Graphiola Leaf Spot

Other Common Names

false smut

Scientific Name of Pathogen

Graphiola phoenicis: Kingdom Fungi, Phylum Basidiomycota

Hosts

Graphiola phoenicis has been reported on numerous palm species, but is most commonly associated with Phoenix canariensis and Phoenix dactylifera.

Other palms on which G. phoenicis has been observed include:  Acoelorrhaphe wrightii, Arenga pinnata, Butia capitata, Chamaerops humilis, Coccothrinax argentata, Cocos nucifera, Dypsis lutescens, Livistona alfredii, Livistona chinensis, Phoenix loureirii, Phoenix paludosa, Phoenix roebelenii, Phoenix sylvestris, Phoenix theophrasti, Prestoea acuminata, Roystonea regia, Sabal minor, Sabal palmetto, Syagrus romanzoffiana, Thrinax morrisii, and Washingtonia robusta.

Distribution

The pathogen has a worldwide distribution.

Symptoms/Signs

With Graphiola leaf spot, the signs of the disease are more prevalent and more easily observed than the symptoms of the disease. Both signs and symptoms will be observed on the oldest leaves, which are the lowest leaves in the canopy.

The initial symptoms of the disease are very tiny (1/32 inch or less) yellow or brown or black spots on both sides of the leaf blade. They are easily missed without close observation. The fungus will emerge from these spots, rupturing the leaf epidermis (leaf surface). It is the resulting fungal reproductive structures (sori) that are most commonly observed, and which obscure any true symptoms (Fig. 1).

The sorus (sori is the plural form) is a fruiting body that is less than 1/16 inch in diameter. As the sorus matures and yellow spores are produced, short, light-colored filaments (thread-like structures) will emerge from the body, and the sorus becomes black (Figs. 2 and 3). These filaments aide in spore dispersal. Once the spores are dispersed, the sori deflate and appear like a black, cup-shaped body or black crater. You can easily see the sori, but you can also feel the sori with your finger as they are raised above the leaf epidermis. The number of sori indicates the level of infection.

This is a disease that can be easily identified by examining the leaf, as the fungus is easily observed with the unaided eye. A simple magnifying glass will provide adequate "close-up" views.

May Be Confused With

Graphiola leaf spot is often confused with potassium deficiency. However, the initial leaf spot symptoms of Graphiola leaf spot are minute in comparison to those associated with potassium deficiency. Furthermore, if a palm is exhibiting potassium deficiency, Graphiola leaf spot can be superimposed on the potassium deficiency (Figs. 1 and 4).

It is quite possible to observe Graphiola leaf spot and another leaf spot disease occurring on the same leaf and to observe the sori of Graphiola phoenicis occurring within the symptomatic leaf spot of the other disease (Fig. 5).

December 1, 2010