Distributional Patterns of Galls of the Cedar/Apple rust – W4D1A

Oct 6, 2015

Distributional Patterns of Galls of the Cedar/Apple rust, Gymnosporangium juniper-virginianae, among the Utah juniper, Osteosperma utahensis, of Western Colorado.

Vyas, D; Marcellus, G; Colmenares, M; Phelps, J; Jennings, B.

Abstract:  Quantitative samples of cedar/apple rust,  Gymnosporangium juniper-virginianae, distribution on Utah juniper, Osteosperma utahensis, were gathered from three sites of varying slope direction and intensity.  Using gathered data a statistically significant positive correlation was observed between incline level and fungus distribution.  It is hypothesized that this pattern is a result of the distribution of Service Berry, an alternate host for Cedar Apple rust and necessary for the multigenerational survival of this fungus. 

Introduction:  Cedar apple rust, Gymnosporangium is a common fungus of western Colorado mesas and an economical important apple pest.  It feeds off the Utah Juniper (Osteosperma utahensis) as well as flora in the Rose family related to apples, like Hawthorn and Service Berry.  In the right conditions, Typically in the spring, the galls will open up with tentacles that release spores.  These spores, depending on the host plant, will spread to the respective opposite.  For example, if the host plant is a Utah juniper, the spores will spread to a rose species like apple or Service Berries.  The same occurs the opposite ways, with the galls on apple related hosts spreading to the Utah Juniper.  In an effort to understand the locational distribution of galls, relation to slope intensity and call density was studied. 

Methods:  On October 5th on Pitkin Mesa three above Paonia Colorado Juniper trees were observed in three zones with differing inclines.  Zone 1 was on a westward-facing slope, zone 2 was on flat ground, and zone 3 sloped down to the east.  Galls were counted on juniper trees within close proximity of three widely-spaced, randomly selected, points within each zone.  The most proximate three trees closest to each point and of approximate equal size, approximately 4 inch diameter at the base of the trunk and 10 feet in height, were selected.  Total gall number was counted on each tree.   

Results: The average number of cedar apple rust galls per tree in juniper trees in zone 1, western facing, was 25.5.  On the flatlands of zone 2, the mean number of galls was 6.8.  Finally, the mean number of galls per tree in zone three, on the east facing slope was 16.2.  The probability of this difference occurring by chance was p <.05 using a two way analysis of variance.

Conclusions:  It was observed that cedar/apple rust was more prevalent on sloped areas than on flatlands.  The rust was also more commonly found on the lower part of the tree.  One potential explanation for these observed distributional patterns is that there may be a higher population of Service Berries found on the inclined area.  Service Berries are an alternate host for Cedar apple rust.  Further investigation about whether Cedar Apple rust density correlate with Service Berry density are warranted.

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