Biocontrol and plant growth promoting properties of Streptomyces mutabilis strain IA1 isolated from a Saharan soil on wheat seedlings and visualization of its niches of colonization

• Biocontrol and wheat growth promoting abilities of Saharan Streptomyces were assessed.
• Bacterial niches of colonization within seedlings were investigated using DOPE-FISH.
• DOPE-FISH confirms the bacterial establishment within various compartments of the plant.
• The bacterial involvement enhanced plant growth and protection against F. culmorum.

In this study, the biocontrol ability and colonization behavior of a highly antagonistic Streptomyces mutabilis strain, named IA1, recently isolated from a Saharan soil, were assessed on wheat seedlings. In this study we showed that strain IA1 secretes IAA and GA3 and is able to enhance growth of wheat seedlings. Using DOPE-FISH coupled with confocal laser scanning microscopy (CLSM), we observed moreover that following caryopsis inoculation and plant growth the strain can colonize the rhizoplane, the surface of caryopsis as well as the endorhiza, crossing from the rhizodermis up to the vascular system. Interestingly, further visualizations revealed that the actinobacterial strain could also be endophytic inside the caryopsis up to the endocarp layer (the dried fruit part, not the seed part of grain). Disease caused by Fusariumculmorum was further evaluated on seedlings and results showed that coated seeds with strain IA1 can reduce both disease occurrence (64.7%) and decrease severity (79.6%). This study showed that strain IA1 derived from a Saharan soil could protect a temperate crop from F. culmorum seedling blight, promote growth and colonize various niches on the surfaces of the phytosphere (roots, seeds) as well as plant endosphere compartments.