لخّصلي

Two key elements of the previous research effort were the availability of crop diversity collections from gene banks and a concerted effort to assemble extensive collec- tions of pathogen isolates, primarily from major crop production regions, in order to sample the diversity within the pathogen population.Indeed, one of the recommended downy mil- dew resistant lines (EBH502) was originally selected for white rust resistance in B. oleracea.Both elements were included in the current study, in an attempt to identify useful sources of downy mildew resistance for vegetable brassica production in the UK. A core diversity collection of more than 400 B. oleracea accessions had previously been screened for downy mildew resistance using two standard isolates of H. parasitica (Leckie et al., 1996).These were included in the current study because co-segregation of downy mildew resistance was observed following selection for white rust resistance in a rapid cycling population of B. rapa (Mitchell-Olds et al., 1995).Doubled haploid lines were also generated from white rust resistant plants selected in the earlier research effort.

Two key elements of the previous research effort were the availability of crop diversity collections from gene banks and a concerted effort to assemble extensive collec- tions of pathogen isolates, primarily from major crop production regions, in order to sample the diversity within the pathogen population. Both elements were included in the current study, in an attempt to identify useful sources of downy mildew resistance for vegetable brassica production in the UK. A core diversity collection of more than 400 B. oleracea accessions had previously been screened for downy mildew resistance using two standard isolates of H. parasitica (Leckie et al., 1996). The potential sources of resistance were heterozygous: an additional component of the current research was to ‘fix’ resistance in genetically uniform experimental lines to allow robust phenotyping to be carried out. Resistant plants were crossed with rapid cycling plants and doubled haploid lines generated from F3 resistant plants as the first step in the current work. Doubled haploid lines were also generated from white rust resistant plants selected in the earlier research effort. These were included in the current study because co-segregation of downy mildew resistance was observed following selection for white rust resistance in a rapid cycling population of B. rapa (Mitchell-Olds et al., 1995). Indeed, one of the recommended downy mil- dew resistant lines (EBH502) was originally selected for white rust resistance in B. oleracea.