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.

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.

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Orobanche cumana is an important parasitic weed of sunflower. The objective of this research was to study seed production and seed quality in O. cumana using three different bag types to isolate flowering plants. Maximum seed production was obtained on unbagged plants (91.2 mg per plant), followed by micro-perforated transparent plastic bags (MPB) (84.2 mg per plant), white paper (46.5 mg per plant) and brown paper bags (37.5 mg per plant). Seed quality, measured as germination percentage and infectivity, did not differ between unbagged plants and plants isolated with MPB, whereas it was considerably reduced in plants isolated with paper bags. A second experiment studied bagging effect on controlled hybridisation. When using white paper bags and MPB, 45.2% and 60.1% of the emasculated and hand-pollinated flowers were fertilised, respectively, compared with 88.6% in unbagged plants. The data suggested that O. cumana plants produce seed under isolation, even though the bag type affects seed production and quality. These results will be useful for basic and applied research demanding O. cumana seed production under isolated conditions. Mean values within each column followed by the same letter are not significantly different (P = 0.05).Plant isolation and seed production in Orobanche cumana 517

Spanish sunflower acreage is basically divided into three main and isolated areas, the Guadalquivir valley, southern Spain, represents 37% of the total acreage, the Cuenca area located in Spain´s central plateau, 28%, and the Castilla-León area, northern Spain, 29%. Sunflower broomrape (Orobanche cumana Wallr.) has been present in Spain since the 1960's. From that time on, different waves of dissemination and dispersion of the parasite have been registered. The latest correspond to the broomrape race E dispersal in the early 1990's and race F dispersal in the first few years of this century. These broomrape dissemination waves have been limited only to the Guadalquivir and Cuenca areas. In the Castilla-León area, the presence of broomrape had not been noticed until now.In 2008, a highly virulent broomrape infection focal point (about 300 m 2 ) was detected in a sunflower plot near Medina del Campo (Valladolid), south of the center of the Castilla-León area. Racial determination has proved that this broomrape inoculum belongs to race F.