Richard K. Gugel

Molecular markers linked to white rust resistance in mustard Brassica juncea

Abstract White rust, caused by Albugo candida (Pers.) Kuntze, is an economically important disease of Brassica juncea (L.) Czern. and Coss mustard, particularly in India. The most efficient and cost-effective way of protecting mustard plants from white rust disease is through genetic resistance. The objective of this study was to identify RAPD markers for white rust resistance in an F1-derived doubled-haploid (DH) population originating from a cross between white rust-susceptible and white rust-resistant breeding lines of B. juncea from the canola-quality B. juncea breeding project of the Agriculture and Agri-Food Canada-Saskatoon Research Centre. The DH population was used to screen for RAPD markers associated with white rust resistance/susceptibility using bulked segregant analysis. Two markers, WR2 and WR3, linked to white rust resistance, flanked the resistance locus Ac21 and were highly effective in identifying the presence or absence of the resistance gene in the DH population. These two markers were shown to be specific to the Russian source of white rust resistance utilized in this project. It is concluded that the availability of these RAPD markers will enhance the breeding for white rust resistance in B. juncea.

RFLP mapping of resistance to the blackleg disease [causal agent, Leptosphaeria maculans (Desm.) Ces. et de Not.] in canola (Brassica napus L.).

We report the tagging of genes involved in blackleg resistance, present in the French cultivar Crésor of B. napus, with RFLP markers. A total of 218 cDNA probes were tested on the parental cultivars Crésor (resistant) and Westar (susceptible), and 141 polymorphic markers were used in a segregating population composed of 98 doubled-haploid lines (DH). A genetic map from this cross was constructed with 175 RFLP markers and allowed us to scan for specific chromosomal associations between response to blackleg infection and RFLP markers. Canola residues infested with virulent strains of Leptosphaeria maculans were used as inoculum and a suspension of pycnidiospores from cultures of L. maculans, including the highly virulent isolate Leroy, was sprayed to increase disease pressure. QTL mapping suggested that a single chromosomal region was responsible for resistance in each of the four environments tested. This QTL accounted for a high proportion of the variation of blackleg reaction in each of the assays. A second QTL, responsible for a small proportion of the variation of blackleg reaction, was present in one of four year-site assays. A Mendelian approach, using blackleg disease ratings for classifying DH lines as resistant or susceptible, also allowed us to map resistance in the region of the highly significant LOD scores observed in each environment by interval mapping. Results strongly support the presence of a single major gene, named LmFr1 controlling adult plant resistance to blackleg in spring oil-seed rape cultivar Crésor. Several RFLP markers were found associated with LmFr1.

Genetic Variation of Ethiopian Mustard (Brassica carinata A. Braun) Germplasm in Western Canada

Information on genetic diversity and genetic relationships among genotypes of Brassica carinata is currently limited. The objectives of this study were to evaluate patterns and levels of genetic diversity in B. carinata based on amplified fragment length polymorphisms (AFLP) as compared with Brassica juncea and Brassica nigra, and to evaluate agronomic and seed quality data for plants grown in the field in western Canada. A total of 296 AFLP bands were generated from four primer pair combinations and scored for presence/absence in 66, 20 and 7 accessions of B. carinata, B. juncea and B. nigra, respectively. B. carinata was less genetically diverse than the other two species. Differences in diversity were evident in the proportion of polymorphic loci within each species: 23, 35 and 50% for B. carinata, B. nigra and B. juncea, respectively. Pair-wise similarity measures based on the Jaccard coefficient were highest among accessions of B. carinata and showed the narrowest range: 0.911 (0.810–0.981) compared to B. nigra: 0.569 (0.438–0.660) and B. juncea: 0.715 (0.345–0.951). AFLP-based genetic distance information can be used by plant breeders to select diverse genotypes. AFLPs are also useful for fingerprinting cultivars and two primer pair combinations were sufficient to uniquely identify all the accessions of B. carinata. More variation among accessions was identified in the agronomic trial than had previously been described in studies of B. carinata in western Canada, but the data were too limited to draw conclusions regarding specific accessions. Overall, the findings were in agreement with other published work describing the favourable agronomic potential of this species.

Genetic variation in the Crambe abyssinica - C. hispanica - C. glabrata complex

Crambe abyssinica Hochst. ex R.E. Fries (n = 45) is an industrial oilseed crop that is high in erucic acid. It is most closely related to C. hispanica L. (n = 30) and C. glabrata DC. (n = 15), although the latter species is most often included in the synonymy of C. hispanica. The species complex extends throughout the Mediterranean region, Ethiopia and East Africa. Crambe abyssinica is endemic to Ethiopia, C. glabrata to Spain, Portugal and Morocco, and C. hispanica is distributed in the Mediterranean region and Middle East. The present study compared genetic relationships among C. abyssinica, C. hispanica and C. glabrata and attempted a taxonomic separation of them using traditional morphological traits, agronomic and seed quality data, chromosome number, and various molecular data sets including nuclear-DNA based RAPD data, chloroplast (cpDNA) restriction site data and ITS sequence data for the internal transcribed spacer region of the nuclear ribosomal DNA. The three species can be distinguished most reliably by chromosome number. Accessions could generally, but not always, be distinguished morphologically by plant branching pattern, fruit articulation and colour, leaf pubescence and leaf shape. cpDNA restriction site data and ITS sequence data, two relatively conserved DNA data sets, supported the recognition of C. glabrata as a distinct species separate from the C. hispanica/C. abyssinica accessions. Within the latter group, both RAPD data and field evaluation data revealed greater amounts of genetic variation in C. hispanica compared with accessions of C. abyssinica, with the latter included as a subset of C. hispanica. Crambe glabrata was genetically distinct for all data sets and warrants separate species status.

Assembling a core collection from the flax world collection maintained by Plant Gene Resources of Canada

Between 1998 and 2008, numerous projects were conducted by the Canadian national genebank, Plant Gene Resources of Canada, for the regeneration, characterization and evaluation of the whole flax (Linum usitatissimum L.) germplasm collection. The whole collection comprised 3378 accessions and, according to the passport data, several of these were probably genetically very similar or even identical. Therefore, a subset of 381 accessions was selected that represented the diversity found in the whole collection. Sampling accessions from the whole collection was made using characterization and evaluation data and followed six different methods: (1) For seven qualitative characters, each unique combination of character expression was represented by three accessions; (2) for quantitative characters, a fixed number of accessions representing the lowest and highest observed values was included; (3) for stem fibre content, disease ratings, seed vigour and drought tolerance, a fixed number of accessions with desirable performance was included; (4) a subset of the 57 most distinct accessions based on RAPD markers was included; (5) a subset of 40 pure lines that were created based on extreme low and high values for 1000 seed weight, seed oil content and fatty acid profiles was included; (6) a subset of fibre flax cultivars of known relevance in European flax breeding and another subset of flax cultivars of known relevance for North American linseed breeding were included. The goal was to maximize the diversity available in a limited number of flax accessions by preserving the range of variation present in the whole collection, while improving evenness. The core collection was assembled in response to requests by flax breeders. This paper compares distribution parameters in the whole and core collections.

Sources of resistance to Plasmodiophora brassicae (clubroot) pathotypes virulent on canola

Abstract A collection of 955 Brassica accessions including B. rapa (718), B. napus (94), B. juncea (93), B. oleracea (30), B. carinata (12) and B. nigra (8) was screened against Plasmodiophora brassicae pathotype 3 (1 × 106 resting spores cc−1 growth medium), the predominant strain of the pathogen on canola in western Canada. A total of 35 accessions (mostly B. rapa) showed at least 50% reduced clubroot severity relative to a susceptible control, with 15 showing complete resistance (clubroot-free). Ten resistant accessions representing Brassica A-, B- and C-genome species were tested further using a 10-fold higher pathogen inoculum dose (1 × 107 resting spores cc−1 growth medium) and by testing them against the five pathotypes (2, 3, 5, 6 and 8) of P. brassicae found in Canada. One B. nigra, two B. oleracea and four B. rapa (oriental vegetable) accessions maintained a high level of resistance under the higher pathogen inoculum pressure, while one B. nigra and two B. rapa (turnip) accessions showed moderate resistance. Most of the selected clubroot-resistant accessions showed consistent resistance to each of the five P. brassicae pathotypes found in Canada, except for one B. nigra and two turnip accessions, which varied slightly against different pathotypes. Several promising sources of clubroot resistance were identified in this study that can be used to develop new canola germplasm with a diverse clubroot resistance background for potentially more durable clubroot resistance.

Genetic diversity of Sinapis alba germplasm as revealed by AFLP markers

Sinapis alba L. is a major specialty crop grown as a condiment in western Canada, but little is known about its genetic diversity. The objective of this study was to assess the level and pattern of genetic diversity in a collection of 127 S. alba accessions held at Plant Gene Resources of Canada using amplified fragment length polymorphism (AFLP) markers. Five AFLP primer pairs were applied, and 134 polymorphic bands were scored for each accession. These scored bands had frequencies of occurrence ranging from 0.02 to 0.99 with an average of 0.69. More AFLP variation was found within single (79.1%) than between (20.9%) S. alba accessions. A small degree of AFLP difference (1.7%) was observed among the accessions of various regions, while relatively large variation (9.2%) existed among the accessions of various countries. A large AFLP difference (15.6%) also existed between the yellow- and brown-seeded accessions, but only 6.2% difference was observed between the cultivar and landrace accessions. Two distinct groups of S. alba germplasm were identified on the basis of the seed colour (yellow or brown), although a few mixtures also existed. No apparent ‘duplicated’ accessions were observed. The most diverse accessions were from Italy, Spain, France and Greece. Among the most genetically distinct accessions were SA97 from Portugal, SA89 and SA88 from France, SA83 from Russia and SA57 from Italy. These findings are significant not only for managing S. alba germplasm, but also for identifying diverse germplasm that can be used by plant breeders to improve S. alba seed yield and quality parameters.