Genetic Diversity Of Agronomic Traits And SSR Markers In Lolium Multiflorum Lam

Lolium multiflorum Lam.is a species of genus Lolium(Poaceae),with a variety of good quality forage.It is also called “Italian ryegrass” and “annual ryegrass”.Italian ryegrass has the advantages of high crude protein content,strong regenerative ability,rich nutrition,good palatability,high digestibility,and is deeply loved by various livestock.In our study,we used 43 SSR markers to describe the genetic diversity and the population structure of 263 individuals from 33 accessions of Italian ryegrass and associated them to 10 agronomic traits including plant height,tiller number,fresh weight per plant,dry weight per plant,etc.The main results as follows:(1)Agronomic diversity of these samples was analyzed using SPSS software version 22.Among all the measured traits,coefficient of variation(CV)ranged from 13.93% to 48.98%,the average CV is 26.06%.Fresh weight per plant(FW)and dry weight per plant(DW)exhibited greater CV than the other traits in favor of selecting high-yielding germplasm.Correlation was observed between the 10 traits showed these traits are not isolated but interrelated.Among them,FW had the highest correlation with DW(r = 0.874,P <0.001),and the correlation between spike length(SL)and DW was the lowest(r = 0.125,P <0.05).(2)Out of 218 tested SSR primers,we picked 43 primers for genetic diversity of 263 individuals of Italian ryegrass.90.7% SSRs were highly polymorphic informative primers,which could reflect the genetic diversity of all tested materials well.The 33 accessions showed high level of heterozygosity with the mean values of observed(Ho)0.605 and expected(He)0.573(Fis <0).The analysis of molecular variance(AMOVA)indicated 33 accessions mainly caused by a higher within-population variation(69% in within-population,31% in among-population).(3)STRUCTURE analysis divided the 263 individuals of Italian ryegrass into four subpopulations(P1,P2,P3,and P4).Neighbor-joining analysis clustered 263 individuals into 5 groups(G1,G2,G3,G4 and G5),which was generally consistent with the results from structure analysis with a few exceptions.3 accessions(C13,C22,and C25),were divided into a new group(G5)in NJ tree analysis based on genetic distance.The results showed that accessions from different continents were contained in each subpopulation,while accessions from same continent could be clustered into different subpopulation,indicating that the population structure was incompletely correlated with their geographical distributions.(4)A total of 17 associations were identified between the 43 SSR markers and the 10 traits using a mixed linear model(MLM),which explained 6.2 %(LMgSSR03-04 F to PH)~ 18.6 %(LMgSSR10-12 F to PH)of the phenotypic variation.4 markers were detected to have associations with PH.And traits TN,LSL,SL,NN,FW and DW were associated to 2markers,respectively.One marker showed associations with WSL,SN and DW.Our results provided potential to shorten the breeding process and to establish the theoretical foundation for molecular marker-assisted breeding of Italian ryegrass.