The use of attenuated isolates of Pepino mosaic virus for cross-protection Martijn F. Schenk & Roel Hamelink & René A. A. van der Vlugt & Adriaan M. W. Vermunt & Ruud C. Kaarsenmaker & Ineke C. C. M. M. Stijger Accepted: 28 January 2010 / Published online: 1 March 2010 # KNPV 2010 Abstract Pepino mosaic virus (PepMV) has recently emerged as a highly infectious viral pathogen in tomato crops. Greenhouse trials were conducted un- der conditions similar to commercial tomato produc- tion. These trials examined whether tomato plants can be protected against PepMV by a preceding infection with an attenuated isolate of this virus. Two potential attenuated isolates that displayed mild leaf symptoms were selected from field isolates. Two PepMV isolates that displayed severe leaf symptoms were also se- lected from field isolates to challenge the attenuated isolates. The isolates with aggressive symptoms were found to reduce bulk yields by 8 and 24% in single infections, respectively. Yield losses were reduced to a 0–3% loss in plants that were treated with either one of the attenuated isolates, while no effects were observed on the quality of the fruits. After the challenge infec- tion, virus accumulation levels and symptom severity of the isolates with aggressive symptoms were also reduced by cross-protection. Infection with the attenu- ated isolates alone did neither affect bulk yield, nor quality of the harvested tomato fruits. Keywords Attenuated isolate . Cross-protection . PepMV . Tomato Introduction Tomato (Solanum lycopersicum) is one of the world’ s most widely grown vegetables. Tomato is susceptible to various viral diseases, and one of the causal agents, Pepino mosaic virus (PepMV), has recently become a major limiting factor with regard to tomato production. After its initial discovery on pepino (Solanum muricatum) in Peru, PepMV was not reported until it was rediscovered in tomato crops in Europe in 1998/1999 (Van der Vlugt et al . 2000; Soler- Aleixandre et al. 2005). Ever since, PepMV has rapidly spread throughout greenhouse tomato produc- tion and is currently found throughout Europe and North-America (Jorda et al. 2001; Cotillon et al. 2002; Verhoeven et al. 2003; Ling et al. 2008). The RNA genome of PepMV encompasses approximately 6.4 kb and contains five open reading frames that encode an RNA-dependent polymerase (RdRp), a triple gene block (TGB), a coat protein (CP), and two short untranslated sequences flanking the coding regions (Aguilar et al. 2002; Cotillon et al. 2002). Eur J Plant Pathol (2010) 127:249–261 DOI 10.1007/s10658-010-9590-4 M. F. Schenk (*) : R. Hamelink : R. C. Kaarsenmaker : I. C. C. M. M. Stijger Wageningen UR Greenhouse Horticulture, Wageningen UR, Bleiswijk, The Netherlands e-mail: Martijn.Schenk@wur.nl R. A. A. van der Vlugt Plant Research International, Wageningen UR, Wageningen, The Netherlands A. M. W. Vermunt : R. C. Kaarsenmaker Groen Agro Control, Delfgauw, The Netherlands