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Current Status of the Transgenic Approach for Control of Papaya Ringspot Virus (PRSV), and the fragile and perishable fruit traits are unfavorable for large-scale export. As a result, papaya lags far behind banana and pineapple in world markets. Table 1. World Papaya Production in 2004 Country Hectares Metric tons (×1,000) (×1,000) Brazil 36.0 1,600 Mexico 26.3 956 Nigeria 91.0 755 India 80.0 700 Indonesia 10.0 650 Ethiopia 11.0 230 Congo 12.5 211 Venezuela 11.0 170 Peru 13.0 170 China 6.2 165 Cuba 7.0 125 Thailand 10.5 125 Colombia 4.0 102 Philippines 6.6 79 Malaysia 6.5 65 Other 34.2 401 Total 365.8 6,504 Source: Food and Agriculture Organization (FAO), Statistical Division, 2004 (http:// faostat.fao.org/faostat/) THE WORLDWIDE THREAT OF PRSV INFECTION Production of papaya has been limited in many areas of the world due to the disease caused by Papaya ringspot virus (PRSV) (Purcifull et al., 1984). Papaya ringspot disease is the major obstacle to large-scale commercial production of papaya (Yeh and Gonsalves, 1984). PRSV was first reported in Hawaii in the 1940s (Jensen, 1949a) and then became prevalent in Florida (Conover, 1964), Caribbean countries (Adsuar, 1946; Jensen, 1949b), South America (Herold and Weibel, 1962), Africa (Lana 1980), India (Capoor and Varma, 1948; Singh, 1969), the Far East (Wang et al., 1978), and Australia (Thomas and Dodman, 1993). To date, most of the major papaya plantation areas of the world suffer from the devastation of this noxious virus. Characteristics of PRSV PRSV, a member of the genus Potyvirus (Purcifull et al., 1984; Murphy et al., 1995), is transmitted nonpersistently by aphids and is also sap-transmissible in nature. The PRSV genome contains a single-stranded positive-sense RNA of about 40 S (De La Rosa and Lastra, 1983; Yeh and Gonsalves, 1985). Strains of PRSV from Hawaii (Yeh et al., 1992) and Taiwan (Wang and Yeh, 1997) have been completely sequenced; both contain 10,326 nucleotides in length. The viral RNA encodes a polyprotein that is proteolytically cleaved to generate 8–9 final proteins, including the coat protein for encapsidation of viral genome (Yeh et al., 1992). The virus has a single type of coat protein (CP) of 36 kDa (Purcifull and Hiebert, 1979; Gonsalves and Ishii, 1980). It induces cylindrical inclusion (CI) (Purcifull and Edwardson, 1967) and amorphous inclusion (AI) (Martelli and Russo, 1976) in the cytoplasm of host cells. The former consists of a protein of 70 kDa (cylindrical inclusion protein CIP; Yeh and Gonsalves, 1984), and the latter – 59 –
Business Potential for Agricultural Biotechnology Products consists of a protein 51 kDa (amorphous inclusion protein, AIP; De Mejia et al., 1985a, 1985b). On papaya plants, PRSV causes severe mosaic and distortion on leaves, ringspots on fruits, and water-soaked oily streaks on upper stems and petioles. It stunts the plant and drastically reduces the size and the quality of the fruit. No Effective Control Measures Although tolerant selections of papaya have been described (Cook and Zettler, 1970; Conover, 1976; Conover et al., 1986), resistance to PRSV does not exist in the species of C. papaya, which makes conventional breeding difficult (Cook and Zettler, 1970; Wang et al., 1978). Tolerance to PRSV has been found in some papaya lines and introduced into the commercial varieties, but their horticultural properties are still not commercially desirable (Mekako and Nakasone, 1975; Conover and Litz, 1978). Other control methods for PRSV include agricultural practices such as rouging, quarantine, intercropping with corn as a barrier crop, and protecting transplanted seedlings with plastic bags. All provide only temporary or partial solutions to the problem (Wang et al., 1987; Yeh and Gonsalves, 1994). PRSV HA 5-1, a cross-protecting mild mutant strain of PRSV that was selected following nitrous acid treatment of a severe strain (HA) from Hawaii (Yeh and Gonsalves, 1984), was tested extensively in the field and has been used commercially in Taiwan and Hawaii since 1985 to permit an economic return from papaya production (Wang et al., 1987; Yeh et al., 1988; Yeh and Gonsalves, 1994). However, the approach of deliberate infection of a crop with a mild virus strain to prevent economic damage by more virulent strains has several drawbacks, including the requirement for a large-scale inoculation program. There may also be reduction in crop yield and losses of cross-protected plants due to superinfection by virulent strains (Stubbs, 1964; Gonsalves and Garnsey, 1989; Yeh and Gonsalves, 1994). CONTROL OF PRSV BY THE TRANSGENIC APPROACH The concept of “pathogen-derived resistance” (Sanford and Johnston, 1985) proposes that transforming plants with a pathogen’s gene would generate resistance to the infection of the corresponding pathogen. By this concept, Powell-Abel et al. (1986) first demonstrated that transgenic tobacco plants expressing the coat protein (CP) gene of Tobacco mosaic virus (TMV) conferred resistance to TMV infection. The CP gene-mediated transgenic resistance has been proven effective for protecting tobacco, tomato, potato, and other crops from infection by many different viruses (Beachy, 1990; Lomonossoff, 1995; Goldbach et al., 2003). Thus, the transgenic approach has become the most effective method of protecting crops from virus infection. In order to solve the problems caused by PRSV, the Gonsalves group at Cornell University and Hawaii started a research project in the late 1980s to develop transgenic papaya. Ling et al. (1991) first demonstrated that the expression of the PRSV HA 5-1 CP gene in tobacco afforded a broad spectrum of protection against different potyviruses. However, effective gene transfer systems require reliable and efficient procedures for plant regeneration from cells. Fitch and Manshardt (1990) reported that somatic embryogenesis from immature zygotic embryos of papaya can be integrated into a useful gene transfer technology. In the same year, Fitch et al. (1990) successfully incorporated the CP gene of HA 5-1 into papaya via microprojectile bombardment and obtained plants resistant to infection by the severe Hawaii HA strain. Among their transgenic papaya lines, line 55-1 was virtually immune to infection by HA. A Successful Application of Transgenic Papaya in Hawaii The plants of transgenic papaya line 55-1 are highly resistant to Hawaiian PRSV isolates under greenhouse and field conditions (Fitch et al., 1992; Lius et al., 1997). The resistance is triggered by the post transcriptional gene silencing (PTGS), an RNA-mediated specific degradation process of the innate nature of plants against pathogens (Baulcombe, 1996; Baulcombe, – 60 –
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From: Business Potential for Agricu
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Report of the APO Multi-country Stu
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Part IV Appendices 5. Agricultural
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Part I Summary of Findings
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Business Potential for Agricultural
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Page 14 and 15: Business Potential for Agricultural
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MANAGEMENT POLITICAL TOOL NATURAL R
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Agricultural Biotechnology Developm
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- 117 - Agricultural Biotechnology
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PROSPECTS - 119 - Agricultural Biot
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Status of Agricultural Biotechnolog
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Status of Agricultural Biotechnolog
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8. TRENDS IN KOREAN ANIMAL BIOTECHN
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10. BUSINESS POTENTIAL FOR AGRICULT
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PUBLIC SECTOR R&D ACTIVITIES Busine
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11. STATUS OF PUBLIC RICE BIOTECHNO
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Status of Public Rice Biotechnology
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Status of Public Rice Biotechnology
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Trademarked GloFish with genetic-en
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Agricultural research contains more
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Mr. Rozhan Abu Dardak Research Offi
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C. Secretariat Dr. Sung Ho Son Prof
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Thurs., 26 May Forenoon Visit Taida
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