Study On The Regulation Mechanism Of Alfalfa Defoliation And Nutrient Quality

High-quality alfalfa hay has become an important resource in the safe production of animal husbandry and its quality is a key factor to enhance the international market competitiveness of alfalfa hay in China.In order to identify the key factors affecting the quality of alfalfa hay,In this study,transcriptome technology was used to study the mechanism of alfalfa variety on defoliation and growth period on nutritional quality,as well as the key factors affecting the drying of alfalfa and the change rule of nutritional indicators during the preparation of alfalfa hay,aimed to provide theoretical basis and technical support for the excellent quality alfalfa hay production of our country.In this study,it was taken five alfalfa varieties(Zhongmu No.l,Zhungeer,Zhongmu No.3,WL232HQ and WL319HQ)as experimental material,studied the mechanism of defoliation of different alfalfa cultivars,the effect of alfalfa growth period on its nutritional quality and the factors affecting alfalfa hay preparation.The results were as follows:(1)Through research on the yield,defoliation and nutritional quality of five alfalfa varieties,the hay yield and plant height of WL319HQ were significantly better than other alfalfa varieties(P<0.05)and the rate of defoliation is low,but the yield and plant height of Zhungeer were poor and the leaves of this variety were easy to fall off.Through the optimal sequence correlation analysis of 6 common indicators such as hay yield,plant height,CP,ADF,NDF and Lignin,it was found that WL319HQ>WL232HQ>Zhongmu No.3>Zhongmu No.1>Zhungeer.(2)In this study,we sequenced the transcriptomes of the Zhungeer variety(with easy leaf abscission)and WL319HQ variety(without easy leaf abscission).Among the identified 1098 differentially expressed genes(DEGs),706 differentially expressed genes upregulated,and 392 unigene downregulated in the Zhungeer vs WL319HQ leaf.KEGG pathway annotations showed that 8414 unigene were annotated to 87 pathways and contained 281 DEGs.6 DEGs belonging to 3 pathways involved in defoliation traits were identified and validated by qRT-PCR analyses,and the six genes(ARF,PIF3,ETR,PHYB,CRY and NCED3)were identified as the key genes for controlling alfalfa defoliation.(3)The mechanism of the effect of growth period on nutritional quality of WL319HQ alfalfa was studied.The results showed that the growth period is a key factor affecting the nutritional quality of alfalfa,in which the nutritional quality of different parts of alfalfa is leaf>whole plant>stem.With the delay of growth period,the contents of each nutritional index changed as follows:The index contents of digestible proteins(CP,SP,RDP)gradually decreased,while the indigestible proteins(ADICP,NDICP)gradually increased;The content of fiber index(Lignin,ADF,NDF)increased gradually,and changes in the expression levels of 8 enzymes,including LAC11,CCOAOMT1,CCR1,CAD6,HCT,PAL1,COMT1 and 4CL,resulted in changes in alfalfa fiber content and composition;The content of carbohydrate index(NSC,ESC,WSC,Starch)decreased gradually,and changes in the expression levels of 9 enzymes,including SPS3,SUS6,AGPS1,AMY,pgmA,SBE3,WAXY,SS1 and ISA2,resulted in changes in alfalfa carbohydrate content and structure;The contents of fat and fatty acid indicators(EE,TFA,UFA,SFA)first increased and then decreased,and changes in the expression levels of 8 enzymes,including FabG,KCS11,GPAT1,ACACA,FAS2,FAD2,KAS1 and FATB,resulted in changes in the content and structure of alfalfa fatty acid;Different amino acids had different trends,and changes in the expression levels of 10 enzymes,including MetE,arg12,glnA,serB,cysK,BCAT2,PAH,ACYI,trpB2 and TSB,resulted in changes in the content and composition of alfalfa amino acids;The content of flavonoids and tannins decreased first and then increased,and changes in the expression levels of 6 enzymes,including CHS4,CHI1,MYB4,FLS,ANS and ANR1,resulted in changes in the content of flavonoids and tannins in alfalfa.(4)Through hay modulation experiment on WL319HQ alfalfa,the results showed that the drying rate of different parts during alfalfa drying was leaf>whole plant>stem.With the extension of drying time,the drying rate and nutrient quality decline rate of alfalfa showed a fast and then slow pattern,and the main environmental factor affecting the drying rate was atmospheric water potential(negative correlation)>solar radiation intensity(positive correlation)>soil temperature(positive correlation)>air temperature(positive correlation)>air relative humidity(negative correlation).The changes of major nutritional indexes were as follows:protein indexes(CP,SP,NDICP,RDP)decreased by 23.85-69.43%,fiber indexes(NDF,ADF,Lignin)increased by 26.21-61.82%,and RPV decreased by 34.42%.