QTL Mapping And Genetic Analysis Of Branche Angle And Grain Shape In Rice

Rice is a staple food for more than half of the world’s population.At present,under the circumstance of arable land becoming saturated,increasing the unit area yield of rice has become the most pressing goal.It is well-known that rice spike traits are directly related to rice yield growth and quality improvement.Among them,the degree of panicle scattering of rice and the shape of grain are the most important components of panicle type.Therefore,an in-depth study of the branch angle and grain shape of rice will have an important impact on rice yield growth and quality improvement.In this study,Oryza longistminata were used as male parents and indica rice cultivars Balilla were used as female parent to rescue Fi by mating with immature embryos to make F2 segregating populations within 169 and 201 individuals respectively by selfing,then we use this mapping population to study the traits of branch angle.In addition,QTL mapping of grain-related traits was performed using an F2 population within 176 individuals constructed from hybrids of long-grained fragrant rice with indica rice variety 02428.Both trials are molecular linkage maps constructed using PCR-based Indel markers.QTL mapping and genetic analysis were performed using QTL analysis software method.The main results are as follows:1.There is a significant difference in the branch angles between the Oryza longistaminata and Balilla,and the branch angles are 29.33±3.12° and 0±0°,respectively.The normal distribution of the angles of branches of F2 population showed that the angle traits of branches were quantitative traits and could be used for QTL mapping.2.A total of 900 pairs of InDel primers were screened between Oryza longistminata and Balilla,and 155 pairs of primers with good polymorphism were screened.These primers were evenly distributed on 12 chromosomes of rice.3.Based on the data of branch angle in 2016 and 2017,a total of 6 QTLs were obtained.(qBA-2-1,qBA-4-1,qBA-4-2,qBA-9-1,qBA-10-1 and qBA-12-1)They are located on chromosomes 2,4,9,10 and 12,respectively,and each QTL can explain 3.7%-43.3%of phenotypic variation.The qBA-4-2 locus on chromosome 4 and the qBA-12-1 locus on chromosome 12 were detected in two years of localization experiments..Among them,qBA-4-2 has the largest contribution rate to the pedicel angular phenotype and is a major effect QTL;qBA-2-1 and qBA-12-1 have not been reported,and may have two new QTLs.4.The qBA-4-2 locus range of branch angle contains a gene OsLG1 that regulates the angle of wild rice twigs.The sequencing results showed that there are many differences in the sequence of OsLGl between wild rice and cultivated rice,including 41 SNP,1 single-based insertion,2 single-based deletions and 2 InDel differences of more than 10 bp.Analysis of the common differences between wild rice and cultivated rice revealed that only SNP6 is a true functionally distinct site that is located 10 kb upstream of the OsLGl gene,therefore its single nucleotide changed from G(wild rice)to A(Oryza sativa)causes rice ears to change from compact to loose type,this further validates the previous results.5.In the study of grain shape traits,the length of the paternal parent fruit 02428 was about 6.89mm,the grain width was about 3.82mm,the aspect ratio was about 1.81,and the grain length of the female long grain fragrant rice was about 12.50mm,and the grain width was about 2.24mm,aspect ratio is about 5.58.There are extremely significant differences in the grain traits of the two parents.The genetic difference between the parents is large,which is conducive to QTL positioning.6.805 pairs of InDel primers were screened between long-grained fragrant rice and 02428,and 143 pairs of primers were found among parents.7.QTL mapping was performed on the mapping population.Five QTLs related to rice grain length,seven QTLs related to grain width,and six QTLs related to aspect ratio were detected in the whole genome.Among them,qGL-3-1 is the highest effect of all detected QTLs affecting grain length,explaining 47.6%of the phenotypic variation;Among the QTLs affected by grain width,qGW-5-1 was the highest effect value,which explained 36.9%of the phenotypic variation;Among the detected QTLs affecting the aspect ratio of rice,the qGAR-5-1 effect was the largest,which can explaine 24.2%of the variance.The qGL-1-1,which controls grain length,and qGW-1-1,which controls grain width,were both on the first chromosome,which have not been reported and may be two new QTLs.