Indigenous and introduced potyviruses of legumes and Passiflora spp. from Australia: biological properties and comparison of coat protein nucleotide sequences

Abstract

Five Australian potyviruses, passion fruit woodiness virus (PWV), passiflora mosaic virus (PaMV), passiflora virus Y, clitoria chlorosis virus (ClCV) and hardenbergia mosaic virus (HarMV), and two introduced potyviruses, bean common mosaic virus (BCMV) and cowpea aphid-borne mosaic virus (CAbMV), were detected in nine wild or cultivated Passiflora and legume species growing in tropical, subtropical or Mediterranean climatic regions of Western Australia. When ClCV (1), PaMV (1), PaVY (8) and PWV (5) isolates were inoculated to 15 plant species, PWV and two PaVY P. foetida isolates infected P. edulis and P. caerulea readily but legumes only occasionally. Another PaVY P. foetida isolate resembled five PaVY legume isolates in infecting legumes readily but not infecting P. edulis. PaMV resembled PaVY legume isolates in legumes but also infected P. edulis. ClCV did not infect P. edulis or P. caerulea and behaved differently from PaVY legume isolates and PaMV when inoculated to two legume species. When complete coat protein (CP) nucleotide (nt) sequences of 33 new isolates were compared with 41 others, PWV (8), HarMV (4), PaMV (1) and ClCV (1) were within a large group of Australian isolates, while PaVY (14), CAbMV (1) and BCMV (3) isolates were in three other groups. Variation among PWV and PaVY isolates was sufficient for division into four clades each (I-IV). A variable block of 56 amino acid residues at the N-terminal region of the CPs of PaMV and ClCV distinguished them from PWV. Comparison of PWV, PaMV and ClCV CP sequences showed that nt identities were both above and below the 76-77% potyvirus species threshold level. This research gives insights into invasion of new hosts by potyviruses at the natural vegetation and cultivated area interface, and illustrates the potential of indigenous viruses to emerge to infect introduced plants.