Unlike pollen, however, it was not until that fungal spores were thought to cause respiratory allergies. Specifically, Puccinia graminis , the wheat rust was identified to be the cause of allergies of three Canadian who were threshing wheat, but further studies indicated that the allergies were caused by mold spores of Cladosporium , Alternaria and Penicillium spores Feinberg, Wherever spores have been monitored, an abundance of these genera may be observed.
In , in Minnesota and the Dakotas, it was estimated that thousands of tons of spores of Cladosporium and Penicillium were present in the air that blew eastward into the ocean and may possibly have blown across the Atlantic Feinberg, Considering the size of spores and the fact that there was an estimated thousands of tons of spores, the number of spores present must have been astronomical.
It is not any wonder then that the above two genera of fungi are significant factors in the cause of allergies. Although simple, the efficiency dispersal of air borne spores should not be underestimated since most fungi utilize this method to disseminate their spores. Since air-borne spores cannot be seen, it is difficult to appreciate the number of spores that are in the air. However, in order to give you an idea as to the number of spores that are in the air, let us make an indirect comparison with small air-borne objects that are visible to the naked eye.
The ability of any small objects to stay afloat can be readily observed. When we look at the morning or afternoon sun shining through a window, in a room, where the air is still , numerous small particulate pieces of "lint" or dusts, in the light beam can be observed to be kept afloat by the convection of heat generated by the light beam.
So it should not be difficult to imagine that spores, which are far smaller and lighter, would and probably are also present in such a light beam. The extent that spores can travel indoors where the air is still was nicely demonstrated with an experiment carried out by Dr. Clyde Christensen , at the University of Minnesota St. Paul Campus, in the plant pathology building. The experiment used Cladosporium resinae as a " marker fungus " whose spores are not usually found in the air.
In nature this fungus is found only in resin permeated soil, and in wood that has been impregnated with coal tar creosote in order to protect them from decay, such as telephone poles and railroad ties. Because of its requirement for creosote, a "selective medium" containing this compound is not only required for growth of C. Christensen demonstrated the selectiveness of this medium by inoculating decaying plant material with known fungi, and soil samples, on campus, infested with common and uncommon fungi into creosote agar plate medium Figure 2.
Neither the fungi known to be infecting the plant material and fungi present in the soil samples were able to grow on this selective medium, nor was C. Tests were also carried out by exposure of blocks of creosote impregnated wood and agar plates to the air around and inside the plant pathology building. Again, C. The four storied, plant pathology building, in which the experiment was carried out, has stairways at each end, with a hallway in the middle of each floor and does not have a central ventilating system.
In testing the extent to which the C. A culture of C. Remember that Christensen had earlier exposed plates of the creosote agar prior to dispersing the spores and had not recover C.
Therefore, any plates that were now discovered to have this fungus growing on it would be due to the brush dispersal of C. Two of the several tests that were carried out are summarized in Tables 1 and 2. Table 1 summarizes the number of colonies recovered on creosote plates exposed at successive five minute intervals.
In Table 2, seven sets of plates were exposed at each location for intervals of , , , , , and minutes. All plates were incubated and later examined for the number of colonies of the fungus formed on each plate. Colonies were recorded because it is assumed here that each colony was produced from a single spore.
Plates with colonies of C. As might be expected, there were generally more colonies on plates closest to the source, i. Another experiment that you can carry out to demonstrate fungal spores ability to stay afloat can be done with a mature mushroom and an elongated cardboard box approximately 10" high and a yard long Fig 4a.
The basidiospores from the mushrooms are initially "shot off" from the basidia to the area between the gills recall from the last lecture that these structures are characteristic of the Basidiomycota Fig 5a-b.
Under these conditions it would be expected that all of the spores would drop directly below the cap of the mushroom. Although most spores will fall directly beneath the cap of the mushroom, some will manage to stay afloat and travel the length of the box, a yard away Fig. The movement of spores indoors is of significance to the aerobiologist. Thus, the common name "puffballs". The distances that fungal spores are dispersed, outdoors, are equally phenomenal.
Puccinia graminis Wheat Rust has been studied extensively because of its economic importance. The disease has probably been known since the beginning of agriculture and even today the occurrence of wheat rust results in billions of dollars in losses, annually. During the Spring, the urediospores from infected wheat plants are carried northward, from northern Mexico, into the United States, from southern Texas, over the Great Plains and into Canada. During the Fall, the urediospores are carried southward, back down into the wheat growing region where the young winter wheat is beginning to grow.
Studies carried out over almost a thirty year period, have traced the path of wheat rust epidemics along this route. Related to how far spores can travel is how high can spores be found. Not only are spores known to travel great distances, but have also are known to go up to high altitudes. In the early days of aerobiology, during the s, planes flying at 10, feet commonly recovered fungal spores from that altitude.
It is probable that they could have recovered spores at much higher altitudes, but because of the cold and the requirement of oxygen mask at higher altitudes, the scientists doing such studies were not quite as curious about fungal spores beyond 10, feet. Even at the altitudes in which studies were carried out, it was the graduate students that actually went up in the planes to sample for fungus spores. After their return from their great scientific effort, the graduate students involved were often welcomed back as great heroes with the graduate students usually exaggerating the significance and daring of their mission.
In the 's, even Charles Lindbergh, in collaboration with the United States Department of Agriculture, participated in surveying spores while he was flying over the Arctic Circle. Although he was flying lower, only 3, feet, compared to the 10, feet above, Lindbergh was able to catch what was described as a "considerable number of spores". This was of interest since Lindbergh was above the open ocean far from land, giving us an indication as to how far these spores must have traveled.
More sophisticated experiments utilized balloons to find spores in still higher elevations. In , the balloon Explorer II, containing a spore trapping device was released at an altitude of 71, feet and was set to close once the balloon reached 36, feet. Although only five living spores were recovered, think of the conditions in which the spores faced at elevations between 36,, feet. The air must have been very thin at that altitude and the temperatures must have been below freezing.
Wind was also measured by the Explorer II. If winds remained constant at those elevations, it was calculated that fungal spores up in this jet stream could be carried 8, miles in a week. The above experiments not only provided results that demonstrated that fungal spores are capable of traveling long distances, but must and can survive adverse environmental conditions in doing so.
Although wind dispersal of fungal spores is the means by which they travel all over the world, other means of spore dispersal are also found in other fungi. Although these other mechanisms are utilized by far fewer number of species, they are nevertheless interesting mechanisms that deserve a cursory coverage. Where wind dispersed spores are hydrophobic, water dispersed readily absorb water and are said to be hydrophilic.
Water dispersed spores often produce their spores in "slime". Due to the weight of the slime and the fact that the slime masses the spores together, wind dispersal is impossible or at least impractical. What occurs in these spores is that when large amounts of water is present, during a rain or in area where there is water flowing freely, such as in a stream, the spores are carried away, passively. The spores are characteristically shaped, usually with long appendages or are coiled Figure 9.
The spores stay afloat due to the surface tension of the spore or air pockets in the spores. The major source of food for these fungi are from leaf litter and other plant material that may fall into streams. There are a large number of fungi that produce flagella and are motile. However, there is probably too much emphasis placed on their motility.
Considering that these spores are microscopic and have a very low food reserve, it is unlikely that even though they have motility that their flagella can take them any significant distance away from the parent mycelium.
Water, however, does play a role in the dispersal of flagellated fungi. As in the case of the non-flagellated spores, water currents and flowing rainwater will disperse spores. However, their flagella do play a role in finding food. Flagellated spores are usually chemotaxic and will swim towards a chemical source. It is difficult to know where to put some mechanisms of dispersal. There are actually more than one mechanism involved in the group of fungi known as the bird's nest fungi Fig.
The common name is due to the strong resemblance that the fruiting body has with a birds nest. Prior to , they were thought to be flowering plants and the eggs, which contains the spores of the fungus, were thought to be the seeds of the plant.
The actual dispersal mechanism of this fungus was not discovered until the 's by Dr. Harold Brodie, a mycologist that would devote his career on studying this group of fungi. How Dr. Brodie determined the mechanism is an interesting story. However, before telling his story, let's look at the actual fruiting body of the bird's nest fungus.
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