Resynthesized (RS) oilseed rape (Brassica napus L.) is potentially of great interest for hybrid breeding. However, a major problem with the direct use of RS B. napus is the quality of seed oil (high level of erucic acid) and seed meal (high glucosinolate content), which does not comply with double-low quality oilseed rape. Thus, additional developments are needed before RS B. napus can be introduced into breeding practice. In this study, RS oilseed rape was obtained through crosses between B. rapa ssp. chinensis var. chinensis and B. oleracea ssp. acephala var. sabellica. RS plant was then crossed with double-low (00) winter oilseed rape lines containing the Rfo gene for Ogura cytoplasmic male sterility (CMS ogu) system. Populations of doubled haploids (DH) were developed from these F1 hybrids using the microspore in vitro culture method. The seeds of semi-RS DH lines were analyzed for erucic acid and glucosinolate content. Among the populations of semi-RS DHs four 00-quality lines with the Rfo gene were selected. Using 344 AFLP markers to estimate genetic relatedness, we showed that the RS lines and semi-RS lines formed clusters that were clearly distinct from 96 winter oilseed rape parental lines of F1 hybrids.

Resynthesized (RS) Brassica napus can be used to increase the genetic diversity of this important crop plant and to develop the heterotic gene pool required for successful hybrid breeding programmes. The level of heterosis in F 1 hybrids depends on the individual performance of the parents and on the degree of genetic difference between them. However, RS forms obtained from crosses of B . rapa ssp. with B . oleracea ssp. possess many undesirable agronomic traits, such as low quality of seeds, low yield and seed oil content, high erucic acid level in the oil and high glucosinolate content in seed meal. Therefore, RS oilseed rape needs to be improved by crossing with natural double-low oilseed rape, leading to selected double-low quality semi-RS lines that can be used for breeding. In this study, we evaluated the seed yield potential of F 1 hybrids derived from crosses between Ogura cytoplasmic male-sterility (CMS) lines and doubled haploid (DH) semi-RS lines with restorer gene in three locations in Poland. The genotype by environment interaction (GE interaction) and general combining ability (GCA) of the restorer and CMS line effects, as well as the effects of heterosis, were also assessed. The results of the study provide the first insights into the use of semi-RS lines as components for the development of new hybrid cultivars. Even the introduction of 50% of the RS oilseed rape genotype to natural restorer lines resulted in a marked heterosis effect, with seed yield ranging from 4.56% to 90.17% more than that of the better parent. The yield of the best hybrid amounted to 108.6% of the seed yield of the open-pollinated cultivar Monolit and 94.4% of that of the hybrid cultivar Arsenal. The best DH semi-RS line S1, which had a significantly positive GCA for seed yield, can be recommended as a possible parent for inclusion in breeding programmes aimed at developing new hybrid cultivars.

Brassica napus is an allopolyploid plant, derived from spontaneous hybridization between Brassica rapa and Brassica oleracea. Intensive breeding has led to a significant reduction in genetic and phenotypic diversity within this species. Newly resynthesized hybrids from progenitor species may restore some diversity in B. napus, but they often are chromosomally and phenotypically unstable. Using fluorescence in situ hybridization, we tested chromosome constitutions in a range of new allopolyploids resynthesized from various parental species. A majority of these allopolyploids were euploid, with the expected chromosome numbers and constitutions, but deviations were also identified. We detected a low level of intergenomic rearrangements in analyzed hybrids and a high level of changes in rDNA loci. Our study revealed a significant effect of maternal cross combination on loss of 35S rDNA loci, especially when B. rapa was the maternal parent. The studied lines were characterized by diversified of pollen viability. In the analyzed hybrids, the erucic acid level in the seed oil ranged from 0 to 43.4% and total glucosinolate content in seeds ranged from 24.3 to 119.2 μmol g −1. Our study shows that cytogenetic analysis of B. napus resynthesized hybrids would be useful in breeding for the selection of lines with important agricultural characters and genetically stable stock seed production. Keywords Allopolyploids. Resynthesis. Brassica napus. Chromosome rearrangements. FISH. rDNA Abbreviations BAC Bacterial artificial chromosome FISH Fluorescence in situ hybridization NOR Nucleolus organizer region RS Resynthesized 00-quality Genotypes with zero erucic acid and low seed glucosinolate content 0+ quality Genotypes with zero erucic acid and high glucosinolate content ++ quality Genotypes with high erucic acid and high glucosinolate content * Katarzyna Sosnowska

Haploids and doubled haploids (DHs) have been produced in Brassica ssp. using anther or isolated microspore cultures. Since 1982, when Lichter developed a method of isolated microspores culture, this technique has been constantly improved and modified. Haploids and DH of Brassica napus have been extensively used in genetic studies, such as gene mapping, location of quantitative trait locus, marker / trait association studies, and genomics. Furthermore, the oilseed rape haploid induction technique can nowadays be efficiently combined with several other plant biotechnological techniques, enabling several novel breeding achievements, such as mutation breeding, the breeding of hybrid varieties, genetic transformation, and resynthesis of B. napus. The development and improvement of in vitro androgenesis of oilseed rape allowed DH populations to be obtained on a large scale. Today DH lines are used in the genetic analysis of quantitative traits and to analyze the impact of the environment on the yield and quality of the seeds. Currently, DH technology has become more efficient and hence can be widely applied in winter oilseed rape breeding. Additionally, DH technology is used to shorten the process of breeding new varieties. An open pollinated B. napus cv. Monolit (Plant Breeding Strzelce Ltd., Co.) is the first Polish winter oilseed rape variety obtained using DH technology. The breeding cycle of this variety is about four years shorter compared to a classical breeding program. The second Polish cultivar obtained using DH technology, cv. Brendy (Plant Breeding Smolice Ltd., Co.) was developed in a similarly short period. In the breeding of new oilseed rape hybrid varieties, homozygous restorer lines are also exploited. Our basic research used oilseed rape DH technology with a focus on improving the qualitative traits of oilseed rape and is presented here, based on the major researches conducted worldwide as well as on the results obtained at the Plant Breeding and Acclimati

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