The inheritance of resistance of some Brassica oleracea L. cultivars and lines to downy mildew - Peronospora parasitica [Pers.] ex Fr.

Resistance to downy mildew was tested on resistant cultivars: Brassica oleracea PI246077 and PI231210, a broccoli-cauliflower line from Polish selection, susceptible cauliflower lines and their F₁ and F₂ progenies. Infection degree of the inoculated plants was determined at the cotyledon and 4-5 leaf stages. To estimate score plant infection at the 4-5 leaf stage the Williams scale designed for plants inoculated at the cotyledon stage was modified. Resistance to the Polish fungus isolate proved to be a dominant character. At the cotyledon stage depending on the source of resistance, it was determined by four (in the broccoli-cauliflower line) or three (in PI USA) dominant complementary genes, while at the stage of 4-5 leaves - by a single dominant gene (in PI231210), two (in PI246077) or three (in the broccoli-cauliflower line) additive dominant genes

The response of oilseed rape (Brassica napus ssp oliefera ) accessions with different glucosinolate and erucic acid contents to four isolates of Peronospora parasitica (downy mildew) and the identification of new sources of resistance

A total of 101 Brassica napus ssp. oleifera accessions with seed differing in glucosinolate and erucic acid contents were screened for resistance to four isolates of Peronospora parasitica at the cotyledon stage. Two groups of accessions with different resistance factors were identified. Lines that were homogeneous for resistance were selected from seedling populations of accessions that exhibited a heterogeneous reaction to some isolates. The resistance of one group differs from that of cv. Cresor, the only oilseed rape cultivar reported to have an isolate-specific gene for resistance to P. parasitica. The isolate specificity of the second group was identical to that of cv. Cresor. A comparison of the response of host accessions which expressed moderate to full susceptibility at the cotyledon stage, with no clear differential response to any of the four P. parasitica isolates, indicated that those with high glucosinolate and high erucic acid contents (12 accessions) were slightly but significantly less susceptible than those with high glucosinolate and low erucic acid (19 accessions), or low glucosinolate and low erucic acid contents (28 accessions). The mean differences between accessions with low erucic acid but differing in glucosinolate content were inconsistent. The last result was further confirmed by investigating the expression of resistance to three isolates of P. parasitica at three different seedling growth stages among 11 accessions of oilseed rape with seeds low in erucic acid but differing in glucosinolate content

Mapping of a locus for adult plant resistance to downy mildew in broccoli (Brassica oleracea convar. italica)

The identification of the gene Pp523, conferring downy mildew resistance to adult plants of broccoli (Brassica oleracea convar. italica), led to the construction of a genetic map that included this resistance locus, 301 amplified fragment length polymorphisms, 55 random amplified polymorphic DNAs, 46 inter-simple sequence repeats, three simple sequence repeats, four other PCR markers and a flower colour locus, all gathered into nine major linkage groups. Nineteen additional molecular markers were clustered into one group of four markers, one group of three markers and six pairs of markers. The map spans over 731.9 cM, corresponding to 89.5% of the 818 cM estimated to be the total genome length. A significant number of the mapped markers, 19.3%, showed distorted segregation. The average distance between mapped adjacent markers is 1.64 cM, which places this map among the densest published to date for this species. Using bulked segregant analysis, we identified a group of molecular markers flanking and closely linked in coupling to the resistance gene and included these in the map. Two markers linked in coupling, OPK17_980 and AT.CTA_133/134, are located at 3.1 cM and 3.6 cM, respectively, at each side from the resistance gene. These markers can be used for marker-assisted selection in breeding programs aiming at the introgression of this gene in susceptible B. oleracea genotypes. The fine mapping of the genomic region surrounding the Pp523 resistance gene is currently being carried out, a basic condition for its isolation via positional cloning