Introduction 
Orobanche crenata (Forsk.), commonly called crenate broomrape, is a serious weed of many economically important crops (Parker 2012). It is one of about 150 species in the genus Orobanche (Orobanchaceae) (Wolfe et al. 2005), which are notable for their parasitic mode of nutrition. Like other members of this family,O. crenata lacks chlorophyll and photosynthetic capacity, so is completely dependent on autotrophic host plants for its nutritional requirements. The geographic distribution of the genus is mostly in the temperate and subtropical regions of the world, but centered in the Mediterranean area (Satovic et al. 2009; Zhang et al. 2014).
O. crenata constitutes a major constraint to faba bean (Vicia faba L.) cultivation (Pérez-de-Luque et al. 2010, Acharya 2013). However, this parasite also attacks crops such as lentil (Lens culinaris Medik.), pea (Pisum sativum L.), chickpea (Cicer arietinum L.), tomato (Solanum lycopersicum  L.), lettuce (Lactuca sativa L.) and carrot (Daucus carota L.) (Román et al. 2007a; Aksoy et al. 2016; Renna et al. 2015). Control ofO. crenata is difficult due to its ability to produce high numbers of tiny seeds (up to 500,000 per plant) that can lie dormant in the soil for up to 20 years in the absence of a host (Habimana et al. 2014; Yahia et al. 2015). The parasite thus persists through seasons when hosts are not present, only to reappear when compatible host crops are replanted. Furthermore, the parasite is largely hidden below ground as the seedlings attach to host roots and inflict much of their damage to the host before the parasite floral shoot emerges from the soil. Several methods have been advocated for control of this weed, ranging from hand pulling, herbicides, biological control, delayed crop sowing and crop rotation, but each of these suffers disadvantages due to economic constraints or limited effectiveness (Eizenberg et al. 2013; Kannan and Zwanenburg, 2014; Sheoran et al. 2014).
In Algeria, O. crenata is the major Orobanche species and is a serious problem for legume crops, mainly faba bean, pea and chickpea. This parasite has been reported in several regions of Algeria, with high levels of infestation leading to the complete destruction of affected crops in some localities which force farmers to give up growing legume crops (Labrada, 2008). Orobanche crenata is a long-standing agricultural problem in Algeria. The oldest herbarium specimens date to 1908 and were collected from legume crops in the region of El-Harrach (previously called ”Maison Carrée” during the French colonial period). History tells us of the extent Orobanchedamage at the beginning of the last century. In 1923 Ducellier wrote the following: “Faba beans and peas cultivation is made impossible in certain localities of the Sahel of Algiers and of the plateau of ”Maison carrée”, so much has become common there, in the last fifteen or twenty years, the crenate broomrape” . At that time, the same author estimated that in some localities 60% of the land had become unsuitable for the cultivation of pea and faba bean as a result of the damage caused by this broomrape, which could lead to the complete crop failure (Blanchard, 1952). More than seventy years after Ducellier’s statements, the Orobanche problem continues to increase. The parasite not only was reported to be still widespread in the Sahel of Algiers on legumes (Zermane, 1998) but also was found in the ”Ain Dem” region (at ”Khemis Méliana” town, about 200 km west of Algiers) causing significant losses on the same crops (Mahmoudi, 1993).
A previous study aimed to understand the genetic diversity of this species in Algeria using RFLP and RAPD markers (Aouali et al. 2007). This showed a proportional increase in genetic distance with geographical distance and suggested that the center of dissemination for this parasitic plant might be the region of ‘Mitidja’, which is near the Ain Taya (Algiers) location used in the present study (Fig 1.).
In recent years, improved molecular techniques have been developed for genetic analysis of populations (Satovic et al. 2009). Advances in next-generation sequencing technologies have enabled a revolution in genetic research through the ability to generate large numbers of Single Nucleotide Polymorphisms (SNPs) (Crossa et al. 2013). Genotyping-By-Sequencing (GBS) is a high-throughput genotyping platform that integrates SNP discovery and genotype calling into one step by reducing genome complexity via restriction enzymes (Elshire et al. 2011). It is an attractive technology for genomic selection by providing new cost-effective opportunities for breeders because it generates large numbers of SNPs for exploring within-species diversity, constructing haplotype maps, genome-wide association studies and genomic selection (Poland and Rife 2012). The reduced representation of the genome and the barcoding of each individual enable multiple samples to be sequenced in one lane, leading to low-cost genotyping of many individuals (Elshire et al. 2011).
Given the tremendous economic impact of O. crenata , the study of the genetic variation of this parasitic weed is important because it could lead to better understanding of O. crenata spread and adaptation. In the present study, the GBS approach was used to identify and genotype SNPs in Algerian O. crenata populations that represent diversity in terms of geography and host species, with the aim to understand the population structure and geographical distribution, environmental adaptation, and host specificity.