Endophytic Microbial Community of Wheat (Triticum aestivum L.) Seeds: Association Between Grain Quality Parameters and Functional Potential

Endophytic microbial communities of wheat seeds are a potential source of microorganisms that stimulate plant growth and participate in biocontrol, and they are also a potential indicator of the phytosanitary condition of grain. Using amplicon sequencing of 16S rRNA genes and the ITS region, we characterized the endophytic community of 11 wheat seed samples, which were divided, based on agronomic and phytopathological assessment, into a reduced-quality group (n = 4) and a comparison group (n = 7). The functional potential of the bacterial component was predicted using Tax4Fun2. PERMANOVA revealed a statistically significant but moderate difference in bacterial composition between groups (R2 = 0.186–0.197; p = 0.014–0.046), whereas a difference in fungal community composition was not supported. At the same time, the Mantel test showed a significant correlation between fungal community composition and the grain quality gradient (r = 0.665; p_adj = 0.004), which persisted after exclusion of the dominant genus Blumeria, the causal agent of cereal powdery mildew. Differential analysis with ANCOM-BC2 revealed a significant decrease in the representation of 58 predicted bacterial KEGG orthologs (KOs) (of 5248 tested) in reduced-quality grain, including bacterial genes for exopolysaccharide biosynthesis and secretion systems, whereas the assessment based on the PGP/biocontrol gene set revealed no such depletion. The preliminary results suggest that the fungal component of the seed endophytic community is more closely associated with grain quality than the bacterial component. Given the small sample size, these results are exploratory; the predicted functional differences and the potential use of seed endophytes for plant growth promotion and biocontrol are hypotheses that require experimental validation.