Exploiting the microbiome associated with normal and abnormal sprouting rice (Oryza sativa L.) seed phenotypes through a metabarcoding approach

Rice germination and seedlings' growth are crucial stages that influence crop establishment and productivity. These performances depend on several factors, including the abundance and diversity of seed microbial endophytes. Two popular rainfed rice varieties cultivated in Cameroon, NERICA 3 and NERICA 8, were used for investigating the seed-associated microbiome using the Illumina-based 16 S rRNA gene. Significant differences were observed in terms of richness index between normal and abnormal seedlings developed from sprouting seeds, although no significant species evenness index was assessed within either phenotype. Two hundred ninety-two bacterial amplicon sequence variants were identified in seed microbiome of the rice varieties, and principal coordinate analysis revealed that microbial communities formed two distinct clusters in normal and abnormal seedling phenotypes. Overall, 38 bacteria genera were identified, belonging to 6 main phyla. Furthermore, the core microbiome was defined, and the differential abundance of 28 bacteria genera was assessed. Based on the collected results, putative bacterial genera were directly correlated with the development of normal seedlings. For most genera that are recognised to include beneficial species, such as Brevundimonas, Sphingomonas, Exiguobacterium, Luteibacter, Microbacterium and Streptomyces, a significant increase of their relative abundance was found in normal seedlings. Additionally, in abnormal seedlings, we also observed an increased abundance of the genera Kosakonia and Paenibacillus, which might have controversial aspects (beneficial or pathogenic), together with the presence of some genera (Clostridium sensu stricto) that are commonly correlated to sick plants. The putative functional gene annotation revealed the higher abundance of genes related to the metabolic biosynthesis of soluble carbohydrates and starch, tryptophan, nucleotides and ABC transporters in normal seedlings. Data presented in this study may help in further understanding the importance of the seed endophyte microbiome for driving a correct development of rice plants at the early stages and to identify possible beneficial bacteria for technological applications aimed to increase seed quality and crop productivity.