Variation in flowering response to pre-vernalisation growth in swedes (Brassica napus ssp. rapifera)

Summary The effect of pre-vernalisation growth (pre-growth) period on time of flowering was examined in four lines of swedes. No effect was found with the line from cv. Marian. The lines from cvs. Ruta Øtofte and Bangholm Wilby showed increases in time to flowering with increased pre-growth period; maximum delay occurred with 4 wk and 6 wk pre-growth, respectively. Most plants from a line of cv. Criffel showed no effects, but a small proportion did show long delays with pre-growth.     

Self-pollination in swedes (Brassica napus ssp Rapifera) and its implications for cultivar production

Summary The degree of selfing on open pollination was examined in four swede cultivars. Three cultivars had over 80 per cent selfing, whilst the fourth had less than 55 per cent. The inbreeding coefficient with these levels of selfing, assuming the cultivars were at equilibrium, would be 0.69 and 0.37 respectively. The cultivar with the high level of outcrossing was found to possess a degree of self-incompatibility. The structure of such populations is demonstrated, and the implications for cultivar production are discussed.     

Inter-plot competition in yield trials of swedes (Brassica napus ssp. rapifera L.)

Summary Two experiments were done to evaluate the use of single-row plots for assessing dry-matter yield of swedes. In the first experiment the correlation between the dry-matter yields of 20 cultivars in unguarded single-row plots and those in guarded double-row plots was poor (r=0.39). It was improved (r=0.58) by adjusting the single-row plot fresh-weight yields for inter-plot competition, through an analysis of covariance in which the covariate was the mean of the adjacent plot yields, and then estimating the pure stand dry-matter yields. However, the correlation was still lower than that between unguarded double-row plots and the guarded double-row plots (r=0.73), and this latter correlation was also improved (r=0.82) by adjusting the fresh-weight yields of the unguarded plots for inter-plot competition.The second experiment provided an explanation for the partial success of the covariance adjustment. The individual neighbour effects of six cultivars were determined. Doon Major and Ruta Øtofte decreased the yields of adjacent cultivars whereas Dryden and Melfort increased them. Angela and Magres had little effect. The correlation between the dry-matter yield neighbour effects of cultivars and their fresh-weight yields was high (r=–0.81), but not complete. So although competitive ability was associated with root fresh-weight yield, other factors must also be involved.It was concluded that a two-replicate trial with unguarded double-row plots is preferable to a four-replicate trial with unguarded single-row plots for dry-matter yield assessment of early generation families in a pedigree swede breeding programme.     

A comparison of methods for hybrid seed production using self-incompatibility in swedes (Brassica napus ssp. napobrassica)

Procedures for producing seed of hybrid swedes using self-incompatibility were examined. Single-cross, double-cross and modified double-cross hybrids were compared in isolation plots using natural pollinators and in polythene tunnels using blow-flies. With good coincidence of flowering and the same flower colour, nearly 100% hybrid seed was produced by natural pollinators with the single-crosses, the double-cross and one of the two modified double-cross hybrids; the other modified double-cross hybrid produced 87%hybrid seed. With poor coincidence of flowering and different flower colours the proportion of hybrids dropped to 61%. Using different flower colours and blow-flies as pollinators in polythene tunnels, higher levels of outcrossing were produced than in isolation plots with natural pollinators; the opposite result was obtained when the same flower colour was used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Lack of interplot competition in Swedes (Brassica napus ssp rapifera L.)

Summary An experiment comparing double row plants with four row plots where only the centre two rows were harvested (guarded double row plots) were laid out in two subsequent years. Fresh weight yields, dry matter yields, bulb dry matter content, refractometer index and harvest index were recorded and analyzed statistically. The cultivar x plot type interactions were in none of the cases significant. The increase in error variances when comparing double row plots with guarded double row plots was significant only for harvest index in the first year.Taking into account the low selection intensity when small plots are used, i.e. in early stages of plant breeding programmes, we conclude from these experiments that guarded plots are not necessary when breeding swedes under our growing conditions.     

The inheritance of quantitative traits in Brassica napus ssp. rapifera (swedes): Augmented triple test cross analyses of production characters

Two F₂ triple test crosses, augmented with F₃s, produced from crosses between different inbred lines of swedes (Brassica napus ssp.rapifera L.) were assessed in field trials at Dundee in 1988 and 1989,respectively. This paper reports the analyses of resistance to powdery mildew, neck length, growth cracks, sugar content and hardness; analyses of yield have been published previously. Additive genetical variation was found for all traits while non-additive variation was less important, the highest degree of dominance being 0.44 for hardness. There was evidence of additive × dominance and dominance × dominance epistasis for mildew and additive × additive epistasis for neck length and hardness. Significant,consistent reciprocal differences were found and these were particularly large for neck length and growth cracks. Sugar determination was carried out on the basic generations of the second cross, the parental lines of which showed large differences in concentration of glucose, fructose and sucrose. Directional dominance was found for high glucose but not for fructose or sucrose. The implications of these results for swede breeding are discussed and it is proposed that inbred cultivars would be a more practical option than F₁ hybrids. This revised version was published online in August 2006 with corrections to the Cover Date.     

Parameter estimates from generation means in swedes (Brassica napus ssp. rapifera L.)

From an experiment involving swede (Brassica napus ssp. rapifera L.) material resulting from a 4 × 4 diallel cross and a 4 × 9 factorial mating design better parent heterosis for dry matter and marketable yield was found in the majority of the hybrids. For breeders preference the better parent heterosis was not that pronounced and the majority of the hybrids were inferior when compared to their better parent. The generation means showed that models containing the mean, m, and the dominance parameter, h, generally resulted in the best fit. In some cases the additive parameter, d, improved the fit. In those cases, however, the additive parameter was substantially smaller than the dominance parameter. The probability of occurrence of recombinant inbred lines that outperform the source F₁-hybrid was, with very few exceptions, found to be low. Implications for swede breeding are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self-incompatibility interactions in Brassica napus

Summary The interactions of nine S-gene lines of Brassica napus were examined. Seven different S-genes were involved in the crosses, with three lines of different origin having the same S-gene. In general, the reactions on selfing the heterozygotes were as expected from the results of test crosses with the homozygous parent lines. All types of dominance relationships were found, including reversal of dominance in pollen and pistil. Weakening of activity of one or both genes was found in several cases. Background genotype was found have to some effect and reciprocal differences in reactions were also observed.     

Methods of producing F1 hybrid swedes (Brassica napus ssp. rapifera)

Summary The methods by which F₁ hybrid swedes can be produced are discussed. The use of self-incompatibility is considered preferable to the use of cytoplasmic male sterility. Several ways of utilising self-incompatibility are available and the integration of self-compatible lines into these methos should simplify their use.     

Self-incompatibility in Brassica napus: seed set on crossing 19 self-incompatible lines

Summary Seed set after self-pollination confirmed that 19 lines of Brassica napus were self-incompatible. Eight lines, H, J, Q, W, X, K, P and Z, were fully cross-compatible. Line R was cross-compatible with these lines but often had a low seed set as female parent. These results are consistent with the activity of nine distinct S-alleles. Line S was cross-incompatible with K, as was V with P, and F with Z. With each of the lines A, E, B, O, G, L and M at least one reciprocal difference was found so that the number of additional distinct S-alleles could not be inferred, but there must be a minimum of seven.Pollen tube counts of intra- and inter-line pollinations using M, B and X confirmed the homozygosity of these lines with respect to self-incompatibility status and the presence of non-reciprocal compatibility between M and B.The results are interpreted in terms of the activity of both B. oleracea and B. campestris S-loci and the implications for hybrid breeding are discussed.     

The transfer of characters from Brassica campestris L. to Brassica napus L.: Production of clubroot-resistant oil-seed rape (B. napus ssp oleifera)

Summary Four oil-seed rape lines were crossed with a clubroot resistant Brassica campestris line from the European Clubroot Differential sct. The allotriploid hybrids were backcrossed to the rape lines to introgress clubroot resistance into oil-seed rape. Using a combination of screening for disease resistance and chromosome number, a high proportion of 38-chromosome, clubroot resistant selections were obtained.     

Heterosis and its possible exploitation in swedes (Brassica napus L. ssp. rapifera)

Summary Considerable heterosis has been demonstrated in inter-cultivar swede hybrids. Increases in dry matter yield of between 5.9 and 25.6% over the superior parent were obtained. Difficulties and possibilities with regard to the commercial exploitation of this phenomenon in swedes are discussed.     

Heterosis and inbreeding depression in forage rape (Brassica napus L.)

Summary Heterosis and inbreeding depression for total fresh and dry weights were studied over two seasons in 15 crosses of six cultivars of forage rape (Brassica napus L.). Some of the hybrids exhibited considerable heterosis over both mid-parent and better parent; followed by depression in the F₂. The cross Windal × Canard had 62% and 25% greater dry matter yield over the best cultivar used in this experiment in 1978 and 1979, respectively. Possibilities of the utilization of this hybrid superiority are discussed.     

Selection for fast germination in rapeseed (Brassica napus L. and B. Campestris L.)

Summary Eleven populations of Brassica napus L. and twelve populations of B. campestris L. were subjected to three cycles of selection for fast germination at 2°C and at 25°C. The seeds from the selected populations, and unselected control populations grown in the same environment as the selected populations, were examined for germination behaviour at 2°C and 25°C, and for growth behaviour at 10°C. The populations in both species responded differently in terms of germination behaviour to selection for fast germination. In most of the populations that did respond positively to selection, selection practised at 2°C was superior to selection at 25°C in improving percent germination at 2°C, and was as good as the selection at 25°C in improving germination rate at the higher temperature. Selection for fast germination had no effect on growth characteristics of B. napus and B. campestris populations grown at 10°C. Thus, selection for fast germination at one low temperature may lead to improvement in germination characteristics over a range of temperatures, but will not necessarily lead to improved growth performance of the selected populations.     

The introgression of S alleles into forage rape,Brassica napus L. from turnip. Brassica campestris L. ssp. Rapifera

Summary Forage rape. B. napus, is self-compatible, the work described illustrates the introgression of functional incompatibility alleles into B. napus from turnips, B. campestris, in two generations. By grading seed, produced by backcrossing turnip/rape hybrids to rape, the frequency of 2n=38 semi articial B. napus recovered, amply justifies the cytological screening involved in such breeding programmes.     

Variation of glucosinolates and nutritional value in nabicol (Brassica napus pabularia group)

Glucosinolate levels in leaves were determined in a collection of 36 varieties of nabicol (Brassica napus pabularia group) from northwestern Spain grown at two locations. Crude protein, acid detergent fibre, and sensory traits were also assessed by a consumer panel. The objectives were to determine the diversity among varieties in total glucosinolate content and glucosinolate profile and to evaluate their sensory attributes in relation to glucosinolate content for breeding purposes. Eight glucosinolates were identified, being the aliphatic glucosinolates, glucobrassicanapin, progoitrin, and gluconapin the most abundant. Glucosinolate composition varied between locations although the glucosinolate pattern was not significantly influenced. Differences in total glucosinolate content, glucosinolate profile, protein, acid detergent fibre, and flavour were found among varieties. The total glucosinolate content ranged from 1.4 μmol g⁻¹ to 41.0 μmol g⁻¹ dw at one location and from 1.2 μmol g⁻¹ to 7.6 μmol g⁻¹ dw at the other location. Sensory analysis comparing bitterness and flavour with variation in glucosinolate, gluconapin, progoitrin, and glucobrassicanapin concentrations suggested that other phytochemicals are probably involved on the characteristic flavour. The variety MBG-BRS0035 had high total glucosinolate, glucobrassicanapin, and gluconapin contents at both locations and could be included in breeding programs to improve the nutritional value of this vegetable crop.     

Identification of AFLP fragments linked to one recessive genic male sterility (RGMS) in rapeseed (Brassica napus L.) and conversion to SCAR markers for marker-aided selection

117AB is a recessive genic male sterility (RGMS) line in which the sterility is controlled by a duplicate recessive gene named ms, located at two separate loci. In the RGMS line, the genotype of the sterile plant (117A) is msmsmsms, and that of the fertile plant (117B) is Msmsmsms. The present study was aimed to identify DNA markers linked to the ms locus by amplified fragment length polymorphism (AFLP). From the survey of 512 AFLP primer combinations, 6 AFLP fragments (y1, k1, k2, k3, k4, k5) were identified as being tightly linked to the Ms locus. The genetic distances between the markers and the Ms locus were all less than 8 cM, among which two fragments, designated as k2 and k3, co-segregated with the target gene in the tested population. Fragment k2 was successfully converted into a sequence characterized amplified region (SCAR) marker. The markers detected could be valuable in marker-assisted breeding of RGMS in Brassica napus.     

In vitro selection for oleic and linoleic acid content in segregating populations of microspore derived embryos of Brassica napus

Microspore derived embryos (MDEs) in Brassica napuscontain large amounts of storage lipids which show a genotype specific fatty acid composition (FAC). One cotyledon of regenerating emblyos can be dissected at an early stage during the in vitro culture and used for fatty acid analysis. Thus, in breeding programmes to modify oil quality, only MDEs having the desired FAC need to be regenerated to plantlets and transferred to the greenhouse. In the present study the applicability of this method for the selection of a high oleic acid content and a low linoleic acid content in the seed oil has been tested by crossing a Brassica napus mutant line having a high oleic acid (C18:1) content in the seed oil (75%) with a wild type doubled haploid line with 62% C18:1 in the seed oil. Microspore culture was applied to the F1 plants. In total 59 MDEs were obtained, from which 31 were cultured with and 28 without 15μM abscisic acid for 3 weeksin vitro. One cotyledon was dissected under aspetic conditions and used for fatty acid analysis. The remaining part of the embryos were further regenerated to plantlets and transferred to the greenhouse to obtain seeds after self pollination. Seeds harvested from the doubled haploid lines in the greenhouse were used for fatty acid analysis and also for growing in the field. The abscisic acid treatment of the MDEs generally improved the correlations for linoleic and oleic acid between the MDEs and the seeds harvested in the greenhouse and the field. The correlations ranged from 0.68** to 0.81**.This indicates that selection for high oleic acid can be started already during an early stage of the in vitro culture. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inbreeding depression and single cross hybrids in leeks (Allium ampeloprasum ssp. porrum)

Summary All current commercial cultivars of leeks are open-pollinated and one of the major problems with the crop is poor uniformity with much of the variation being genetic in origin. Inbred lines and single cross hybrids were produced to try to reduce the genetic variation. Inbreds were generated by single seed descent from 5400 plants taken from six commercial cultivars and performance data for uniformity, yield and quality are presented for the S₁-S₃ generations. A few relatively vigorous inbred lines were obtained but overall, inbreeding depression was very severe with no compensating increase in uniformity as measured by coefficients of variation. In contrast, the experimental hybrids gave significant uniformity, yield and quality benefits compared to open-pollinated commercial cultivars and can be used as the basis for developing a range of commercial hybrid cultivars.Abbreviations SSD Single Seed Descent - HRI Horticulture Research International     

Oligonucleotide fingerprinting of resynthesized Brassica napus

Brassica napus plants, artificially synthesized through somatic hybridization of B. oleracea and B. campestris protoplasts, were analyzed by oligonucleotide fingerprinting. While the fingerprint patterns of the different hybrid plants looked very much alike, they did not simply represent a combination of the parental patterns. Instead, the absence of parental bands as well as the presence of new bands suggest that elimination and/or rearrangements occurred during or after the fusion of the two genomes. The fingerprints of individual F1 progeny plants of selfed hybrids did not detect major changes. Thus, once formed, the artificially resynthesized amphidiploid B. napus genome appears to be stable. Taken together, our experiments demonstrate the usefulness of oligonucleotide fingerprinting for the characterization of artificial hybrids in the genus Brassica.