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identiFication and management oF ornamental Plant disease ProBlems

seen without a microscope. They have no chlorophyll and though they do have cell walls,
the walls are not made of cellulose as in true plants. Many species of fungi produce spores,

reproductive structures that aid in dispersal and survival. Most fungi can be identified by mor-

phological characteristics such as shape and size of their spores. Some fungi have no spores

(i.e. Rhizoctonia). Rhizoctonia can be identified by the very characteristic right angle branching

of fungal threads.

Fungi can penetrate directly through the cuticle of plants; therefore, they do not need na-

tural openings in the plant or wounds for access. Though fungi cause more diseases than bac-

teria, bacterial diseases can be some of the most difficult to control and can be devastating to

plants. Bacteria definitely are not plants. Again, they are classified in a Kingdom separate from
Plants, Animals, and Fungi. They are one-celled organisms that are so small that they can be

seen only with a powerful light microscope. Though some bacteria do produce spores, there

are no plant pathogenic bacteria that produce spores. Some bacteria can survive in the soil in

decaying plant material for a time. Unlike fungi, they usually need a host to survive.

Bacteria are dependent on outside agents for dispersal. Splashing water is the chief means

by which bacteria are disseminated. Another important means of dispersal is through human

contact. Simply touching an infected plant and then touching a healthy plant can spread many
bacterial diseases. Bacteria cannot penetrate the cuticle of plants, but must enter the plant

through a wound or natural opening.

Nematodes belong to the kingdom Animalia. Nematodes are wormlike in appearance,

but taxonomically distinct from true worms. Numerous species of nematodes attack and pa-

rasitize humans and animals, in which they cause various diseases. Several hundred species,

however, are known to feed on living plants, obtaining their food with spears or stylets and

causing a variety of plant diseases worldwide.

Universidad Autónoma de Chiapas