Weed Hosts Represent an Important Reservoir of Turnip Yellows Virus and a Possible Source of Virus Introduction into Oilseed Rape Crop.

Turnip yellows virus (TuYV) is one of the most important pathogens of oilseed rape worldwide. The virus has a large host range including many crop species (e.g., oilseed rape, pea, chickpea) and weeds from more than twenty plant families. Other than oilseed rape, we detected TuYV in many commonly grown weed species that share the fields and vegetation period together with canola crops in Czech and Slovak Republics. TuYV was detected by reverse-transcription polymerase chain reaction (RT-PCR) in at least 26 species including main crop hosts (oilseed rape), intercrops and weeds such as Amaranthus retroflexus , Atriplex patula (Amaranthaceae) , Arctium lappa , Lactuca serriola , Taraxacum officinale , Tripleurospermum inodorum (Asteraceae) , Phacelia tanacetifolia (Boraginaceae) , Brassica napus , Capsella bursa-pastoris , Descurainia Sophia , Raphanus raphanistrum , Sinapis alba , Sisymbrium officinale , Thlaspi arvense (Brassicaceae) , Silene alba , Stellaria media (Caryophyllaceae) , Euphorbia helioscopia (Euphorbiaceae) , Geranium rotundifolium (Geraniaceae) , Lamium purpureum (Lamiaceae) , Fumaria officinalis , Papaver rhoeas (Papaveraceae) , Veronica persica (Plantaginaceae syn. Scrophulariaceae) , Fallopia convolvulus (Polygonaceae) , Solanum nigrum (Solanaceae) , Urtica dioica (Urticaceae) and Viola arvensis (Violaceae) . The detection of TuYV was further confirmed by RT-qPCR as well as Sanger sequencing of the PCR fragments. We discovered four new weed species as hosts of TuYV such as T. inodorum , S. alba , G. rotundifolium and E. helioscopia , representing their three respective plant families. The readthrough domain (RTD) gene sequence analysis of the Czech and Slovak TuYV isolates from oilseed rape and weed species showed similar within-group nucleotide divergence (7.1% and 5.6%, respectively) and the absence of geographical- or host-based phylogenetic clustering. The high-throughput sequencing of the P. rhoeas sample enabled the obtention of a nearly complete genome of TuYV and revealed the mixed infection of TuYV with turnip mosaic virus and cucumber mosaic virus. Our results thus show that weed species are an important TuYV reservoir and play a significant role in the spread and incidence of the disease in field crops such as oilseed rape.