Page 77 - ORNAMENTALES DEL TRÓPICO

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identiFication and management oF ornamental Plant disease ProBlems

A mycelium is a mass of fungal “threads” that can often be seen on or around a lesion. Sclerotia
are small, hard bodies which are the resting state of the fungus. Fungi can survive for years in this

state. If a fungus is suspected as the cause of a disease, but there is no sign of the fungus, a mois-

ture chamber can be made. This is an enclosed bag or container (e.g. coffee can) in which moist

paper towel is put along with a piece of the diseased tissue. After a day or two in the closed can,

mycelium will often be evident if the disease is indeed caused by a fungus.

Along with the symptoms related above for fungi, bacterial infections often produce water

soaking around the area where the pathogen entered. Later the lower surface of the leaf will

take on a dark, greasy appearance. This greasy appearance is most evident in foliar infections,

but can sometimes be seen on other plant organs. Though, these are good indications of a
bacterial disease, one must again look for signs of the pathogen. Often, bacterial ooze can

be seen coming from a lesion, especially in the morning hours. Some bacterial diseases have

distinctive odors. An easy test to determine if bacteria cause wilt symptoms is called a bacterial

streaming test. This may be done by cutting the stem horizontally and inserting it into a jar of

water. If bacteria are present, they will produce a cloudy stream within a few minutes. This

stream is composed of millions of bacteria.

Nematode infections of plants result in the appearance of symptoms of roots as well as
on the above ground portion of the plants. Root symptoms may appear as root lesions, root

knots or root galls, excessive root branching, injured root tips, and as root rots especially when

accompanied by pathogenic fungi and bacteria. The above ground portions of nematode in-

fected plants often appear as stunted, chlorotic, and wilted in hot or dry weather resulting in

poor quality plants. Some species of nematodes invade the aboveground portion of the plants

rather than the roots and on these they cause galls, necrotic lesions and rots, twisting or dis-

tortion of leaves and stems, and abnormal development of the floral parts.

Universidad Autónoma de Chiapas