Detection and genetic diversity of alfalfa dwarf disease-associated viruses in lucerne pastures in Argentina and Australia

SAMARFARD, SAMIRA; BEJERMAN NICOLAS; SHARMAN, M.; DIETZGEN RALF

Workshop; 13th Australasian Plant Virology Workshop; 2018

In 2010 a devastating disease of lucerne, named alfalfa dwarf disease (ADD) occurred in commercial fields in Argentina causing reduced seed yield. Next generation sequencing of ADD-infected lucerne plants in Argentina revealed the presence of a new cytorhabdovirus, alfalfa dwarf virus (ADV), the (+) RNA viruses, alfalfa mosaic virus (AMV), bean leafroll virus (BLRV) and alfalfa enamovirus 1 (AEV-1) and the DNA virus alfalfa leaf curl virus (ALCV). Due to the economic impact of ADD in Argentina and its potential threat to the Australian lucerne industry, we developed a set of diagnostic assays to determine the potential presence of ADD-associated viruses in Australia. In this study, lucerne leaves with virus-like symptoms were collected from seed crops in South Australia and fodder crops in Victoria and Queensland. A sensitive duplex RT-PCR was developed for detection of ADV and AMV. Similarly, the presence of BLRV and AEV-1 was determined by duplex RT-PCR and ALCV by PCR. Neither ADV, AEV-1 nor ALCV were detected in any lucerne samples we tested from 2015-17. However, AMV and BLRV were detected in some samples, with a high incidence of AMV in symptomatic seed production paddocks. ADV genetic diversity across Argentine lucerne regions was 1% or less indicating it may have arrived recently. Genetic diversity of AMV and BLRV in Australia was 2% or less, and isolates in both countries are also very similar. Ongoing epidemiological studies in Argentina will assist in the development of a biosecurity plan to prevent ADD from occurring in Australia.