Summary Orobanche cumana (sunflower broomrape) is found in Spain as an allochthonous species parasitising exclusively sunflower. For many years, it was distributed in the Guadalquivir Valley and Cuenca province, but in recent years, it has spread to new areas. The objective of this research was to study genetic diversity of O. cumana populations from Spain using robust co‐dominant molecular markers. Cluster analysis on a set of 50 populations using 15 microsatellite markers revealed the existence of two distant gene pools, one in Cuenca province and another one in the Guadalquivir Valley. Within each gene pool, both inter‐ and intrapopulation variability were extremely low. This population structure probably reflects a founder effect, with the two genetically distant gene pools deriving from separate introduction events. Different races occurred within the same gene pool, suggesting that current races might have evolved through mutation from a common genetic background. Most of the populations from new areas were identical to the populations from the Guadalquivir Valley. Only a few populations showed larger intrapopulation variation. In these cases, our results suggested the co‐existence of both gene pools within the same population, as well as the occurrence of genetic recombination between them. Genetic recombination between distant gene pools is an important mechanism for creating new variation, which might also have an effect on race evolution. These results will contribute to the establishment of improved crop breeding and management strategies for O. cumana control.

Brassica carinata is a potential oilseed crop for the Mediterranean area. Chemical mutagenesis has been applied to microspores of B. carinata with the purpose of identifying lines with altered erucic acid content. From a population of nearly 400 doubled haploid plants recovered, nine lines have been identified that exhibit promising useful changes in erucic acid concentration in the seed oil. Three lines showed erucic acid contents below 25%, with a minimum of 17.1%, and in six lines the level of this fatty acid was greater than 52%. Changes in other fatty acids are also described and discussed.

Summary Orobanche cumana is a weed that grows as a root parasite on sunflower. In general, the O. cumana–sunflower parasitic system is regarded to follow the gene‐for‐gene model, although this has never been demonstrated at the genetic level in O. cumana. The Or5 dominant gene in sunflower confers resistance to O. cumana race E, but not to race F. The objective of this research was to study the inheritance of avirulence/virulence in crosses between plants of O. cumana lines classified as races E and F. Four race E and three race F lines were developed, from which four race E × race F cross‐combinations were made, in three cases including reciprocals. In all cases, F1 seeds did not have the ability to parasitise sunflower line P‐1380 carrying the Or5 gene, indicating dominance of race E avirulence allele(s). Five F2 populations comprising a total of 387 F2:3 families were evaluated on sunflower line P‐1380. In all cases, one‐fourth of the F2:3 families did not possess the ability to parasitise P‐1380 plants, suggesting that race E avirulence and race F virulence on P‐1380 are allelic and controlled by a single locus. This study demonstrated the gene‐for‐gene interaction in the O. cumana–sunflower parasite system and provided useful information to identify genes involved in O. cumana virulence. The approach followed in this research can contribute to define precisely races of the parasite on the basis of the presence of avirulence genes.

Ethiopian mustard (Brassica carinata Braun) is a potential oil crop in which genes for low erucic acid content of the seed oil have not yet been found. In order to solve this problem the potential of rapeseed [B. napus L.) varieties as a source of these genes has been tested. Reciprocal F, hybrids between B. cartnata and a low erucic acid variety of B. napus. FT, and backcrosses with B. carinata were obtained. The fatty acid composition was determined in half seeds of F; and segregating generations from reciprocal interspecific crosses. The genetic analysis indicated that the erucic acid content of the seed oil of B. carinata is controlled by two genes writh no dominance and additive in action.

Rodríguez‐Ojeda MI, Velasco L, Alonso LC, Fernández‐Escobar J & Pérez‐Vich B (2011). Inheritance of the unpigmented plant trait in Orobanche cumana. Weed Research51, 151–156. Summary Unpigmented plants characterised by yellow stems and white flowers have been observed in several Orobanche spp. The objective of this research was to study the inheritance of the unpigmented plant trait in Orobanche cumana. Plants of the unpigmented line EK‐A1 that had been self‐pollinated for three generations (S3) were crossed with plants of the wild‐type line EK‐12 using hand emasculation and pollination. F1 plants showed an intermediate phenotype, characterised by a greenish stem compared with a yellow stem in EK‐A1 plants and bluish‐violet stem in EK‐12 plants. F2 plants segregated in a 1:2:1 (bluish‐violet: greenish: yellow) ratio, suggesting that plant pigmentation in O. cumana is controlled by a partially dominant allele at a single locus. Monogenic inheritance was confirmed in the F3 plant generation, which also revealed that the lack of pigmentation has no effect on O. cumana parasitism. This study demonstrated for the first time the feasibility of using hybridisation techniques for developing segregating populations in this species. Because of its simple mode of inheritance, the unpigmented plant trait may have a particular use as a morphological marker in basic and applied studies on O. cumana.