Cytogenetic and Molecular Characterization of B-Genome Introgression Lines of Brassica napus L.

Brassica napus introgression lines (ILs), having B-genome segments from B. carinata, were assessed genetically for extent of introgression and phenotypically for siliqua shatter resistance. Introgression lines had 7-9% higher DNA content, were meiotically stable, and had almost normal pollen fertility/seed set. Segment introgressions were confirmed by fluorescent genomic in situ hybridization (fl-GISH), SSR analyses, and SNP studies. Genotyping with 48 B-genome specific SSRs detected substitutions from B3, B4, B6, and B7 chromosomes on 39 of the 69 ILs whereas SNP genotyping detected a total of 23 B-segments (≥3 Mb) from B4, B6, and B7 introgressed into 10 of the 19 (C1, C2, C3, C5, C6, C8, C9, A3, A9, A10) chromosomes in 17 ILs. The size of substitutions varied from 3.0 Mb on chromosome A9 (IL59) to 42.44 Mb on chromosome C2 (IL54), ranging from 7 to 83% of the recipient chromosome. Average siliqua strength in ILs was observed to be higher than that of B. napus parents (2.2-6.0 vs. 1.9-4.0 mJ) while siliqua strength in some of the lines was almost equal to that of the donor parent B. carinata (6.0 vs.7.2 mJ). These ILs, with large chunks of substituted B-genome, can prove to be a useful prebreeding resource for germplasm enhancement in B. napus, especially for siliqua shatter resistance.

Resynthesis of Brassica napus through hybridization between B. juncea and B. carinata.

KEY MESSAGE: First report for the resynthesis of Brassica napus by recombining A and C genome from B. juncea and B. carinata , respectively. Also documents B genome introgressions in resynthesized B. napus. Resynthesis of Brassica napus (AACC) was achieved by hybridizing Brassica juncea (AABB) with Brassica carinata (BBCC). This was facilitated by spontaneous chromosome doubling in the F1 hybrid (ABBC) to yield octaploid (AABBBBCC), elimination of extra B genome chromosomes in the resulting octaploid and in subsequent selfed generations, aided with directed selection for fertile plants having B. napus morphology. Twenty-five plants with varying degrees of resemblance to natural B. napus were identified from 17 A5 progenies and assayed for cytogenetic stability and genetic diversity. Majority of these plants, except six (2n = 38) were hyperploids (2n = 40-56). The six plants with 2n = 38 were designated as derived B. napus types. These showed an expected meiotic configuration of 19II at metaphase-I, with 19-19 distribution at anaphase-I. Genotyping based on A and C genome specific primers confirmed genetic identity of six derived (2n = 38) B. napus plants with natural types whereas genotyping with B genome specific primers indicated introgression of B genome segments. This was also confirmed by genomic in situ hybridization (GISH). Strong signals of B genome probe were detected, proving hitherto unreported genetic exchanges between B and A/C chromosomes. These introgressions possibly occurred en route five generations of selfing. Derived plants yielded fertile hybrids in crosses with natural B. napus var. GSC 6. The selfed derived plants as evaluated in A6 plant to progeny rows were morphologically similar to natural B. napus, and meiotically stable. Agronomic assessment of these progenies revealed variation for key morpho-physiological traits. Of special interest were the progenies with plants having oil content exceeding 47% as against about 39-41% in existing cultivars.