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     

A genetic study of growth characters and yield characters of oilseed rape

Summary Analysis of single plants in parental, F₁ and F₂ populations of three crosses of oilseed rape indicated cytoplasmic effects in F₁ or F₂ generations for most of the observed characters. There was evidence of dominance for early flowering and early maturity. Heterosis was exhibited for yield and yield components. The heritabilities for the characters under study were generally very low.     

Degradation of oxalic acid by transgenic oilseed rape plants expressing oxalate oxidase

Summary Oxalic acid is thought to have a primary role in the pathogenicity of several plant pathogens, notably Sclerotinia selerotiorum. A gene coding for the enzyme oxalate oxidase was isolated from barley roots and introduced into oilseed rape as a means of degrading oxalic acid in vivo. This report describes the production of several transgenic plants of oilseed rape and the characterisation of these plants by Southern, Western and enzyme activity assays. Plants were shown to contain an active oxalate oxidase enzyme and were tolerant of exogenously supplied oxalic acid.     

Comparison of aluminium tolerance in the brassicas and related species

The aluminium tolerance of 31 varieties within 11 species in six genera of the Cruciferae was determined by measuring root length under aluminium stress. Variance analysis indicated highly significant differences of aluminium tolerance among the species compared. Raphanus sativus (2n= 18, RR) had the highest aluminium tolerance, followed by Brassica carinata (2n= 34, BBCC), Brassica oleracea (2n= 18°C) and Brassica napus (2n= 38, AACC), which had the C genome. There might be more than one gene for aluminium tolerance in the R and C genomes. Those species such as Brassica campestris (2n= 20, AA), Brassica nigra (2n= 16, BB), Brassica juncea (2n= 36, AABB), Arabidopsis thaliana (2n= 10, arar), Sinapis alba (2n= 24, alal), Cheiranthus cheiri (2n= 12, chch) and Orychophragmus violaceus (2n= 24, OO) that did not include the R or C genome had lower aluminium tolerances. Transfer of aluminium tolerance from R. sativus into the cultivated brassicas seems possible by intergeneric hybridization and the production of addition, substitution or translocation lines.     

Induced polygenic variation and genetic architecture in Indian mustard

Summary The F₁ seed obtained from an eight-parent diallel (excluding reciprocals) in Indian mustard was treated with 100 Kr of gamma rays, grown and selfed to obtain F₂M₂. The mean was decreased in the majority of the crosses in an irradiated set whereas the coefficient of variation increased. Combining ability analysis revealed the change in relative ranking of the parents and crosses and suggested the genotype-specific responses to irradiations. Components of combining ability and heterosis were also changed considerably. In some cases irradiation resulted into an increase in additive genetic variance.     

Self-incompatibility as a pollination control mechanism for spring oilseed rape,Brassica napus L.

Summary Self-incompatibility was shown to be an effective method of pollination control in spring rapeseed (B. napus L. ssp. oleifera (Metzg.)) by comparing the yield of a Westar-Topas syn-1 produced by crossing two SI lines with the yield of the corresponding syn-1 produced by hand pollination. Although the trial showed high-parent heterosis in the syn-1s, there was insufficient replication to determine the level of heterosis.Abbreviations SI self-incompatible - SC self-compatible     

Modification of oilseed rape to produce oils for industrial use by means of applied tissue culture methodology

Summary A programme of research was designed to investigate methods for the modification of the fatty acid profiles of high performance lines of oilseed rape (Brassica napus L.) in an attempt to produce lines with enhanced levels of industrially useful fatty acids. The methodology employed to achieve these objectives was based on the exploitation of somaclonal or protoclonal variation, and targeted somatic hybridization using wild cruciferous germplasm as fusion partners.A range of somaclonal lines was produced from shoot regeneration protocols. These lines underwent replicated, randomised glasshouse trials for morphological assessment followed by gas chromatographic analysis to monitor any changes in fatty acid profile. It was found that a small number of lines exhibited potentially useful changes in oleic acid and polyunsaturated fatty acid content. Protoplast regeneration and electrofusion protocols for a range of winter oilseed rape lines were developed, and methods for the isolation and fusion of protoplasts of the wild crucifer Lunaria annua (chosen for its high nervonic acid content) established.Abbreviations GC Gas Chromatography     

Variation of prezygotic barriers in the interspecific hybridization between oilseed rape and wild radish

Escape of transgenes from genetically modified oilseed rape, Brassica napus, into wild radish, Raphanus raphanistrum, depends on sexual compatibility. The variation in prezygotic barriers of two different cultivars for interspecific hybridization with a population of wild radish was investigated by hand crossing and fluorescence microscopy of pistils. Significant differences were observed between oil seed rape cultivars in their ability to accept wild radish pollen germinating onto their stigma and the rate of fertilization of ovules. Some differences among the pollen donor plants were also detected. These results suggest that the rate of interspecific hybridization in the field would depend upon the oilseed rape cultivar and the genotype composition of the local wild populations. The implication of S-related genes, as revealed through identification by pistil tissue prints of class I and II S-types of SLG (S-Locus Glycoprotein) and SLR1 (S-Locus Related),and immuno-IEF, was not significant. This revised version was published online in August 2006 with corrections to the Cover Date.     

Segregation and linkage analysis of DNA markers in microspore derived and F2 populations of oilseed rape (Brassica napus L.)

Summary The segregation of RFLP and RAPD markers was compared in two oilseed rape (Brassica napus L.) breeding populations from the cross Topas x R4, the latter being a low linolenic mutation line. A total progeny of 68 F₂ and 40 microspore derived plants were studied with 25 markers. The results indicated a significant excess of Topas alleles at five RAPD loci in the microspore derived population. This suggests that genomic regions which probably affect microspore culture ability do not have identical distribution in the two population types.     

Resistance to Brevicoryne brassicae in horticultural brassicas

Summary A wide range of cultivated brassica accessions including broccoli, Brussels sprouts, Chinese cabbage, cauliflower, collard, kale and swede material was tested against the cabbage aphid, Brevicoryne brassicae, at HRI, Wellesbourne in the field and laboratory in both 1992 and 1993. In the field, B. brassicae attack was assessed as the proportion of infested plants and the numbers of aphid colonies present. In the laboratory, aphid performance was measured in terms of the pre-reproductive and reproductive period, population increase, and insect mortality. Interpretation of the data was facilitated by plotting sorted accession means against normal order statistics. This statistical approach indicated the spread of variation amongst the accessions and permitted identification of extremes. Partial levels of antixenosis resistance were discovered in red brassicas. Glossy accessions of cabbage and cauliflower possessed antixenosis and antibiosis resistance that lasted throughout the season of crop growth in the field. Other accessions were shown to withstand aphid attack and therefore possessed tolerance. The laboratory studies provided information on mechanisms of antibiosis resistance. The potential value of the different sources of resistance is discussed.     

Leaf glucosinolate profiles and their relationship to pest and disease resistance in oilseed rape

Summary Glucosinolates are sulphur-containing glycosides which occur within vegetative and reproductive tissue of oilseed rape. Following tissue damage, glucosinolates undergo hydrolysis catalysed by the enzyme myrosinase to produce a complex array of products which include volatile isothiocyanates and several compounds with goitrogenic activity. Many of these products have been implicated in the interaction betweenBrassica and their pests and pathogens and some may have a role in defence mechanisms. Low glucosinolate (00) oilseed rape cultivars have been shown to possess similar concentrations of leaf glucosinolates as high glucosinolate (0) oilseed rape cultivars. Likewise, despite considerable speculation to the contrary, 00 cultivars have been shown not to be more susceptible to pests and pathogens than 0 cultivars. The potential to enhance pest and disease resistance of oilseed rape by manipulating the leaf glucosinolate profile without reducing seed quality is discussed.     

Genetic variation of tocopherol content in a germplasm collection of Brassica napus L.

The genetic variation for tocopherol contents was investigated in a very divergent collection of 87 winter rapeseed genotypes grown in the greenhouse and in two years in the field. Genotypic and environmental effects were highly significant for alpha-, gamma- and total tocopherol contents and the alpha-/gamma-tocopherol ratio. Field and greenhouse environments differed significantly (p < 0.001) for tocopherol traits, with greenhouse means up to 19% higher than field means. Alpha-tocopherol content ranged from 63 to157 mg kg^-1 seed, gamma-tocopherol content from 114 to 211 mg kg^-1 seed, total tocopherol content from 182 to367 mg kg^-1 seed, and the alpha-/gamma-tocopherol contents ratio from0.36 to 1.23. The resynthesized lines often have a remarkably low alpha-tocopherol content and consequently a low alpha-/gamma-tocopherol contents ratio. The lines with altered fatty acid composition displayed the highest variation for both tocopherol content and composition. No significant differences were observed among groups with different seed quality types [00], [0+] and [++]. Total tocopherol content was not correlated with the alpha-/gamma-tocopherol ratio, indicating that total tocopherol content is independent from tocopherol composition. Alpha- and gamma-tocopherol contents were also not correlated. Gamma-tocopherol contents showed a significant positive correlation with oil content (r = 0.34^**). This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationships between seed yield and growth characters,yield components,seed quality of summer-type oilseed rape (Brassica napus L.)

Summary Five genotypes of rapeseed were observed in the field on a single plant and plot basis to evaluate growth characteristics, yield, yield components and seed quality. Observations were made in two years at two locations on three seeding date and three seeding rate treatments. Correlation of seed yield with growth characters demonstrated no consistent trend, indicating that an early maturity and high seed yield should be possible. Harvest index was strongly correlated with seed yield. Percent seed oil and protein were not directly related to seed yield.     

Effects of Agrobacterium tumefaciens-mediated transformation and tissue culture on storage lipids in Brassica napus

The variation obtained in storage fatty acids induced by the procedures of tissue culture and transformation with Agrobacterium tumefaciens was investigated and compared in rapeseed, Brassica napus, cv. Hanna. An increased variation in the fatty acid profiles was noted after tissue culture and transformation compared with plants derived directly from seeds. In the second generation of rapeseed transformants, T₂, the content of oleic acid ranged from 39–72%, 12–31% for linoleic acid and 7–16% for linolenic acid. This could be compared with the oleic acid content in the T₂ generation of tissue culture-derived plants which ranged between 47–76% and in seed-derived material where oleic acid ranged between 55–69%.In the T₃ generation the ranges in transgenic seeds were decreased but still larger than in the seed derived plants. The range in transgenic plants was 49–64% for oleic acid, 20–28% for linoleic acid and 9–18% for linolenic acid. The most extreme individuals, both highest and lowest in the common fatty acids, were found in the group of transformed plants independent of generation. The total lipid content was also affected by the two treatments and seeds with the lowest and highest lipid content were both found among the transformed plants. In conclusion, care should be taken to use proper controls when performing transformation experiments in order to distinguish variation in the fatty acid profiles induced by the transformation procedure and tissue culture treatments from the changes due to transgenic expression. This revised version was published online in July 2006 with corrections to the Cover Date.     

Superior performance of two homozygous diploid lines from naturally occurring polyhaploids in oilseed rape (Brassica napus)

Summary Homozygous diploids in oilseed rape were produced by pipetting drops of 0.1 per cent colchicine into the leaf axils of rooted cuttings from naturally occurring polyhaploids after removing the waxy covering with a scalpel. Trial results from spring and winter rape showed that occasional homozygous diploid lines yielded consistently more oil per ha than the parental varieties. Prospects for breeding oilseed rape as a self-fertilised crop are discussed.     

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.     

Molecular genetics and breeding of vegetable brassicas

Summary Genetic traits relevant to breeding vegetable brassicas are surveyed to determine the effects that recent advances in molecular genetics and molecular marker technology might have on breeding priorties and practices. The problems peculiar to breeding horticultural crops are addressed. The application of DNA restriction fragment length polymorphisms (RFLPs) as an aid to breeding brassicas is discussed and genes amenable to molecular analysis are considered in the light of both experimental and economic factors.     

Rapid and efficient screening of phosphinothricin tolerant oilseed rape (Brassica napus) with a novel germination test

A novel screening test is described for the discrimination of transgenic phosphinothricin tolerant oilseed rape from non transgenic rape seedlings. The method is based on the germination of rape seeds on filter paper soaked with a 0.005% phosphinothricin solution. Under these conditions inhibition of seedling development by the herbicide can be observed after 10 days. The germination test gains an advantage over the routinely used herbicide spraying, because it is rapid, needs little space and allows efficient screening of huge numbers of seeds. The assay has been successfully applied to the screening of different transgenic and non transgenic rapeseed varieties/lines and has been compared to other methods such asBasta® spray test, drop test, ELISA-technique and PCR-amplification of the pat gene. This test allows on one hand large screening programmes to monitor the foreign gene in the environment and on the other quality control of seedlots before market introduction of herbicide tolerant oilseed rape.     

Prediction of F6 line performance from F3 families in spring oilseed rape. I. Yield and other agronomic traits

Summary The reliability of a selection among crosses based on a cross prediction in early generations was investigated in spring rapeseed. The performance of the parents, the F₂ generation, and random F₃ lines from four crosses were used to predict the probability of finding superior recombinant lines. These predictions were made for two years and compared with the observed performance of F₆ lines in the second of these two years and in an additional year. Predicted and observed performances coincided reasonably for the characters plant height, standability, maturity and an index calculated from seed yield, oil content and protein content. For seed yield and flowering time, the predictions were very unreliable. In conclusion, prediction methods may be useful in rapeseed breeding, if quality traits are of major commercial interest.     

Heritability estimates of variation for NaCl tolerance in Sorghum bicolor (L.) Moench seedlings

Summary Data on root lengths of two-week-old seedlings of 51 Sorghum bicolor (L.) Moench accessions germinated in 50, 100, 150, 175, and 200 mM NaCl solutions were used to estimate broad sense heritabilities of variation for salinity tolerance.Estimates of broad sense heritabilities ranged from 0.38 to 0.73, the highest being in 50 mM NaCl, suggesting that there is potential for improving salinity tolerance in the species through selection and breeding.