SCAR and CAPS markers flanking the Brassica oleracea L. Pp523 downy mildew resistance locus demarcate a genomic region syntenic to the top arm end of Arabidopsis thaliana L. chromosome 1

We recently mapped the Pp523 locus that includes a single, dominant gene conferring resistance to downy mildew expressed in adult plants to a 75.1 cm long linkage group on a genetic linkage map of Brassica oleracea L. More recently, we identified a new AFLP marker 2.8 cm downstream from the resistance gene. The five DNA markers within an 8.5 cm region encompassing the Pp523 gene were cloned and sequenced. Three of these markers were transformed into SCARs (sequence characterised amplified regions), however, two among them were monomorphic and were analysed as CAPS (cleaved amplified polymorphic sequence) markers among the mapping population. Searched against genomic databases, the five B. oleracea DNA-marker sequences matched Arabidopsis thaliana L. gene sequences that delimit a conserved syntenic region in the top arm end of chromosome 1 of this last species. Considering the close genetic relatedness between both species, the information on this specific genomic region in A. thaliana is particularly useful for the construction of a fine-scale map of the corresponding genomic region in B. oleracea. The identified SCAR and CAPS markers can be used for marker assisted selection (MAS) in breeding programs aimed at the introgression of the Pp523 resistance locus, allowing the reliable indirect identification of plants harbouring the resistance gene with a margin of error of approximately six in ten-thousand selected plants

Identification of DNA markers linked to an induced mutated gene conferring resistance to powdery mildew in pea (Pisum sativum L.)

We have recently induced two powdery mildew (Erysiphe pisi Syd) resistant mutants in Pisum sativum L. via ethylnitrosourea (ENU) mutagenesis. Both mutations (er1mut1 and er1mut2) affected the same locus er1 that determines most of the identified natural sources of powdery mildew resistance (PMR) in this crop. The mutated gene er1mut2 was mapped to a linkage group of 16 DNA markers combining three main strategies: near isogenic lines (NILs) analysis, bulked segregant analysis and genetic mapping of randomly identified polymorphic markers, together with three DNA-markers techniques: ISSR, RAPDs and AFLPs. Markers located closer to the PMR locus, OPO06(1100y) (0.5 cM), OPT06(480) (3.3 cM) and AGG/CAA(125) (5.5 cM), were cloned and converted into SCAR markers. Markers AH1R(850) and AHR(920y) were found to be allelic and converted into the co-dominant marker ScAH1 (16.3 cM). Two previously known DNA markers, ScOPE16(1600) and A5(420y,) were mapped at 9.6 and 23.0 cM from the PMR locus, respectively. The novel markers identified in this study are currently being transferred to a new F2 mapping population derived from a cross between the induced PMR mutant line F(er1mut2) and a more genetically distant susceptible line of Pisum sativum var. arvense

A new broccoli × broccoli immortal mapping population and framework genetic map: tools for breeders and complex trait analysis

A unique broccoli x broccoli doubled haploid (DH) population has been created from the F-1 of a cross between two DH broccoli lines derived from cultivars Green Duke and Marathon. We genotyped 154 individuals from this population with simple sequence repeat and amplified fragment length polymorphism markers to create a B. oleracea L. var. italica 'intra-crop' specific framework linkage map. The map is composed of nine linkage groups with a total length of 946.7 cM. Previous published B. oleracea maps have been constructed using diverse crosses between morphotypes of B. oleracea; this map therefore represents a useful breeding resource for the dissection of broccoli specific traits. Phenotype data have been collected from the population over five growing seasons; the framework linkage map has been used to locate quantitative trait loci for agronomically important broccoli traits including head weight (saleable yield), head diameter, stalk diameter, weight loss and relative weight loss during storage, as well as traits for broccoli leaf architecture. This population and associated linkage map will aid breeders to directly map agronomically important traits for the improvement of elite broccoli cultivars