OCCURRENCE AND VARIABILITY OF LITTLE CHERRY VIRUS 1 AND 2 IN BELGIUM

BACKGROUND and OBJECTIVES Little Cherry disease (LChD) can be caused by two distinct viruses (Little cherry virus 1 and 2), and is having a large impact on yield and quality in commercial sweet (Prunus avium L.) and sour cherry (Prunus cerasus L.) production (Rott and Jelkmann, 2001). Several other Prunus spp. can be infected - yet often latently - by both viruses, including the popular oriental flowering cherry (P. serrulata L.). For LChV-1, no vector has been identified so far, but at least two distinct species of mealybugs (Hemiptera, Coccoidea, Pseudococcidae) are known to transmit LChV-2, namely the apple mealybug (Phenacoccus aceris Signoret) and grape mealybug (Pseudococcus maritimus Ehrhorn) (Slykhuis et al., 1980; Mekuria et al. 2013). MATERIALS and METHODS During 2014 and 2015, an intensive survey has been conducted to monitor the incidence and spread of LChV- 1 and -2 in symptomatic and non-symptomatic host trees, eventually leading to re-evaluate the status of LChV infections in Belgium. Leaf symptoms such as premature reddening or bronzing, as well as the development of small fruits, uneven ripening and an insipid taste were observed in many orchards. A total of 306 trees were sampled and tested by RT-PCR for the 2 viruses. LChV-1 or -2 -specific PCR products spanning different open reading frames, were subsequently sequenced and used as markers for characterization. RESULTS Both viruses were widely detected in individual or mixed infections, with a slightly higher incidence for LChV-2 in samples from sweet and sour cherries. The disease was found to be prevalent in many cherry production areas in nearly all places where cherries are grown. Additionally, both viruses were also found in ornamental Prunus spp. in private gardens and in lane trees. Along with published homologous genomic data from other isolates, the genetic diversity of Belgian Little cherry virus (LChV-1 & 2) isolates originating from different hosts and geographic locations was assessed, based on sequences corresponding to the partial RNA-dependent RNA polymerase (RdRp), Heat-Shock Protein homologue (HSP70h) and Coat Protein (CP) genes. CONCLUSIONS Preliminary phylogenetic analysis revealed a low genetic variability for the Belgian LChV-1 and LChV-2 isolates, yet suggests a long-term establishment for both viruses in our region.