Download Garden, Easter Lilies Infected by Viruses, Vol.15, Issue 1

OREGON
June 1971
ORNAMENTAL AND
Vol. 15, Issue 1
NURSERY DIGEST Page 1,2
Thomas C. Allen
Department of Botany and
Plant Pathology
Oregon State University
Corvallis, OR
GARDEN, EASTER LILIES INFECTED BY VIRUSES
I have not examined an Easter or garden lily in Oregon that did not contain at least one virus.
Lily researchers in Denmark and Holland report a similar situation with their home-grown lilies.
Therefore, Oregon cannot be blamed for the virus content in lilies. The blame must be placed on
the lily itself and its method of propagation. Any crop that is vegetatively propagated, such as
lilies, is bound to contain viruses. For instance, potatoes grown in Oregon have at least one and
probably two viruses.
Good control programs protecting plants from insect vectors of viruses and removing plants with
obvious virus symptoms can reduce viruses in lilies. Even if all lily plants with virus symptoms
are removed, virus-infected plants which appear to be healthy will be present. Some plants may
have been infected recently and the virus has not built up enough to cause symptoms, and some
viruses do not produce plant symptoms. In both of these cases, symptoms are not visible and the
viruses are spread unknowingly by growers.
One virus affects lilies universally
One lily virus, aptly named the "lily symptomless virus," appears to infect lilies universally. Why
should we be concerned about a virus that does not visibly affect a plant? The concern is not for
the present appearance of the virus-infected lily, but for the future, knowing that symptoms will
show under certain environmental conditions. F. P. McWhorter, Professor Emeritus of Plant
Pathology at Oregon State University, told me of an experiment with Ace lilies infected with a
virus disease named curl-stripe. When the infected lilies were harvested from coastal fields, half
of them were replanted in the Willamette Valley and appeared healthy. Yet the other half,
planted along the coast, showed curl-stripe symptoms. Thus, the grower along the coast had to
pay for roguing the diseased plants, while the Willamette Valley grower saved his money.
Subsequently, bulbs from both areas were forced in greenhouses for Easter lily production. The
forcing environment favored curl-stripe symptom expression. Now the formerly healthy appearing
bulbs from the Willamette Valley produced many more plants with curl-stripe than the rogued
coastal lot. The virus content was originally equal in both lots, but symptom expression depended
upon environmental conditions.
When I have taken curl-stripe diseased plants into a greenhouse, the plants consistently recovered
and appeared healthy. When symptomless, the virus was called " lily symptomless virus"; when
leaves curled and were striped, the virus was called "curl-stripe virus." Obviously, the virus did not
change, but was one virus. Serology and electron microscopy have confirmed this conclusion.
The length of the virus particles from
healthy Ace lilies and those diseased with
curl-stripe was the same, 640 nanometers
(nm). When magnified 57,000 times, these
virus particles appear about 1½ inches long
(Figure 1). In comparison, a 6-foot-tall man
magnified 57,000 times would have a height
of 65 miles. Virus particles 640nm long also
have been associated with Lilium
longiflorum ‘Nellie White,’ L. speciosum
with mild mottle symptoms, L. wilsoni,
various hybrid garden lilies, and tulips with
tulip breaking or tulip mosaic.
Necrotic fleck caused
This same lily virus when combined with
cucumber mosaic virus caused necrotic
fleck in Ace and Nellie White lilies. Since
neither virus alone causes symptoms under
some environmental conditions, the
presence of one or the other virus in a
healthy-appearing lily is a potential hazard.
Figure 1. Electromicrograph of virus
particles extracted from a curl-stripe diseased
Ace lily. Virus particles have been plated with
a platinum: palladium alloy to enhance
contrast and create a shadow. Magnification
is 57,000X.
Another virus found in Oregon lilies has particles 750nm long. Lilies infected with this virus are
immediately recognized as virus diseased by the bright yellow mottled leaves. This virus is present in
hybrid garden lilies, in tulips, and in Ace lilies with classical fleck disease. In this latter disease, the
640nm virus and cucumber mosaic virus also are present. In some plants of L. wilsoni and tulips,
both the 750nm virus and the 640nm virus are present.
When ultrathin sections of leaves containing the 750nm virus are examined, pinwheel or tubular
inclusions are present (Figure 2). These inclusions are characteristic of viruses 750nm long.
Serological tests indicate that this is the tulip virus.
Figure 2. Electromicrograph
of pinwheel (PW) and
tubular (T) inclusions within
a leaf cell of the hybrid
garden lily ‘Bright Star.’
These configurations are
characteristic of a 750nm
virus infection Magnification
is 35,100X.
Thus, we know there are at least three distinct viruses in Oregon lilies. None are unique to Oregon,
and the three viruses are associated with various virus diseases whose names do not indicate the virus
involved. All three viruses are aphid or vegetatively transmitted and therefore are controllable.
Oregon Ornamental and Nursery Digest was published from 1957 to 1975 by the Agricultural Experiment Station,
Oregon State University, Corvallis.
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