Senuvr, J. L. eNo SrsraNssoN, B. R. 1983. Heterosis in summer rape (Brassica napus L.) Can. J. Plant The degree of heterosis for seed yield in F, hybrids of summer rape (Brassica napus L.) was examined in replicated yield trials during 2 yr (1980 and 1981) using intervarietal hybrids produced by manual crossing.

Development of cultivars of both tetraploid (Brassica napus L.) and diploid (B. rapa L.) rapeseed with reduced levels of polyunsaturated fatty acids and increased levels of oleic acid could increase both the utility and value of the oil. The objective of this experiment was to use chemcical mutagenesis to induce mutations for these traits in rapeseed. Imbibed seed of ‘R‐500’ (B. rapa) and ‘Cascade’ (B. napus) were treated with 5% v/v of ethyl methanesulfonate. The M2 generations of these populations were screened to identify mutants with low levels of polyunsaturated fatty acids (PUFA) using a modified thiobarbituric acid procedure. Putative mutants and their derived progeny were increased in the greenhouse and the seed analyzed for fatty acid composition using gas chromatography. The most promising mutant identified from 4 734 M2 seeds of B. rapa, was M‐30, which had 2.1% linoleic acid and 3.0% linolenic acid, vs. 11.9% linoleic and 8.6% linolenic acid in the original cultivar. This mutant was crossed with ‘Tobin’ to derive F4 lines having <6% total PUFA and oleic acid concentrations >87%. The most promising mutant identified from 39 504 M2 seeds of B. napus was X‐82, which had 6.6% PUFA, vs. 27.4% PUFA in Cascade. Several M3 and M4 lines derived from X‐82 had <6% total PUFA and >88% oleic acid. The development of commercial cultivars with reduced levels of polunsaturated fatty acid in both B. rapa and B. napus could develop new markets for both industrial rapeseed and edible canola oil.

A genetic linkage map has been constructed based on restriction fragment length polymorphism DNA markers for Brassica rapa L. using a segregating F2 progeny from a cross between the yellow sarson type 'R500' and the canola-type 'Horizon'. The map contains 360 marker loci detected by 269 genomic clones derived from a PstI library of 'Westar' (Brassica napus L.). The map consists of 10 linkage groups, covering a total of 1876 recombination units. The occurrence of substantial genome rearrangement during the evolution of B. rapa is evident from (i) a large number of homologous duplicate sequences either at genetically adjacent locations or in different linkage groups and (ii) a number of missing sequences in one or the other parental genome, detected as null alleles. Divergence of the parental genotypes is further supported by the frequency of loci with skewed allele segregation ratios. Comparison of molecular and cytogenetic data on genome structure is discussed. The probe set and map are being used to facilitate rapeseed breeding.Key words: Brassica campestris, Brassica rapa, genome structure, linkage map, restriction fragment length polymorphism.

No abstract

Bannerot et al. (191'7) into this cytoplasm using intergeneric crossing followed by backcrossing. Shiga and Baba (19'71, 1973) and ThomPson (19'72) Heyn (1979) and Rouselle (1979) found that all rape cultivars tested in their studies were maintainers for the ogu CMS. Bonnet (1975) China and Japan were winter types. The seedlings from these strains were vernalized at 4 C"