Study of root colonization in vitro demonstrated that some of the strains have more ability to root colonization
than others. The population density on roots of plants treated with PE and AE reached to 8.40 and 7.81 log10 CFU
g
-1
root respectively. Strains FE1 and FE2 were not effective root- colonizers as their cell count was less than 5
log10 CFU g−1 root. It seems there is a correlation between root colonization talent of selected strains and their
growth promoting ability, as in the most cases the strains with a high efficacy of root colonization resulted in
Intl J Farm & Alli Sci. Vol., 2 (22): 965-970, 2013
969
increasing growth of plants. In this study, the strains with high ability of root colonization were more effective in
suppressing of Sclerotinia stem rot on cucumber plants. In the most cases, strains with a higher level of root
colonization caused to higher growth of plants. Growth promotion of plants can increase their resistance to disease