Study On The Genetic Basis Of Seed Color In Resynthesized Yellow-seeded Brassica Napus Line No.2127-17

Rapeseed (Bracissa napus) is one of the most important oilseed crops in the world, as well as in China. It plays a role in the national economy and popular daily live. As it is extracted for oil and meal, increasing the oil and protein contents is the most important breeding goal of canola quality improvement. Based on the advantages of yellow seeds characters, the genetic mechanism and molecular bases studying in yellow seed are being a hotspot of quality breeding in Brassica napus. In this study, we resolved the genetic mechanism based on analyses of phenotypic segregations in the hybridize combinations and their population derived from a resynthesized yellow-seeded B. napus line no.2127-17 with 9 different lines with black-seeded coat. Meanwhile, we identified QTLs related seed color in a Quantum×no.2127-17 DH population and no.2127-17×94570 F2 population. The results were as follows:1. The conventional genetic analyses were studied in 37 generations of B. napus derived from the crosses between a yellow-seeded line (no.2127-17) and nine different black-seeded parents. On the one hand, in the combinations including black-seeded parents SWO780,94560,94545 and 1141B, the yellow seed is partially dominant over black with two or three genes plus one dominance epistasis. A dominant yellow-seeded gene Y which exhibits epistatic effect on the two independent dominant black-seeded genes B and C was identified in yellow-seeded line no.2127-17. On the other hand, in the rests, including the crosses with HS no.4, HS no.3, XY no.15,94570 and ZS no.10, the black seed color was dominant over yellow seed color. The inheritance of this trait in the segregating populations fits into the model of a digenic dominance epistasis or triplicate dominance epistasis. One new locus was identified and designated as D:the dominant gene D for black seed color could inhibit the dominant gene Y. Therefore, in combined with the Y, B and C, we found that the seed color was influenced by at least four genes.2. One genetic linkage map of Quantum/no.2127-17 DH population, spanning 1747.4 cM with an average interval of 4.4 cM, divided into 19 linkage groups, was constructed using 207 simple sequence repeat (SSR) markers and 190 sequence-related amplified polymorphism (SRAP) markers. At the same time, another genetic linkage map on no.2127-17/94570 F2 population, spanning 1055.4cM with an average interval of 4.42cM, divided into 19 concatenations, was constructed using 94 simple sequence repeat (SSR) markers and 179 Amplified fragment length polymorphism (AFLP) markers. Based on the public information of microsatellites (SSR markers), the maps were aligned with the reference maps.3. The QTL analysis was undertaken using the two populations derived from the crosses Quantum/no.2127-17 (HZ-1) and no.2127-17/94570 (HZ-2). In the HZ-1 population, three putative QTLs were detected in the linkage groups N18, N5, and N3, respectively. For all of them, yellow seed color arose from the no.2127-17 alleles. Of these QTLs, the one in linkage group N18 (qBnsc-18a) behaved as a partially dominant yellow seed color gene and explained more than half of the phenotypic variation. In the HZ-2 population, three QTLs were found in the linkage groups N9, N18, and N8, respectively. Of these QTLs, the one in linkage group N9 (qBnsc-9a) behaved as a completely dominant black seed color gene and explained more than half of the phenotypic variation, whereas the QTL (qBnsc-18a) had a low seed color value and explained only 9.03-11.72% of the phenotypic variation.4. Twenty AFLP markers were found to link closely with seed color locus SC in no.2127-17/94570/no.2127-17 BC1 population by bulked segregant analysis (BSA). To decipher the relationship between the SC and the QTLs detected in the HZ-1 and HZ-2 populations,5 markers (EA7MG8₂10, EA8MG5₁70, EA5MC4₂40, EA9MC4₁10 and EA10MC9₂20) of those AFLP markers were random selected for mapped in the two populations (HZ-1 and HZ-2). All of them were located in the region of the qBnsc-9a in the HZ-2 population. This result confirmed that the SC could be the same as the QTL (qBnsc-9a) in the HZ-2 population.5. Based on the sequence information of markers which mapped in the region of the major QTL, IP primers and SSR primers were designed and used to screen the individuals of the HZ-1 and HZ-2 population. The six IP markers and three SSR markers were found to be more tightly linked to the qBnsc-18a, and qBnsc-18a was narrowed to a linkage group approximately 6.5cM in length. One IP marker and three SSR markers were detected to be more tightly linked to the qBnsc-18a, and qBnsc-9a was fixed to a linkage group approximately 5.7cM in length.6. Following the strategy of NIL development by consecutive backcrossing (CB-NIL), one pair of near-isogenic lines for seed color were constructed in the no.2127-17 background according to the primary QTL identified in no.2127-17/94570 (HZ-2) F2 population. Progeny test indicated the near isogenic lines showed the segregation ratio of single Mendelian factor.