Greasy spot

Scientific name

[Fungus] Mycosphaerella citri Whiteside

Anamorph Stenella citri-grisea (F.E.Fisher) Sivanesan; (syn. Cercospora citri-grisea Fisher)

Other common names

Greasy spot rind blotch

Disease cycle

The major source of inoculuminoculum:
a.) the pathogen or its part that causes infection of the host b.) small amount of a microorganism that is transferred to a substrate or a culture medium in order to propagate it
for greasy spot are wind-dispersed sexual spores (ascospores) produced during periods of wetness on decomposing fallen leaves. The disease cycledisease cycle:
the chain of events involved in disease development, including the stages of development of the pathogen and the effect of the disease on the host
of this pathogenpathogen:
an organism, usually a microorganism, which causes disease by intimate association with its host
is unusual because most of the infection occurs on mature leaves. In areas with high temperature and high rainfall the disease cycledisease cycle:
the chain of events involved in disease development, including the stages of development of the pathogen and the effect of the disease on the host
continues year round and infection may occur at any time.

Symptoms

Leaf - foliar symptoms first appear as yellow spots on the upper leaf surface, with a corresponding slightly raised, pale orange to yellowish brown blister on the lower surface. Later the symptoms on both surfaces become darker brown or black and show a more 'greasy' appearance.

Fruit - fruit exhibit necroticnecrotic:
a cell, group of cells, or tissue that has suffered a rapid destruction and quick death; typically localized and may be caused by injury, radiation, chemicals, toxic substances, or microbiological interactions
specks in the epidermis between the oil glands.

Host range

Greasy spot affects all commercial citrus cultivars. It is most severe on grapefruit, lemon, tangelos and early season sweet oranges.

The fruits and leaves of grapefruit are highly susceptible.

Greasy spot is also known to affect the leaves of other rutaceous genera closely related to citrus, such as Aeglopsis, Fortunella, Murraya, and Poncirus.

Distribution

Greasy spot is found in parts of Asia, Central and South America, the Caribbean, Texas, and Florida.

Other Mycosphaerella spp. have been found in California, Australia, and the Mediterranean, but do not cause greasy spot symptoms.

Easily confused with

Citrus varigated chlorosischlorosis:
an abnormal yellowing or whitening in green plant tissue due to insufficient chlorophyll production
(CVC)

Greasy spot foliar lesions can be differentiated from CVC based on their distribution on the whole tree and individual leaves. CVC symptoms will be restricted to a single branch while Greasy spot symptoms will be throughout the tree and grove. On leaves CVC "lesions" will be interveinal while greasy spot lesions are numerous and random.