Received: 4 September, 2007. Accepted: 7 October, 2007. Invited Review Plant Viruses ©2007 Global Science Books Viruses Infecting Papaya (Carica papaya L.): Etiology, Pathogenesis, and Molecular Biology Paula F. Tennant 1,2* • Gustavo A. Fermin 3 • Marcia E. Roye 1 1 Biotechnology Centre, 2 St. John’s Close, University of the West Indies, Mona, Jamaica 2 Department of Life Sciences, 4 Anguilla Close, University of the West Indies, Mona, Kingston 7, Jamaica 3 Faculty of Sciences, Universidad de Los Andes, Mérida 5101, Mérida, Venezuela Corresponding author: * paula.tennant@uwimona.edu.jm ABSTRACT During the last few decades, over 20 plant virus species capable of infecting papaya (Carica papaya L.) have emerged in tropical and subtropical regions. The extent and severity of disease symptoms vary widely from minor or unapparent to reduced tree vigor, yield, and impaired fruit quality. Existing data on molecular characteristics of viruses infecting papaya also vary; while phenotypic data are available for the majority, the genotype of many have not been characterized and partial or complete nucleotide sequences have not been determined. As a result, some virus species are classified in recognized taxa while others are tentatively assigned to genera or have not been sufficiently distinguished from viruses in recognized genera so as to form a new genus. This paper presents an overview of the virus species capable of infecting papaya, diseases they elicit, genetic structure and diversity, and factors contributing to their emergence where molecular data are available. _____________________________________________________________________________________________________________ Keywords: Cucumoviruses, Geminiviruses, Ilarviruses, Nepoviruses, papaya, Papaya lethal yellowing virus, Papaya meleira virus, Papaya mild yellow leaf virus, Potexviruses, Potyviruses, Rhabdoviruses, Tobraviruses, Tospoviruses CONTENTS INTRODUCTION...................................................................................................................................................................................... 178 POTYVIRUSES......................................................................................................................................................................................... 179 RHABDOVIRUSES .................................................................................................................................................................................. 181 POTEXVIRUSES ...................................................................................................................................................................................... 182 GEMINIVIRUSES..................................................................................................................................................................................... 182 TOSPOVIRUSES ...................................................................................................................................................................................... 183 NEPOVIRUSES......................................................................................................................................................................................... 184 ILARVIRUSES .......................................................................................................................................................................................... 184 TOBRAVIRUSES ...................................................................................................................................................................................... 184 CUCUMOVIRUSES.................................................................................................................................................................................. 184 UNASSIGNED VIRUSES......................................................................................................................................................................... 184 CONCLUDING REMARKS ..................................................................................................................................................................... 185 ACKNOWLEDGEMENTS ....................................................................................................................................................................... 185 REFERENCES........................................................................................................................................................................................... 185 _____________________________________________________________________________________________________________ INTRODUCTION Papaya (Carica papaya L.) is a large fast growing arbo- rescent herb cultivated for its climacteric, melon-like fruit. It is native to Central and South America and is widely dis- tributed throughout many tropical and subtropical countries (Manshardt 1992). Papayas can usually be found in home gardens intermixed with other fruit trees or in the wild. More recently, organized commercial plantings have been established across various regions in attempts to satisfy growing local and international markets. In 1997, the Food and Agriculture Organization (FAO) estimated that papaya production accounted for 10% of the volume of the four major tropical fruits (including mangoes, pineapples, and avocados) produced worldwide. Since then papaya produc- tion has doubled. About 6.6 million metric tonnes were pro- duced in 2005, with countries of Latin America and the Caribbean accounting for roughly 45% (FAO Statistics 2007). Brazil is the largest producer of papaya, harvesting 1.6 million metric tonnes in 2005. Nigeria followed produ- cing 834,000 metric tonnes in the same year, India with 783,000, Mexico 710,000, Indonesia 647,000, and Ethiopia which produced 259,000 (FAO Statistics 2007). This increase in demand for papaya, particularly in the Unites States and Europe, is claimed to have been triggered by the new trend in health consciousness. Papaya is rich in vitamin A, vitamin C, potassium, high in crude fiber, and carbohydrates but is low in protein, fats, and calories (Manshardt 1992; Reiger 2006). Apart from being widely produced and marketed as fresh fruit, as a preserve, and for juice, various parts of the fruit and plant have pharmaceu- tical, medicinal and industrial purposes. Unripe fruit is commonly used to dress wounds (Wimalawansa 1981; Star- ley et al. 1999; Hewitt et al. 2000) and to treat insect bites. The latex of green fruit contains proteinases of broad spec- trum activity that are employed in the treatment of digestive disorders, in the manufacture of cosmetics, meat tenderizers, and in the clarification of beer (Madrigal et al. 1980). Green