The exploitation of genetic resources of Brassica oleracea in breeding for resistance to clubroot (Plasmodiophora brassicae)

Summary About 1000 Brassica oleracea accessions were evaluated in glasshouse tests for response to Plasmodiophora brassicae (clubroot). Resistance was confirmed in some north and west European kales and cabbage. A new source of resistance in cabbage, from Eire, is reported. Most other accessions were highly susceptible but lower levels of susceptibility were observed in open pollinated Brussels sprouts and forms of south European cabbage, cauliflower and broccoli. Modern breeding (as in the production of hybrid cultivars) appears to have resulted in increased susceptibility in several crop types. The implications of these results for the exploitation of germplasm are discussed.     

Association of RFLP markers with trait loci affecting clubroot resistance and morphological characters in Brassica oleracea L.

Summary Resistance to Plasmodiophora brassicae Wor. race 7, the causal agent of the disease clubroot, was examined in an F₂ population of a cross between a clubroot resistant broccoli (Brassica oleracea var. italica) and a susceptible cauliflower (B. oleracea var. botrytis). A genetic linkage map was constructed in the same population based on the segregation of 58 dispersed restriction fragment length polymorphism (RFLP) markers. Associations between the inheritance of RFLP marker genotypes and segregation for disease resistance, morphological and maturity characteristics were examined. For each triat examined, several chromosomal regions marked by RFLP probes appeared to contain trait loci, suggesting that each trait was under polygenic control. RFLP marker linkage to a major factor imparting dominance for clubroot resistance from the broccoli parent was observed in this population. Additionally, RFLP marker linkage to an independently segregating factor contributing clubroot resistance from the cauliflower parent was observed, indicating that it should be possible to use RFLP markers to facilitate selection of transgressive segregants having the combined resistance from both parental sources. In some instances, RFLP markers from the same or closely linked chromosomal regions were associated with both clubroot resistance and morphological traits. Analysis of RFLP marker genotypes at linked loci should facilitate the selection of desired disease resistant morphotypes.     

Transfer of resistance to race 2 of Plasmodiophora Brassicae from Brassica napus to cabbage (B. oleracea var. Capitata). I. Interspecific hybridization between B. napus and B. oleracea var. Capitata

Summary Interspecific hybridization between Brassica napus L. (2n=38, a₁a₁c₁c₁) and B. oleracea var. capitata L. (2x- and 4x-cabbage; 2n=2x=18, cc and 2n=4x=36, cccc) was carried out for the purpose of transferring clubroot disease resistance from the amphidiploid species to cabbage. Nineteen hybrids with three different chromosome levels (2n=28, a₁c₁c; 2n=37, a₁c₁cc and 2n=55, a₁c₁cccc) were obtained. The F₁ plants were mostly intermediate between the two parents but as the number of c genomes in the hybrids increased, the more closely the hybrids resembled the cabbage parent. All F₁ hybrids were resistant when tested against race 2 of Plasmodiophora brassicae wor. The complete dominance of resistance over susceptibility suggested that the gene(s) controlling resistance to this particular race of the clubroot pathogen is probably located on a chromosome of the a genome in Brassica.Contribution No. J654.     

Plasmodiophora brassicae: aspects of pathogenesis and resistance inBrassica oleracea

Summary Clubroot is one of the most damaging diseases inBrassica oleracea crops world-wide. The pathogenicity ofPlasmodiophora brassicae is highly variable between as well as within field populations. Several sources of resistance to clubroot have been identified inB. oleracea. Generally, resistance tends to inherit partly as a recessive, partly as an additive trait, and appears to be controlled by few major genes. Progress in the understanding of the inheritance of resistance is being made through the use of single-spore isolates of the pathogen, and the use of molecular markers for resistance genes.Abbreviations cv cultivar - DH doubled haploid - ECD European Clubroot Differential set - RFLP Restriction Fragment Length Polymorphism     

Evaluation of French Brassica oleracea landraces for resistance to Plasmodiophora brassicae

A total of 240 kale, 38 cabbage and 126 winter cauliflower French landraces from the B. oleracea genepool of INRA were assessed for resistance to clubroot caused by Plasmodiophora brassicaeWoron. Two French isolates of the pathogen (K and SJ) were used in the experiments under controlled conditions. The reaction of the 126 cauliflower accessions to naturally occurring clubroot was also evaluated in field trials. Kales exhibited considerable variation for expression of disease resistance and high levels of resistance were found in several accessions. In this group, single resistant plants were observed in most of the morphological types and from quite different geographical origins. Cabbage accessions were moderately to highly susceptible to both isolates. All cauliflower populations proved to be highly susceptible to K isolate and moderately susceptible to SJ isolate. In field trials, cauliflowers were also severely infected. Two lines selected from a resistant kale population were highly resistant against a large range of pathotypes of the pathogen. These lines presented a sufficient level of resistance to be directly useful in the breeding program in order to develop cauliflower and broccoli hybrids resistant to clubroot. This revised version was published online in July 2006 with corrections to the Cover Date.     

油菜感抗品种混播对根肿病防控效果的影响

近年来,油菜根肿病危害在我国呈蔓延趋势,主要原因是化学防治成本高且效果差。实际生产中,种植抗性品种是最经济、最有效的措施。不同抗感品种混播,在保证产量稳定的前提下可减轻对病原菌小种的选择压,从而稳定病原菌种群结构,延长抗性品种使用寿命。本试验在安徽绩溪、云南临翔2个油菜根肿病严重发生区域,选择2组互为近等基因系的感病、抗病的油菜品种,按不同比例混播(感病、抗病比例分别为10:0、1:9、2:8、3:7和0:10),在根肿病明显发生后调查发病率等指标。结果表明:不同比例感病、抗病油菜品种混播均降低了根肿病发病率和病情指数,并稳定油菜产量和品质;且油菜发病株率随抗病品种的比例下降而升高,但均低于理论发病率;不同抗性组合间混播的相对防效(REM)均低于1,且随着作物生育期的推迟呈现下降趋势。以上结果表明,油菜感抗品种混播对根肿病有较好的防控效果。本研究主要在大田条件下明确了2组不同抗感近等基因组合混播对油菜根肿病的防治效果,可为油菜根肿病防治提供思路和对策。     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. Oleracea spp. Capitata). IV. A resistant 18-chromosome B1 plant and its B2 progenies

Summary The somatic karyotype and meiotic chromosome behavior were studied in an 18-chromosome B₁ plant derived from backcrossing a triploid (Brassica napus x B. oleracea ssp. capitata) F₁ hybrid to cabbage. It is considered that cabbage chromosomes no. 1 and no. 7 were substituted by two shorter B. napus chromosomes. Meiotic disturbances were more apparent during the late stages of second division. Seed fertility of this plant was largely restored in the second backcrosses with both cabbage and broccoli. 18-chromosome B₂ plants resistant to race 2 of Plasmodiophora brassicae were recovered among the progenies.Contribution no. J. 725 from the Research Station, Research Branch, Agriculture Canada, St-Jean, Québec J3B 6Z8.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea var. capitata). II. Meiosis in the interspecific hybrids between B. napus and 2x and 4x cabbage

Summary Meiosis in 14 interspecific F₁ hybrids with three chromosomal levels (triploid, tetraploid, hexaploid; 2n=28, 37 and 55) between Brassica napus L. and 2x and 4x cabbage (B. oleracea var. capitata L.) was studied. The oleracea genome from B. napus maintained close homology with the c genome of cabbage while the campestris genome of B. napus showed partial homology with the c genome contained in the hybrids. Genotypic influence on chromosome pairing was indicated. Structural chromosome differences and spontaneous chromosome breakage and reunion were suggested as causes for the abnormalities which related to the unbalance of the genotypes. The divergence of the genomes of B. napus and B. oleracea and the need for the qualification of the term secondary association were discussed.Contribution No. J. 673, Research Station, Agriculture Canada, St. Jean, Québec.     

Selection for resistance to Plasmodiophora brassicae Wor. in oriental subspecies of Brassica rapa L.

Summary Selection for resistance to Plasmodiophora brassicae Wor. in oriental groups of Brassica rapa L.Two hundred and sixty-five cultivars of leafy, oriental bassicas were tested for resistance to 18 collections of Plasmodiophora brassicae, the causal agent of clubroot. The tests were conducted in the greenhouse at low and high level inoculum concentrations. Eleven cultivars of B. rapa pe-tsai, five cultivars of B. rapa pak-choy and three cultivars of B. rapa choy-sum consistently segregated for resistance at the lower concentration of inoculum (1000 spores/ml). All 265 cultivars were susceptible at the higher concentration (1 000 000 spores/ml). Three cultivars were used in pedigree and recurrent selection schemes for increased resistance. After three cycles of selfing resistant individuals, significantly more resistant S₃ lines were derived from each cultivar. Lines derived from two cultivars. Chinese White and PI 257236, continued to improve with each cycle of selection and demonstrated increased resistance to higher levels of inoculum (up to 1 000 000 spores/ml) New cultivars based on intercrosses of S₂ resistant individuals also had significantly better resistance than the original cultivar. After two cycles of selection in the third cultivar, PI 419007, resistance did not increase and its S₂ mass did not differ significantly from the original cultivar. Evidence that indicates resistance is pathotype-non-differential and offers an alternative to major gene, pathotype-differential types of resistance currently being introduced to the leafy oriental brassicas from other Brassica rapa groups.     

Screening of Portuguese cole landraces (Brassica oleracea L.) with Peronospora parasitica and Plasmodiophora brassicae

Summary Forty-four landraces of Portuguese coles (Brassica oleracea L.), representing different morphotypes, were screened at the cotyledon stage for downy mildew resistance, caused by Peronospora parasitica. Two isolates of the pathogen, PHW 630 and PHW 828, were used in the experiment. The mean disease interaction phenotype varied among the landraces. Overall, the Portuguese coles have shown resistance to both isolates, particularly to isolate PHW 828. Some landraces were identified with differential reaction to the two P. parasitica isolates. Some of the Portuguese coles are, therefore, good sources of resistance genes to P. parasitica, and could be used in breeding programs or in the development of a downy mildew host differential set. Among the morphotypes tested, Couve Algarvia (ISA 207), Couve Galega (ISA 243 and 187) and Couve Glória de Portugal (ISA 84) have presented the highest resistance interaction. For the development of host differential sets, the landraces ISA 2 (Penca de Mirandela), ISA 35 (Couve de Valhascos) and ISA 600 (Penca Espanhola) could be further selected for the differentiation of P. parasitica isolates. They are resistant to PHW 828 and susceptible to PHW 643.The same morphotypes and landraces were also screened at the seedling stage for resistance to clubroot, caused by Plasmodiophora brassicae Woron.. Although some variation for resistance could be noticed in some the landraces tested, mainly Galega kale types, none of them presented a sufficient level of resistance as to be directly be useful in breeding for resistance to race 6 of P. brassicae.     

The somatic karyotype of cabbage (Brassica oleracea ssp. capitata)

Summary The individual chromosomes of cabbage are identifiable in nucellar cells found in the ovaries of immature pistils by the combination of their relative length, arm ratios, secondary constrictions, chromatic and achromatic regions and the presence of satellites.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. oleracea ssp. capitata). III. First backcross and F2 progenies from interspecific hybrids between B. napus and B. oleracea ssp. capitata

Summary The first backcross and F₂ progenies from triploid F₁ and tetraploid F₁ hybrids between B. napus and 2x and 4x B. oleracea ssp. capitata (cabbage) were studied for their general morphology, resistance to race 2 of the clubroot pathogen, chromosome number and meiotic chromosome behavior. No linkage was apparent between resistance and the major morphological characters. Unreduced gametes played a large part in the successful formation of seed of the B₁ and F₂ progeny. B₁ plants with low chromosome numbers were selected for use in recurrent backcrosses. The potential use of anther culture to extract gametic progenies from resistant B₁ and F₂ plants with higher chromosome numbers was suggested. The presence of homoeologous pairing observed in all the plants is considered advantageous for selecting suitable progeny in later generations.     

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.     

The use of an evolutionary scheme for cauliflowers in the screening of genetic resources

Summary A hypothetical scheme is given for the evolution of the different types of cauliflower (Brassica oleracea var. botrytis L.). This has been useful in identifying sources of reduced susceptibility to cabbage root fly (Delia radicum (L.)), and may also be useful in the search for reduced susceptibility to clubroot (Plasmodiophora brassicae Woron.). It is argued that knowledge of the phylogeny of types within each crop species is of great importance in the exploitation of genetic resources.     

Inheritance of resistance to tipburn in cabbage

Summary Tipburn resistance was identified as being highly but not completely dominant in three nearly isogenic populations of cabbage. Narrow sense heritability estimates of 0.14, 0.34, and 0.49 and broad sense heritability estimates of 0.64, 0.74, and 0.77 were obtained with 2–4 genes controlling resistance. Analysis of resistance was made under conditions of high fertility, especially high N and plentiful moisture and generally high humidity which together resulted in very severe tipburn in susceptible plants.Journal Paper No. 3038 of the New York State Agricultural Experiment Station, Geneva, New York, USA.     

Identificaiton of a clubroot resistance locus conferring resistance to a Plasmodiophora brassicae classified into pathotype group 3 in Chinese cabbage (Brassica rapa L.)

In Chinese cabbage (Brassica rapa), the clubroot resistance (CR) genes Crr1 and Crr2 are effective against the mild Plasmodiophora brassicae isolate Ano-01 and the more virulent isolate Wakayama-01, but not against isolate No. 14, classified into pathotype group 3. ‘Akiriso’, a clubroot-resistant F₁ cultivar, showed resistance to isolate No. 14. To increase the durability of resistance, we attempted to identify the CR locus in ‘Akiriso’. CR in ‘Akiriso’ segregated as a single dominant gene and was linked to several molecular markers that were also linked to CRb, a CR locus from cultivar ‘CR Shinki’. We developed additional markers around CRb and constructed partial genetic maps of this region in ‘Akiriso’ and ‘CR Shinki’. The positions and order of markers in the genetic maps of the two cultivars were very similar. The segregation ratios for resistance to isolate No. 14 in F₂ populations derived from each of the two cultivars were also very similar. These results suggest that the CR locus in ‘Akiriso’ is CRb or a tightly linked locus. The newly developed markers in this study were more closely linked to CRb than previously reported markers and will be useful for marker-assisted selection of CRb in Chinese cabbage breeding.     

Giemsa N-banding pattern in cabbage and Chinese kale

Summary In cabbage (Brassica oleracea var. capitata) and Chinese kale (B. oleracea alboglabra) four types of N-bands can be distinguished: pericentromeric, telomeric (terminal), intercalary and satellite bands. Typical NOR bands were not observed. The pericentromeric bands appear at the pericentric regions, possibly even at the centromeres of all chromosomes. Telomeric bands are observed on the short arms of chromosomes 1,5 and 6 in cabbage and chromosomes 1 and 5 in Chinese kale. Intercalary bands stained weakly in the long arms of chromosome 3 in cabbage and chromosome 2 in Chinese kale. Satellite bands cover the entire satellites in both Brassica species. The N-banding pattern is very similar in appearance to the C-banding pattern in both species and much more convenient to apply.     

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.     

Organic varieties for cauliflowers and cabbages in Brittany: from genetic resources to participatory plant breeding

Plant breeding for organic agriculture (OA) was stimulated when it came under the European Organic Agriculture Regulation (2092/91) in 2004. In Brittany, the need for specific varieties for organic farming arose early for the Brassica species because of the unsuitability of most of the modern varieties to the principles of OA. Moreover, the private sector of plant breeding finds it economically difficult to satisfy the demands of OA. The aim of the present study is to provide varieties and seed for organic farmers for two vegetable Brassica crops, and to show how genetic resources can contribute to this purpose in the framework of a Participatory Plant Breeding (PPB) programme. The emergence of PPB in Brittany is the result of several concomitant and favourable circumstances: the will of the professionals (represented by IBB, Inter Bio Bretagne), their organization (an experimental station, the PAIS, Plateforme Agrobiologique d’IBB à Suscinio), the research initiative in INRA and the availability of genetic resources. From genetic resource observations, our experience showed several breeding situations: reviving a traditional activity (Roscoff cauliflower and local cabbages), extending tradition (autumn cauliflower), diversifying production by new introductions (coloured cauliflowers), and creating new forms of population varieties (broccoli and coloured cauliflowers). Farmers have taken charge of population breeding by mass selection and the PAIS, with INRA scientific support, has taken up innovative selection and the improvement of varieties completing the farmers’ initiatives. The PAIS remained the central point for information and for providing the seed for trials. Seed production will be managed in a collective way. Until now, the exchange of seed remained an experimental dimension of PPB. French seed legislation represents a limitation on the development of seed exchange by PPB.     

Life history studies of the leafminer Liriomyza trifolii on susceptible and resistant cultivars of Dendranthema grandiflora

Summary The feeding, fecundity, mortality and rate of development of Liriomyza trifolii (Burgess) on 12 cultivars of Dendranthema grandiflora (Tzvel.) (Syn. Chrysanthemum morifolium (Ramat.)) were determined in no choice experiments. Number of feeding punctures, number of eggs laid and total number of larvae varied between cultivars but these characters were not strongly associated with leafminer population increase. Good indicators of host plant resistance were larval mortality, number of pupae and duration of the larval period. Of these three, larval mortality which could be as high as 98% was most suitable.Based on life history data it was predicted that Liriomyza trifolii cannot survive on the resistant cultivar Penny Lane. This prediction was verified experimentally.