Chitin amendment raises the suppressiveness of soil towards plant pathogens and modulates the actinobacterial and oxalobacteriaceal communities in an experimental agricultural field

A long-term experiment on the effect of chitin addition to soil on the suppression of soil-borne pathogens was set up and monitored for eight years in an experimental field, Vredepeel, the Netherlands. Chitinous matter obtained from shrimps was added to soil top layers at two different occasions and the suppressiveness of soil towards Verticillium dahliae as well as plant-pathogenic nematodes was assessed, in addition to analyses of the abundances and community structures of members of the soil microbiota. The data revealed that chitin amendment had raised the suppressiveness of soil, in particular towards Verticillium dahliae, 9 months after the (second) treatment, extending to two years following treatment. Moreover, major effects of the added chitin on the soil microbial communities were detected. First, shifts in both the abundances and structures of the chitin-treated soil microbial communities were found, both of total soil bacteria and fungi. In addition, the abundances and structures of soil actinobacteria and Oxalobacteriaceae were affected by chitin. At the functional gene level, the abundance of specific (family-18 glycoside hydrolase) chitinase genes carried by the soil bacteriota also revealed upshifts as a result of the added chitin. The effects of chitin noted for the Oxalobacteriaceae were specifically related to significant upshifts in the abundances of the species Duganella violaceinigra and Massilia plicata. These effects of chitin persisted over the time of the experiment.