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First Report of Sunflower Broomrape (Orobanche cumana) in Portugal

González-Cantón, E., Velasco, A., Velasco, L., Pérez-Vich, B., Martín-Sanz, A.
Plant disease 2019 v.103 no.8 pp. 2143
Artemisia, Helianthus annuus, Orobanche cernua, agricultural land, crop production, hosts, hybrids, inbred lines, parasites, parasitism, pathotypes, pseudogenes, races, resistance genes, ribulose-bisphosphate carboxylase, shoots, species identification, surveys, virulence, Black Sea, Iberian Peninsula, Portugal, Spain
Sunflower broomrape (Orobanche cumana Wallr.) is a holoparasitic plant species with a restricted range of hosts both in the wild, where it mainly parasitizes Artemisia spp., and in agricultural fields, where it only grows on sunflower (Fernández-Martínez et al. 2015). It is not present in the wild in the Iberian Peninsula but is exclusively found in agricultural fields parasitizing sunflower (Pujadas-Salvà and Velasco 2000). In this geographical region, Spain has suffered from the presence of broomrape in sunflower fields since the 1950s. Currently, the parasite is a major threat for sunflower production in Spain, but Portugal was so far thought to be free of O. cumana. In June 2017, broomrape was observed in a sunflower field near Serpa (37°55′N, 7°31′W, 198 m above sea level), in the Alentejo region. Broomrape plants were identified morphologically as O. cumana according to Pujadas-Salvà and Velasco (2000). The field was planted with a commercial hybrid carrying the Or5 gene that confers resistance to races A through E. Reduced growth of the crop and emergence of typical O. cumana nonbranched shoots were observed. Incidence was estimated to be 60%, and infected plants had an average of 14 broomrape shoots per plant. Species identification was conducted by amplification of the rubisco subunit rbcL1 pseudogene (Delavault and Thalouarn 2002). A sequence of 1,208 bp was deposited in GenBank (accession MK577840). BLAST analysis showed that the best two matches were to O. cumana GenBank accessions KT387722.1 and AF090349.1, with a number of base pairs matching of 1,204/1,208 (99.67%) and 1,195/1,202 (99.42%), respectively. Sunflower broomrape is characterized by the existence of physiological races generally controlled by dominant resistance genes (Fernández-Martínez et al. 2015). Populations overcoming the Or5 resistance gene and named as races F, G, and H are predominant in countries around the Black Sea and Spain. Because the broomrape sample in Portugal was collected on a hybrid carrying the Or5 gene, it was preliminarily expected to be more aggressive than race E. Subsequently, the pathogenic characterization of this broomrape population was done using the host commercial hybrid, line P96, CH-1, CH-2, and line DEB2; they are resistant to races E, F, F, G, and G, respectively. The universal susceptible control B117 was also included. CH-1 and CH-2 were used previously by Martín-Sanz et al. (2016) and named in that paper as hybrid 1 and hybrid 2. Evaluation of the virulence of the broomrape population was done following the methodology described by Martín-Sanz et al. (2016), but instead of a multipot system, pots of 3 liters were used. The Or5 hybrid was heavily parasitized with an average of more than 25 broomrape shoots per plant, whereas P96 and CH-1 had an average of 1.5 and 3 broomrape shoots per plant, respectively. CH-2 and DEB2 genotypes were completely resistant. This indicated that the broomrape population should be classified as race G. The presence of broomrape in the P96 inbred line indicates that this race G from Alentejo region is different from the race GGV found recently in the neighboring area of Guadalquivir Valley (south Spain), which was able to parasitize CH-1 1 but not P96, and more similar to race G populations from the Black Sea area (Martín-Sanz et al. 2016). This is the first report of O. cumana on sunflower in Portugal. Prospective surveys are required to identify the affected areas by broomrape and start urgently an integrated control program to avoid its expansion.