Chromosomal stability and performance of resynthesized Brassica napus produced for gain in earliness and short‐day response

Brassica napus (AACC) was resynthesized by sexual hybridization between the two diploid progenitors, B. campestris (AA) and B. oleracea (CC), represented by short‐day adapted accessions selected from a larger collection brought together. The aim to produce a photoperiod insensitive, artificial rapeseed possible to grow during the dry winter season in Bangladesh proved successful. A plant breeding programme adjusting more general features is started. Preliminary results are reported, proving the superior seed yield structure of napus but at the cost of a prolonged period between flowering and maturity. With the aim to evaluate the most convenient approach for the resynthesis, four different methods were applied in combining campestris (always as mother) and oleracea: Method A (2x × 2x), Method B (2x × 2x, followed by colchicine treatment), Method C (4x × 2x) and Method D (4x × 4x). Irrespective of method applied, the euploid AACC (B. napus) constitution proved to have a very high selective advantage. Even hybrids from Method A and C with the constitution AC (2n=19), AAC (2n=29) or ACC (2n=28) had a clear tendency to produce balanced AACC types. This trend was considerably strengthened and followed up by improved pollen‐ as well as seed fertility, if the primary hybrids were crossed with a natural B. napus. Method D gave the highest frequency of balanced AACC offsprings, but it is questionable whether the extra work to produce 4x progenitors really pays economically.