Biology and Epidemiology

- Survival and sources of inoculum

Ralstonia solanacearum easily survives in many soils for several years, especially in plant debris and soils with a high water holding capacity. R. solanacearum has been found down to 30 cm in depth. The inoculum density of soil can be maintained or increased during the production of any susceptible plants in the field. This bacterium is able to infect many crops (sunflower, peanut, pepper, cassava, etc.) and weeds. Over 200 plant species, mostly dicotyledons, are susceptible to be attacked. Severity of outbreaks often depends on the density of the soil inoculum of and on the aggressiveness of the particular strain present.

 
- Penetration into the plant 
 
As a root system grows in soil, various injuries may occur:
- either natural, especially at the point of emergence of lateral roots;
- or wounds related to use of tools, damage caused by root-knot nematodes (Meloidogyne spp.) (figure 1), or insect bites.

These wounds, more or less temporary, form effective avenues for Ralstonia solanacearum. They facilitate its entry into the roots and movement to the vessels where bacterial multiplication is faster.

 
- Dissemination  
 
R. solanacearum can be disseminated by water, through runoff from contaminated soil, or contaminated plants and farming tools. It can also be spread by the workers during topping and sucker removal.

 
- Favourable conditions for the bacteria development 
 
This bacterium develops in warm temperatures. It grows well at temperatures between 25 and 35 ° C. Moist soils with moderate pH are most favorable to infestation and pathogen activity. R. solanacearum does not do well in dry soil conditions or at temperatures below 10 ° C. Adding high levels of nitrogen fertiliser makes plants more susceptible to the disease.