Hiking With A Field Microscope
Copyright © 2004, Wayne Lanier, PhD
Secrets of a San Francisco Deck Garden
TABLE OF CONTENTS
Secrets of a San Francisco Deck Garden
Giant Bacteria Found in Golden Gate Park Flowers...!
Cryptobiotic Soil Unearthed in Utah
Revealing Films of Life in a Cliff-side Seep
A Hard Life Out in the Salt Flats
Beneath the Tufas in Mono Lake
I won't start with a strenuous hike. That comes after everyone is used to carrying a slightly heavier pack and has all the hiking equipment. This first chapter will start with a slight walk out the back door...
Using a field microscope does not always involve heavy hiking. Sometimes staying home can be just as exciting. One hunting ground for the field microscope is a home garden, even if it is only a pot and planter garden on a deck over the garage.
One August day Mary Helen called me out to the deck garden.
She had found curious black and red spots on on the rose leaves. Turns out that she had noticed these spots some time earlier, but the few red spots in the late spring had turned into a forest of both red and black spots by the end of the summer. Since she could not find any insects, she thought it might be a plant virus, or a mold of some kind. Would I take a look...?
One look told me the infestation was serious. In the photograph below you can easily see that some leaves are dull red, or have dull red areas. Close inspection showed almost every leaf had a few spots.
In a close-up view, you can see the many red spots on the upper surface of every leaf. Had I noticed this while hiking I would have immediately realized an opportunity. As it was, I passed these roses many times in a week and never thought to look closer.
Using the mechanical zoom of the camera, I was able to capture a close-up of the leaves at the equivalent of about 2X magnification. In both pictures you can see the leaf veins, as well as many red, or orange spots.
It did not look like a virus. I put one of the leaves under the low-power objective of the field microscope [40X].
I was expecting to see mycelium, the fine filamentous body of a fungus, and some type of spores.
The Swift FM-31 is an inverted microscope, which makes it possible to backlight a leaf for crude photomicrographs of objects on the leaf surface.
I cut a small section of leaf, about 3-mm X 3-mm, placed it on a drop of water on a slide, and pressed a cover slip down over the leaf. This crude preparation enabled me to see some of the structures near a leaf vein. The black objects appeared to be the teliospores of a rust.
Here is why I thought it was a rust: (1) It was clearly a fungal parasite; (2) The rusty-red to orange color on the leaves, which resolve into spores under the microscope; and, (3) the presence of black masses of smaller spores growing on stalks out of the leaves.
The first thing I did was to gently scrape the leaf surface onto a drop of water on a slide. Under the 200X objective, the rusty-red masses were resolved into Urediospores and developing Teliospores. The black masses were mature Teliospores. One of the photomicrographs from that study is shown here.
From several articles, I was able to identify and confirm the structures I was seeing and learn a lot about this fungal plant parasite.
Rusts are parasitic fungi that infect plants. Rusts belong to the basidiomycete fungi, considered to be highly advanced.
The rust life cycle is very complex, sometimes involving alternate life stages on different plant hosts.
The rusty-red Urediospores are round and larger than Teliospores, and born on stalks, forming masses breaking out of the leaf surface.
Stage II is the continuing stage of the rust life cycle.
The network of mycelium in and around the leaf cells produces stalks called “uredinia”. Each uredinium buds off a single-celled haploid urediniospore. Urediniospores are found in clusters, giving the leaves the rusty-red or orange color for which “rust fungi” are named.
Blown or shaken from leaf to leaf, the urediniospores spread the infection over the plant and to leaves of other plants. Landing on a leaf, the urediniospore germinates almost immediately, producing the mycelium that invades the leaf cells. This Stage II cycle continues throughout the summer.
As the summer comes to a close, the rust life cycle turns to Stage III, as the mycelium begins to produce a new kind of spore.
Stage III is composed of Telia, beginning with a stalk arising out of the mycelium. Each Telium produces a number of binucleate teliospores.
Unlike the urediniospores, the teliospores do not germinate immediately and spread the infection. Instead, the teliospores are an over-wintering dikaryotic stage. The two haploid nuclei in the telispore will unite, and the teliospore is then called a probasidium with a diploid nucleus.
In the spring, the probasidium germinates to form a “basidium”, entering Stage IV of the life cycle.
The basidium is the sexual organ of a fungus. The diploid nucleus then undergoes “meosis”, or reduction division, producing 4 haploid gametes called “basidiospores”. This is the infective stage of the life cycle, with the tiny basidiospores blowing in the wind to spread the infection from plant to plant.
1University of Illinois Extension (1989) Report on Plant Disease – Common Rust of Roses. RPD No. 630.