Phytochemicals induced in chickpea roots selectively and non-selectively stimulate and suppress fungal endophytes and pathogens

Plant roots shape the structure of the soil microbiome by producing a wide array of phytochemicals, which in turn impact plant growth and health. The synthesis of root metabolites is a dynamic process that is modulated by interactions with soil microorganisms. This study explored the regulation of soil-borne fungal endophytes and pathogens by the production of phytochemicals in chickpea (Cicer arietinum L.) roots colonized or not colonized by the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis. Proteins and low-molecular-mass phytochemicals were extracted from chickpea roots and fractionated by flash chromatography and high pressure liquid chromatography (HPLC). The effects of these metabolites on the soil-borne fungal endophytes Trichoderma harzianum and Geomyces vinaceus and on the pathogens Fusarium oxysporum and Rhizoctonia solani were tested in 96-well plate assays. One protein fraction from the AM roots, which contained an apparent 34 KDa chitinase/chitin-binding domain and 24 KDa non-specific lipid transfer protein, non-selectively repressed the fungal endophytes and pathogens. By contrast to the protein fraction, the low-molecular-mass fractions were often selective. Eighteen fractions stimulated specific fungal species and seven fractions inhibited others. Several protein and low-molecular-mass phytochemicals in chickpea roots influence fungal endophytes. The difference in the response of fungal species to the phytochemicals suggests that these metabolites could be involved in the so called host 'preference' of fungal endophytes or 'resistance' to pathogens. This research reveals that the majority of the bioactive root metabolites could be involved in the selective association of chickpea and fungal endophytes while a few compounds provided resistance by suppressing the pathogenic species.