Page 76 - ORNAMENTALES DEL TRÓPICO

76 Ornamentales del trópicO

Viruses are the smallest of the three pathogens mentioned here. They can only be seen
with an electron microscope. They are not plants or animals; in fact, they may not be alive at

all. Viruses are genetic material (RNA or DNA) wrapped in a protein coat. They must have a

living host in order to reproduce. Viruses are usually vectored from diseased to healthy plants

by insects. In Florida, aphids or whiteflies vector most viruses.

Common Symptoms and Signs in the nursery and landscape

Symptoms are abnormal states that indicate something is wrong. It is important to be able to use

the proper name for a symptom. Many are self-explanatory. A spot is just that, a spot. It is ne-

cessary to also mention the part of the plant, which is infected. If there are spots on the leaves,

it will be called a leaf spot; on the fruit, a fruit spot. As spots grow and coalesce, the symptom

may be termed a blight. This differs from a spot because larger amounts of tissue are affected.

Galls or tumors may be found on stems or sometimes on leaves. These are masses of undiffe-

rentiated tissue growth (similar to cancerous tumors in people). Cankers, found most often on

stems, are sunken lesions. Wilts and rots are just what the names imply. It is important to note
that a rot does not have to be wet and “yucky”; there are dry rots. Damping off is another term

that is often used to describe the rotting of seedlings as they emerge from the soil. Most of these

symptoms can be caused by any of the pathogen groups at one time or another.

It is important to remember that a positive diagnosis of a plant disease is often difficult or

nearly impossible on the basis of symptoms alone. Too often, symptoms of specific diseases

overlap. To properly identify a disease, one must look for the signs of the pathogen. A sign of

the pathogen is the presence of the pathogen, itself.
In fungi, one can often see the actual fungal growth. Examples of these signs are mycelium

directly invading plant tissue, powdery or downy mildew, rusts, sclerotia, conks and mushrooms.

Universidad Autónoma de Chiapas