Intergeneric crosses for the transfer of resistance to the beet cyst nematode from Raphanus sativus to Brassica napus

Summary The possibilities to transfer important traits and in particular resistance to the beet cyst nematode (Heterodera schachtii, abbrev. BCN) from Raphanus sativus to Brassica napus were investigated. For these studies B. napus, R. sativus, the bridging hybrid ×Brassicoraphanus (Raparadish) as well as offspring of the cross ×Brassicoraphanus (Raparadish) ×B. napus were used. Reciprocal crosses between B. napus and R. sativus were unsuccessful, also with the use of embryo rescue. Crosses between ×Brassicoraphanus as female parent and B. napus resulted in a large number of F₁ hybrids, whereas the reciprocal cross yielded mainly matromorphic plants. BC₁, BC₂ and BC₃ plants were obtained from backcrosses with B. napus, which was used as the male parent. F₁ hybrids and BC plants showed a large variation for morphology and male and female fertility. Cuttings of some F₁ and BC₁ plants, obtained from crosses involving resistant plants of ×Brassicoraphanus, were found to possess a level of resistance similar to that of the resistant parent. These results and indications for meiotic pairing between chromosomes of genome R with those of the genomes A and/or C suggest that introgression of the BCN-resistance of Raphanus into B. napus may be achieved.     

Disease response of resynthesized Brassica napus L. lines carrying different combinations of resistance to Plasmodiophora brassicae Wor.

Resistance responses of resynthesized Brassica napus lines to infection with Plasmodiophora brassicae were investigated. Lines that were derived from interspecific crosses between clubroot-resistant B. rapa and resistant B. oleracea exhibited very broad and effective resistance in both greenhouse and field tests. When clubroot resistance was introduced into resynthesized lines from the B. oleracea parent only, the plants were mainly susceptible. Interspecific hybrids from the most resistant parental genotypes, i.e. B. campestris ECD-04 and the B. oleracea cultivars ECD-15 or ‘Bohmerwaldkohf’, were used to initiate a B. napus resistance-breeding programme. These artificial rapeseed lines were resistant to isolates that were virulent on all B. napus differential lines and/or parental lines. Preliminary segregation analysis suggests that their resistance is due to at least two dominant and unlinked genes. In some cases progenies from selfed resynthesized plants exhibited resistance reactions that differed from those of the parental hybrid plant; this may have been the result of cytological instability.     

Inheritance of seed colour in Brassica campestris L. and breeding for yellow-seeded B. napus L.

Summary Seed colour inheritance was studied in five yellow-seeded and one black-seeded B. campestris accessions. Diallel crosses between the yellow-seeded types indicated that the four var. yellow sarson accessions of Indian origin had the same genotype for seed colour but were different from the Swedish yellow-seeded breeding line. Black seed colour was dominant over yellow. The segregation patterns for seed colour in F₂ (Including reciprocals) and BC₁ (backcross of F₁ to the yellow-seeded parent) indicated that the black seed colour was conditioned by a single dominant gene. Seed colour was mainly controlled by the maternal genotype but influenced by the interplay between the maternal and endosperm and/or embryonic genotypes. For developing yellow-seeded B. napus genotypes, resynthesized B. napus lines containing genes for yellow seed (Chen et al., 1988) were crossed with B. napus of yellow/brown seeds, or with yellow-seeded B. carinata. Yellow-seeded F₂ plants were found in the crosses that involved the B. napus breeding line. However, this yellow-seeded character did not breed true up to F₄. Crosses between a yellow-seeded F₃ plant and a monogenomically controlled black-seeded B. napus line of resynthesized origin revealed that the black-seeded trait in the B. alboglabra genome was possibly governed by two independently dominant genes with duplicated effect. Crossability between the resynthesized B. napus lines as female and B. carinata as male was fairly high. The sterility of the F₁ plants prevented further breeding progress for developing yellow-seeded B. napus by this strategy.     

Crossability and cytology of hybrid progenies in the cross between Brassica campestris and three wild relatives of B. oleracea,B. bourgeaui,B. cretica and B. montana

Summary Crossability and cytology were examined in F₁, F₂, B₁ and hybridsplants of F₁ hybrids of Brassica campestris and three wild relatives of B. oleracea, B. bourgeaui, B. cretica and B. montana, respectively. The F₂ plants were obtained after self-and open pollination of the F₁ hybrids. The B₁ and hybrid plants were produced after the F₁ hybrids backcrosses with B. campestris and crossed with B. napus, respectively. After crossing the F₁ hybrids, many seeds of the F₂, B₁ and hybrid plants were harvested. Multivalent formation was high in the chromsome configuration for the PMCs of F₂, B₁ and hybrid plants, suggesting that crossing over might occur between them. Many different types of aneuploids were obtained in the progenies of the F₂, B₁ and hybrid plants. It is suggested that different types of normal egg cells may be produced by one-by-one or little-by-little chromosome addition. The possibility is discussed of gene transfer from B. bourgeaui, B. cretica and B. montana, to cultivated plants, B. campestris and B. napus.     

Genetic effects on biomass yield in interspecific hybrids between Brassica napus and B. rapa

This study was conducted to estimate the genetic effects on biomass yield in the interspecific hybrids between Brassica napus and B. rapa, and to evaluate the relationship between parental genetic diversity and its effect on biomass yield of interspecific hybrids. Six cultivars and lines of oilseed B. napus and 20 cultivars of oilseed B. rapa from different regions of the world were chosen to produce interspecific hybrids using NC design II. Obvious genetic differences between B. rapa and B. napus were detected by RFLP. In addition, Chinese B. rapa and European B. rapa were shown genetically differences. Plant biomass yield from these interspecific hybrids were measured at the end of flowering period. Significant differences were detected among general combining ability (GCA) effects over two years and specific combining ability (SCA) effects differences were detected in 2000. The ratios of mean squares, (σ² _GCA(f) + σ² _GCA(m)) / (σ² _GCA(f) + σ² _GCA(m) + σ² _SCA), were 89% and 88% in 1999 and 2000, respectively. This indicates that both additive effects and non-additive effects contributed to the biomass yield of interspecific hybrids and the former played more important role. Some European B. rapa had significant negative GCA effects while many of Chinese B. rapa had significant positive GCA effects, indicating that Chinese B. rapa may be a valuable source for transferring favorable genes of biomass yield to B. napus. Significant positive correlation between parental genetic distance and biomass yield of interspecific hybrids implies that larger genetic distance results in higher biomass yield for the interspecific hybrids. A way to utilize interspecific heterosis for seed yield was discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of black rot resistant interspecific hybrids between Brassica oleracea L. cultivars and Brassica accession A 19182, using embryo rescue

Black rot is a bacterial disease of Brassica oleracea caused by Xanthomonas campestris pv. campestris. Resistance to the major black rot races 1 or 4 has been identified in related Brassica species including B. carinata and B. napus. In this study, two B. juncea accessions (A 19182 and A 19183) that are resistant to races 1 and 4 of Xcc were used as maternal and paternal parents to generate interspecific hybrids with B. oleracea cultivars. Interspecific hybrids were recovered using the embryo rescue technique and confirmed through inheritance of paternal molecular markers. Twenty-six interspecific hybrid plants were obtained between A 19182 and B. oleracea cultivars, but no interspecific hybrids were obtained using A 19183. Although interspecific hybrid plants were male sterile, they were used successfully as maternal parents to generate backcross plants using embryo rescue. All hybrid and BC₁ plants were resistant to black rot races 1 and 4.     

Intergeneric hybridization of Diplotaxis erucoides with Brassica napus. I. cytogenetic analysis of F1 and BC1 progeny

Summary Intergeneric hybrids (F₁) Diplotaxis erucoides (DeDe) x Brassica napus (AACC) and the first backcross to B. napus (BC₁) have been obtained through in vitro culture of excised ovaries. The chromosome numbers of F₁ and BC₁ plants proved the occurrence of unreduced gametes. The study of metaphase I chromosome pairing showed that autosyndesis in De genome and allosyndesis between De and A/C genomes might exist. The male fertility of the F₁ plants was low. Some male-sterile plants were found in F₁ and BC₁ progeny. The possibilities of creating addition lines B. napus-D. erucoides and of obtaining a new cytoplasmic male sterility in B. napus are discussed.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. I. Production of F1 hybrids through embryo rescue

Summary Triazine resistant Brassica napus ssp. oleifera and ssp. rapifera were hybridized to cultivars of B. oleracea ssp. italica, ssp. botrytis, ssp. capitata and ssp. fimbriata. The interspecific embryos did not survive in vivo but could be rescued in vitro using a culture medium developed by Monnier (1973). The embryos did not grow directly into normal plants but were successfully regenerated using the protocol developed by Keller (1984). Hybridization efficiency ranged from 0 to 2.64 hybrids per pollination. Interspecific embryo abortion may be related to abnormal endosperm development.     

The transfer of triazine resistance from Brassica napus L. to B. oleracea L. III. First backcross to parental species

Summary Atrazine resistant Brassica napus × B. oleracea F₁ hybrids were backcrossed to both parental species. The backcrosses to B. napus produced seeds in both directions but results were much better when the F₁ hybrid was the pollen parent. Backcrosses to B. oleracea failed completely but BC₁s were rescued by embryo culture both from a tetraploid hybrid (2n = 4x = 37; A₁C₁CC) and sesquidiploid hybrids (2n = 3x = 8; A₁C₁C). Progeny of crosses between the tetraploid hybrid and B. oleracea had between 25 and 28 chromosomes. That of crosses between the sesquidiploid hybrid and B. oleracea had between 21 and 27. A few plants that had chromosome counts outside the expected range may have originated from either diploid parthenogenesis, unreduced gametes or spontaneous chromosome doubling during in vitro culture. Pollen stainability of the BC₁s ranged from 0% to 91.5%. All the BC₁s to B. oleracea were resistant to atrazine.     

Transfer of disease resistance within the genus Brassica through asymmetric somatic hybridization

Summary Asymmetric somatic hybrid plants between Brassica napus L. (oilseed rape genome AACC) and a transgenic line of Brassica nigra L. Koch (black mustard genome BB) were tested for their resistance against rapeseed pathogens Phoma lingam (black leg disease) and Plasmodiophora brassicae (club root disease). The transgenic B. nigra line used (hygromycin-resistant, donor) is highly resistant to both fungi, whereas B. napus (recipient) is highly susceptible. The asymmetric somatic hybrids were produced using the donor-recipient fusion method (with X-irradiation of donor protoplasts) reported by Zelcer et al. (1978) for the production of cybrids. Using hygromycin-B for selection, a total of 332 hybrid calli were obtained. Regenerants, resistant or susceptible to both diseases, were selected. Many hybrids expressed resistance to only one pathogen. Dot blot experiments showed that the asymmetric hybrid plants contained varying amounts of the donor genomic DNA. Furthermore, a correlation was detected between the radiation dose and the degree of donor DNA elimination.     

A cytogenetic study of the progenies of hybrids between Brassica napus and Brassica oleracea, Brassica bourgeaui, Brassica cretica and Brassica montana

In this cytogenetic study the progeny of all crosses were investigated in F₁, F₂ and backcross (BC₁) hybrids. Brassica napus and F₁ hybrids between B. napus and B. oleracea, and between B. napus and three wild relatives of B. oleracea (B. bourgeaui, B. cretica and B. montana). Each of the wild relatives has 18 somatic chromosomes. Interspecific F₁ hybrids were obtained through ovary culture mean. These had 28 and 37 chromosomes and their mean pollen fertility was 10.7% and 93.0%, respectively. Many F₂ and BC₁ seeds were harvested from the F₁ hybrids with 37 chromosomes after self‐pollination and open pollination of the F₁ hybrids, and backcrossing with B. napus. Many aneuploids were obtained in the F₂ and BC₁ plants. It is evident from these investigations that the F₁ hybrids may serve as bridge plants to improve B. napus and other Brassica crops.     

Interspecific cross of Brassica oleracea var. alboglabra and B. napus : effects of growth condition and silique age on the efficiency of hybrid production, and inheritance of erucic acid in the self-pollinated backcross generation

Interspecific hybrids were produced from reciprocal crosses between Brassica napus (2n = 38, AACC) and B. oleracea var. alboglabra (2n = 18, CC) to introgress the zero-erucic acid alleles from B. napus into B. oleracea. The ovule culture embryo rescue technique was applied for production of F₁ plants. The effects of silique age, as measured by days after pollination (DAP), and growth condition (temperature) on the efficiency of this technique was investigated. The greatest numbers of hybrids per pollination were produced under 20°/15°C (day/night) at 16 DAP for B. oleracea (♀) × B. napus crosses, while under 15°/10°C at 14 DAP for B. napus (♀) × B. oleracea crosses. Application of the ovule culture technique also increased the efficiency of BC₁ (F₁ × B. oleracea) hybrid production by 10-fold over in vivo seed set. The segregation of erucic acid alleles in the self-pollinated backcross generation, i.e. in BC₁S₁ seeds, revealed that the gametes of the F₁ and BC₁ plants carrying a greater number of A-genome chromosomes were more viable. This resulted in a significantly greater number of intermediate and a smaller number of high-erucic acid BC₁S₁ seeds.     

Hybridization of Sinapis alba L. and Brassica napus L. via Embryo Rescue

Embryo rescue techniques were used to obtain hybrids between Sinapis alba L. (white mustard) and Brassica napus L. (oilseed rape) with the goal of improving the disease tolerance of oilseed rape. Hybrid plants with 31 or 43 chromosomes were only recovered, when S. alba, was used as the female parent. One hybrid was obtained from the cross S. alba L. cv. ‘Kirby’×B. napus L. cv. ‘Topas’, while 26 hybrids were obtained, when various S. alba L. cultivars were pollinated with the rapid cycling B. napus line CrGC 5006. All F₁, hybrid plants were male sterile; however, the first generation backcross to B. napus L., also obtained by embryo rescue, produced plants with 50 chromosomes and 61–84 % pollen viability. Second backcross generation seed was produced by normal sexual crossing. Preliminary cytological analyses of pollen mother cells of hybrid plants suggests the possibility of genetic exchange between the two species.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea var. capitata). II. Meiosis in the interspecific hybrids between B. napus and 2x and 4x cabbage

Summary Meiosis in 14 interspecific F₁ hybrids with three chromosomal levels (triploid, tetraploid, hexaploid; 2n=28, 37 and 55) between Brassica napus L. and 2x and 4x cabbage (B. oleracea var. capitata L.) was studied. The oleracea genome from B. napus maintained close homology with the c genome of cabbage while the campestris genome of B. napus showed partial homology with the c genome contained in the hybrids. Genotypic influence on chromosome pairing was indicated. Structural chromosome differences and spontaneous chromosome breakage and reunion were suggested as causes for the abnormalities which related to the unbalance of the genotypes. The divergence of the genomes of B. napus and B. oleracea and the need for the qualification of the term secondary association were discussed.Contribution No. J. 673, Research Station, Agriculture Canada, St. Jean, Québec.     

Resynthesis of rapeseed (Brassica napus L.): A comparison of sexual versus somatic hybridization

Sexual and somatic Brassica napus hybrids produced from the same parental plants were compared. Sexual crosses between a white-flowered, self-compatible broccoli selection (B. oleracea var. italica, cc genome) as the maternal parent and a flowering pak choi accession (B. chinensis, aa genome) yielded one unique spontaneous hybrid and four hybrids through embryo rescue. Thirty-nine somatic hybrids were recovered from a protoplast fusion experiment. Hybridity was confirmed by morphology, isozyme expression, flow cytometry, and DNA hybridization. Sexual and somatic hybrids exhibited differences in leaf morphology, flower colour, flowering habit, and organellar inheritance. Sexual hybrids were all fertile amphidiploids (2n = 38, aacc) following spontaneous chromosome doubling. All somatic hybrids had high nuclear DNA contents; most were probably hexaploids (aaaacc or aacccc) from the fusion of three portoplasts. Two initially sterile hexaploid (aaaacc) regenerates eventually set selfed seed after the loss of the putative extra aa genome following regrowth from axillary buds. A bias toward inheritance of B. chinensis chloroplasts was observed with somatic hybrids.     

The effect of the cytoplasms of Brassica napus and B. juncea on some characteristics of B. carinata, including flower morphology

This study was conducted to assess the cytoplasm effects of Brassica napus and B. juncea on the some characteristics of B. carinata, as well as the phylogenetic distances separating the three species. Alloplasmic lines of B. carinata were developed from B. napus × B. carinata and B. juncea × B. carinata hybrids by recurrent backcrossing to the BC₇ generation. Sixteen populations from three generations were compared for a number of characteristics. Plants with the cytoplasm of B. napus flowered later, had shorter filaments and longer pistils, lower pollen amount, lower seed set, lower petal length and width and different petal color; plants with the cytoplasm of B. juncea had shorter pistils and filaments, and lower petal length and width than their corresponding euplasmic sibs, respectively. The results suggest that the cytoplasm is involved in the development of flower organs. The natural species, B. carinata showed a balance between the nucleus and cytoplasm. The cytoplasm from B. napus showed a stronger disturbing effect than that of B. juncea, suggesting that B. carinata might be genetically closer to B. juncea than to B. napus. The significant difference in the alloplasmic effect of the cytoplasms of B. napus and B. juncea also suggests that in B. carinata the B genome may play a greater role than the C genome. An erratum to this article can be found at     

Comparisons of Isozyme Patterns in Resynthesized Amphihaploid Rapeseed (Brassica napus) and Their Parental Species Brassica campestris and Brassica oleracea

Resynthesized rapeseed plants produced by embryo culture and the progeny of their selfed parents from Brassica oleracea and Brassica campestris were analyzed by starch gel electrophoresis staining of enzymes GPI, LAP and SDH. In at least one unequivocal case it could be proved for each enzyme system studied that the alleles of both parents arc independently expressed in the newly synthesized individuals and that in the pattern of the dimeric enzyme GPI interlocus bands of the homoeologous loci arc visible. Comparisons with enzyme patterns in cultivated B. napus leads to the conclusion that in general active enzyme loci of both parental genomes are present. This is of great significance in estimating slide frequencies, degree of heterozygosity and other genetic parameters of B. nupus populations/cultivars.     

Brassilexin accumulation and resistance to Leptosphaeria maculans in Brassica spp. and progeny of an interspecific cross B. juncea × B. napus

Summary Resistance to Leptosphaeria maculans was assessed in Brassica napus, B. juncea, B. carinata, B. nigra and progeny issuing from an interspecific cross B. napus × B. juncea, using a cotyledon-inoculation test. In these individual plants, brassilexin accumulation was determined following an abiotic, non-specific, elicitation. All the tested B. napus cultivars were highly susceptible to the parasite and weakly accumulated brassilexin. In contrast, B. juncea, B. carinata, and B. nigra usually displayed a hypersensitive response to the inoculation and accumulated more brassilexin than B. napus. The same correlation between resistance to L. maculans and phytoalexin accumulation was observed in the interspecific hybrid progeny. The cotyledon-inoculation test allowed the discrimination of plants displaying a hypersensitive response to the inoculation from those highly sensitive to the parasite, but intermediate disease severity classes were not usually representative of resistance or susceptibility. In this respect, brassilexin determination allowed differentiation, within a set of plants presenting an intermediate response to the pathogen, of plants with a high (B. juncea-like), and with a weak (B. napus-like) ability to accumulate brassilexin.Abbreviations IHP interspecific hybrid progeny - JR B. juncea-type complete resistance to blackleg (Roy, 1984) - W&D test cotyledon-inoculation test as described by Williams & Delwiche (1979)     

Risk assessment of outcrossing of transgenic rapessed to related species:

Summary The risk for a gene dispersal is reported for reciprocal crosses between a transgenic rapeseed variety resistant to the herbicide phosphinotricin and five related species. The first stages after pollination were cytologically observed and fertilized ovaries were established in in vitro culture for the production of interspecific hybrids. A similar classification was observed for the index of pollination compatibility and embryo yield. From the 243 embryos produced, 109 plantlets were obtained in a greenhouse. All the interspecific combinations tested were able to produce hybrid plants. A higher number of hybrids was obtained when rapeseed was used as the female parent. The hybrids had the expected triploid structure except for two amphidiploid, B. napus × B. oleracea, and one amphidiploid, B. napus × S. arvensis, plants with 56 chromosomes. The triploid hybrids were sterile or partially fertile but two of the amphidiploid plants, B. napus × B. oleracea, were fully fertile. The cytoplasm source did not seem to affect the fertility of the hybrids.     

Nuclear genetic control of variation in simazine tolerance in oilseed brassicas

Summary Brassica napus is a natural allotetraploid derived from the diploid species B. rapa L. (syn. campestris L.) and B. oleracea L. Somatic hybrids synthesized from highly heterozygous lines of these two diploid species were evaluated for fertility. The hybrids were obtained from two fusion experiments which differed in the B. rapa full-sibling parent used as the source of protoplasts. Both B. rapa siblings were lelf-incompatible (SI) yet contained different S-alleles; the B. oleracea species parent was self-compatible (SC). Eight tetraploid hybrids examined had very high female and male fertility; eight hybrids with higher ploidy had low fertility. Hybrids derived from one B. rapa sibling were self-incompatible, whereas those derived from the other B. rapa sibling were fully self-compatible. These data suggest that the different S-alleles of each B. rapa sibling displayed varying penetrance relative to the SC of the B. oleracea parent when combined in B. napus.Abbreviations SC self-compatibility - SI self-incompatibility