The role of soil structure on colonization efficiency of the pathogen Rhizo
ctonia solani is analysed by linking experimental techniques that control a
nd quantify soil structure with epidemiological concepts that deal with the
fungal dynamics of colonization.
The dynamics of colonization efficiency are quantified for the fungal colon
y spreading through replicated samples of a nonsterile sandy loam with diff
erent physical properties. The effect of bulk-density and aggregate-size on
the air-filled pore volume is assessed by examination of thin soil section
s and by quantification of pore-size distributions estimated from water-ret
ention characteristics.
An increase in bulk-density and a reduction in aggregate size increased the
fraction of micropores in the air-filled pore volume at the expense of lar
ger pores. These changes resulted in smaller, more slowly expanding fungal
colonies and significantly reduced the volume of soil from which a nutrient
source can become colonized.
It is concluded that colonization efficiency is a convenient way to summari
ze the complicated dynamics of mycelial growth through soil. We use the res
ults to discuss the effect of soil structure on the saprotrophic and parasi
tic invasion of soil by fungi.