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Journal of Pathology (2009), 91 (2), 475-478 Edizioni ETS Pisa, 2009 475

SHORT COMMUNICATION COMPARATIVE TRANSMISSION EFFICIENCY OF TWO BROAD BEAN WILT 1 ISOLATES BY MYZUS PERSICAE AND APHIS GOSSYPII

B. Belliure, M. Gómez-Zambrano, I. Ferriol, M. La Spina*, L. Alcácer, D.E. Debreczeni and L. Rubio

Instituto Valenciano de Investigaciones Agrarias (IVIA), Centro de Protección Vegetal y Biotecnología, Apartado Oficial, 46113 Moncada, Valencia, Spain

SUMMARY lates. This genetic difference presumably affects differ- ent aspects of their biology, such as replication, move- We tested the transmission efficiency of two geneti- ment and transmission by aphids. Transmission efficien- cally divergent isolates of Broad bean wilt virus 1 (BB- cy of BBWV-1 by its aphid vectors has little been ex- WV-1), PV-132 from the USA, and Ben from Spain, by plored (Stubbs, 1960; Gracia and Gutierrez, 1982; two aphid species, Myzus persicae (Sulzer) and Aphis Makkouk et al., 1990), and never compared between gossypii (Glover) collected in Spain. Efficiency was esti- different virus isolates. This information is relevant to mated as the number of infected divided by the understand virus epidemiology and to develop control number of single-aphid-inoculated plants. The two methods based on preventing or decreasing the spread aphid species transmitted the virus isolates with equiva- of BBWV-1. In this study, the transmission efficiencies lent efficiency, but the transmission rate was significant- of the Ben and PV-132 isolates by two of the most im- ly higher for isolate Ben than for PV-132. It is hypothe- portant aphid pests in vegetable crops, Myzus persicae sized that the specificity determinants for vector-virus (Sulzer) and Aphis gossypii (Glover), were evaluated interaction might be similar for M. persicae and A. and compared. gossypii, whereas transmission rate could be affected by The PV-132 isolate of BBWV-1 was collected in 1972 amino acid differences in the coat proteins of the two from a spinach (Spinacea oleracea) field in New York isolates. State, USA (Schroeder and Provvidenti, 1970), while the Ben isolate was collected in 2001 from a pepper (Cap- Key words: Comoviridae, , BBWV-1, insect sicum annuum) field at Benincarló (Calstellón province. vector, aphids. Comunidad Valenciana, Spain) (Rubio et al., 2002). Both isolates were maintained on broad bean () plants by mechanical inoculation and plants were grown Broad bean wilt virus 1 (BBWV-1), the type species of in an insect-free greenhouse. Virus-source plants were the genus Fabavirus (Le Gall et al., 2005), infects a wide used one month after inoculation to maintain similar range of host plants including economically important virus concentrations. A. gossypii was collected at Carlet horticultural and ornamental species. It is distributed (Valencia provimce, C. Valenciana, Spain) whereas M. worldwide, and is transmitted by different species of persicae came from Onda (Calstellón province, C. Valen- aphids in a non-persistent manner (Lisa and Boccardo, ciana, Spain). Isofemale lines were obtained for each 1996). The genome of BBWV-1 is composed of two sin- aphid species by parthenogenesis from a single female, gle stranded positive-sense RNAs and virions are icosa- thus all individuals of each line were genetically identical. hedral particles composed of two coat proteins (Lisa Aphid transmission assays were performed as fol- and Boccardo, 1996). The complete genomes of isolate lows: aphids (apterous adults and fourth instar apterous PV-132 from USA and isolate Ben from Spain, have nymphs) were starved for 1h and then carefully placed been sequenced (Kobayashi et al., 2003; Ferrer et al., on an infected leaf (five aphids at a time). As soon as the 2005). Sequence analysis showed a high divergence (nu- aphids started feeding on the infected leaf, they were cleotide identity about 80%) between these two iso- moved to the top leaf of a healthy broad bean seedling. For each virus-aphid combination, 30 plants were inoc- ulated. Mock inoculations were performed as negative controls with aphids not having access to the virus. In- Corresponding author: L. Rubio Fax: +34 963424001 dividual test plants were covered with transparent plas- E-mail: [email protected] tic cylinders with the tops covered with a fine mesh for aeration and the lower ends pushed into the soil to pre- * Current address: Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA), Departamento. de Biotecnología y Protec- vent movement of aphids between plants. Virus acquisi- ción de Cultivos. C/ Mayor, s/n., 30150 La Alberca, Murcia, Spain tion and inoculation took place at 25-28ºC. Inoculated 026_JPP416SCRubio_475 25-06-2009 12:52 Pagina 476

476 Aphid transmission of BBWV-1 Journal of Plant Pathology (2009), 91 (2), 475-478

plants were sprayed 24 h later with 0.3% Pirimicarb infected plants; N = number of receptor plants; I = plus Endosulfan (Aphox, Syngenta) to kill the aphids, number of aphids per receptor plant. then kept in an insect-free greenhouse. Plants were eval- Preliminary assays with isolate Ben and M. persicae uated for virus infection 10-15 days post inoculation by showed no significant differences between the transmis- inspection for symptoms (chlorotic blotches) and by sion rate obtained using one aphid per receptor plant or molecular hybridization using probes specific for the five aphids per plant calculated using this formula (data two isolates (Ferrer et al., 2008). not shown), thus confirming its validity. Transmission Virus transmission rate was calculated as the number assays were performed in parallel for the two BBWV-1 of infected plants divided by the number of inoculated isolates and two aphid species using broad bean as plants. Comparisons between transmission rates of dif- donor and receptor plant. ferent isolates and aphid species were made using the χ2 Transmission assay data showed no significant differ- (Chi2) test corrected for continuity (Siegel and Castel- ences in transmission rate between A. gossypii and M. lan, 1988). Differences were considered significant persicae either for the Ben isolate (χ2 test corrected for when p < 0.1. The transmission rate of a single aphid continuity, p = 1.0000, Figure 1), or the PV-132 isolate was calculated by using the formula proposed by Gibbs (χ2 test corrected for continuity, p = 0.5900, Figure 1). and Gower (1960): This suggests that A. gossypii and M. persicae have simi- lar specificity determinants for the interaction with BB- P* = 1 - (1 - T) 1/I (1), WV-1 (Uzest et al., 2007). where P*= estimated transmission rate for a single In contrast, the transmission rates for the two virus aphid; T = transmission rate as T= R/N; R = number of isolates differed considerably. Ben was transmitted at a

Table 1. Transmission rate for a single aphid calculated for diverse BBWV-1 isolates, aphid species, and plant hosts.

Origin aHost bVector cP* Reference Spain V. faba A. gossypii 0.418 Our results ““ M. persicae d0.369 “ USA “ A. gossypii 0.167 “ ““ M. persicae 0.214 “ Australia “ M. persicae 0.333 Stubbs, 1960 ““ A. craccivora 0.194 “ ““ M. euphorbiae 0.133 “ “ T. subterraneum M. persicae 0.194 “ ““ A. craccivora 0.055 “ Germany N. clevelandii M. persicae 0.200 Sahambi et al., 1973 ““ A. craccivora 0.030 “ Argentina P. hybrida M. persicae 0.104 Vega et al., 1980 Morocco C. quinoa “ 0.044 Lockhart and Fischer, 1977 “ P. sativum “ 0.186 “ Italy V. faba “ 0.366 Boccardo and Conti, 1973 ““ M. euphorbiae 0.313 “ ““ A. nasturtii 0.167 “ “ P. hybrida M. persicae 0.150 “ ““ M. euphorbiae 0.000 “ ““ A. nasturtii 0.000 “ Syria V. faba M. persicae 0.275 Makkouk et al., 1990 ““ A. pisum 0.098 “ ““ A. fabae 0.014 “ ““ A. craccivora 0.089 “ aHosts: Chenopodium quinoa, Nicotiana clevelandii, Petunia hybrida, Pisum sativum, Trifolium subterraneum, and Vicia faba bVectors: Acyrthosiphon pisum, Aphis craccivora, Aphis fabae, Aphis gossypii, Aphis nasturtii, Macrosiphum euphorbiae, and Myzus persicae. cP*=Transmission rates for single aphids according to the formula of Gibbs and Gower (1960). See text. dTransmission rates for V. faba and M. persicae are written in bold to facilitate comparisons. 026_JPP416SCRubio_475 25-06-2009 12:52 Pagina 477

Journal of Plant Pathology (2009), 91 (2), 475-478 Belliure et al. 477

management strategies in a given area, but more factors affecting virus epidemiology need to be studied, such as aphid population dynamics, transmission rates under field conditions and the frequency of different virus iso- lates in the field.

ACKNOWLEDGEMENTS

We thank Drs. Aránzazu Moreno and Alfonso Her- moso de Mendoza (IVIA) for technical advice on trans- mission assays, Dr. Emilio Carbonell and Jordi Pérez- Fig. 1. Transmission rate of BBWV-1 isolates Ben (white bars) Panadés for their advice on statistical analysis, Diego and PV-132 (black bars) by Aphis gossypii and Myzus persicae. Conchilla and Amparo Palanca for taking care of the plants, and Drs. Aránzazu Moreno and José Guerri for critical reading of the manuscript. This work was sup- significantly higher rate than PV-132 by A. gossypii ported by the Spanish Ministerio of Educación y Cien- (93% vs. 60%; χ2 test corrected for continuity, p = cia (AGL-2005-07754). B.B. was supported by the Eu- 0.0060, Figure 1). A similar trend was observed for M. ropean Social Fund and a INIA-CCAA contract. persicae, the difference being marginally significant (90% vs. 70%; χ2 test corrected for continuity, p = 0.1066, Figure 1). REFERENCES These results suggest that the higher transmission rate of Ben with both aphids might be related to the Boccardo G., Conti M., 1973. Purification and properties of similar geographical origin of this isolate and the aphid nasturtium ringspot virus. Phytopathologische Zeitschrift populations tested. This could have allowed the virus to 78: 14-24. adapt to the local aphid population and become more Ferrer R.M., Guerri J., Luis-Arteaga M.S., Moreno P., Rubio efficiently transmitted (Moya et al., 2004). L., 2005. The complete sequence of a Spanish isolate of Broad bean wilt virus 1 (BBWV-1) reveals a high variability The differences in transmission efficiency of the two and conserved motifs in the genus Fabavirus. Archives of virus isolates could be caused by differences in the Virology 150: 2109-2116. amino acid sequences that determine recognition be- Ferrer R.M., Escriu F., Luis-Arteaga M., Guerri J., Moreno P., tween virus and vector (Perry et al., 1998; Liu et al., Rubio L., 2008. New molecular methods for identification 2002; Moreno et al., 2005; Uzest et al., 2007). of Broad bean wilt virus 1. Molecular and Cellular Probes It is difficult to compare our data with results of pre- 22: 223-227. vious studies as transmission efficiency can vary accord- Gracia O., Gutierrez L.S., 1982. Broad bean wilt virus in pep- ing to different factors such as temperature, develop- per crops in Argentina. Phytopathologia Mediterranea 21: mental stage of aphid and plant, acquisition time, ma- 107-109. nipulation, etc., as well as by the genetic variation of Gibbs A.J., Gower J.C., 1960. The use of a multiple-transfer , hosts and aphids. Nevertheless, to facilitate this method in plant virus transmission studies: some statistical comparison, we calculated the transmission rate for a points arising in the analysis of results. Annals of Applied single aphid (P*) from our data and from data of previ- Biology 48: 75-83. ous studies (Table 1). The transmission rates of BBWV- Kobayashi Y.O., Kobayashi A., Nakano M., Hagiwara K., 1 isolates between broad bean plants by M. persicae ob- Honda Y., Omura T., 2003. Analysis of genetic relations tained in this work were similar to those obtained previ- between Broad bean wilt virus 1 and Broad bean wilt virus ously (Stubbs, 1960; Boccardo and Conti, 1973; 2. Journal of General Plant Pathology 69: 320-326. Makkouk et al., 1990). Although we found similar Le Gall O., Iwanami T., Karasev A.V., Jones T., Lehto K., transmission rate for A. gossypii and M. persicae, other Sanfaçon H., Wellink J., Wetzel T., Yoshikawa N., 2005. authors found a higher transmission efficiency for M. Family Comoviridae. In: Fauquet C.M., Mayo M.A., persicae than for other aphid species: Macrosiphum eu- Maniloff J., Desselberger U., Ball L.A. (eds). Virus Taxon- omy. Eighth Report of the International Committee on phorbiae, A. nasturtii, A. fabae, A. craccivora and Taxonomy of Viruses, pp. 807-818. Elsevier Academic Acyrthosiphon pisum (Table 1). To our knowledge, this Press, London, UK. is the first evaluation of the transmission rate of BBWV- Lisa V., Boccardo G., 1996. Fabaviruses: Broad bean wilt 1 by A. gossypii, and the first time that aphid transmis- virus and allied viruses. In: Harrison B.D., Murant A.F. sion has been compared between two BBWV-1 isolates. (eds.). Polyhedral Virions and Bipartite RNA Genomes. Evaluation of the transmission rate is fundamental The Plant Viruses, vol. 5, pp. 229-250. Plenum Press, New for epidemiological assessment and the deployment of York, NY, USA. 026_JPP416SCRubio_475 25-06-2009 12:52 Pagina 478

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Received November 22, 2008 Accepted February 6, 2009