AccAge

Healthy seeds are an important component of global food security, and their microbiome was recently identified as crucial for plant growth, resilience, and health. Seed vigor is highly affected by, amongst others, storage conditions and aging. To study the impact of seed aging on the Brassica napus seed microbiome, we conducted accelerated aging tests with seed lots of four genotypes originating from two field sites in Germany. We found a strong effect of aging on germination, seedling phenotypes, as well as the seed microbiota. Seeds of the control treatment developed mainly into normal seedlings (according to ISTA definition) and were characterized by diverse bacterial communities comprising the main phyla Proteobacteria, Firmicutes, and Actinobacteria, and contained typical core seed microbes. Accelerated aging resulted in abnormal germination and a reduced germination rate up to 50%. In the microbiome, the accelerated aging stress was visible at all levels by i) a reduced diversity, evenness, and specificity, and ii) a shift from Gram-negative to Gram-positive bacteria. This effect, especially the enrichment of Firmicutes, was found irrespective of the genotype and field site; however, which way stress affected microbiota varied, depending on both factors. Tumebacillus and Bacillus showed a significant negative correlation with germination performance, whereas microbial diversity correlated positively with a high germination rate. At the functional level, the majority of isolated bacteria demonstrated plant-beneficial characteristics, showing a greater beneficial potential in the aged seeds. Our results show how accelerated aging tests affect the seed microbiome, that a diverse seed microbiome is crucial for seedling health, and can be used to identify indicator bacteria to predict and optimize the seed storability, germination, or seedling vigour performance.