Inheritance Law Of Flower Size And Expression Analysis Of Related Genes In Petunia Hybrida

Petunia（petunia hybrid）is a perennial herbaceous plant,often cultivated as annual or biennial herbaceous flower.Due to its rich colours,long flowering period and easy cultivation,petunia enjoys the reputation of‘king of flower bed’and widely used in gardens.Flower size is one of the most important quality of ornamental plants,and researches on this character can greatly improve the garden application and ornamental value of petunia,which meet the needs of people for different flower size.In addition,the basic research of candidate gene prediction can provide important theoretical guidance and technical methods for breeding.In this study,multiple pure petunia breeds with different flower sizes（including large,medium and small flowers）were used as experimental materials.Different combinations were prepared by hybridization and F₂and BC₁ generations were obtained through selfing and backcross of F₁.The genetic law of flower size was studied and analyzed in the F₂ population;the morphological characters of F₂ generation and backcross population were observed and analyzed;the chlorophyll content of the backcross population was determined.In addition,this study determined the relative expression levels of genes related to organ size in parent materials and F₂ population.The main results of this study are as follows:1.Forty-one hybrid combinations were prepared by reciprocal crosses with petunia inbred pure lines and wild pure lines with different flower sizes.The flower diameter of F₁ population was statistically analyzed.The coefficient variation of flower diameter ranged from 2.37%to 17.79%,and the average was 6.06%.According to the comparison of flower diameter between parents and F₁ generation,most of F₁generation was the median of parents,some of them exceeded their parents,and a few F₁ generations showed the separation of flower diameter,indicating that some parents need further selfing and selection for purification.2.The F₁ generation with the same flower diameter was used as the experimental material to construct the segregation population of F₂ generation through selfing.Populations with sigenificant segregation were screened for genetic analysis according to the flower diameter performance of F₂ generation.Using large flower‘Dabai’and medium flower‘S’and‘S26’as experimental materials,the segregation population of F₂generation was constructed,and BC₁,BCF₂ populations were obtained by selfing and backcrossing.Two genetic laws were found:（1）The F₁ population of‘Dabai×S’was large flower,and the F₂ population appeared large,medium and small flower segregation.The ratio of large flower:medium flower:small flower was close to 9:6:1,which was basically consistent with Mendelian genetic law.It was preliminarily determined that large flower trait was semi-dominant inheritance controlled by two pairs of genes.（2）The F₁population of‘Dabai×S26’was large flower,the segregation ratio of large flower and medium flower in F₂population was close to 3:1,the segregation ratio of large flower and medium flower in BC₁population was close to 1:1,the segregation ratio of large flower and medium flower in BCF₂population was close to 3:1,and the selfing progenies of medium flower of BCF₂population were medium flower,which was consistent with Mendelian genetic law.It was preliminarily determined that the large flower trait was dominant inheritance controlled by a pair of genes.3.Using‘Dabai×Xiaobai’to obtain F₂ generation and backcross population,21indexes of 12 morphological characters（including flower diameter,corolla tube,sepal,pistil,stamen,pedicel,bract,the first leaf,the fourth leaf,stem,height and leaves number）were observed and analyzed.Variance analysis showed that there were 14extremly significant differences and 5 significant differences in backcross population.In the F₂ population,19 indexes showed extremely significant or significant differences,and FS（flower size）,PD（pedicel diameter）,SL（sepal length）and SW（sepal width）showed significant differences between large,medium and small flowers.The correlation analysis showed that in the backcross population,50 pairs of indexes were extremely significant positive correlation,5 pairs were significant positive correlation,and one pair was extremely significant negative correlation.In the F₂ population,49pairs of traits were extremely significant positive correlation,12 pairs were significant positive correlation,and one pair was extremely significant negative correlation.Principal component analysis showed that four principal component factors(4^th leaf length、bract length/width、leaves number and height)were extracted from backcross population,and the cumulative contribution rate reached 85.69%.Four principal component（flower size,bract width middle stem and height）factors were extracted from F₂ population,and the cumulative contribution rate reached 77.83%.4.Chlorophyll content in bracts and leaves of small flower plants was significantly higher than that of large flower plants.Chlorophyll content in bracts of small flower was 2.67 times of large flower,and chlorophyll content in leaves of small flower was2.15 times of large flower.5.The expression of organ size related genes was carried out by real-time quantitative PCR（q PCR）analysis in parent materials with different flower size and F₂generation.The results showed that the expression of CKX2,CKX1,ARGOS459,ARR1029,ARR828,ARR496,CKI1 and HK genes in large flower varieties was significantly higher than that in medium and small flower varieties.In F₂ population,the relative expression levels of genes in large flower were higher than those in medium and small flower,including GATA354,GATA366,TCP4a,ELIP1,ELIP2,ARGOS057,ARGOS459,ARR496,ARR1029,KLUH,CKI1,CKX1 and CKX2.The relative expression levels of TCP3b,ARR970,ARR828 and HK were higher in medium flower than in large and small flower.Overall,the expression of each gene in small flower was lower than that in large or medium flower.The expression of ARGOS057,ARGOS459,KLUH and CKI1 in F₂ population showed that the expression of CKI1 in each part was higher in large flower than that in medium and small flower.6.The expression levels of genes related to chlorophyll synthesis regulation was determined by q PCR analysis in testcross population.The results showed that the expression levels of GATA354 and GATA366 genes were significantly different in large and small flower plants,and the expression levels in small flower was significantly higher than that in large flower.The ELIP1 and ELIP2 genes expression levels of large flowers were significantly higher than that of small flowers.