Creating And Evaluation Of New-Type Brassica Juncea By Backcrossing With Hexaploid Derived From B.Rapa And B. Carinata

Interspecific hybridization is an important evolutionary force and powerful method for breeding of crops. It is being effective in introgressing advantages genes and manipulating hybrids for desired characters in crop breeding programs.In our previous study, our research team created Brassica hexaploid lines (ArArBcBcCcCc) by crossing of B. rapa and B. carinata. The hexaploid lines were crossed with traditional B. juncae (AJAJBJBJ) to obtain pentaploid (ArAJBCBJCC). These pentaploid hybrids were selfed with successive generations and a kind of new-type B. juncea was created with partial sub-genome introgression (Ar/jAr/jBc/jBc/j). To introgress more exotic subgenomic components in new-type B. juncea we used the back cross strategy in this study. Pentaploid (ArAJBcBJCc) hybrids were crossed with Brassica hexaploid. The new-type B. juncea was created through backcross of pentaploids to Brassica hexploid and the average content of Ar and Bc approximately increases into 75%. When, BC1F1 (ArArBcBcCc) was selfed, the new-type B. 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.Further, stability and seed setting rate of new-type B. juncea was studied in subsequent generations. BC1F2 seed was grown in field to produce BC1F3 and BC1F4 generations. Stability of new type B. juncea was assessed in various agronomic traits such as plant height, days taken to flower, branches plant-1, pod length,1000-seed weight and yield plant-1. Results indicated that the expression of these traits was higher in new-type B. juncea as compared to traditional B. juncea which suggesting the stability of subgenome introduction in B. juncea. Both new-type B. juncea and traditional B. juncea were distinguishable each other in morphology. Seed setting rate of new-type B. juncea was increased in BC1F4 generation recorded 11 seeds per pod. The new-type B. juncea shown good seed setting rate, rich phenotypic diversity, and better performance of some traits than that of the traditional B. juncea.Cytological studies revealed that chromosome number was also stable in BC1F4 generation indicating that 96.7% of plants were observed having desirable 36 chromosome number. Correlation is an important breeding parameter which measure the degree of association between two traits. Results showed that yield per plant exhibited significant correlations with other yield contributing traits which indicate that selection of any these trait will improve the yield of the new-type B. juncea. Forty six (15 from A genome and 31 from B genome of Brassica) SSR molecular markers were employed to analyze the genetic variances among different lines of new-type B. juncea along with their original parental accessions. Considering the genetic variation between diverse lines of new-type B. juncea, it was assumed that the orientation of the genomic components from B. rapa and B. carinata could extend the genetic diversity of rapeseed. Overall, compared to the traditional B. juncea population, one-third of the genetic make-up of the population of the new-type B. juncea were created by interspecific crosses and genome alteration during the hybridization process. Principal component analysis revealed genetic variations new type B. juncea plants, traditional B. juncea, B. rapa and B. carinata which suggest that the introducing Ar and Cc genome constituents from B. rapa and B. carinata could significantly differentiate the genetic basis of B. juncea.Intersubgenomic heterosis between hybrids of new-type B. juncea (ArArBcBc) and traditional B. juncea (AJAJBJBJ) was evaluated.10 plants of new-type B. juncea and 10 plants from traditional B. juncea were crossed to each other to produced 10 different combinations of F1 hybrids. High potential of intersubgenomic heterosis in hybrids over mid parent and better parent for different traits such as plant height (16.97 and 12.37%), branches per plant (26.00 and 14.45%), pod length (19.48 and 9.20%),1000-seed weight (22.92 and 17.04%) and better parent (43.26 and 35.16%) for has been observed except days taken to flower (-0.09 and-1.36%) which expressed negative heterosis which is acceptable in plant breeding. These higher values of hybrids over mid parent heterosis (MPH%) and heteriobeltiosis (HB%) indicated that B. juncea yield could be improved by introgression of subgenomes from B. rapa and B. carinata into B. juncea. The potential for intersubgenomic heterosis would be strengthened by pyramiding higher introgression by intercrossing new-type B. juncea plants and selecting based on genomic components and agronomic traits.Overall, the genetic analysis showed that the new-type B. juncea was rich with genetic diversity in comparison to their parents which revealed that introgression of Ar genome of B. rapa and Bc genome of B. carinata could significantly differentiate the genetic basis of the B. juncea and play significant role in the development of new-type B. juncea with novel characters. The intersubgenomic heterosis could be improved by increasing Ar and Bc in the new-typed B. juncea. It was also noted that new-type B. juncea created by backcross was more vigorous and expressed more genetic variability than new-type B. juncea which was created be self-pollination of pentaploid hybrids.