Improvement Of A Dwarf CMS Restore Line In Brassica Napus By Marker-assisted Selection

Rapeseed(Brassica napus L.) is one of the major oilseed crops in China.Lodging is serious problem in hybrid rapeseed because of significant increase of its plant height, which can lead to a significant yield loss and difficulty mechanical harvesting.Lodging can be decreased by reducing plant height,and this can be achieved through the use of dwarf genes.Therefore,development of dwarf hybrid can be a great asset for the rapeseed production.In this study,we transfer a dwarf gene from Ds-1 to 8-7963(a CMS restore line in Brassica napus) by using the marker-assisted backcross technique.Several elite and dwarf restorer lines were obtained,which will be useful for oilseed rape dwarf breeding. The main results were as follows:1.Observation on the agronomic traits of F₁.Plant height of hybrid F₁ was lower than the recurrent parent,reaching extremely significant difference.Compared with the recurrent parent,seed number per pod of hybrid F₁ was less and the difference was significant.The differences of the first effective branch number;effective pod number per plant and 1000-grain weight between F₁ and 8-7963 were not significant.The reduction of plant height is mainly caused by the decrease of height of first branch.These results showed that there was no negative defect in Ds-1.It was a elite dwarf germplasm resource.2.Validation of molecular markers associated with dwarf gene.Three molecular markers associated with dwarf gene(AX49;SCM07 and SSR578) were detected polymorphisms between two parents.The result indicated that two co-dominant markers (AX49 and SCM07) can are tight liked to dwarf gene DS1 in the breeding populaiton and therefore can be used in foreground selection.3.Foreground selection of BC₁F₁ and BC₃F₁ generations.Two SCAR markers (AX49 and SCM07) were used for the foreground selection of BC₁F₁ and BC₃F₁ generations,got the same result.The ratio of(normal:dwarf) was calculated as 41:25 in BC₁F₁ and 73:55 in BC₃F₁.Chi-square text indicated they fitted into 1:1 segregation ratio. 4.Background selection of BC₁F₁ and BC₃F₁ generations.The AFLP technique was used to analyze the background of the dwarf individuals in BC₁F₁ and BC₃F₁ generations. About 30 pairs of primers were detected in the BC₁F₁ generation,85 polymorphic bands were identified and then applied to cluster by UPGMA method.The individual with the highest rate of background recovery was chosen to backcross to the recurrent parent. AFLP analysis in the BC₃F₁ generations showed that polymorphic bands was less than that in BC₁F₁,and the amplified bands were very similar to the recurrent parent.This result indicated high genetic background recovery rate in the BC₃F₁ generations. Subsequently,the well-growing dwarf individuals were selfed to obtain improved restore lines with homozygous dwarf gene.5.Observation on the traits of BC₃F₁.Plant height,the height of first branch and internode length of hybrid BC₃F₁ was lower than the recurrent parent,reaching extremely significant difference.The differences of the length of main inflorescence and node number between BC₃F₁ and 8-7963 were not significant.These results showed that DS1 is stable inheritance.