Germination of seeds during the transportation or after prolonged storage naturally and inevitably decreases because of ageing, but germination potential can be partially restored with seed priming treatments. A novel attempt was made to investigate the effects of combined treatments and to optimize the conditions for naturally aged seeds of tall fescue (
Festuca arundinacea
Schreb.), orchardgrass (
Dactylis glomerata
L.) and Russian wild rye (
Psathyrostachys juncea
(Fisch.) Nevski) using an orthogonal activity level experimental design [factor A:
Azospirillum brasilense
concentration, factor B: three seed priming treatments (H
2
O, MgSO
4
and H
2
O
2
) and factor C: different priming times]. Multivariate regression model analysis was applied to determine the interactive effects of pairwise factors (A and C) and to optimize experimental conditions. The results showed that the mixed treatments positively affected seed germination and seedling growth. The three seed priming treatments were the dominant factors for germination promotion, whereas the bacterial concentration had the largest effect on seedling growth and the activity of superoxide dismutase (SOD), especially root elongation. The malondialdehyde content was reduced, the activities of SOD, peroxidase and catalase were triggered, and ascorbate peroxidase activity was also affected by the co-treatment. The combined results of all determined attributes showed that
A
.
brasilense
bio-priming with H
2
O
2
priming constituted the optimal combination. The optimal bacterial concentration of
A
.
brasilense
and the time of seed priming were 52.3 × 10
6
colony forming units (CFU) mL
-1
and 17.0 h, respectively.
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 × 106 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.
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