Cool season food legumes (faba bean, chickpea, lentil and pea) are one of the world’s most important staple food crops and can suffer from biotic and abiotic constraints that affect both their yield and phenotypic marketability. Luteoviruses cause some of the most devastating crop losses in cool season food legumes, in some cases up to 95%. These severe yield losses can occur in the Central West Asia and North Africa (CWANA) region, where many of the suspected Luteovirids remain either unknown or uncharacterised. As germplasm is sourced from CWANA areas and incorporated into international resistant germplasm breeding programs, there is a need for improved and more definitive detection methods for Luteovirids. Bean leafroll virus (BLRV, genus Luteovirus, family Luteoviridae) was first described in 1954 and has since been reported in USA, Europe, Asia, Africa, the Middle East and Australia. Here we report a survey of BLRV in the CWANA region and Australia.
Freeze dried samples were selected from a collection held at the International Centre for Agricultural Research in the Dry Areas (ICARDA, Syria), the samples selected were required to fit the following criteria: (I) previously test positive for Luteovirus using a broad spectrum monoclonal antibody 5G4 (II) sourced from a cross section of different countries, years and plant species and (III) were sampled from independent fields. Of the samples testing positive to Luteovirus 5G4 monoclonal antibody, 76 were positive when using the BLRV coat protein (CP) PCR test. Of these 76 BLRV CP PCR positive samples, only 19 were positive to the BLRV specific monoclonal antibody 6G4. Considerable variation was observed in the 370 bp BLRV CP region that was sequenced between these isolates when compared to the Syrian strain of BLRV; with sequence similarities ranging from 53.2 to 94%. Notably, one isolate testing positive to both serological and molecular BLRV assays only held a 53.2% sequence similarity with BLRV, being more closely related to the Luteovirid Chickpea chlorotic stunt virus.
The full length genome sequence of three BLRV isolates of importance to the Syrian/Australian BLRV resistance breeding program (from Horsham, Tamworth and Syria) are being generated and will be used to determine conserved and variable regions of the virus genome. This sequence analyses will be used to:
Additional surveys will be conducted in the Wimmera/Mallee and Central New South Wales regions to identify the possibility of geographic influence on BLRV sequence variation and/or conservation. The use and accurate identification of type strains of luteovirid species such as BLRV, are critical for the delivery of virus resistant germplasm by international breeding programs.