Inheritance And QTL Analysis Of Lodging Resistance In Brassica Napus L.

Oilseed rape is one of the most important oil crops in the world.Lodging damage results in not only lower seed yield and oil quality,but also easier infection to the infection of Sclerotinia and more difficulties for mechanized harvest.So it is of a great significance to study lodging resistance in B.napus L..At present,studies on lodging resistance in B.napus are less.There are not unified approaches to define the type of lodging in Brassica napus L.and much difficulties in assessing lodging resistance capacity of plants before lodging happens,This study proposed a method "Resistant pressure per plant"(RPPP) to test field conditions of lodging resistance capacity at the early flowering period.The results showed that using RPPP to measure field conditions of lodging resistance capacity of plant was truly reliable and simple.Both external factors such as wind,rain,soil and genotype differences in the internal factors are affecting lodging resistance capacity in crops.To improve lodging resistance capacity of crop varieties,we have to find out the genetic rule of lodging resistance in order to guide our breeding programs.Many scholars have been doing a lot of works in rice, wheat,corn and other crops to reveal the genetic rule of lodging resistance and related traits. However,the previous classical quantitative genetic researches can only study the combined effects of genes instead of detecting the individual gene,and can not distinguish the different effects of different genes.In recent years,the joint segregation analysis method of a mixed genetic model of major gene plus polygene which was developed by Gai etc.in 2003 has been widely used. But this approach has not been used in lodging resistance trait of crops.In addition,the great development of molecular marker technology and QTL mapping has brought hope to analysis the complex issue of quantitative genetic traits,and precise positioning of QTL makes lodging resistance gene be clormed possibly.Molecular markers and QTL mapping of lodging resistance trait have been done a lot in other crops,but so far have not yet been reported in rape in home and abroad.In this paper,the joint segregation analysis method of a mixed genetic model of major gene plus polygene was used to analyze the inheritance of lodging resistance trait in B. napus L.Further more,molecular markers such as SSR,SRAP were used to construct a genetic linkage map,and QTL mapping technology was used to position the QTLs which linked to lodging resistance trait,so as to lay the foundation for molecular marker-assisted selection breeding and map-based cloning of lodging resistance gene.1 Genetic analysis of lodging resistance in Brassica napus L.Inheritance of lodging resistance was analyzed applying the joint segregation analysis of a mixed genetic model of major gene plus polygene in six generations(P₁,P₂,F₁,B₁,B₂ and F₂ ) derived from two crosses of Zheping 1(lodging resistance)×04Pb11(lodging) (Crossâ… ) and Ning 1243(lodging resistance)×04Pb11(Crossâ…¡) in B.napus L.. Resistant pressure per plant(RPPP) was measured at flowering time by Digital Force Gauge,which was used to assess the ability of lodging resistance,and the correlation between RPPP and lodging scale was scored at mature time(r=- 0.38,P=0.01).The results showed that lodging resistance was dominated by two major genes with additive-dominance-epistatic effects plus polygenes(E-0 model) in Crossâ… ,and two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects(E-1 model) in Crossâ…¡.The additive effects of two major genes in two crosses were more powerful than the dominant one(｜h/d｜＜1).On average, Hereditability of major genes(h_mg²) was 54.71%in F₂ population,and that of polygenes(h_pg²) only detected in B₁ population was 10.56%.It indicated that the lodging resistance in B. napus L.was dominated by major genes.In addition,the environmental variance and the genetic variance accounted for 46.57%and 53.43%of the phenotypic variance in each population respectively,indicating that the environmental factors have a great effect on lodging in B.napus L..However,higher hereditability of major genes can be favorable to an efficient selection in early generation of lodging resistance breeding.2 QTL analysis of lodging resistance in Brassica napus L.Based on the F₂ population with 189 plants derived from the cross of Zheping 1×04Pb11,a genetic linkage map of Brassica napus L.was constructed,which was made up of 19 linkage groups,including 24 SSR and 137 SRAP markers,covering 2154.0cM in total with an average interval of 13.5cM between adjacent loci.Three QTLs called qLR2, qLR18-1 and qLR18-2 linked to RPPP in rapeseed were identified by using composite interval mapping method in Windows QTL Cartographer V2.0.qLR2 was located in the region of m3e20-m2e20 on LG2(LOD 4.14),which could explain 42.38%of the phenotypic variation,qLR18-1 was located in the region of m6e7a-m6e5 on LG18(LOD 3.08),which could explain 7.88%of the phenotypic variation,qLR18-2 was located in the region of m3e56-m6e45a on LG18(LOD 3.51),which could explain 13.52%of the phenotypic variation.The distance between qLR18-1 and qLR18-2 was just 16.2cM on LG18.