First Report of Sunflower Broomrape, Orobanche cumana Wallr., in Morocco

Abstract

Sunflower broomrape (Orobanche cumana Wallr.) is a chlorophyll-lacking and holoparasitic plant that parasitizes a limited range of hosts. In the wild, it parasitizes on a few species of the Asteraceae, whereas in agricultural fields, it is exclusively found growing on sunflower (Fernandez-Martinez et al. 2015). Sunflower broomrape is a serious threat for sunflower production in Europe and Asia (Shi et al. 2015). In northern Africa, this parasitic weed was first identified in Tunisia in 2010 (Amri et al. 2012). It was not until 2016 that sunflower broomrape was observed for the first time in Morocco, when some sunflower fields were heavily infested with this parasite in the area of Souk Al Arbaa (34°41′N, 5°59′W, 37 m above sea level), in the province of Kenitra. The degree of virulence varied from 0 to 20 shoots per sunflower plant, and seed yield losses reached more than 80%, according to farmers’ statements and our own estimations. Sunflower broomrape populations are classified into physiological races, named A through H in the literature. Races F, G, and H are the most commonly reported in several countries (Martin-Sanz et al. 2016). However, no differential lines are currently available to differentiate between races G and H. Therefore, a nomenclature has been proposed to name populations overcoming race F resistance as race G with an indication of the region of collection (Martin-Sanz et al. 2016). To identify the race of sunflower broomrape population collected in Souk Al Arbaa, eight differential sunflower lines were used, from line B117, having no resistant genes, to line DEB2, resistant to all race G populations evaluated thus far. Evaluation of the virulence of the broomrape population against these lines was conducted under growth chamber conditions at 25/20°C (day/night) with a 16-h photoperiod and photon flux density of 300 µmol/m²·s. Twenty plants of each differential line were evaluated in multipot tray with a pot volume of 40 cm³. Pots were filled with a soil mixture of sand and peat (1:1 by volume) inoculated with broomrape seeds at a concentration of 0.28 mg per gram of soil. Sunflower seeds were germinated in moistened filter paper and then planted in the pots. Evaluation of parasitization symptoms was done after 8 weeks by uprooting the plants and counting the number of nodules in the roots of each sunflower plant. All differential lines resistant to races B to F were parasitized by the sunflower broomrape population, and only line DEB2 was completely resistant, which indicated that the Moroccan population should be classified as a race G. Because the evaluation included line P96, which is resistant to the race G populations of the Guadalquivir Valley in Southern Spain (Martin-Sanz et al. 2016), which is the closest infested area, it can be discarded that the Moroccan broomrape population originated from that area. Following the recently proposed nomenclature, the name of the Souk Al Arbaa (Province of Kenitra) population is proposed as race GKE. This is the first report of O. cumana on sunflower in Morocco. Urgent measures must be taken to manage this population of broomrape and protect sunflower cultivation in Morocco.