Effect Of Plant Growth-promoting Rhizobacteria Inoculation And The Seed Priming On The Germination And Seedling Growth In Aged Grass Seeds

Seed ageing or deteriorating events can naturally and inevitably occur over long-term storage or during the transportation,resulting in loss of seed vigor and reduced yield and quality of plant.Delaying seeds ageing and repairing them is the primary challenge in seed ecology and agricultural science.The conventional plant breeding method for“delayed ageing”varieties and conventional seed priming treatments for repairing aged seeds are time-consuming,tedious,have a high labour cost or are only slightly effective.Recently,the effects of plant growth-promoting rhizobacteria?PGPR?have attracted considerable attention due to their eco-friendly and highly effective effects on the growth and health of host plants.To date,PGPR have been actively applied worldwide as bio-inoculants to facilitate plant growth and alleviate various stresses.However,little attention has been paid to study the effects and mechanism of PGPR on seed aging which is a kind of physiological stress.Thus,we performed 2 group experiments using an orthogonal array,?1?using an[L9?3⁴?]orthogonal activity level experimental design[factor A:Azospirillum brasilense concentration,B:three seed priming treatments and different priming times?C?],we investigated the effects of combined treatments on the germination,seedling growth and physiological characteristic(the malondialdehyde MDA content and antioxidant enzyme?superoxide dismutase SOD,peroxidase POD,catalase CAT and ascorbate peroxidase APX?activities of naturally aged seeds of tall fescue?Festuca arundinacea Schreb.?,orchardgrass?Dactylis glomerata L.?and Russian wild rye?Psathyrostachys juncea Nevski?and optimized the conditions.?2?Meanwhile,to explore effective PGPR to repair aged seeds,we also tried to isolate the PGPR which could repair the seed aging from rescue grass?Bromus cartharticus Vahl?roots,and to evaluate the effects of PGPR on the germination and seedling growth of aged rescue grass seeds using an orthogonal matrix experimental design with four factors[A:the duration of artificial ageing,B:the bacterial concentration,different seed priming treatments?C?and different priming time?D?].Finally,the condition of combined pre-treatment was optimized via two-variable quadratic regression model analysis.The corresponding results were showed as follows:?1?A.brasilense inoculation and the three seed priming treatments repaired aged grass seeds by the specific operation mode of co-allocation during the different developmental stages.The three seed priming methods were the most effective factors for stimulating germination,whereas the bacterial concentration had the largest effect on early seedling growth,especially on root elongation.The combined treatments that elicited ageing-related repair reduced the MDA content and improved antioxidant enzyme activities.Overall,A.brasilense bio-priming with H₂O₂-priming was the optimal combination for reinvigorating aged seeds.The final optimal conditions consisted of the bacterial concentration of A.brasilense of 52.3×10⁶ CFU mL^-1 and a seed priming time of 17.0 h,given the interactive effects.?2?A potential ageing-repair bacterium,the isolate BCR5,was selected from rescue grass roots and was identified as Pseudomonas geniculata based on the analysis of the 16S rDNA sequences.The co-treatment of P.geniculata BCR5 bio-priming with three seed priming approaches had positive effects on the germination,root and shoot length of aged rescue grass seeds.The MDA content and activities of SOD and POD were affected.The range and variance analyses results indicated that the bacterial concentration?B?had the largest effect on seed germination,vigour and root length,while the prming time was the most effective factor for shoot enlongation.The optimal conditions of the four factors were artificial ageing duration of 54.2 h,bacterial concentration of 527.5×10⁶ CFU/mL,H₂O₂ priming and a priming time of 14.5 h based on binary quadratic regression analyses,analyses of the range and variance.Moreover,the appropriate artificial ageing treatment could release seed dormancy.In conclusion,PGPR inoculation could repair the damage caused by seed ageing,recover seed vigor and stimulate seedling growth.Physiologically,the MDA content and antioxidant enzyme activities were affected.The combined treatment is more practical and simpler than co-inoculation of PGPR strains,and is the promising technology for seed recovery from ageing in agriculture industry.