The Primary Investigation Of Seed Shattering Mechanism And Novel Accession Creation In Siberian Wildrye (Elymus Sibiricus L.)

Siberian wildrye(Elymus sibiricus L.)is a perennial,cool-season,self-pollinating,and allotetraploid forage grass with good palatability,forage quality and excellent adaptability to local environments with low temperature and high altitude.E.sibiricus germplasm is greatly affluent in China.In recent years,E.sibiricus was widely used in Qinghai-Tibet Plateau and northwest China for improving degraded grassland and developing grassland agriculture.However,seed shattering causes a great loss in seed production of E.sibiricus,which limits the popularization and application of excellent E.sibiricus.At present,there were 8 bred E.sibiricus cultivars released in China,but their severe seed shattering still keep unimproved in breeding progress.In this study,three types of experiment were conducted to further understand seed shattering mechanism of E.sibiricus and developed novel E.sibiricus breeding materials with low seed shattering.The main results involved in this study were as follows:1.A total of 28 E.sibiricus accessions were used for seed shattering evaluation,as well as other 14 agronomic trait measurement.Then subordinate function was also used for the comprehensive evaluation of agronomic traits.The results indicated the higher seed shattering rate were found at about 31 days after flowering.Seed shattering variation varied among tested accessions.Meanwhile,seed shattering variation greatly varied respectively among individual plants within populatons of ZhN01,HZ03 and LQ05.Based on two-year data,XH09 had the highest seed shattering rate,followed by XH03,LQ03 and LQ04,while ZhN03 had the lowest seed shattering rate,followed MQ01.The correlative analysis revealed that significantly negative correlation was found between seed shattering rate and flag leaf width,as well as internode number;Length of the second leaf from the inflorescence was highly significantly negative correlative with seed shattering rate.Phenotypic variation was also found in other traits,of which tiller number has the greatest variation with the CV of 17.07 %.The cluster results and subordinative function analysis showed ZhN03 had the best comprehensive performance.2.A total of 15 accessions(9 cultivated/cultivars and 6 wild materials)were used for seed shattering ability(BTS value)measurement and seed shattering mechanism study.The results showed cultivated/cultivars had higher average breaking tensile strength(BTS)value than wild accessions across seed development stages,of which PI655199 had the highest average BTS value(144.51 gf)and LQ 04 had the lowest average BTS value(47.17 gf)during seed development.Seed shattering was caused by degradation of abscission layers.Abscission zone had formed at early heading stage,and degradation of abscission zone occurred at 14 days after heading(DAH).High seed shattering genotype had a smooth fracture surface on the rachus due to higher degradation degree of abscission zone.Staining of pedicels of two contrasting genotypes showed that lignin deposition was much lower in high seed shattering genotype than in low seed shattering genotype.Furthermore,two cell wall degrading enzymes,polygalacturonase and cellulose,had different activity in the abscission zone at different developmental stages,indicating their roles in differentiation of abscission zone.3.E.sibiricus L.with great seed shattering variation and the other agronomic traits difference was used for parents to conduct hybrid breeding and their F1 was identified by EST-SSR molecular markers.Then the population structure analysis and genetic diversity study of F1 and parent populations was conducted.Based on DNA fingerprinting,15 genuine F1 plants were identified finally from 5 hybrid combinations.The average percentage of polymorphism among 5 parent and F1 populations was 70.51 %.