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VIRUS IN ROSES IN NEW ZEALAND
There are three virus known to
affect roses in NZ - rose petal fleck (RPF), prunus necrotic
ringspot (PNR or Rose Mosaic), and rose Hunter's Colour Break
(RHCB), although only the first two appear to be common.
Rose Petal fleck affects the
veins of the petals, causing streaking and blotchiness of the
colour pigment (most obvious in the darker colour range of
flowers) and often distorting the flowers also. The virus
causes the pigmentation to collect in groupings in the veins,
hence the streaking blotching distortion etc sometimes put
down to "weather damage". Prunus necrotic ringspot
(Rose Mosaic) manifests as yellowish mottling and veining on
the leaves, reducing vigour and causing dieback on mature
canes. It may also cause premature leaf drop in autumn.
Hunter's Colour break virus creates green veining of the outer
flower petals and often a green "cabbage" centre.
It has been scientifically proven
that these diseases reduce plant vigour and flower production
by 20% to 40% and that the flowers are smaller and do not last
as long when picked, that the petal texture is weakened, and
that the plant declines in health.
A plant may be virused and show
no symptoms at all, or the symptoms may appear sporadically,
most often in spring. This is termed masking and is the only
reason some people think the virus spreads in their roses.
It must be emphasised rose virus
do NOT spread from plant to plant in your garden and they are
not transmitted by pruning secateurs or other gardening tools,
or by insects such as aphids.
Dr Phil Gardner, New Zealand's
recognised rose virus expert now deceased, did considerable
work in this area and he verified that the only way of spreading the virus is by using
propagation material from infected plants or understock. Our
observations over the many years of testing verify this.
The disease is systemic, so the
entire plant is affected, and will remain so, and although I
have seen the virus in many countries overseas, (the virus is
common in those areas using cutting understocks), the visual
affect (manifestation) is very dominant here in New Zealand.
In the early 1970's when it was
realized just how widespread and serious the virus problem was
in NZ, a procedure for preventing their spread and eventually
totally eliminating them from the production cycle of a
commercial nursery was devised, largely initiated by Dr Phil
Gardner.
This on-going programme involves
a testing procedure to identify whether or not the virus
is present, as well as sourcing virus-free plant material for understocks and clean varieties to propagate from.
New stockbeds of virus free understocks are
established, and only these, along with virus free varieties,
many re-imported from overseas, are used for propagation
material.
Originally the term "High
Health" was used to describe those superior virus free
plants. Unfortunately the elimination, inspection and accreditation
programme proposed by Dr Gardner (where a grower was permitted
to use the trademarked "High Health" logo only after
achieving the required virus -free accreditation of modern
varieties grown) was not implemented by rose growers in
the country. Virus infected plants continued to be produced
and marketed by some nurseries even while advertised as
"High Health" to gain the marketing advantage.
Because no nationwide publicity programme is undertaken to
educate the gardening public of its real meaning, many
interpreted the "High Health" logo to mean varieties
that are not susceptible to any form of fungal disease or
insect attacks. With the gradual realization that this was not
the case, and the on-going problem of many supposedly
"High Health" roses in the market place still being
virus infected, the logo term lost much of it's meaning
and impact.
The continued abuse and
misinterpretation of this logo by grower retailers, and the
general public is an unfortunate fact.
Always passionate about roses and
the importance of virus free plants, Bob and Cath Matthews of
Matthews Nurseries, Wanganui, have maintained this programme
on an ongoing basis for many years now, at considerable
expense of time and money. Becoming disillusioned with past
politicking and the laissez-faire attitude that prevented a
united move by rose growers to wholeheartedly embrace the
virus-free concept and programme, Matthews, one of the largest
and oldest nationwide rose wholesalers have introduced their
own registered logo (Matthews Virus Tested, MVT) so that they
are able to supply the market with certified, genuine virus
free roses.
The introduction of this logo may
also help eliminate some of the confusion about the "High
Health" logo.
All the nurseries modern
varieties are put through their own virus-free test for both
petal fleck and colour break virus, and were tested for prunus necrotic ringspot at Massey University using the enzyme
linked immunosorbent assay serological test method. (Elisa).
This nursery testing programme
can take up to three years or more before Matthews can certify
a variety is clean. Records are held for all testing and the
logo is used for that variety only when all tests are
completed.
In recent years Matthews
Nurseries have become introducers and agents of many world
class breeders and this has enabled them to ensure that all Matthews recent and future introductions are
guaranteed virus free. Where necessary they have re-imported
other varieties, to ensure these varieties are properly
represented here in New Zealand with virus free roses.
Bob Matthews
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