Transfer of resistance to clubroot (Plasmodiophora brassicae) to swedes {Brassica napus L. var. napobrassica Peterm) from B. rapa

Abstract

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.

Swedes and Turnips

“…Breeding for powdery mildew resistance can be considered a major success as the susceptible cultivars Acme and Doon Major have been replaced with resistant ones in which the resistance is controlled by partially recessive genes and is likely to prove durable . In contrast, breeding for clubroot resistance can be considered only a partial success as major genes were used which have proved useful in the UK, but are unlikely to be durable in the long term (Bradshaw et al, 1997). In New Zealand the main diseases affecting swede yields are clubroot and dry rot.…”

“…In Scotland the main diseases affecting swede yields are clubroot (Plasmodiophora brassicae) and powdery mildew (Erysiphe cruciferarum). The first cultivar to combine resistance to these diseases was 'Invitation,' released in 1995 (Bradshaw et al, 1997), followed by 'Gowrie' and 'Lomond' in 2006 (Bradshaw et al, 2009) (Table 8.1). Breeding for powdery mildew resistance can be considered a major success as the susceptible cultivars Acme and Doon Major have been replaced with resistant ones in which the resistance is controlled by partially recessive genes and is likely to prove durable .…”

“…Namai and Hosoda (1968) produced artificial swedes by pollinating grafted plants at relatively low temperatures (below 20 • C) and doubling the hybrids with colchicine. Starting with a synthetic B. napus produced by crossing a tetraploid kale (B. oleracea) with an autotetraploid form of ECD04 (B. rapa) (see Section 7.4.1), and using embryo culture (Snell, 1978), Bradshaw et al (1997) produced the clubroot-resistant swede 'Invitation.' Embryo rescue techniques are usually used these days to obtain hybrids, from crosses made with diploid parents.…”

Agronomic and horticultural characters of rutabaga in eastern Canada

“…Evidently, the race-specific resistance of Fortune and York has broken down for races now prevalent in Newfoundland. The European-bred cultivars Marian and Invitation, both incorporating race-specific resistance genes (Bradshaw et al 1997), do appear tolerant to clubroot races prevalent in Newfoundland, and hence other regions of eastern Canada where clubroot is not as widely established.…”

“…The Newfoundland-bred varieties and Invitation also exhibited good early-season vigour and high yield potential, underscoring the importance of clubroot tolerance to yield potential. Bradshaw et al (1997) suggested that breeding for clubroot resistance was challenging, as it is difficult to distinguish between actual resistance and escape from attack, Can. J.…”