Article

Transgenic Papaya: A Case for Managing Risks of Papaya ringspot virus in Hawaii

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Abstract

In May 1992, Papaya ringspot virus (PRSV) was detected in the Puna district of Hawaii Island, the main papaya growing region of the state of Hawaii. By 1994 Hawaii's papaya industry was facing devastating damage from PRSV. Efforts to develop resistant transgenic papaya were started in the mid 1980s and a resistant line was identified in 1991. Two cultivars were developed from this line and were commercialized in 1998. Rainbow, an F1 hybrid from a cross of the transgenic SunUp, and nontransgenic Kapoho are now widely planted and have helped save the papaya industry. In addition, PRSV inocula in Puna were greatly reduced as abandoned infected fields were replanted with transgenic papaya. These conditions have allowed growers to continue the production of nontransgenic Kapoho in Puna to keep the Japanese market supplied, since transgenic papaya is not yet deregulated in that country. Accepted for publication 5 November 2003. Published 13 November 2003.

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... The widely cultivated 'Sunset' papaya was transformed with a gene derived from a Hawaiian strain to produce the transgenic papaya 'SunUp', which is completely resistant to PRSV in Hawaii 10 . 'SunUp' papaya was crossed with 'Kapoho', a non-engineered cultivar, to obtain the yellow-flesh 'Rainbow' papaya, which is also resistant to PRSV 23 ...
... In the US, PRSV-resistant papaya has been commercially grown in Hawaii since 1999 and it has prevented the collapse of the Hawaiian papaya industry due to the prevalence of PRSV in orchards of conventional varieties 23 . In 1992, when PRSV was first detected on Hawaii, the Puna district produced 95% of all Hawaiian papaya grown (~24,000 tons) but yields had fallen to~12,000 tons in 1998. ...
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Breeding has been used successfully for many years in the fruit industry, giving rise to most of today’s commercial fruit cultivars. More recently, new molecular breeding techniques have addressed some of the constraints of conventional breeding. However, the development and commercial introduction of such novel fruits has been slow and limited with only five genetically engineered fruits currently produced as commercial varieties—virus-resistant papaya and squash were commercialized 25 years ago, whereas insect-resistant eggplant, non-browning apple, and pink-fleshed pineapple have been approved for commercialization within the last 6 years and production continues to increase every year. Advances in molecular genetics, particularly the new wave of genome editing technologies, provide opportunities to develop new fruit cultivars more rapidly. Our review, emphasizes the socioeconomic impact of current commercial fruit cultivars developed by genetic engineering and the potential impact of genome editing on the development of improved cultivars at an accelerated rate.
... 16 . Preliminary field studies in São Paulo (SP) State, Brazil, showed that the use of suitable host plants for D. citri as barriers reduced the number of marked psyllids recaptured on yellow stick traps deployed on citrus trees 7 . ...
... Finally, in order to avoid the use of insecticides, a genetically modified trap crop, able to interfere with D. citri survival, could be used in the citrus edges to attract and kill D. citri. An analogous approach has been used in Hawaii, where borders of transgenic papaya plants resistant to Papaya ringspot virus reduced the spread of aphid-vectors and then viral incidence on non-transgenic papaya crops 16 . Supplementary Fig. 1c,d) with spacing of 6.5 × 2.8 m. ...
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Novel, suitable and sustainable alternative control tactics that have the potential to reduce migration of Diaphorina citri into commercial citrus orchards are essential to improve management of huanglongbing (HLB). In this study, the effect of orange jasmine (Murraya paniculata) as a border trap crop on psyllid settlement and dispersal was assessed in citrus orchards. Furthermore, volatile emission profiles and relative attractiveness of both orange jasmine and sweet orange (Citrus × aurantium L., syn. Citrus sinensis (L.) Osbeck) nursery flushes to D. citri were investigated. In newly established citrus orchards, the trap crop reduced the capture of psyllids in yellow sticky traps and the number of psyllids that settled on citrus trees compared to fallow mowed grass fields by 40% and 83%, respectively. Psyllids were attracted and killed by thiamethoxam-treated orange jasmine suggesting that the trap crop could act as a ‘sink’ for D. citri. Additionally, the presence of the trap crop reduced HLB incidence by 43%. Olfactometer experiments showed that orange jasmine plays an attractive role on psyllid behavior and that this attractiveness may be associated with differences in the volatile profiles emitted by orange jasmine in comparison with sweet orange. Results indicated that insecticide-treated M. paniculata may act as a trap crop to attract and kill D. citri before they settled on the edges of citrus orchards, which significantly contributes to the reduction of HLB primary spread.
... The Papaya ringspot virus (PRSV) resistant transgenic papaya was commercially released to growers in 1998 and virtually saved Hawaii's papaya industry from destruction by PRSV (Gonsalves, 1998). Transgenic papaya accounts for 85% of Hawaii's papaya production, with the transgenic 'Rainbow' papaya now the dominant cultivar (Gonsalves and Ferreira, 2003). ...
... The presence of 'Rainbow' papaya in both Kahuwai and Puna in 1999 reduced the incidence of PRSV compared to Puna in 1992-1998. These observations suggested that transgenic papaya reduced PRSV disease pressure and served as a buffer to allow the cultivation of non-transgenic papaya (Gonsalves and Ferreira, 2003). ...
... Genetic modifications has been known in agriculture for rescuing many food crops from invisible beasts that could have led to total extinction. A popular success story in this regard has been the transgenic Hawaiian Rainbow Papaya, which was developed to rescue this crop when it was devastated by ringspot virus in the 1990s (Gonsalves, 1998;Gonsalves & Ferreira, 2003). Production of papaya in Puna district of Hawaii, which was contributing 95% of the total, dropped from 27,762.5 tons in 1994 (after 2 years of the occurrence of the papaya ringspot virus, PRSV) to 12,805 tons in 1998, which was a 53.88% loss in just 4 years, Figure 2, extracted from Gonsalves and Ferreira (2003). ...
... A popular success story in this regard has been the transgenic Hawaiian Rainbow Papaya, which was developed to rescue this crop when it was devastated by ringspot virus in the 1990s (Gonsalves, 1998;Gonsalves & Ferreira, 2003). Production of papaya in Puna district of Hawaii, which was contributing 95% of the total, dropped from 27,762.5 tons in 1994 (after 2 years of the occurrence of the papaya ringspot virus, PRSV) to 12,805 tons in 1998, which was a 53.88% loss in just 4 years, Figure 2, extracted from Gonsalves and Ferreira (2003). The release of the transgenic rainbow papaya helped to revive the production to 20,000 tons, a 35.98%, increase in just 2 years. ...
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Global population is increasing at an alarming rate, posing a threat on the supplies of basic needs and services. However, population increase does not seem to be a common agendum of the global scientists and political leaders. People in the developed countries are more concerned about new technologies and their products. Pseudo‐threats related to the uncertainties of genetic engineering of crops and their outputs present on consumers are more audible and controversial than the real difficulties the world is experiencing at the moment and in the future. This review presents brief summaries of the real reasons to worry about and the uncertainties about genetically modified organisms. This article also presents the real uncertainties shared by consumers and scientists with respect to the past, present, and future of genetically engineered organisms. Developments in the field of precision genetics in the recent years and the implications on regulatory, breeding, and socio‐cultural dimensions of the global settings are included. This review article presents competing and contradicting human interests. On one hand, we are opposing great agricultural technologies such as genetically modified organisms (GMO) and the genetic engineering techniques. On the other hand, we are challenged with the need for feeding humanity into the future, where the global population and food production are not keeping pace of one another.
... A pervasive misconception is that the products of ag-biotech are being developed solely in the private sector. To cite a few examples: such products as nutritionally enhanced rice (Ye et al. 2000), virus resistant papaya (Ferreira et al. 1997), and vaccine carrying bananas (Zhu et al. 1999) and potatoes (Arakawa et al. 1997 ) are under development in the PUBLIC sector. These innovations are specifically targeted at reducing the ills of poor populations and small farmers. ...
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The continuous discovery of best possible combiners and their outcome has replaced the superior varieties by hybrids in watermelon. Nowadays several types of watermelons are being marketed-some are having red flesh, some with yellow, some with white flesh. Even with the differences in its shape and size, some are round, some are oval, some are square. Some are with seeds some are seedless. This all happened because of the efforts of crazy mind and fast changing market needs. The introduction of new watermelon genes and marker genes have equipped us to deal with pest and pathogens. Beyond that, using the genes of a rootstock of a related cucurbit, we can combat soil pests as well as adverse environmental conditions. Use of male sterility can reduce the cost of hybrid seed. Seed production requires good cultural practices and timely harvest. Triploid hybrid seed production varies considerably.
... Such a process of silencing does not generate a biochemical pathway or produce a novel protein. Integrating the need of the hour with the potential of the strategy of RNA silencing proved profitable for the papaya industry in Hawaii [88,89]. Such applications are observed in cases where severe strains of the virus can be reduced in case of an infection by a mild strain. ...
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Antibiotics have been used globally to manage the bacterial plant diseases irrespective of the expense involved. Although plant pathogenesis by bacteria is far lower than fungal counterparts, disrupted monitoring and surveillance for drug resistance with respect to human health raise serious concerns. The resistance derived by the plant as the host by the antibiotics used for many generations has now posed as a problem in phyto-systems. Although we currently lack the molecular understanding of the pathogens rendering antibiotic resistance to plants, robust resistance management strategies are critical to ensure management of critically important diseases that specifically target crops of high value and/or global agrarian importance. This chapter discusses evolution of plant-pathogenic bacteria, application of antibiotics and its repercussions on the microbiome of plant agricultural systems, and sustainable crop disease management by genetic engineering.
... R0 clones of a transgenic line "55-1," were highly resistant to PRSV HA in greenhouse experiments (Fitch et. al., 1992 ). Field experiments also showed that R0 and R1 plants were highly resistant under severe disease pressure in Hawaii (Ferreira et al., 1997; Lius et al., 1997). Two commercial cultivars (SunUp and UH Rainbow) were 62 CAI ET AL. developed from line 55-1 (Manshardt, 1998 ). ...
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A reproducible and effective biolistic method for transforming papaya (Carica papaya L.) was developed with a transformation-regeneration system that targeted a thin layer of embryogenic tissue. The key factors in this protocol included: 1) spreading of young somatic embryo tissue that arose directly from excised immature zygotic embryos, followed by another spreading of the actively growing embryogenic tissue 3 d before biolistic transformation; 2) removal of kanamycin selection from all subsequent steps after kanamycin-resistant clusters were first isolated from induction media containing kanamycin; 3) transfer of embryos with finger-like extensions to maturation medium; and 4) transferring explants from germination to the root development medium only after the explants had elongating root initials, had at least two green true leaves, and were about 0.5 to 1.0 cm tall. A total of 83 transgenic papaya lines expressing the nontranslatable coat protein gene of papaya ringspot virus (PRSV) were obtained from somatic embryo clusters that originated from 63 immature zygotic embryos. The transformation efficiency was very high: 100% of the bombarded plates produced transgenic plants. This also represents an average of 55 transgenic lines per gram fresh weight, or 1.3 transgenic lines per embryo cluster that was spread. We validated this procedure in our laboratory by visiting researchers who did four independent projects to transform seven papaya cultivars with coat protein gene constructs of PRSV strains from four different countries. The method is described in detail and should be useful for the routine transformation and regeneration of papaya.
... Successful examples of commercial release of GM disease resistant crops in general, are rare, currently limited to the example of ring spot virus resistant papaya genetically modified with the coat proteins from mild virus strains of the pathogen inserted. 15 The lack of GM disease resistant crops could be attributed to lower level of disease resistance conferred (compared to other traits such as herbicide resistance), which is below economic threshold for producers or a high level of resistance but only to a very specific pathogen. 16 Several approaches have been used to engineer plants for fungal resistance (for reviews, see ref [16][17][18] such as introduction of resistancegenes (R-genes)(utilizing plants basal defense responses), 19 detoxification of virulence factors, 16 expression of antimicrobial secondary metabolites like phytoalexins and pathogenesis related (PR) proteins (inhibiting the pathogen's capacity to degrade polysaccharides within cell wall or RNA), 16,20 and modification of plant signaling pathways including transcription factors genetically. ...
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... Genetic engineering for virus resistance in papaya has been found effective whereby transgenic plants expressing viral genome sequence resist attack by corresponding viruses. Transgenic papaya resistant to PRSV has been developed and commercialized in 1998 in Hawaii, USA by Dennis Gonsalves and his team (Gonsalves et al., 2003). Later transgenic papaya was deregulated in countries like Japan and Canada (Gonsalves et al., 2010). ...
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Papaya is the first fruit crop which was not only successfully genetically engineered but also deregulated and commercialized. Pathogenic derived resistance was utilized for harnessing PRSV resistance. Coat protein gene from PRSV was invariably used to confer resistance against papaya ring spot virus. Microprojectile transformation has been the most preferred pathway. However, several reports are also available involving Agrobacterium pathway. Majority of workers found somatic embryos as the explant of choice for genetic manipulation in papaya compared to other explants. This paper highlights the global status of development of genetically engineered papaya for viral resistance.
... The papaya industry in Hawaii was saved by transforming papaya with the coat protein gene of papaya ringspot virus. This gene elicits RNAi against this highly destructive virus [21,80]. Such a GE application mimics cross-protection, a phenomenon in which symptoms due to severe strains of a virus can be reduced by prior infection by a mild strain. ...
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Genetic engineering (GE) offers an expanding array of strategies for enhancing disease resistance of crop plants in sustainable ways, including the potential for reduced pesticide usage. Certain GE applications involve transgenesis, in some cases creating a metabolic pathway novel to the GE crop. In other cases, only cisgenessis is employed. In yet other cases, engineered genetic changes can be so minimal as to be indistinguishable from natural mutations. Thus, GE crops vary substantially and should be evaluated for risks, benefits, and social considerations on a case-by-case basis. Deployment of GE traits should be with an eye towards long-term sustainability; several options are discussed. Selected risks and concerns of GE are also considered, along with genome editing, a technology that greatly expands the capacity of molecular biologists to make more precise and targeted genetic edits. While GE is merely a suite of tools to supplement other breeding techniques, if wisely used, certain GE tools and applications can contribute to sustainability goals.
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... The most common approach to preventing damage caused by poor trap crop retention is removing the pest while it is on the trap crop. In fact, of the 14 successful trap cropping studies we were able to review, 11 used this strategy, seven by pesticide applications to the trap crop (Hokkanen 1989;Srinivasan & Krishna Moorthy 1991;Pair 1997;Dogramaci et al. 2004;Leskey, Pinero & Prokopy 2008;Cavanagh et al. 2009;Lu et al. 2009), one by a trap plant that increased pest parasitism by natural enemies (Khan et al. 1997), one by cutting the trap plants (Godfrey & Leigh 1994), one by using disease resistant plants that allowed the insect vector to rid itself of the disease while feeding on the trap crop, preventing dispersal of the disease back into the cash crop (Gonsalves & Ferreira 2003) and one by vacuuming insects off of the trap crop (Swezey, Nieto & Bryer 2007). ...
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1. Trap cropping, the use of alternative host plants to reduce pest damage to a focal cash crop or other managed plant population, can be a sustainable strategy for pest control, but in practice it has often failed to reach management goals. Of the few successful trap cropping examples at a commercial scale, nearly all have included supplemental management strategies that reduce pest dispersal off the trap crop. In contrast, the trap cropping literature has focused extensively on trap plant attractiveness.
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Introduction Papaya and Papaya Ringspot Virus Development of Transgenic Papaya for Hawaii Development of Transgenic Papaya for other Regions Breeding through Intergeneric Hybridizations Development of PRSV-Tolerant Papaya Future Aspects for Developing PRSV-Resistant Papaya Summary Comments Literature Cited
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Papaya (Carica papaya L.) is currently the fastest growing tropical fruit crop in the world. It is a tree-like, herbaceous, short-lived perennial plant 3–8 m in height native to tropical America. It is cultivated on farms as well as backyard gardens worldwide in tropical and subtropical regions within 32 degrees latitude north and south of the equator. Fruits can be harvested as early as 9 months after sowing and are anywhere from 255 g to 6 kg, depending on the variety. Papaya is grown largely for its nutritious fresh fruit which contains relatively high amounts of vitamins A, C, and E as well as calcium, potassium, and iron, but also for by-products such as papain, a proteinase found in the latex of unripe fruit used to tenderize meat and in pharmaceutical industries. Transgenic varieties “Rainbow” and “SunUp” were developed in Hawaii to be resistant to papaya ringspot virus (PRSV), the most devastating disease threatening papaya production worldwide. Development and commercialization of the transgenic papaya in Hawaii serves as a model for successful biotechnology application to specialty crop improvement. Advances in transformation and development of transgenic papaya and the prospects of commercialization in various countries are also discussed.
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Several types of trap crops have been recommended for managing the diamondback moth, Plutella xylostella, including collards (Brassica oleracea var. acephala) and Indian mustard (Brassica juncea L.). However, results have been variable perhaps because populations of P. xylostella develop on these trap crops and spill over to the cash crop. To overcome this problem, we sought to develop “dead-end” trap crops that were more attractive for oviposition than the cash crop but on which P. xylostella larvae cannot survive. We have produced Bacillus thuringiensis (Bt)-transgenic collard and Indian mustard lines with a cry1C gene that have the potential to be used as a “dead-end” trap crop for P. xylostella. Greenhouse and small cage studies confirmed the control of P. xylostella larvae on the Bt crops. Furthermore, Indian mustard was significantly preferred over cabbage and collards for oviposition, regardless of whether the Indian mustard was Bt or non-Bt. The use of Bt Indian mustard as a trap crop significantly reduced the number of larvae that appeared on a cabbage cash crop, compared with using a non-Bt Indian mustard trap crop. However, this reduction also occurred when using Bt collards as a trap crop, despite collards being less preferred for oviposition. In fact, despite the overall increase in oviposition caused by the presence of Indian mustard compared with collards, the use of either Bt Indian mustard or Bt collards provided the same level of protection to the cash crop. Both plants also resulted in significant suppression of a P. xylostella population over 3 generations in the greenhouse test and 2 generations in the small cage experiment, suggesting that in places where immigration may be limited some long-term population suppression may occur. We suggest that Bt trap crops may be useful tools in situations where the cash crop may not be suitable or desirable for genetic engineering.
Article
In 1992, papaya ringspot virus (PRSV) was discovered in the Puna district of Hawaii island where 95% of the state of Hawaii’s papaya was being grown. By 1998 production in Puna had decreased 50% from 1992 levels. A PRSV-resistant transgenic papaya ‘Rainbow’ containing the coat protein gene of PRSV was released commercially in Hawaii in 1998, and saved the papaya industry from further devastation. In the ensuing years since the release of the transgenic papaya, a number of farmers grew hermaphrodite nontransgenic ‘Kapoho’ papaya in close proximity to plantings of hermaphrodite transgenic ‘Rainbow’ papaya. These plantings provided a unique opportunity to assay for transgenic-pollen drift under commercial conditions. Between 2004 and 2010, assays for the GUS (beta-glucuronidase) transgene in embryos were done to study transgenic-pollen drift in commercial ‘Kapoho’ plantings and in replicated field plots. Very low pollen drift (0.8%) was detected in fruit of ‘Kapoho’ trees in the border row of one plantation when 90 embryos were assayed per fruit, while no pollen drift was detected in four other commercial plantings in which eight embryos were tested per fruit. Pollen drift averaged 1.3% of tested embryos in field plots where individual hermaphrodite ‘Kapoho’ trees were adjacent to two or four ‘Rainbow’ trees. In contrast, 67.4% of tested embryos were GUS positive in similarly located female ‘Kapoho’ trees. The very low transgene flow to close-by ‘Kapoho’ plantings is likely due to the fact that hermaphrodite trees are used commercially in Hawaii and that these trees are largely self-pollinated before the stigma is exposed to external pollen.
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In May 1998, papaya ring spot virus (PRSV)-resistant transgenic “Rainbow” and “SunUp” papaya were released to growers and helped save the papaya industry in Hawaii. This review provides a personal account of the Hawaii transgenic papaya story from 1978 to 2012. It traces the general technical development of the papaya, but more importantly, it provides a personal account of the events in the story. These events include the rationale to proactively develop control methods in the event the PRSV would enter Puna, where 95 % of Hawaii’s papaya were being grown in 1992; the formation and motivation of the research team; the coinciding of the transgenic papaya development with the invasion of Puna by PRSV; the deregulation and commercialization of the transgenic papaya in the US; and the long road to its deregulation and commercialization in Japan. And it describes activities in the “red zone” of translational biotechnology.
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Trap crops are plants grown before or with the main crop in a smaller area (the trap crop). They are the more preferred hosts when grown with the main crop. Trap crops can increase the efficiency of control by concentrating the pests in one location and by applying a chemical treatment without spraying the main crop, or by destroying the trap crops and associated pests through tillage or burning. It is also possible to release biological control agents into the trap crops, using it as a nursery for beneficial organisms that will then spread into the main crop. The trap crops are effectively employed for the control of several herbivores, nematodes, and weeds in several agroecosystems. Trap cropping is economical to adopt, saves on input use, and is effective against pests, resulting in increased productivity.
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Arising from a relatively isolated center of origin, papaya has spread throughout all tropical and subtropical countries through human intervention. This global dispersal has coincided with continuous improvement of the cultivated plants through breeding programs often designed to improve the agronomic characters and to address biotic and abiotic stresses that affect papaya production. Papaya production is threatened by a myriad of problems including devastating pests and diseases as well as the inability for both farmers and researchers alike to differentiate among the three sex types, male, female and hermaphrodite at the seedling stage, among others. Many attempts have been made by researchers over the years to resolve the problems through conventional and biotechnological techniques. Conventional plant breeding has given rise to varieties that are resistant to diseases as well as high yielders of quality fruits. However, conventional techniques require 12–14 years to develop new papaya varieties. Besides, devastating viral diseases like papaya ringspot virus (PRSV) have proved almost impossible to control through conventional means. The innovative technologies and growing understanding to manipulate the papaya phenotype at the molecular level provide new opportunities for the improvement of papaya. Through gene transfer technology, it is possible to develop transgenic papaya with pest and disease resistance as well as improved nutritional quality. This chapter provides insight into conventional breeding of papaya, the role of tissue and protoplast culture as well as molecular techniques in papaya improvement such as genetic transformation, mutation breeding and marker assisted selection and breeding. In addition, the potential of parthenocarpy as well as polyploidy and somaclonal variation in papaya breeding are discussed.
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Die Züchtung von Pflanzen und Tieren hat eine jahrtausendealte Tradition. Sie begann mit einer einfachen Selektionszüchtung. Hinzu kam die gezielte Kreuzung von Sorten und Rassen. Ab den 1930er Jahren wurden Methoden zur zufälligen Erzeugung genetischer Veränderungen (Mutationen) mit Chemikalien und Strahlung entwickelt. So kam 1934 die erste durch radioaktive Strahlung erzeugte Tabak-Sorte zum Anbau. Egal wie drastisch die Veränderungen der genetischen Information bei dieser Mutationszüchtung sind: Sie ist von Gentechnikgesetz explizit ausgenommen. Mehr und mehr verlagerte sich die Züchtung in das Labor. Bei der Protoplastenfusion werden Zellen fusioniert und bei der Präzisionszüchtung Erbinformation analysiert. Mit dem Einzug der Gentechnologie in den 1970er Jahren wurde die Züchtung präziser. Im Jahr 1992 kam die erste gentechnisch erzeugte Tabak-Sorte auf den Markt, 1994 folgte mit der FlavrSavr-Tomate die erste zum Verzehr zugelassen Pflanze. Während gentechnisch veränderte Bakterien und Pilze als Arbeitspferde der Pharma- und Lebensmittelindustrie ausserhalb des Blickwickels der Öffentlichkeit stehen, unterliegt die Tierzucht einer strengen ethischen Kontrolle. Erst seit den 2000er Jahren gibt es Zulassungen. Und so tief die Gräben zwischen ökologischer und gentechnischer Landwirtschaft sind, so spannend sind die Möglichkeiten, wenn Brücken geschlagen werden. Ähnlich stellt sich die Lage bei der Risikobewertung dar, wo das Wissenschafts- und das Vorsorgeprinzip um die Erklärungshoheit ringen.
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Many Gram-negative plant and animal pathogens share a common virulence strategy that relies on the specialized type III secretion system. This apparatus is used to secrete virulence factors, called effectors, into the extracellular host environment and directly into the cytoplasm of host cells. Effectors interfere with host signaling and host metabolism to create an optimal environment for pathogen replication. The identification of effectors in plant pathogens was limited for many years to those effectors that elicit strong plant defenses on some hosts. The members of this subset, called avirulence proteins, can be readily identified because they dominantly confer strong defense-inducing properties to a heterologous virulent strain. This chapter describes two methods to identify type III-secreted effectors in plant pathogens independently of their phenotype. The first method consists of an in vivo molecular genetic screen that uses the activity of an avirulence protein to identify effectors without avirulence activity. It should be possible to apply this method to most Gram-negative plant pathogens. The second method consists of a bioinformatic approach applicable to those pathogens for which at least a draft genome sequence is available.
Article
Papaya ringspot virus (PRV) is a serious disease of papaya (Carica papaya L.) that has only been partially controlled by conventional methods. An alternative control method is coat protein-mediated protection (CPMP) through the transfer and expression of the PRV coat protein (cp) gene in papaya. We report an efficient gene transfer system utilizing microprojectile-mediated transformation of 2,4-D-treated immature zygotic embryos with a plasmid construction that contains the neomycin phosphotransferase II (NPTII) and -glucuronidase (GUS) genes flanking a PRV cp gene expression cassette. Putative transgenic RO papaya plants, regenerated on kanamycin-containing medium, were assayed for GUS and PRV coat protein expression, for the presence of NPTII and PRV cp genes [with the polymerase chain reaction (PCR) and genomic blot hybridization analysis], and for PRV cp gene transcripts by Northern analysis. Four RO transgenic plant lines that contained the PRV cp gene showed varying degrees of resistance to PRV, and one line appeared to be completely resistant. These results represent the first demonstration that CPMP can be extended to a tree species such as papaya.
Article
Transgenic Carica papaya plants (cv. Sunset, R0 clone 55-1) carrying the coat protein gene of papaya ringspot virus (strain HA 5-1) remained symptomless and ELISA-negative for 24 months after inoculation with Hawaiian strains of papaya ringspot virus under field conditions. Non-transgenic and transgenic control plants lacking the coat protein gene developed disease symptoms within one month after manual inoculation or within four months when natural aphid populations were the inoculum vectors. Mean trunk diameter was significantly greater in cloned 55-1 plants compared with virus-infected controls (14.7 cm versus 9.3 cm after 18 months). Fruit brix, plant morphology, and fertility of 55-1 plants were all normal, and no pleiotropic effects of the coat protein gene were observed. These results indicate that pathogen-derived resistance can provide effective protection against a viral disease over a significant portion of the crop cycle of a perennial species.
Article
Since 1992, Papaya ringspot virus (PRSV) destroyed nearly all of the papaya hectarage in the Puna district of Hawaii, where 95% of Hawaii's papayas are grown. Two field trials to evaluate transgenic resistance (TR) were established in Puna in October 1995. One trial included the following: SunUp, a newly named homozygous transformant of Sunset; Rainbow, a hybrid of SunUp, the nontransgenic Kapoho cultivar widely grown in Puna, and 63-1, another segregating transgenic line of Sunset. The second trial was a 0.4-ha block of Rainbow, simulating a near-commercial planting. Both trials were installed within a matrix of Sunrise, a PRSV-susceptible sibling line of Sunset. The matrix served to contain and trace pollen flow from TR plants, and as a secondary inoculum source. Virus infection was first observed 3.5 months after planting. At a year, 100% of the non-TR control and 91% of the matrix plants were infected, while PRSV infection was not observed on any of the TR plants. Fruit production data of SunUp and Rainbow show that yields were at least three times higher than the industry average, while maintaining percent soluble solids above the minimum of 11% required for commercial fruit. These data suggest that transgenic SunUp and Rainbow, homozygous and hemizygous for the coat protein transgene, respectively, offer a good solution to the PRSV problem in Hawaii.
Article
A chimeric gene containing a cloned cDNA of the coat protein (CP) gene of tobacco mosaic virus (TMV) was introduced into tobacco cells on a Ti plasmid of Agrobacterium tumefaciens from which tumor inducing genes had been removed. Plants regenerated from transformed cells expressed TMV mRNA and CP as a nuclear trait. Seedlings from self-fertilized transgenic plants were inoculated with TMV and observed for development of disease symptoms. The seedlings that expressed the CP gene were delayed in symptom development and 10 to 60 percent of the transgenic plants failed to develop symptoms for the duration of the experiments. Increasing the concentration of TMV in the inoculum shortened the delay in appearance of symptoms. The results of these experiments indicate that plants can be genetically transformed for resistance to virus disease development.
Article
The papaya crop is severely affected by papaya ringspot virus (PSRV) worldwide. This review focuses on efforts to control the destructiveness of the disease caused by PSRV in Hawaii, starting from the use of cross protection to parasite-derived resistance with transgenic papaya expressing the PSRV coat protein gene. A chronology of the research effort is given and related to the development of technologies and the pressing need to control PSRV in Hawaii. The development of commercial virus-resistant transgenic papaya provides a tangible approach to control PSRV in Hawaii. Moreover, the development of transgenic papaya by other laboratories and employment of a mechanism of effective technology transfer to different countries hold promise for control of PSRV worldwide.
UH Rainbow' papaya. University of Hawaii College of Tropical Agriculture and Human Resources. New Plants for Hawaii-1
  • R M Manshardt
Manshardt, R. M. 1998. 'UH Rainbow' papaya. University of Hawaii College of Tropical Agriculture and Human Resources. New Plants for Hawaii-1:2pp.