Agriculture Reference
In-Depth Information
spo re germinat ion and active fungal growth. Spores can spread from plant to
plant and crop to crop. Mildew and smut are examples of fungus diseases.
2.
Bacteria
Bacteria are microscopic, one-celled organisms. They usually reproduce
by single cell division. Each new cell possesses all the characteristics of the
parent cell. Bacteria can multiply fast under warm, humid weather conditions.
Some can divide every 30 minutes. Bacteria may attack any part of a plant,
either above or below the soil surface. Many leaf spots and rots are caused by
bacteria. Table 3.8 shows examples of leaf spots and fruit rot.
Figure 3.9
Fungal infection of fruit tree (EPA,
Applying Pesticides Cor-
rectly: A Guide for Private and Commercial Applicators,
1983).
3.
Viruses and Mycoplasmas
Viruses and mycoplasmas are so small that they cannot be seen with an
ordinary microscope. They are generally recognized by their effects on plants.
Often it is difficult to distinguish between diseases caused by viruses or my-
coplasmas and those caused by other plant disease agents such as fungi and
bacteria.
Viruses depend on other living organisms for food and to reproduce. They
cannot exist separately from the host for very long and technically are not
considered to be living organisms. They can induce a wide variety of re-
sponses in the host plants. A few can kill the plant. More commonly the
response is lowered product quality and reduced yields. Mosaic diseases, for
example, are usually caused by viruses.
