SummaryIn 1975, tests with UK populations of Plasmodiophora brassicae not only revealed a lack of effective clubroot resistance in swedes (Brassica napus), but also the outstanding resistance of the European Clubroot Differential (ECD)04 (B. rapa). It was, therefore, decided to transfer the resistance genes from ECD04 to swedes, using the most pathogenic UK population of clubroot (C56) available for screening purposes. An autotetraploid form of ECD04 was crossed with tetraploid kale (B. oleracea) using the latter as female parent. One of the euploid, 2n = 38, hybrids secured by embryo rescue in 1976 was crossed to the swede cultivars Marian and Ruta Øtofte. Three further backcrosses of clubroot resistant plants to lines derived from modern swede cultivars were made over the period 1980 to 1982. Selfing commenced in 1983 to produce F2 populations. From F3 to F5 there was family selection for yield and agronomic characters, as well as single plant selection for clubroot resistance. In 1991, the six most promising F5 families were multiplied for subsequent evaluation in replicated yield trials in Dundee. The most promising family entered official trials at the beginning of 1993 and, 2 years later, was added to the National List as cv. Invitation and granted Plant Breeders' Rights. The first certified seed was sold in 1996, 20 years after the original synthetic B. napus was produced.The breeding programme provided evidence for only one of the three postulated dominant genes in ECD04 being required for resistance to C56 and also good evidence of differential resistance from tests with other clubroot populations. Hence, whilst the differential resistance in cv. Invitation should prove useful in the UK in the immediate future, it may not be durable in the longer term. It is, therefore, argued that the next and more difficult goal to achieve should be to introduce high levels of non‐differential resistance from B. oleracea.
Eighteen plants of each of four cultivars and two inbred lines of swede (Brassica napus ssp rapifera L ) were harvested at monthly intervals from 25
A complete diallel set of crosses, including selfs, was produced from 11 inbred lines of swedes and assessed for adult plant resistance to powdery mildew in a replicated field trial. The plants were inoculated with powdery mildew spores on 23 July 1987. Traces of mildew were visible on 3 August. By 14 September the most susceptible inbred line had 95% of its leaf area infected, whereas the three most resistant lines derived from cvs Bangholm Dima (two lines) and Bangholm Magres (one line) had only 5%. Resistance was controlled by partially recessive genes. There was no evidence of maternal effects. The implications for breeding inbred and F, hybrid swede cultivars are discussed.
The glucosinolate contents of six kales and five cabbages (Brassica oleracea L.), four stubble turnips and six turnips ( B . campestris L.), and six swedes and six fodder rapes ( B . napus L.) were determined. As fodder brassica breeders wish to reduce the goitrogenicity of these crops, the concentrations of 2-hydroxybut-3-enylglucosinolate (5-vinyloxazolidine-2-thione is the goitrogenic hydrolysis product) and 3-indolylmethylglucosinolate (the thiocyanate ion is the goitrogenic hydrolysis product) were of particular interest. High concentrations (mmol kg-' dry matter) of 2-hydroxybut-3-enylglucosinolate were found in stubble turnip leaf (8.12) and bulb (9.20), turnip bulb (9.97), swede bulb (5.66), and rape leaf (8.99) and stem (21.81) but not in kale or cabbage. In contrast, the concentration of 3-indolylmethylglucosinolate was relatively high in cabbage head (6.39) and kale leaf (3.25) but not in the other crops.
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, 0, 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 .
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