Biology and Epidemiology

- Survival and sources of inoculum
 
Aphelenchoides ritzemabosi is a nematode that can easily survive for several months in the soil or on plant debris.
 
 
- Penetration into the plant and invasion
 
Rain or sprinkling irrigation, splashes the nematode on the leaves. Then it moves in the  presence of free water on the leaves and enter the host through stomata. It then gradually colonises the mesophyll cells, where it multiplies abundantly.
 
 
- Dissemination
 
Numerous nematodes formed in the plant tissues exit the tissue through stomata, move easily on the surface of wet leaves and spread on other leaves in contact with the ones they have been originated from. They may also spread to nearby healthy plants by water splash. Aphelenchoides ritzemabosi can also be spread by seed in aster.
 
 
- Favourable conditions for the nematode development
 
The nematode and the disease appear rather late in tobacco crops, when leaves approach maturity. The disease developement is favoured by rainy periods.