Downloaded from www.microbiologyresearch.org by IP: 93.91.26.97 On: Fri, 04 Dec 2015 05:22:20 Journal of General Virology (2002), 83, 2575–2585. Printed in Great Britain ................................................................................................................................................................................................................................................................................... On the evolution and molecular epidemiology of the potyvirus Papaya ringspot virus Marion F. Bateson, 1 Rosemarie E. Lines, 1 Peter Revill, 1 Worawan Chaleeprom, 1 † Cuong V. Ha, 2 Adrian J. Gibbs 3 and James L. Dale 1 1 School of Life Sciences, Queensland University of Technology, GPO Box 2434, Brisbane, Queensland 4000, Australia 2 Hanoi Agricultural University, Gia Lam, Vietnam 3 School of Botany and Zoology, Australian National University, ACT 2000, Australia The potyvirus Papaya ringspot virus (PRSV) is found throughout the tropics and subtropics. Its P biotype is a devastating pathogen of papaya crops and its W biotype of cucurbits. PRSV-P is thought to arise by mutation from PRSV-W. However, the relative impact of mutation and movement on the structure of PRSV populations is not well characterized. To investigate this, we have determined the coat protein sequences of isolates of both biotypes of PRSV from Vietnam (50), Thailand (13), India (1) and the Philippines (1), and analysed them together with 28 PRSV sequences already published, so that we can better understand the molecular epidemiology and evolution of PRSV. In Thailand, variation was greater among PRSV-W isolates (mean nucleotide divergence 76 %) than PRSV-P isolates (mean 26 %), but in Vietnamese populations the P and W biotypes were more but similarly diverse. Phylogenetic analyses of PRSV also involving its closest known relative, Moroccan watermelon mosaic virus, indicate that PRSV may have originated in Asia, particularly in the Indian subcontinent, as PRSV populations there are most diverse and hence have probably been present longest. Our analyses show that mutation, together with local and long- distance movement, contributes to population variation, and also confirms an earlier conclusion that populations of the PRSV-P biotype have evolved on several occasions from PRSV-W populations. Introduction The potyvirus Papaya ringspot virus (PRSV) is an important pathogen of papaya and cucurbits. The virus is classified into two biotypes that have virions which cannot be distinguished in serological tests, but that differ in their ability to infect papaya (Purcifull, 1984). PRSV-P naturally infects papaya (Carica papaya) and is a major limiting factor in papaya production worldwide (Purcifull, 1984). PRSV-W, which has a natural host range within the Cucurbitaceae and is unable to Author for correspondence : Marion Bateson. Fax 61 7 38641534. e-mail m.batesonqut.edu.au †Present address : Faculty of Agricultural Production, Maejo University, Samsai, Chiang mai 50290, Thailand. GenBank accessions for sequences used in this study are AF506840–AF506904. infect papaya, has been described as one of the five most important viruses in field-grown vegetables (Tomlinson, 1987). Although PRSV-P can usually be transmitted experimentally to cucurbits, it is not usually found in cucurbits in the field (Gonsalves, 1998). PRSV-P was first described in 1949 after isolation from papaya in Hawaii (Jensen, 1949), and has since been reported from many other countries where it has often devastated papaya production within a few years of the first infection (Gonsalves, 1998). The epidemiology of PRSV-P in papaya is similar to that of other non-persistent, aphid-borne viruses and it is not found in intercropped cucurbits, suggesting that the virus spreads directly from papaya to papaya. There is, however, little information on the epidemiology of PRSV-W in cucurbits. In addition, there is evidence that PRSV-P evolved from PRSV-W (Bateson et al., 1994), presumably by mutation. This was first indicated by the very close sequence similarity of the coat protein (CP)-coding regions of P and W isolates within Australia, and the fact that PRSV-W was found to be 0001-8419  2002 SGM CFHF