Aphelenchoides ritzemabosi

(checkered leaf disease)
 

Polygonal spots that indicate the presence of this nematode in the leaf lamina are very characteristic (figures 1 to 3), hence the name of the disease ("checkered leaf disease"). The spots  appear first on lower leaves. Their colour is yellowish to light green at first and then turn dark brown and sometimes even black. The spots are always limited by the veins, which is the reason for their polygonal appearance. This disease is vermicular, due to Aphelenchoides ritzemabosi (figure 4) and affects mainly the chrysanthemum. It is relatively uncommon in France where it has been reported mainly in the Southwest, particularly in the Pyrénées Atlantiques region.
 
The genus Aphelenchoides has been  reported on tobacco in many countries but it  has  never been accurately described and it is unclear if the species involved is Aphelenchoides ritzemabosi, except in Japan, where this species causes damage only occasionally.
 
For further information concerning this pathogen, please see the fact sheet of Aphelanchoides ritzemabosi describing this species.