Higher Seed Production Techniques Of Cleistogenes Songorica Cv. Tenggeli

Cleistogenes songorica cv.Tenggeli is a new variety which was bred by College of Pastoral Agriculture Science and Technology,Lanzhou University,and approved and released by Chinese Herbage Variety Registration Board in 2016?No.499?.This new variety has excellent tolerance to drought,cold and barren sandy conditions,which play an important role in grass-livestock industry,landscaping and ecological restoration in arid and semi-arid areas.Based on previous researches concerning seed production of C.songorica,laboratory and field experiments were carried out from2016 to 2019 in Minqin County,Gansu Province for higher seed production techniques and higher seed yield?SY?of C.songorica cv.Tenggeli.Firstly,the physiological and cellular mechanisms underlying the influence of priming treatments on seed germination and seedling emergence under drought stress were investigated.Then field trials were conducted over a 4-yr period to evaluate the impacts of irrigation,nitrogen fertilization and six plant growth regulators on seed production of C.songorica cv.Tenggeli;Besides,the impacts of irrigation and nitrogen treatments on water use characteristics were also determined and calculated.In addition,a 2-yr research regarding seed threshing and cleaning techniques for smallholder farmers was also implemented.The main results are as follows:1.The seed priming treatments effectively assuaged the detrimental effects of drought stress on seed germination and seedling emergence of C.songorica cv.Tenggeli.Under-0.8 MPa PEG-6000-induced drought condition,germination percentage of seed primed with H₂O?hydropriming?,-0.3 MPa PEG-6000?osmopriming?and 0.5 mM spermidine?spd-priming?was increased significantly by10%,16.5%,and 23.5%,as compared with non-priming treatment,while improved seedling growth performance was also obtained.This phenomena due to seed priming was associated with reduced electrical conductivity?29.8%⁶3.7%?of seed leakage and malondialdehyde content under drought condition?19.3%³5.1%?,which maintained the integrity of cell membrane.Meanwhile,greater antioxidant enzyme?including SOD,CAT,and POD?activities were also observed in germinating seeds of priming treatments,this caused significant lower generation of reactive oxygen species?H₂O₂ content??P<0.05?.As compared with non-priming seeds,greenhouse and field emergence percentage in primed seeds was increased by 4%¹7%and9%¹9%,respectively,with the spd-priming treatment resulting in the best emergence performance.Flow cytometry analysis revealed that there was an increase in the nuclear DNA contents of seeds from 2C to 4C occurred during priming,indicating progression from the G₁ to G₂ phase of cell cycle,the positive effects of priming treatments was closely related to the percentage of cells at the G₂ stage of the cell cycle and to the G₂/G₁ ratio?P<0.05?,which indicated improved seed vigour of primed seeds.2.Field trials over a 4-yr period were implemented to investigate the effects of two irrigation?I1:watering at tillering stage;I2:watering at tillering,spikelet initiation,and early flowering stages,respectively?,three nitrogen timing?tillering,spikelet initiation,and split application?,and four nitrogen rate(0,60,120,and 180kg ha^-1)treatments on C.songorica cv.Tenggeli seed production and water use characteristics.Results revealed all main factors had a significant influence on SY?P<0.01?.As for interaction effects,nitrogen timing×nitrogen rate showed a very significant effect on SY?P<0.001?,and there is also a significant influence of year×irrigation,irrigation×nitrogen timing and year×irrigation×nitrogen rate?P<0.05?.As compared with I1 treatment,4-yr average SY in I2 treatment was improved by71.4%,and evapotranspiration was increased by 59.1 mm.Besides,water productivity and precipitation use efficiency for SY and aboveground biomass was significantly increased in I2 treatment,but irrigation use efficiency was markedly decreased.The SY and water use related parameters was increased with the increasing of N rate,but in most of cases,no significant difference was observed between 120 and180 kg ha^-1 treatments.Serious SY losses were found when nitrogen applied at spikelet initiation stage.In I1 treatment with relatively low nitrogen application rate(0 and 60 kg ha^-1),tillering treatment and split application resulted in the similar SY;However,when in I2 treatment and N rate was sufficient(120 and 180 kg ha^-1),split application caused up to 14.7%greater SY as compared with tillering treatment?P<0.05?.Another beneficial influence of split application included greater harvest index and water productivity.Overall,the optimum management practice was I2+120 kg ha^-1+split application,4-yr average SY reached 507.3 kg ha^-11 in this treatment combination.3.Field experiments over a 4-yr period were carried out to determine the influence of foliar application of six plant growth regulators?PGRs?on seed production of C.songorica cv.Tenggeli.Each PGR was applied twice at tillering and anthesis stage,respectively,with foliar application of water as control.The results showed that SY was significantly increased by four PGRs among all treatments.The4-yr average SY in 1-naphthylacetic acid,gibberellic acid 3,brassinolide,and6-benzylaminopurine treatments were 634.6,666.7,654.8,and 611.7 kg ha^-1,respectively,which increased by 18.1%,24.1%,21.8%,and 13.8%when compared to control(537.4 kg ha^-1)?P<0.05?,respectively.Little influence on SY was detected in another two PGRs treatments,compound sodium nitrophenolate and triacontanol.The above-mentioned four PGRs treatments did not affected grass aboveground biomass but harvest index was increased by 2.4⁶.4%.Correlation analysis indicated that fertile tillers m^-2 and seed number m^-2 correlated best with SY?P<0.01?.4.Field trials over a 2-yr period were conducted to evaluate the suitability of the C.songorica cv.Tenggeli seed threshing and cleaning techniques developed,for use by smallholder farmers.The results showed that 45⁵5 passes under a 50 kg roller resulted in the highest harvest rate?up to 70%of total seed present?,without loss of seed quality.Among several airflow velocity and sieve passes treatments for seed cleaning,the optimum airflow velocity was 4.5 m s^-1.Seed purity attained with this velocity combined with passes twice over a sieve of 0.7 mm mesh size,was up to85%,which increased by more than 50%as compared with previous research.These data are also of great value for the development of seed harvest machine for C.songorica cv.Tenggeli.