The Breeding Of New Type Brassica Juncea (A~rA~rB~cB~c)

Brassica napus (AnAnCnCn,2n=38), Brassica juncea (AjAjBjBj,2n= 36) and Brassica rapa(ArAr,2n= 20)are the three most important Brassica oil crops cultivated in the world at present, and the yield of Brassica juncea is the lowest which is approximately 900～1200 kg/ha when using hybrids, but it hardly meets the production. There are 3 basic chromosome genomes (A, B, C) and 3 corresponding subgenomic groups(Ar, An, Aj; Bn, BJ, Bc; Co, Cn, Cc) in Brassica crops with abundant genetic variations in the latter. Previous work had proved that utilization of subgenomic heterosis was an effective way to increase the yield of rapeseed and strong intersubgenomic heterosis was observed in hybrids between traditional and new type B. napus, which wass constructed by introgressing the Ar and Cc genomes to replace the An and Cn of traditional B. napus. This research attempts to introgress the Ar genome of Brassica rapa and Bc genome of Brassica carinata into traditional Brassica juncea to breed new type B. juncea, enlarge the genetic diversity of new type Brassica juncea and traditional Brassica juncea, lay foundation for exploring the intersubgenomic heterosis in Brassica juncea and improving the yield of Brassica juncea in the future.Abundant Ar and Bc genomes are introgressed into traditional Brassica juncea firstly, Brassica hexaploid lines (ArArBcBcCcCc,2n= 54) originated from Brassica carinata and Brassica rapa are crossed with traditional Brassica juncea and obtain Brassica pentaploid (ArAjBcBjCc,2n= 45) from F1 generation with the method of cytological identification. The new type Brassica juncea (2n= 36) is achieved from self-pollinated generation of Brassica pentaploid whose C genome chromosomes are completely lost and the total chromosome number is 36 then, whilethe average content of Ar genome from Brassica rapa and Bc genome from Brassica carinata would be 50%.In order to increase the content of exogenous Ar and Bc genome further, the Brassica pentaploids in F1 are backcrossed with Brassica hexaploids originated from Brassica carinata and Brassica rapa to obtain BC1F1 (ArAjBcBjCc,2n= 45) later, and the average content of Ar and Bc approximately increases into 75%. Selfcross BC1F1, the new type Brassica juncea (2n= 36) is obtained not only the proportion of exotic subgenomic components are 75%, but also the number of chromosomes in BC1F2 is 36 and C genome chromosomes are absolutely lost. Subgenomic hybrids would be developed with crosses between new type Brassica juncea (ArArBcBc,2n= 36) and traditional Brassica juncea (AjAjBjBj,2n= 36) finally for the basic research of intersubgenomic heterosis.One hundred and two combinations of F1 hybrids were harvested through crosses between Brassica hexaploid and traditional Brassica juncea. Fourteen combinations were selected to identify the true and false hybrids by SSR molecular markers. Ten plants were randomly chose for each combination. At last one hundred and thirty-eight plants were confirmed to be true hybrids. By the method of counting the number of chromosomes in somatic cells of F1 plants,52 pentaploids whose number of chromosome was 45 and 169 candidate pentaploid with chromosome number of 43,44 and 46 respectively were chose. Afterwards, we did backcrosses were carried out when pentaploid and candidate pentaploid were uesd as female parents. Fourty-eight BC1F1 backcrosses were obtained and sowed them later. At the same time selfcrosses of pentaploid and candidate pentaploid with chromosome amount of 44,45 and 46 were underway. Self-pollilated seeds from 102 F1 were obtained, and 95 rows seedlings of F2 were developed.Ninety-nine plants from F2 were randomly chosed to conduct the counting of number of chromosome. Four F2 plants were found whose somatic cell chromosome numbers were 36 and predicted to be candicate new type Brassica juncea whose Ar and Bc average proportion were 50%. Also chromosome numbers of 302 BC1F1 plants were identified and 38 BC1F1 plants with 45 chromosomes were found out, whose genomic structure should be AABBC expectedly. The second new type Brassica juncea with 36 chromosomes will be obtained in BC1F2 and the average content of Ar and Bc could be 75%Fourteen-pair specific SSR primers for A and B genome were used to distingusih Brassica hexaploids from traditional Brassica juncea. These primers were applied to analyse the introgressed contents in 27 plants of 4 combinations from BC1F1. The results of molecular markers showed that the introgressed Ar and Bc proportion were 75.88% which was in accordance with the expectancy. This also indicated that the proportion of Ar and Bc in in the new type Brassica juncea could improved to 75% or even more than 90% in BC1F2 with molecular markers selection compared with 50% in F2.