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.