Arch Virol (1999) 144: 309–316
Australian isolates of ryegrass mosaic rymovirus
and their relationships
A. M. Mackenzie
, D. E. Webster
, B. J. Thomas
, and A. J. Gibbs
Research School of Biological Sciences, Australian National University, Australia
Botany Department, University of Otago, Dunedin, New Zealand
Institute of Grassland Environmental Research, Aberystwyth, U.K.
Accepted September 7, 1998
Summary. The sequences of the 3
-terminal 1.8 kb of the genomes of three
Australian and three Welsh isolates of ryegrass mosaic rymovirus (RGMV) were
determined, as too were the virion protein genes of two New Zealand isolates of
RGMV. They were compared with each other and with the published sequences
of a Danish and a South African isolate by distance and maximum likelihood
methods, and found to be very closely related (mean nucleotide difference 5.5%).
All three Australian isolates and one from North Island of New Zealand formed
one consistent cluster, and the Danish and South African isolates formed another.
However the relationships between these two clusters and the other isolates were
not consistent; they depended on the method of comparison used, and on the
protein, gene or codon position compared. Nonetheless the European (Welsh and
Danish) sequences were 2–4 times more different from one another than those
than the Antipodean. The Danish isolate has 39 nucleotides of the 5
region of its virion protein gene frameshifted -1 relative to the ‘common’
sequence. Interestingly the South African isolate has a similar frameshift, but
sequence comparisons indicate that this frameshift must have occurred indepen-
dently; a possible example of ‘convergent frameshifting’.
Ryegrass mosaic rymovirus (RGMV) [3, 24] infects Lolium perenne and many
other temperate species of the Poaceae. It is transmitted by an eriophyid mite,
Abacarus hystrix, and causes signiﬁcant yield losses. It was ﬁrst found in the
U.S.A. , but has been reported since from Eurasia [21, 22, 25], Africa ,
North America [2, 23], Australia  and New Zealand [9, 26], and is probably
distributed in all temperate parts of the world.