hawaii shows that Penna 1999). The development of tional breeding for dwarf plants because transgenic virus resistance is an excel- Golden Rice with enhanced beta- their natural habits do not fit into mar- lent approach for controlling viral dis- carotene (pro-vitamin A) in the grain keting systems requiring compact plants. eases in horticultural crops. This (Ye et al. 2000) demonstrated the poten- The manipulation of GA metabolism via industry was fortunate to have a poten- tial for biotechnology to increase nutri- biotechnology has the potential to pro- tial product already under develop- tional value. Whether such products duce ornamental and flowering plants ment when PRSV was discovered in the will have sufficient consumer appeal in with reduced-height phenotypes (Clark main growing area of Puna. There are fully developed markets to drive their et al. 2003). The development of lawn many reports that virus-resistant commercialization remains to be seen. grasses that require significantly less fre- transgenic plants are being developed quent mowing is another obvious appli- , ornamental plants in diverse crops, but few have been cation. Early experiments suggest that commercialized. The papaya story Since floricultural and ornamental expression of genes controlling height shows that this approach can provide a plants are grown for aesthetic or other can be applied to many plant species. stable and safe option for virus protec- nonedible purposes, there may be less Leaf life. Engineering of plants to de- tion that can be essential for the success potential for public concern about GE lay leaf senescence (yellowing) is also be- of specific horticultural crops. varieties than there has been with ing pursued in ornamental crops. For biotech food crops. years, ornamental breeders have selected Flower color. Several ornamental new cultivars of plants with more attrac- plants, including carnation, rose and tive “stay green” phenotypes. Cytokinins gerbera, have been engineered for are plant hormones well known to delay D. Gonsalves is Director, Pacific Basin Ag- modified flower color. Research has fo- the loss of chlorophyll in leaves; using ricultural Research Center, USDA-ARS, cused on the manipulation of either an- biotechnology, targeted expression of Hilo, Hawaii. thocyanins (red and blue colors) or genes involved in cytokinin synthesis is Reference carotenoids (yellow and orange colors), now possible. When a gene promoting with the intent of creating a wider cytokinin biosynthesis is inserted into Gonsalves D. 1998. Control of papaya ringspot virus in papaya: A case study. Annu range of flower colors than occurs natu- plants in conjunction with a regulator Rev Phytopathol 36:415–37. rally, as well as to produce natural dyes (promoter) that turns the gene on only

http://CaliforniaAgriculture.ucop.edu • APRIL-JUNE 2004 93 Biotechnology expands pest-management options for horticulture

Leonard Gianessi

ruit and vegetable crops are under Withdrawn variet-

Scott Bauer/USDA-ARS Fconstant pressure from pests such ies. Two transgenic as weeds, viruses, fungi, bacteria, in- horticultural varieties sects and nematodes. If not controlled, were available for a many of these pests substantially short time in the lower yields. Successful agricultural United States but were production has depended on the use withdrawn due to of pesticides for 100 years, and, yet, marketing concerns. losses still occur due to certain pests Insect- and virus- that are poorly controlled. Some crops resistant New Leaf po- incur high costs for hiring laborers to tatoes were planted on hoe weeds because there are no effec- 4% of the nation’s tive herbicides. In addition, new pests acreage in 1999 and were credited with re- Plums resistant to the plum pox virus have been developed by routinely arrive for which effective scientists with the U.S. Department of Agriculture but are not controls have not yet been developed. ducing insecticide use. yet available to growers. Agricultural researchers continu- If the transgenic vari- ously seek out new methods to control eties had not been withdrawn due to and replace the use of 4.2 million pounds pests, including biological agents, new processor resistance they could have of fumigants. chemicals and plant resistance been planted extensively in the North- UC researchers have tested herbicide- through classical breeding. Biotechnol- west, reducing insecticide use by 1.4 tolerant lettuce that could reduce herbi- ogy also offers a solution in some situ- million pounds. cide use by 140,000 pounds a year. ations where traditional methods are In 1999, the U.S. Environmental Pro- Herbicide-tolerant strawberries could ineffective or costly. Nu- tection Agency (EPA) save Eastern growers several hundred merous researchers If plum pox virus granted Wisconsin dollars per acre in weed-control costs. around the world are in- sweet-corn growers Nematode-resistant pineapple is being vestigating biotechno- reaches California, emergency permission to developed at the University of Hawaii to logical solutions to pest the transgenic plum spray herbicide-tolerant replace 1.4 million pounds of fumigants. problems of horticultural varieties (see sidebar, Insect-resistant broccoli developed at crops. In 2002, the Na- could help prevent page 110). The transgenic Cornell University could improve yields tional Center for Food losses to the state’s varieties were not widely in years of heavy insect pressure. Virus- and Agricultural Policy multibillion dollar planted due to marketing resistant raspberries developed by U.S. released a study of cur- concerns and growers Department of Agriculture (USDA) re- rent and potential bio- stone-fruit industry. have not reapplied for searchers in the Northwest could help technological approaches the use despite continued combat bushy dwarf virus, which is to pest management in a wide array of production losses. present in 80% of Northwest plantings. crops (Gianessi et al. 2002). Crops currently being tested. Nu- And transgenic apples resistant to fire Current plantings. The study iden- merous fruits and vegetables have blight bacteria have been developed and tified three varieties of transgenic been transformed through genetic en- tested at Cornell University; the fruits and vegetables that are currently gineering and are being tested for transgenic varieties would replace the planted on small acreages in the their potential role in improving pest use of antibiotics, which are used to kill United States: virus-resistant squash is management. For example, University the bacteria on 25% of U.S. apple acreage. grown on 5,000 acres in the Southeast, of Florida researchers are testing virus- Emerging pests. Several research pro- to prevent late-season losses to mosaic resistant tomatoes as a substitute for grams are focused on biotechnological viruses; virus-resistant papaya is the extensive insecticide spraying cur- approaches to control emerging pest widely planted in Hawaii (2,000 rently utilized to control insects vector- problems. Plum pox virus was detected acres)(see sidebar, page 92); and ing geminiviruses. In California, in the United States for the first time in insect-resistant sweet corn is planted herbicide-tolerant processing tomatoes Pennsylvania, where efforts are under on a small number of acres and has re- have been tested and have the potential way to eradicate it by destroying in- duced use of insecticide sprays. to reduce grower costs by $30 million fected trees. USDA researchers have de-

94 CALIFORNIA AGRICULTURE,AGRICULTURE, VOLUMEVOLUME 5858,, NUMBERNUMBER 22 Monsanto

veloped a virus-resistant plum that is being tested in Europe. If plum pox virus reaches California, the trans- genic plum could help prevent losses to the state’s multibillion dollar stone- fruit industry. Pierce’s disease threatens Califor- nia , and insecticide spray- ing has occurred to control the Cotton has been genetically engineered to express a protein from a naturally occurring bacterium, Bacillus thuringiensis, which is toxic to insect pests such as bollworm and disease carrier, the glassy-winged budworm. This cotton is widely planted in California and elsewhere in the United States. sharpshooter. A researcher at the Uni- versity of Florida (a state where when the leaf starts to senesce, leaf life rooting of vegetative cuttings, have Pierce’s disease has been a problem is extended in transgenic plants ex- limited the commercial use of these for 80 years) has transformed grape posed to drought, and patho- technologies. The key to effective ma- tissue by inserting an antibacterial gen stress (Gan and Amasino 1995; nipulation of ethylene sensitivity will protein from another species into the Clark et al. 2004). be the use of promoters limiting grape genome. As a result, the trans- Ethylene sensitivity. As in fruit rip- transgene expression to the target tis- formed grape plant can destroy the ening, manipulation of ethylene syn- sue, leading ultimately to plants that bacteria without the need for insecti- thesis or sensitivity has applications in have longer lasting flowers with no cide sprays targeting the carrier. the ornamental plant industry. Ethyl- negative side effects. Tristeza virus has killed 45 million ene accelerates floral and foliar senes- citrus trees in Latin America and cence, and chemical methods have been Hurdles to commercialization threatens the Texas citrus industry. developed to mitigate its effects (Sisler The lag in commercialization of Researchers at Texas A&M University and Serek 2003). Ethylene sensitivity transgenic horticultural crops clearly is have developed and are field testing can be reduced in floriculture crops not due to a lack of useful genes or virus-resistant trees. through applications of the ethylene valuable applications. However, sev- Bacterial canker is present in antagonist silver thiosulfate (STS), but eral fundamental issues inherent to Florida citrus orchards, and the state unfavorable environmental aspects horticultural crops create significant is trying to eradicate the disease by such as metal contamination of ground- hurdles (see sidebar, page 84). destroying infected trees, including water restrict its commercial use. An- Biological diversity. Simply the di- millions of and backyard other compound, versity of crops utilized in horticul- citrus trees. A University of Florida 1-methylcyclopropene, also blocks the ture slows the adoption of new researcher has developed and is test- ethylene receptor protein and makes technologies. For any given crop, there ing a canker-resistant citrus tree. plant tissues insensitive to ethylene, may be several different species and delaying ripening or senescence. Al- dozens of cultivars that are currently though this compound is effective in marketed, and the turnover of new cul- many crops, its action decreases with tivars from year to year is tremendous. L. Gianessi is Director, Crop Protection time after treatment as the tissues syn- For example, as many as 60 distinct cul- Research Institute, CropLife Foundation, thesize new ethylene receptor proteins tivars of iceberg lettuce alone may be Washington, D.C. The foundation is an in- during postharvest transit. By express- grown throughout the year as produc- dependent, nonprofit research organization. ing a mutant form of the ethylene re- tion locations shift seasonally. Add to ceptor protein or by blocking this the dozens of additional varieties Reference expression of components of the for romaine, leafy, red and other spe- Gianessi LP, Silvers CS, Sankula S, Carpen- ethylene-signaling pathway, petunia cialty types, and it is evident that intro- ter JE. 2002. Plant Biotechnology: Current plants with longer lasting floral dis- ducing a new biotech trait for lettuce and Potential Impact for Improving Pest plays have been produced (Wilkinson requires developing not just one but Management in U.S. Agriculture; An Analy- sis of 40 Case Studies. National Center for et al. 1997). Unfortunately, negative many new varieties. In perennials such Food and Agricultural Policy, Washington, side effects, such as higher susceptibil- as trees and vines, on the other hand, DC. www.ncfap.org/40CaseStudies.htm. ity to fungal pathogens and decreased the choice of a variety is a long-term

http://CaliforniaAgriculture.ucop.edu • APRIL-JUNE 2004 95 Transgenic trap crops and rootstocks show potential

John Driver Javier Castillón Abhaya Dandekar

iotechnology may offer unique Bopportunities for pest control in perennial tree and vine crops (Dandekar et al. 2002). Trap crops — plants that an insect pest prefers to the commercial crop — have been tested in a number of agricultural settings, but in most cases have not achieved control levels high enough to completely replace chemical pesticides. Insects are attracted to the trap plant, but they multiply there and Left, apple roots engineered to silence bacterial genes are resistant to crown gall can spread to the adjacent crop. A vari- formation. Right, control (nontransgenic) roots infected with the same bacterial ant on this concept is to incorporate ex- strain show extensive gall proliferation. pression of the Bacillus thuringiensis (Bt) insecticidal protein into the trap plant. have also been transformed to express ease (Agrobacterium tumefaciens). Infec- When the insect feeds on the transgenic the Bt protein directly (Dandekar et al. tions by the bacterium result in the for- trap plant, it dies and the insect popula- 2002), an attractive feature of this mation of a gall, an unorganized mass tion is reduced, thereby protecting the scheme is that the walnuts themselves of plant cells that results from overpro- nearby commercial crop. are not transgenic and the method could duction of two plant hormones. The Dry Creek Laboratories of Hughson, be used to protect existing orchards by bacterium has the natural ability to Calif., demonstrated this concept with interplanting the Bt-expressing apple or transfer some of its genes into the host codling moth (Cydia pomonella), a major crabapple trees. Broader application of plant’s genome following infection. The pest of apples, pears, walnuts and other this approach could result in more effec- transferred genes code for three specific fruits. The female moth lays eggs on the tive trap crops for a number of annual enzymes. When the plant expresses leaves or fruit, which then hatch into and perennial crops. Unfortunately, Dry these genes, the enzymes synthesize the larvae that burrow into the fruits, mak- Creek Laboratories is unable to move two hormones that induce the plant to ing them unmarketable. forward at this time with commercializa- form the tumor, or gall, on which the sprays and pheromone disruption are tion of the Bt apple plants due to the costs bacteria live. Eventually, the galls can girdle the stems and When the insect feeds on the transgenic trap plant, it dies and the insect reduce the vigor of the population is reduced, thereby protecting the nearby commercial crop. tree or vine. A biotechnology tool called “gene si- generally used to control this pest. associated with the regulatory process re- lencing” has been used to generate re- However, the female moth prefers to quired for biotech crops (see page 106). sistance to crown gall. This method lay its eggs on apple trees. Under li- Another opportunity for biotechnol- involves transforming plants with cense from Monsanto, Dry Creek Labo- ogy in perennial crops that are normally DNA that, when expressed, produces ratories developed apple trees capable grafted is to engineer only the rootstock signals that block the expression of any of expressing a Bt protein that was toxic for desirable traits. Commercial tree cul- genes with the same sequence as the in- to the codling moth larvae, with the in- tivars grafted onto transgenic rootstocks serted DNA. Plants transformed with tention of using these plants as trap could benefit from increased rootstock these interfering versions of the three crops in and adjacent to walnut or- productivity or disease resistance while enzyme genes would be primed to chards. producing nontransgenic pollen and block the function of the corresponding A 90-acre field trial was established fruit. For example, such applications in bacterial genes in infected plants. This in 1997, and in the 4 subsequent years grapes could offer new solutions to would prevent the formation of the worm damage to the walnuts was al- Pierce’s disease or Phylloxera by grafting damaging galls without even needing most completely controlled without traditional varieties onto resistant to kill the bacterium itself. The feasibil- pesticide applications, equivalent to transgenic rootstocks. The feasibility of ity of this approach was demonstrated that in the plots sprayed three times per this approach was recently demon- in tomato and Arabidopsis plants season with pesticides. While walnuts strated for resistance to crown gall dis- (Escobar et al. 2001). Furthermore, both

96 CALIFORNIA AGRICULTURE,AGRICULTURE, VOLUMEVOLUME 5858,, NUMBERNUMBER 22 commitment, making growers cautious of products in the distribution channels in selecting novel varieties. may be required when marketing in lo- Market acceptance. Currently, the cations where they are not approved. largest impediment to adoption of at Herbicide applications to diverse horti- least some biotech horticultural prod- cultural crops have the potential to in- ucts is the lack of market acceptance. crease the Average Daily Intake (ADI) Biotech products having documented over the maximum permitted level for agronomic, economic and environmen- the pesticide active ingredient. (ADI is tal advantages have been removed the total residues of a pesticide that a from the market due to the concerns of consumer can be exposed to, consider- processors and distributors about po- ing all sources; the government sets tential consumer rejection. limits for each pesticide.) An agro- Intellectual property. Large corpo- chemical company will not approve the Crown gall formation was suppressed in walnut plants engineered to turn off rations focused on the major agronomic use of its herbicide-resistance trait in a specific bacterial genes. (A) The control crops own the majority of patents on small acreage crop if it endangers the shoot exhibits a large, undifferentiated the genes and enabling technologies registration of that herbicide for mil- tumor at 5 weeks after inoculation with a virulent A. tumefaciens strain, while (B) a (such as transformation protocols and lions of acres of field crops. shoot engineered for resistance exhibits promoters) required for genetically en- Regulatory requirements. Extensive no tumor. Source: Escobar et al. 2002. gineering plants. They are generally not safety testing is required for regulatory interested in the smaller horticultural approval (deregulation) of biotech walnut (see photo; Escobar et al. 2002) markets, and may not want to license crops beyond what is required for vari- and apple (see photo; J. Driver et al., their technologies, depending on the eties bred using traditional methods unpublished results) plants resistant impact it could have on their other ap- (see page 106). If the trait has already to crown gall have been produced. As proved crops (see page 120). been approved in other crops, the costs most crown gall infections occur in Post-commercialization. Post- are lower as prior data can be used to the rootstock, nontransgenic scions commercialization stewardship is also support an application. However, for grafted on resistant transgenic an increasingly important consider- novel traits likely to be of interest for rootstocks would be protected from ation to technology owners in deciding horticultural crops, the costs could be the disease. Rootstock engineering whether to license their intellectual millions of dollars. For example, by holds great promise for the improve- property. In Bt crops, for example, some estimates it will cost $20 million ment of tree and vine crops by pre- insect-resistance management pro- to achieve deregulation of Golden Rice serving the horticultural grams must be developed and moni- for humanitarian purposes in six devel- characteristics of existing varieties tored after commercialization. Identity oping countries (I. Potrykus, UC Davis used as scions while incorporating preservation programs and segregation seminar, Jan. 22, 2003). Since each beneficial traits into the rootstocks.

Syngenta

J. Driver is former President and J. Castillón is Director of Research, Dry Creek Laboratories, Hughson, Calif.; and A. Dandekar is Professor, Department of Pomology, UC Davis. References Dandekar AM, Fisk HJ, McGranahan GH, et al. 2002. Different genes for differ- ent folks in tree crops: What works and what does not. Hort Sci 37:281–6. Escobar MA, Civerolo EL, Summerfelt KR, Dandekar AM. 2001. RNAi-mediated oncogene silencing confers resistance to crown gall tumorigenesis. Proc Natl Acad Sci USA 98:13437–42. Escobar MA, Leslie CA, McGranahan GH, Dandekar AM. 2002. Silencing crown “Golden Rice” has been genetically engineered to produce beta-carotene, the precursor to gall disease in walnut (Juglans regia L.). vitamin A. However, for a variety of reasons it is not yet available to farmers in Plant Sci 163:591–7. developing countries, where vitamin A deficiencies are common.

http://CaliforniaAgriculture.ucop.edu • APRIL-JUNE 2004 97 transgenic event (each insertion of a References gene in a genome) must be separately Clark DG, Dervinis C, Barrett tested and approved, it is not feasible to JE, Klee HJ. 2004. Drought-in- transform multiple varieties with a duced leaf senescence and hor- ticultural performance of given trait to amortize the research and transgenic psag12-IPT petunias. technology investment across a given J Amer Soc Hort Sci 129:93–9. crop. Instead, a single insertion event is Clark DG, Loucas H, Shibuya K, et al. 2003. Biotechnology of approved for commercialization and floriculture crops — scientific then must be transferred via standard questions and real world an- backcrossing to other varieties. This is swers. In: Vasil IK (ed.). Plant highly inefficient and often makes it Biotechnology 2002 and Be- yond. Dordrecht, Netherlands: difficult to regain the unique proper- Kluwer Academic. p 337–42. ties of all the diverse varieties. Public- Cornell Cooperative Exten- private partnerships are one way to re- sion. 2003. Am I eating GE pota- toes? Genetically Engineered duce the costs of commercialization Organisms: Public Issues Educa- (see page 116). The IR-4 program could tion Project. www.geo- also assist with chemical residue testing pie.cornell.edu//crops/ and with other aspects of meeting the potato.html (accessed 3/16/04). Dandekar AM, Fisk HJ, regulatory requirements for release of McGranahan GH, et al. 2002. transgenic horticultural crops (see Different genes for different sidebar, page 110). folks in tree crops: What works The first transgenic crop to receive U.S. government and what does not. Hort Sci approval was a tomato engineered to soften more Compelling benefits key 37:281–6. slowly than conventional tomatoes, allowing it to be Dandekar AM, Gutterson N. picked later for improved flavor and taste. The commercial applications of bio- 2000. 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Nature Biotech 15:444–7. Vainstein A, Lewinsohn E, Pichersky E, ISAAA Briefs No 30. Ithaca, NY. D. Clark is Associate Professor, Environ- www.isaaa.org. Weiss D. 2001. Floral fragrance. New inroads mental Horticulture Department, and H. Lincoln JE, Richael C, Overduin B, et al. into an old commodity. Plant Physiol Klee is Eminent Scholar, Horticultural Sci- 2002. Expression of the antiapoptotic 127:1383–9. Ye XD, Al-Babili S, Kloti A, et al. 2000. ences Department, University of Florida, baculovirus p35 gene in tomato blocks pro- grammed cell death and provides broad- Engineering the provitamin A (beta-carotene) Gainesville; and A. Dandekar is Professor, spectrum resistance to disease. Proc Natl biosynthetic option into (carotenoid-free) Department of Pomology, UC Davis. Acad Sci USA 99:15217–21. rice endosperm. Science 287:303–5.

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