RSS | Register/註冊 | Log in/登入
Site search:
Home>FFTC Document Database>Extension Bulletins>Current Status of Transgenic Approach for the Control of Papaya Ringspot Virus
facebook分享
Current Status of Transgenic Approach for the Control of Papaya Ringspot Virus
Shyi-Dong Yeh
Department of Plant Pathology
National Chung-Hsing University
Taichung 402, Taiwan ROC, 2005-11-01

Abstract

Production of papaya has been limited in many areas of the world due to the disease caused by the Papaya ringspot virus (PRSV). The coat protein (CP) gene-mediated transgenic resistance has become the most effective method to prevent crops from this virus infection. In the late 1980s, the group of Gonsalves at Cornell University and Hawaii started a research project to develop transgenic papaya resistant to PRSV by biolistic transformation method. By May 1998, PRSV-CP gene transgenic papaya Rainbow and SunUp were deregulated by the U.S. Animal and Plant Health Inspection Service and Environmental Protection Agency, and granted the approval from the Food and Drug Administration (FDA) for commercial application. This is the first successful case of transgenic fruit tree commercialized in the world. Although the transgenic varieties are not resistant to most other PRSV strains from different geographic areas, the breakdown of the resistance in Hawaii has not been observed. Other than in Hawaii, a CP gene of a native Taiwan strain PRSV YK was used to transform Taiwan papaya cultivars by Agrobacterium-mediated transformation. The transgenic lines obtained showed various levels of resistance, ranging from delay of symptom development to complete immunity. However, during the four-year field test period, the PRSV CP-transgenic papaya lines were found susceptible to an unrelated potyvirus Papaya leaf-distortion mosaic virus (PLDMV) when evaluated under greenhouse conditions. Therefore, in Taiwan PLDMV is considered as a serious threat to papaya production once PRSV CP-transgenic papaya has been widely applied for the control of PRSV. Through the posttranscriptional-gene-silencing mechanism, transgenic papaya plants carrying a chimeric transgene including parts of the CP genes of PRSV and PLDMV were developed to confer resistance against both PRSV and PLDMV under greenhouse conditions. These transgenic papaya plants with double resistance are considered having a great potential for the control of PRSV and PLDMV in Taiwan. During the field test period, a super strain PRSV-519 was found able to breakdown the resistance of PRSV YK-CP transgenic lines. The breakdown of the transgenic resistance was found controlled by a strong gene-silencing suppressor of the super strain in a transgene-homology independent manner. It is suggested that a chimeric construct targeting multiple viral genes including the gene determining viral virulence and gene silencing suppression, such as the HC-Pro gene of a potyvirus, may minimize the chance of emergence of a super virus in overcoming the transgenic resistance.

Papaya As an Important Cash Crop in the Tropics and Subtropics

There are many common names for papaya (Carica papaya L.), such as papaw or paw paw (Australia), mamao (Brazil), tree melon (China), etc. The species is believed to be a native of southern Mexico and neighboring Central America and brought to Caribbean countries and Southeast Asia during the Spanish exploration in the sixteenth century (Storey 1996). It then spread rapidly to India, Africa, and today it is widely distributed throughout the tropical and subtropical areas of the world.

A papaya plant has a single, erect and treelike herbaceous stem, with a crown of large, palmately and deeply lobed leaves. The main stem is cylindrical, hollow, with prominent leaf scars and spongy-fibrous tissue. Leaves are spirally arranged, with petioles extending horizontally up to 1 m long. Trees contain white latex in all parts. Flowers are male, female, or hermaphrodite, found on separate trees, and are borne in the axils of the leaves. The modified cymose inflorescences structure allows the flowers to be easily pollinated by wind and insects. The type of flowers produced may change on the same tree, depending on age and environmental factors such as drought and broad temperature fluctuations. Hermaphroditic trees consistently produce male flowers, with few female flowers that produce fruits during warmer or cooler seasons, whereas, female trees are more stable and always produce pistillate flowers under these conditions.

Papaya fruits are fleshy berry and superficially resemble melons. Fruits from female trees are spherical, whereas, those from hermaphroditic trees are pyriform, oval, or cylindrical with grooved surface. Since the female fruits contain thinner flesh and more seeds in the central cavity, the hermaphrodite fruits are more demanded by consumers. The fruit is a good source of vitamin A and C (Manshardt 1992). Ripe fruits are largely used as fresh desert fruits, and green fruits are often used as salad, and pickled or cooked as vegetable. Papain, a proteolytic enzyme present in the latex, collected mainly from green fruits, has various usage in beverage, food and pharmaceutical industries, e.g. chill-proofing beer, tenderizing meat, and drug preparations for digestive ailments (Chan and Tang 1978). It is also used in bathing hides, softening wool, and as soap for washing cloth.

Papaya grows relatively easily and quickly from seeds. It can grow up to 10 or 12 feet in height. Fruits are ready to be harvested 9-12 months after planting and a tree can continue producing fruits for about 2-3 years up to when plant height is too tall for efficient harvesting. Since plant sex can not be distinguished before flowering, 3-5 seedlings are normally planted together and only the most vigorous hermaphrodite ones during flowering are selected and cultivated. In 2004, the FAO estimated that about 3.7 hundred thousand harvested hectares, and about 6.5 million metric tons of fruits were harvested ( Table 1(1236)). Brazil, Mexico, Nigeria, India, and Indonesia yield more than 70 percent of the total world production. The extensive adaptation of this plant and wide acceptance of the fruit offer considerable promise for papaya as a commercial crop for local and export purposes. Like banana, pineapple, and mango, papaya is one of the most important cash crops in the tropics and subtropics. However, the production of this economically important fruit crop is limited by the destructive disease caused by the Papaya ringspot virus (PRSV), and the fragile and perishable fruit traits unfavorable for large-scale exportation make papaya lag far behind banana and pineapple in the world market.

Worldwide Threat by PRSV Infection

Production of papaya has been limited in many areas of the world due to the disease caused by 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 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 devastation by this noxious virus.

Characteristics of PRSV

PRSV is a member of the genus Potyvirus (Purcifull et al. 1984; Murphy et al. 1995), is transmitted nonpersistently by aphid, and is sap-transmissible in nature. PRSV genome contains a single-stranded positive sense RNA of about 40 S (dela 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 containing 10,326 nucleotides in length. The viral RNA encodes a polypolyprotein that is proteolytically cleaved to generate 8-9 final proteins including the coat protein for encasidation 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 consists of a protein 51 kDa (amorphous inclusion protein, AIP; de Mejia et al. 1985a & b). In papaya, PRSV causes severe mosaic and distortion on leaves, ringspots on fruits, and water-soaking oily streaks on upper stems and petioles. It stunts the plant and drastically reduces the size and the quality of the fruit.

Absence of 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, making the conventional breeding approach difficult (Cook and Zettler 1970; Wang et al. 1978). Tolerance to PRSV has been found in some particular papaya lines and introduced into commercial varieties, but their horticultural properties are still not commercially desirable (Mekako and Nakasone 1975; Conover and Litz 1978). Other control methods for PRSV including agricultural practices such as roughing, quarantine, intercropping with corn as a barrier crop, and protecting transplanted seedlings with plastic bags, provide only temporary or partial solutions to the problems (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 in order to achieve a good economic return from papaya production (Wang et al. 1987; Yeh et al. 1988; Yeh and Gonsalves 1994). However, using the approach of deliberately infecting 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, the 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 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) confer 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 to prevent crops from virus infection.

In order to solve the problems caused by PRSV, in the late 1980s the group of Gonsalves at Cornell University and Hawaii started a research project to develop transgenic papaya. Ling et al. (1991) first demonstrated that the expression of the PRSV HA 5-1 CP gene in tobacco affords a broad-spectrum 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. By 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.

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 posttranscriptional gene silencing (PTGS) _ an RNA-mediated specific degradation process of innate nature of plants against pathogens (Baulcombe 1996; Baulcombe 1999; Hamilton and Baulcombe 1999; Gonsalves 2002). However, the resistance is affected by the sequence identity between the CP transgene and the CP coding region of the challenge virus (Tennant et al. 1994). For example, Rainbow (a CP-hemizygous line derived from SunUp crossed with non-transgenic Kapoho) is susceptible to PRSV isolates outside Hawaii, and SunUp (a CP-homozygous line of 55-1) is resistant to a wider range of isolates from Jamaica and Brazil, but susceptible to isolates from Thailand and Taiwan (Gonsalves 1998; Tennant et al. 2001; Gonsalves 2002). This characteristic of sequence homology-dependent resistance limits the application of CP-transgenic papaya for controlling PRSV in other geographic regions other than Hawaii (Gonsalves 2002).

The field trial of the homozygous line SunUp and hemizygous line Rainbow indicates that both of them offer a good solution to the PRSV problem in Hawaii (Ferreira et al. 2002). By May 1998, Rainbow and SunUp were deregulated by the U.S. Animal and Plant Health Inspection Service and Environmental Protection Agency, and granted the approval from the Food and Drug Administration (FDA) for commercial application (Gonsalves 2002). This is the first successful case of transgenic fruit tree being commercialized in the world.

Transgenic Papaya Generated in Taiwan

Other than Hawaii, a CP gene of a native Taiwan strain PRSV YK was used to transform Taiwan papaya cultivars by Agrobacterium-mediated transformation (Cheng et al. 1996). The transgenic lines obtained showed various levels of resistance, ranging from delay of symptom development to complete immunity (Bau et al. 2003). Several lines highly resistant to the homologous strain (PRSV YK) provide wide-spectrum resistance to three different geographic strains from Hawaii, Thailand, and Mexico (Bau et al. 2003). During four repeats of field trials from 1996 to 1999, the transgenic papaya exhibited high degrees of protection against PRSV in Taiwan (Bau et al. 2004). Unfortunately, 18 months after plantation in the fourth field trial, unexpected symptoms of severe distortion on fully expended leaves, stunning on apex, water-soaking on petioles and stem, and yellow ringspot on fruit were noticed on PRSV CP-transgenic papaya plants. The causal agent was distinguished from PRSV by host reactions and serological properties (Bau 2000) and later identified as Papaya leaf-distortion mosaic virus (PLDMV), a potyvirus which originated from Okinawa, Japan, in 1954 (Maoka et al. 1996). All of the PRSV CP-transgenic papaya lines were susceptible to PLDMV infection when evaluated under greenhouse conditions. Therefore, in Taiwan, PLDMV is considered as a serious threat to papaya production once PRSV CP-transgenic papaya is widely applied for the control of PRSV.

Multiple and Durable Resistance against Different Viruses

In order to control two or more viruses, transgenic plants with multiple resistances have been generated by combining the entire CP gene of more than one virus, with each gene driven by a promoter and a terminator (Fuchs and Gonsalves 1995). Transgenic lines expressing these chimeric CP constructs were resistant to the corresponding viruses and protected from mixed infection such as Cucumber mosaic virus, Watermelon mosaic virus, and Zucchini yellow mosaic virus (Fuchs and Gonsalves 1995; Tricoli et al. 1995; Fuchs et al. 1998). Furthermore, the novel approach proposed by Jan et al. (2000) described that transgenic plants with resistance to a potyvirus and a tospovirus can be obtained through the PTGS mechanism by fusing a segment of tospoviral N gene to a segment of potyviral CP gene. The same strategy was used to develop double resistance to both PRSV and PLDMV. An untranslatable chimeric construct that contained the truncated PRSV CP and PLDMV CP genes was then transferred to papaya. Through the PTGS mechanism, transgenic papaya plants carrying this chimeric transgene indeed conferred resistance against both PRSV and PLDMV under greenhouse conditions (S. D. Yeh, unpublished results). These transgenic papaya plants with double resistance are considered to have a great potential for the control of PRSV and PLDMV in Taiwan.

In a four-year field trial, a super PRSV strain 5-19 infected transgenic papaya lines were found (Tripathi et al. 2004). The nucleotide identity between the transcript of the CP transgene and PRSV 5-19 RNA is less divergent than those between the CP transgene and other PRSV geographic strains that are not able to overcome the transgenic resistance (Tripathi et al. 2004), indicating that the breakdown of the transgenic resistance is not correlated to the sequence divergence between the infecting virus and the transgene. In order to analyze the role of the gene-silencing suppressor HC-Pro of this super strain, the virus recombinant was constructed by replacing a HC-Pro region of PRSV YK with that of 5-19 and the resistance against recombinant was evaluated on transgenic papaya. Results showed that heterologous HC-Pro region of 5-19 alone provides the ability to breakdown the transgenic resistance in a transgene sequence-homology independent manner, even though the sequences of the transgene transcript shares 100 percent identity with the genome of the infecting virus (S. D. Yeh, unpublished results). The breakdown of the transgenic resistance by a strong gene-silencing suppressor of a super strain has strong impacts on the application of transgenic crops for virus control. It issuggested that a chimeric construct targeting multiple viral genes including the gene determining viral virulence and gene silencing suppression, such as the HC-Pro gene of a potyvirus, may minimize the chance of emergence of a super virus for overcoming the transgenic resistance.

Transgenic Papaya Generated in Other Geographic Areas

Because of the apparent homology dependence of PRSV CP transgene-associated resistance, the utilization of a CP gene of a local prevalent strain is a prerequisite to obtain effective PRSV resistance in transgenic papaya lines for a particular geographic region, as long as genetic variation among virus strains in that region is not a limiting factor (Gonsalves 2002). Using the CP genes of local PRSV isolates to transform local papaya cultivars have been successfully reported in different countries. Lines et al. (2002) used an untranslatable PRSV CP coding region as a transgene to develop two Australian transgenic papaya cultivars which showed immunity to the local PRSV isolate in the greenhouse and field tests. Fermin et al. (2004) constructed PRSV-resistant plants by transforming independently with the CP genes of PRSV isolates from two different areas in Venezuela. All of the transgenic lines including R0 and intercrossed or self-crossed progenies, revealed different levels of resistance to homologous and heterologous isolates from Hawaii and Thailand. In Florida, transgenic papaya lines carrying the CP gene of the local strain were generated, and the transgenic resistance were introduced to elite papaya cultivars by conventional breeding (Davis and Ying 2004). In addition to the CP gene, the truncated replicase (RP) gene of PRSV was used as a transgene to generate transgenic papaya through Agrobacterium-mediated transformation (Chen et al. 2001). PRSV inoculation tests showed that the RP gene conferred resistance to PRSV in transgenic papaya.

References

  • Adsuar, J. 1946. Studies on virus disease of papaya (Carica papaya) in Puerto Rico, I. Transmission of papaya mosaic. Puerto Rico Agric Exp Stn Tech Pap 1.
  • Bau, H.J. 2000. Studies on the resistance of transgenic papaya conferred by the coat protein gene of Papaya ringspot virus. PhD Dissertation in Department of Plant Pathology, National Chung Hsing University, Taichung, Taiwan. pp.135.
  • Bau, H.J., Y.H. Cheng, T.A. Yu, J.S. Yang, P.C. Liou, C.H. Hsiao, C.Y. Lin and S.D. Yeh. 2004. Field evaluation of transgenic papaya lines carrying the coat protein gene of Papaya ringspot virus in Taiwan. Plant Dis 88:594-599.
  • Bau, H.J., Y.H. Cheng, T.A. Yu, J.S. Yang and S.D. Yeh. 2003. Broad spectrum resistance to different geographic strains of Papaya ringspot virus in coat protein gene transgenic papaya. Phytopathology 93:112-120.
  • Baulcombe, D.C. 1996. Mechanisms of pathogen-derived resistance to virus in transgenic plants. Plant Cell 8:1833-1844.
  • Baulcombe, D.C. 1999. Viruses and gene silencing in plants. Arch. Virol. 15:189-201.
  • Beachy, R. 1990. Coat protein-mediated resistance against virus infection. Annu Rev Phytopathol 28:451-474.
  • Capoor, S.P., P.M. Varma. 1948. A mosaic disease of Carica papaya L. in the Bombay province. Current Sci 17:265-266.
  • Chan, H.T., C.S. Tang. 1978. The chemistry and biochemistry of papaya. In: Inglett GE, Charolambous G. (Eds): Tropical Foods. Vol 1:33-55. Academic Press, New York.
  • Chen, G., C.M. Ye, J.C. Huang, M. Yu and B.J. Li. 2001. Cloning of the Papaya ringspot virus replicase gene and generation of the PRSV-resistant papaya through the introduction of the PRSV replicase gene. Plant Cell Rep 20:272-277.
  • Cheng, Y.H., J.S. Yang and S.D. Yeh. 1996. Efficient transformation of papaya by coat protein gene of Papaya ringspot virus mediated by Agrobacterium following liquid-phase wounding of embryogenic tissues with carborundum. Plant Cell Rep 16:127-132.
  • Conover, R.A. 1964. Distortion ringspot, a severe disease of papaya in Florida. Proc Fla State Hortic Soc 77:440-444.
  • Conover, R.A. 1976. A program for development of papaya tolerant to the distortion ringspot virus. Proc Fia State Hortic Soc 89:229-231.
  • Conover, R.A., R.E. Litz. 1978. Progress in breeding papaya with tolerance to Papaya ringspot virus. Proc Fia State Hortic Soc 91:182-184.
  • Conover, R.A., R.E. Litz and S.E. Malo. 1986. `Cariflora'- a Papaya ringspot virus-tolerant papaya for south Florida and the Caribbean. HortScience 21:1072.
  • Cook, A.A., F.W. Zettler. 1970. Susceptibility of papaya cultivars to papaya ringspot and papaya mosaic virus. Plant Dis Rep 54:893-895.
  • Davis, M.J., Z. Ying. 2004. Development of papaya breeding lines with transgenic resistance to Papaya ringspot virus. Plant Dis 88:352-358.
  • De La Rosa, M, R. Lastra. 1983. Purification and partial characterization of papaya ringspot virus. Phytopathol. Z. 106:329-336.
  • De Mejia MVG, E. Hiebert and D.E. Purciful. 1985a. Isolation and partial characterization of the amorphous cytoplasmic inclusions protein associated with infections caused by two potyviruses. Virology 142: 24-33.
  • De Mejia MVG, E. Hiebert, D.E. Purcifull, D.W. Thornbury, and T.P. Pirone. 1985b. Identification of potyviral amorphous inclusion protein as a nonstructural, virus-specific protein related to helper component. Virology 142:34-43.
  • Fermin, G., V. Inglessis, C. Garboza, S. Rangle, M. Dagert and D. Gonsalves. 2004. Engineered resistance against Papaya ringspot virus in Venezuelan transgenic papaya. Plant Dis 88:516-522.
  • Ferreria, SA, K.Y. Pitz, R. Manshardt, F. Zee and M. Fitch. 2002. Virus coat protein transgenic papaya provides practical control of Papaya ringspot virus in Hawaii. Plant Dis 86:101-105.
  • Fitch, MMM, R.M. Manshardt. 1990. Somatic embryogenesis and plant regeneration from immature zygotic embryos of papaya (Carica papaya L.). Plant Cell Rep 9: 320-324.
  • Fitch, MMM, R.M. Manshardt, D. Gonsalves, J.L. Slightom and J.C. Sanford. 1990. Stable transformation of papaya via microprojectile bombardment. Plant Cell Rep 9: 189-194
  • Fitch, MMM, R.M. Manshardt, D. Gonsalves, J.L. Slightom and J.C. Sanford. 1992. Virus resistance papaya plants derived from tissues bombarded with the coat protein gene of Papaya ringspot virus. Bio/Technology 10:1466-1472.
  • Fuchs, M, D. Gonsalves. 1995. Resistance of transgenic hybrid squash ZW-20 expressing the coat protein genes of Zucchini mosaic virus and Watermelon mosaic virus 2 to mixed infections by both potyviruses. Bio/Technology 13: 1466-1473.
  • Fuchs, M, D.M. Tericoli, K.J. Carney, M. Schesser, J.R. McFerson and D. Gonsalves. 1998. Comparative virus resistance and fruit yield of transgenic squash with single and multiple coat protein genes. Plant Dis 82:1350-1356.
  • Goldbach, R, E. Bucher, M. Prins. 2003. Resistance mechanisms to plant viruses: An overview. Virus Res 92:207-212.
  • Gonsalves, D. 1998. Control of Papaya ringspot virus in papaya: a case study. Annu Rev Phytopathol 36:415-437.
  • Gonsalves, D. 2002. Coat protein transgenic papaya "acquired" immunity for controlling papaya ringspot virus. Curr Top Microbiol Immunol 266:73-83.
  • Gonsalves, D, S.M. Garnsey. 1989. Cross-protection techniques for control of plant virus diseases in the tropics. Plant Dis 73:592-597.
  • Gonsalves, D., M. Ishii. 1980. Purification and serology of papaya ringspot virus. Phytopathology 70:1028-1032.
  • Hamilton, A.J., D,C Baulcombe. 1999. A species of small antisense RNA in posttranscriptional gene silencing in plants. Science 286:950-952.
  • Herold, F, J. Weibel. 1962. Electron microscopic demonstration of papaya ringspot virus. Virology 18:307-311.
  • Jan F.J., C. Fagoaga, S.Z. Pang, D. Gonsalves. 2000. A single chimeric transgene derived from two distinct viruses confers multi-virus resistance in transgenic plants through homology-dependent gene silencing. J Gen Virol 81:2103-2109.
  • Jensen, D.D. 1949a. Papaya virus diseases with special reference to papaya ringspot. Phytopathology 39:191-211.
  • Jensen, D.D. 1949b. Papaya ringspot virus and its insect vector relationship. Phytopathology 39:212-220.
  • Lana, A.F. 1980. Transmission and properties of virus isolated from Carica papaya in Nigeria. J Hortic Sci 55:191-197.
  • Lines, R.E., D. Persley, J.L. Dale, R. Drew and M.F. Bateson. 2002. Genetically engineered immunity to Papaya ringspot virus in Australian papaya cultivars. Mol Breed 10:119-129.
  • Ling, K, S. Namba, C. Gonsalves, J.L. Slightom and D. Gonsalves. 1991. Protection against detrimental effects of potyvirus infection in transgenic tobacco plants expressing the Papaya ringspot virus coat protein gene. Bio/Technology 9:752-758.
  • Lius, S, R.M. Manshardt, MMM. Fitch, J.L. Slightom, J.C. Sanford and D. Gonsalves. 1997. Pathogen-derived resistance provides papaya with effective protection against Papaya ringspot virus. Mol Breed 3:161-168.
  • Lomonossoff, G.P. 1995. Pathogen-derived resistance to plant viruses. Annu Rev Phytopathol 33:323-343.
  • Manshardt, R.M.. 1992. Papaya. In: Hammer-schlag FA, Litz RE (eds) Biotechnology of Perennial Fruit Crops. CAB International. Kew, UK, p 489-511.
  • Maoka, T, S. Kashiwazaki, S. Tsuda, T. Usugi and H. Hibino. 1996. Nucleotide sequence of the capsid protein gene of the Papaya leaf-distortion mosaic potyvirus. Arch Virol 141:197-204.
  • Martelli, GP, M. Russo. 1976. Unusual cytoplasmic inclusions induced by Watermelon mosaic virus. Virology 72:352-362.
  • Mekako, H.U., H.Y. Nakasone. 1975. Interspecific hybridization among 6 Carica species. Jour. Am Soc Hortic Sci 100:237-242.
  • Murphy, FA, C.M. Fauquet, D.H.L. Bishop, S.A. Ghabrial, A.W. Jarvis, G.P. Martelli, M.A. Mayo and M.D. Summer. 1995. Virus Taxonomy. Springer-Verlag, Vienna. pp.350-354.
  • Purcifull, D.E., J.R. Edwardson. 1967. Watermelon mosaic virus: tubular inclusion in pumpkin leaves and aggregates in leaf extracts. Virology 32:393-401.
  • Purcifull, D.E., J.R. Edwardson, E. Hiebert and D. Gonsalves. 1984. Papaya ringspot virus. CMI/AAB Description of Plant Viruses. No 292.
  • Purcifull, D.E., E. Hiebert. 1979. Serological distinction of Watermelon mosaic virus isolates. Phytopathology 69:112-116.
  • Powell-Abel, P, R.S. Nelson, B. De, N. Hoffmann, S.G. Rogers, R.T. Fraley and R.N. Beachy. 1986. Delay of disease development in transgenic plants that express the Tobacco mosaic virus coat protein gene. Science 232:738-743.
  • Sanford, J.C., S.A. Johnston. 1985. The concept of parasite-derived resistance: deriving resistance gene from the parasite's own genome. J Thero Biol 113:395-405.
  • Singh, A.B. 1969. A new virus disease of Carica papaya in India. Plant Dis Rep 53:267-269.
  • Storey, W.B. 1969. Papaya (Carica papaya L.). In: Outline of perennial crop breeding in the tropics. Ferwerda FP, Wit F (eds) H. Veenman en Zonen BV, Wageningen, pp 389-407.
  • Stubbs, L.L. 1964. Transmission and protective inoculation studies with viruses of the citrus tristeza complex. Aust J Agr Res 15:752-770.
  • Tennant, P., G. Fermin, MMM. Fitch, R. Manshardt, J.L. Slightom and D. Gonsalves. 2001. Papaya ringspot virus resistance of transgenic Rainbow and SunUp is affected by gene dosage, plant development, and coat protein homology. Eur J Plant Pathol 107:645-653.
  • Tennant, P.F., C. Gonsalves, K.S. Ling, M. Fitch, R. Manshardt, J.L. Slightom, D. Gonsalves. 1994. Differential protection against Papaya ringspot virus isolates in coat protein gene transgenic papaya and classically cross-protected papaya. Phytopathology 84:1359-1366.
  • Thomas, J.E., R.L. Dodman. 1993. The first record of Papaya ringspot virus-type P in Australia. Aust Plant Pathol 22:2-7.
  • Tricoli, D.M., K.J. Carney, P.F. Pussell, J.R. McMaster, D.W. Groff, K.C. Hadden, P.T. Himmel, J.P. Hubbard, M.L. Boeshore and H.D. Quemada. 1995. Field evaluation of transgenic squash containing single or multiple virus coat protein gene constructs for resistance to Cucumber mosaic virus, Watermelon mosaic virus 2, and Zucchini yellow mosaic virus. Bio/Technology 13:1458-1465.
  • Tripathi, S., H.J. Bau, L.F. Chen and S.D. Yeh. 2004. The ability of Papaya ringspot virus strains overcoming the transgenic resistance of papaya conferred by the coat protein gene is not correlated with higher degrees of sequence divergence from the transgene. Eur Jour. Plant Pathol 110:871-882.
  • Wang, C.H., S.D. Yeh. 1997. Divergence and conservation of the genomic RNAs of Taiwan and Hawaii strains of Papaya ringspot virus. Arch Virol 142:271-285.
  • Wang, H.L., C.C. Wang, R.J. Chiu and M.H. Sun. 1978. Preliminary study on Papaya ringspot virus in Taiwan. Plant Prot Bull 20:133-140.
  • Wang, H.L., S.D. Yeh, R.J. Chiu and D. Gonsalves. 1987. Effectiveness of cross protection by mild mutants of papaya ringspot virus for control of ringspot disease of papaya in Taiwan. Plant Dis 71:491-497.
  • Yeh, S.D., D. Gonsalves. 1984. Evaluation of induced mutants of Papaya ringspot virus for control by cross protection. Phytopathology 74:1086-1091.
  • Yeh, S.D., D. Gonsalves. 1985. Translation of papaya ringspot virus RNA in vitro: Detection of a possible polyprotein that is processed for capsid protein, cylindrical-inclusion protein, and amorphous-inclusion protein. Virology 143: 260-271.
  • Yeh, S.D., D. Gonsalves. 1994. Practices and perspective of control of papaya ringspot virus by cross protection. Adv Dis Vector Res 10:237-257.
  • Yeh, S.D., D. Gonsalves, H.L. Wang, R. Namba and R.J. Chiu. 1988. Control of Papaya ringspot virus by cross protection. Plant Dis 72:375-380.
  • Yeh, S.D., F.J. Jan, C.H. Chiang, T.J. Doong, M.J. Chen, P.H. Chung and H.J. Bau. 1992. Complete nucleotide sequence and genetic organization of Papaya ringspot virus RNA. J Gen Virol 73:2531-2541.

Index of Images

Table 1 World Papaya Production, 2004<Sup>a</Sup>

Table 1 World Papaya Production, 2004 a

Download the PDF. of this document(709), 184,698 bytes (180 KB).