A newly discovered ageing-repair bacterium, Pseudomonas geniculata, isolated from rescuegrass (Bromus cartharticus Vahl) promotes the germination and seedling growth of aged seeds

Plant-growth-promoting rhizobacteria (PGPR) have been shown to relieve various biotic and abiotic stresses, but little information is available regarding their influence on germination and seedling growth of aged seeds. We isolated a promising PGPR from rescuegrass (Bromus cartharticus Vahl) roots and investigated the effect of PGPR biopriming combined with another seed priming treatment on aged rescuegrass seeds using an orthogonal matrix design with four factors. A potential ageing-repair bacterium, BCR5 (Pseudomonas geniculata), was selected from the screening trials and was identified. The reintroduction of strain BCR5 into the aged seeds pre-primed with different approaches had positive effects on germination and seedling growth. The results indicated that the bacterial cell density was the most effective factor for seed germination and vigour. Four factors were optimized for this study, including an artificial ageing duration of 54.21 h, bacterial cell density of 527.50 x 10(6 )CFU.mL(-1), and priming with H2O2 for 14.50 h, after analyzing the range and variance, and using binary quadratic regressions. Furthermore, the treatment also affected the content of malondialdehyde and the activities of superoxide dismutase and peroxidase. Bio-priming of the PGPR with another seed priming approach could be exploited as a promising technique for reinvigorating aged seeds. Moreover, we unexpectedly found that an appropriate artificial ageing treatment could break seed dormancy.