Detection and distribution of alfalfa dwarf disease-associated viruses infecting lucerne pastures: potential biosecurity implications for Australia

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

Congreso; Science Protecting Plant Health; 2017

Virus diseases can cause significant economic losses in agricultureand may pose biosecurity risks for crop production and trade. In 2010 adevastating disease of lucerne, named alfalfa dwarf disease (ADD) with an incidencegreater than 70%, occurred in several commercial fields in Argentina and causedup to 30% annual yield and seed weight reduction. Next generation sequencing andfield surveys of ADD-infected lucerne plants in Argentina revealed the presenceof a new cytorhabdovirus, alfalfa dwarf virus (ADV), the (+) RNA viruses alfalfamosaic virus (AMV), bean leafroll virus (BLRV) and alfalfa enamovirus 1 (AEV-1)and the DNA virus alfalfa leaf curl virus (ALCV). All these viruses appear tobe transmissible by Aphis craccivora.Due to the economic impact of ADD in South America and its potential threat to theAustralian lucerne industry, we developed diagnostic assays to determine the potentialpresence of ADD-associated viruses in Australia. In this study, lucerne leaveswith virus-like symptoms were collected from seed crops in South Australia andfodder crops in Victoria and Queensland. A sensitive duplex RT-PCR assay wasdeveloped for simultaneous detection of ADV and AMV using a clonednon-infectious ADV RNA as positive control. Similarly, the presence of BLRV andAEV-1 was determined by duplex RT-PCR and ALCV by PCR assay. None of the exoticviruses ADV, AEV-1 and ALCV were detected in any lucerne samples we tested in2015/16. However, the endemic AMV and BLRV were detected in some samples, witha high incidence of AMV in symptomatic seed paddocks. Symptoms in the collectedsamples varied widely and there was no obvious correlation between the symptomsobserved in individual samples and presence of individual viruses. Futureepidemiological studies in Argentina will assist in the development of abiosecurity plan to prevent ADD from coming to Australia.