. Agricultural plant pest control : a study manual for commercial and governmental pesticide applicators . Weeds; Pests. nucleoid ? Bacteria Bacteria are one-celled microorgan- isms (Figure 1-5) found in air, soil, and water and are common on or in all plants, animals, and humans. In- dividual cells can be seen only with a high powered (900 x) microscope. There are over 170 species of bac- teria causing diseases in plasma membrane ribosomes mesosome cell wall slime layer Figure 1-5. Illustra- tion of a bacteri cell. cell septum Bacteria reproduce by simple cell division at extremely r
. Agricultural plant pest control : a study manual for commercial and governmental pesticide applicators . Weeds; Pests. nucleoid ? Bacteria Bacteria are one-celled microorgan- isms (Figure 1-5) found in air, soil, and water and are common on or in all plants, animals, and humans. In- dividual cells can be seen only with a high powered (900 x) microscope. There are over 170 species of bac- teria causing diseases in plasma membrane ribosomes mesosome cell wall slime layer Figure 1-5. Illustra- tion of a bacteri cell. cell septum Bacteria reproduce by simple cell division at extremely rapid rates. If a single bacterium divided to produce two new cells and all its descendants did likewise every 20 minutes for just 12 hours, 70 billion bacteria would be produced. In 24 hours, 2,000 tons of bacteria would be derived from just a single cell. It's no wonder that flowers, fruits, and vegetables sometimes rot and wilt so quickly. Fortunately, bacterial reproduction is limited by nutrients, temperature, and availability of space. Bacteria enter plant tissue through wounds or natural openings such as the stomata of leaf surfaces. Once inside, pathogenic bacteria multiply rapidly, kill cells or cause them to grow abnormally, break down tissue, and often migrate throughout the plant. Certain bacteria, such as fire blight, produce chemical toxins that poison the plant. Bacteria are spread by people through cultivation, pruning and transporting diseased plant material, such as seeds, bulbs, nursery stock, or transplants. Animals, insects, mites, nematodes, splashing rain, flowing water, and windblown dust are also common disseminating agents for bacteria. ? Viruses Viruses are complex macro-molecules composed of ribonucleic acid (RNA) with a protective protein "overcoat" (Figure 1-6). They resemble the chromosomes present in all living plant and animal cells - both are self-reproducing nucleoproteins. Viruses can only function and reproduce in a living cell. Vir
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