plant diseases and fungi

         About 85% of all plant diseases are caused by fungi. Therefore, on a statistical basis alone, you are likely to encounter fungal diseases much more often than those caused by other types of pathogens. We will now proceed to a description of the main characteristics of fungi.
Fungi include the molds and mildews that we are all familiar with in Florida.
At one time fungi were considered to be types of plants. Indeed, mycology, the scientific study of fungi, is still done today in botany departments. However, in modern biology, fungi are not considered plants. They are placed in their own Kingdom (Mycota, for the serious biologists out there), with equivalent status to the familiar Animal and Plant Kingdoms.
Sometimes, growth of fungi is so profuse that a large enough mass (mycelia - multicelled microscopic strands) will accumulate to be seen with the naked eye. A good example is the growth of the target spot fungus on this ripe tomato fruit.

Figure 1
Target spot on ripe tomato fruit.

Most of the time, however, careful examination with a microscope is needed to see fungi and ultimately identify them. Fungi consist of multi-celled microscopic strands. Often, spores, or the reproductive structures of fungi are readily visible, as seen in this photomicrograph of the fungus Botrytis.
Figure 2

It is the peculiar size, shape, coloration, etc. of these Botrytis spores that are most useful in identification of fungi, including those that cause plant disease.
Figure 3
Sometimes, we encounter important pathogenic fungi that do not readily form spores. A good example is the root-infecting fungus, Rhizoctonia, shown here.

We take note of the distinctive right-angle branching of the fungal threads (mycelia) in making an identification of Rhizoctonia.