Analysis Of Dwarf Mutant And Dwarf Gene Mapping In Brassica Napus L.

Brassica napus L.is one of the most important oil crops in China and even in the world.Plant height is an important agronomic character of rape,which is closely related to lodging resistance,high yield and high quality breeding.Therefore,it can provide fresh materials,genetic basis and practical guidance for rapeseed breeding to explore new dwarf genes controlling plant height and analyze the genetic mechanism of dwarf phenotypes.In the early stage of our laboratory,the seeds of polima cytoplasmic sterile line and maintainer 2B in Brassica napus L.were induced by ethyl methane sulfonate（EMS）and a dwarf mutant bnd2（Brassica napus dwarf 2）was obtained.And its phenotypes,genetic characteristics,hormone treatment and cytological characteristics were observed.The genetic mapping population was constructed with bnd2 and a normal-height material L329 for BSA re sequencing.The candidate genes were precisely located by developing molecular markers and the results are as follows:（1）Through the analysis of phenotypes and agronomic characters,it was found that the plant height of the dwarf mutant bnd2（100.65±8.09 cm）was significantly lower than that of the mutant parent 2B（168.2±7.61 cm）.In addition,the first branch height（24.95±3.17 cm）,main inflorescence length（52.91±7.72 cm）,internode length（6.55±1.46 cm）and the number of elongation internodes（13.6±2.11）were significantly reduced compared with the mutagenic parent 2B,indicating that the dwarf phenotype of bnd2 may be related to the decrease of effective branch height,main inflorescence,internode length and the number of elongation internodes.The thousand seed weight and yield per plant of dwarf mutant were significantly lower than that of parent 2B.（2）The cell area and length of the parenchyma cells of the mutant bnd2 were significantly reduced than 2B,which led to the shortening of the internode of the mutant.（3）2B x bnd2 was used to construct genetic population,the investigation results of plant height at maturity show that:the plant height of backcross F₁ generation was between two parents and deviated to parent 2B,the results of plant height measurement of F₂ generation showed that the number of dwarf plants and tall plants accorded with 1:3 Mendelian segregation ratio,indicating that the dwarf traits of bnd2 were controlled by a single recessive gene.（4）It was found that the response of hypocotyls of bnd2 seedlings to gibberellin（GA）was weakened and the phenotypes of bnd2 could not be restored by GA treatment.While the response of bnd2 mutant seedlings to brassinosteroid（BR）was enhanced,and BR could restore the seedling phenotypes of bnd2 mutant.It is speculated that the GA signaling pathway and/or BR synthesis in bnd2 mutants may be affected,which provides clues for subsequent gene mapping and cloning.（5）The mutant bnd2 and a normal-height material L329 were used to construct the mapping population,and through the BSA resequencing,BND2 was located in the 13.77Mb-18.08 Mb range of A08 chromosome,with a length of 4.317 MB.After gene fine mapping,combined with SNP and Indel markers,the candidate region was narrowed to 190Kb between 15.57-15.76 Mb.