NAME AND AGENCY:
T. Hsiang and J. Richter
Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1
tel: (519) 824-4120x2753, fax: (519) 837-0442, email: firstname.lastname@example.org
TITLE: JUNIPER RUST SPECIES IN AN ONTARIO NURSERY
In early May, 1998, samples of juniper rust were collected from Guelph,
Ontario and Georgetown, Ontario to determine the prevalent species. In
mid-May, 1998, a nursery near Georgetown, Ontario was examined for the
occurrence of juniper rust diseases on six different cultivars of Juniperus
scopulorum. Each tree was inspected for at least five minutes to inventory
all rust infections. The number of infections by each rust species, and
the height and location of each tree were recorded. Ten trees per cultivar
Only cultivars of J. scopulorum were found to have rust infections.
Although species and cultivars were mixed between rows in the nursery near
Georgetown, no rust infections were found on any cultivar of J. chinensis.
Three rust species were found on samples collected.
clavipes was readily distinguishable due to the fusiform swellings
on twigs and larger branches (Fig. 1). While
both G. globosum (Fig. 2) and G. juniperi-virginianae
( Fig. 3) formed galls, those of G. juniperi-virginianaewere
much larger. When present, telial horns could also be used to distinguish
these latter two species: those of G. juniperi-virginianae were
longer and more cylindrical than those of G. globosum, which were
shorter and wider. These descriptions of the Gymnosporangium species
agree with those found in Sinclair et al. (1989).
In addition to macromorphology, microscopic features were also used
especially where identification was not certain. Teliospores of G. clavipescan
be identified by the carotiform shape of the pedicel (Fig.
4). Spores of G. globosum (Fig. 5)
and G. juniperi-virginianae ( Fig. 6)
have cylindrical pedicels, but these species are distinguishable by the
shape and size of the spore body. Spores of G. globosum are 30.0
to 53.6 m in length (Parmelee, 1965), and are ellipsoid with obtuse ends
( Fig. 5). Spores of G. juniperi-virginianaerange
in length from 40 to 75 m (Parmelee, 1965; Laundon, 1977), and are also
ellipsoid but with tapered ends (Fig. 6). After
exposure to water, teliospores will swell and form distinctive jelly-like
structures. Here is an example of teliospores of G. globosum (Fig.
There were striking differences between J. scopulorum cultivars
in incidence of different rust infections (Table 1). Only the cultivar
Moffettii had visible infections of G. juniperi- virginianae. Among
juniper species, J. scopulorum and J. virginiana are the
most susceptible to this fungus, with only a few cultivars of J. chinensisand
J. horizontalis susceptible (Sinclair et al. 1987). Wichita blue
showed a very high level of infection by G. globosum, but all cultivars
showed some level of infection. The most common juniper hosts of this fungus
are J. scopulorum and J. virginiana, with J. horizontalis
and J. communis to a lesser extent (Sinclair et al., 1987). .Gymnosporangium
clavipes was found on all cultivars except Gray Gleam. This fungus
is found on J. virginiana, J. scopulorum, J. horizontalis,
J. communis and a few other species (Sinclair et al., 1987)
In an early paper on susceptibility of Juniper cultivars to two rust species in Illinois, cultivars of J. scopulorum were found to be very susceptible to G. juniperi-virginianae but resistant to G. clavipes.
A more recent report on susceptibility of juniper cultivars to G.
juniperi-virginianae in Kansas found almost no infections on J.
chinensis cultivars, and low to heavy infections on different cultivars
of J. virginiana and J. scopulorum (Tisserat & Pair,
1997). Among the cultivars in common between that study and the current
one, moderate levels of rust infection were found on Moffettii and Gray
Gleam, low levels on Skyrocket and Wichita Blue, and none on Medora. This
illustrates that disease ratings may differ between different locations,
and hence more local testing of susceptibility should be conducted before
recommending juniper cultivars for rust disease resistance.
Laundon, G. 1977. Gymnosporangium juniperi-virginianae. CMI Descriptions of Pathogenic Fungi and Bacteria No. 547. Commonwealth Mycol. Inst., Kew, England.
Parmelee, J.A. 1965. The genus Gymnosporangium in eastern Canada. Can. J. Bot. 43, 239-267.
Sinclair, W.A., H.H. Lyon and W.T. Johnson. 1989. Diseases of trees and shrubs. Comstock Publishing Assoc. Ithaca, New York. p.240-249.
Tisserat, N.A., and J.C. Pair. 1997. Susceptibility of selected juniper
cultivars to cedar-apple rust, Kabatina tip blight, Cercospora needle blight
and Botryosphaeria canker. J. Environ. Hort. 15:160-163.
Table 1. Incidence of Gymnosporangium rusts on Juniperus scopulorum cultivars in an Ontario nursery in late May 1998.
|G. clavipes||G. globosum||G. juniperi-virginianae|
|Skyrocket||27.2 ± 0.97a||27.3 ± 1.10||0 ± 0||163 cm|
|Wichita blue||7.9 ± 0.36||84.1 ± 2.43||0 ± 0||169 cm|
|Greenspire||2.4 ± 0.53||5.3 ± 0.38||0 ± 0||139 cm|
|Medora||0.3 ± 0.05||9.3 ± 0.72||0 ± 0||140 cm|
|Gray Gleam||0 ± 0||2.6 ± 0.20||0 ± 0||108 cm|
|Moffettii||12.5 ± 0.74||27.4 ± 1.26||0.2 ± 0.04||158 cm|
NOTE: another site with photos of Juniper