The number of rDNA sites can differ up to 5-fold in species with the same chromosome number. In addition to the eight previously reported chromosomal types with ribosomal genes, three new variant types are described. The extent of polymorphism is genome dependent. Comparing the A, B and C genomes revealed the highest rDNA polymorphism in the A genome. The loci carrying presumably inactive ribosomal RNA genes are particularly prone to polymorphism. It can also be concluded that there is no obvious polyploidization-related tendency to reduce the number of ribosomal DNA loci in the allotetraploid species, when compared with their putative diploid progenitors. The observed differences are rather caused by the prevailing polymorphism within the diploids and allotetraploids. This would make it difficult to predict expected numbers of rDNA loci in natural polyploids.

Oat (Avena sativa) is unusual in comparison with other cereals since there are varieties with up to 18% oil content. The lipid content and fatty acid composition in different parts of the grain during seed development were characterized in cultivars Freja (6% oil) and Matilda (10% oil), using thin-layer and gas chromatography, and light and electron microscopy. The majority of lipids (86-90%) were found in the endosperm. Ninety-five per cent of the higher oil content of cv. Matilda compared with cv. Freja was due to increased oil content of the endosperm. Up to 84% of the lipids were deposited during the first half of seed development, when seeds where still green with a milky endosperm. Microscopy studies revealed that whereas oil bodies of the embryo and scutellum still contained a discrete shape upon grain maturation, oil bodies of the endosperms fused upon maturation and formed smears of oil.

Brassica napus L, u'as resynthestzed through interspecific hvbridtzation between B. aiboglahra Bailev and B. campesiris L. with the objective of developing vellow-seeded forms of this species. For hybridizaiion, one black-seeded form and one light brownseeded form of B. aiboglahra (a subordinate of B. oleracea) and one brown and ten yellow-seeded forms of B. campestris Ts-ere chosen as parents. Crosses with B. alhoglahra as the female parent were more successful than crosses witb B. campestris as female. The use of the embrv'O rescue culture technique greatly increased the number of surMvmg hybrid embri'OS. Colchicine treatment was required for doubling the chromosome number of the amphihaploid hybrid plants. In the newly-resynthestzed rape forms, the white petal of B. alhoglabra was partialKepistatic over the yellow petal of 8. campestris. The self compatibility of B. aiboglahra was hypostatic to the self incompatibility of B. campestris. Tbe blackseeded character of B. alhoglabra and the brownseeded character of B. campestrts were completely epistatic over the yellow-seeded character of B. campestris and the light brown-seeded character of B. alhoglahra. Implications of the results from this study in breeding yellow-seeded B. napus are discussed.Oilseed rape {Brassica napus L.) is one of the important oleiferous Brassica species. The amphidiploid nature oi this species was brilliantly elucidated sO'ine 50 years ago (U 1935). interspecific hybridization between Brassica species has since been practised widely lor the improvement of Brassica erops. Resynthesis of B. napus (genome constitution AACC) through interspecific crosses between the parental species B. campestris (AA) and 8. oleracea (CC) allows the combination of desirable variation from these species m B. napHS. A recent example of this breeding strateg)' i.s the successful resynthesis ol B. napus adapted to Bangladesh short da)' agroregime (AKB.\K 1987a, b).Rapeseed meai remaining after extraction of the oil from the seeds can contain as much as 41-49 % protein (BKNGTSSON 1985). Utilization of this high-protein meal in animal rations is limited due to the presence of glucosinolates whose breakdown products are toxic to animals (RoBBELEN and THIES 1980), The meal of the new 'double low' cultivars (low erucic acid oil and lo'R' glucosinolate meal) contains very little glucosinolate. Meal from these cultivars is a very valuable source of high-quality protein for livestock feeding, but the nutritional value of rapeseed meal is still limited due to its relatively high crude fibre content. The crude fibre content of the meal of yellow seeds is lower than that of black or brown seeds (STRIN-CAM et al. 1974, THEANDER et al. 1977, for 8. campestris; SHIRZ.«3EGAN and ROBBELEN 1985, for B. napus).

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 BCI (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 F 4. Crosses between a yellow-seeded F 3 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.

Brassica campestris-alboglabra monosomic addition lines were developed from a trigenomic Brassica hybrid (2 n=3 x=29, AAC) obtained by backcrossing a resynthesized B. napus (2 n=4 x=38, AACC) line to its parental B. campestris (2 n=2 x=20, AA) line. One addition line was characterized genetically with three loci specific for the alien chromosome and cytologically by meiotic analysis. The following results were obtained. (1) The same chromosome in the B. alboglabra (2 n= 2 x=18, CC) genome carried the three loci, E c, W c and Lap-1 C (c), which control the biosynthesis of erucic acid, white flower colour and the faster migrating band of leucine aminopeptidase, respectively. The linear order and possible positions of the three loci were inferred. The meiotic behaviour of the alien chromosome was documented and its transmission frequency was assessed. (2) Intergenomic recombination frequently occurred in the monosomic addition line, resulting in the introgression of one or two loci from the alien chromosome into the B. campestris genome. (3) B. campestris trisomics were found in the progeny of the monosomic addition line. (4) The removal of the other eight C-genome chromosomes from the trigenomic Brassica hybrid led to a dramatic increase in the erucic acid content of the monosomic addition line. (5) No offspring of the trigenomic Brassica hybrid showed evidence of intergenomic recombination and introgression of the W c locus into the B. campestris genome. It is questioned whether such a difference might be due to a possible regulating mechanism for homoeologous chromosome pairing.