A virus of an isolated indigenous flora spreads naturally to an introduced crop species

Hardenbergia mosaic virus (HarMV) is an aphid‐borne potyvirus widespread in its natural host Hardenbergia comptoniana, a legume endemic to the isolated flora of southwestern Australia. As populations of wild Lupinus angustifolius (narrow‐leafed lupin) became naturalised in the region in the 1930s and cultivars were introduced in 1967, both species have sometimes grown in close proximity. The aim of this research was to determine whether HarMV, present in H. comptoniana, could be transmitted naturally by aphids to L. angustifolius in the field. Field plots of L. angustifolius cv. Mandelup were established and interplanted with H. comptoniana plants infected with HarMV. Naturally occurring aphids were relied on to spread the virus. Plants were monitored for virus symptoms. Potyvirus infection was detected in leaf samples by enzyme‐linked immunosorbent assay (ELISA) and reverse transcription‐polymerase chain reaction (RT‐PCR), and HarMV presence by nucleotide sequencing. Seed from infected L. angustifolius plants was sown and the seedlings tested for virus infection by ELISA. In 2009 and 2010, HarMV was spread from H. comptoniana plants to L. angustifolius plants by naturally occurring aphids in field plots. In 2009 and 2010, respectively, 5% and 31% of L. angustifolius plants became infected with HarMV. In 2009, the infected plants died, but in 2010, symptoms included plant stunting, necrotic stem streaking, tip wilting and, occasionally, death. Grain yield was reduced by 86%. Seed transmission was not detected. Three aphid species identified in the test plots were Myzus persicae, Acyrthosiphon kondoi and Rhopalosiphon padi. These results indicate that in a simulated new encounter scenario, indigenous HarMV spreads naturally from its native plant host to the recently introduced crop species L. angustifolius.