Branched broomrape, Phelipanche ramosa (L.) Pomel (syn. Orobanche ramosa L.), is a chlorophyll-lacking, obligate root parasitic plant that infests Brassicaceae, Solanaceae, and legumes (3). In western France, P. ramosa has invaded oilseed rape fields since the 1990s, causing significant yield losses (1). This crop has now become the primary host for the parasite, along with buckwheat (Fagopyrum esculentum L.), hemp (Cannabis sativa L.), and tobacco (Nicotania tabacum L.). In September 2013, a field survey indicated that a celeriac (Apium graveolens L. var. Prinlz) crop on clay soil in the Champagne-Ardennes region (48°20′19″ N, 04°01′57″ E, 140 m above sea level, eastern France) was infested with branched broomrape where hemp had been grown 4 years before. The celeriac field was planted to wheat (Triticum aestivum L.) in 2012 in rotation with lentils (Lens culinaris Medik.) in 2011. About 2% of the total celeriac field was infested and the estimated yield losses were approximately 25% for this infested area. The host symptoms observed were a slower growth of celeriac, along with leaf chlorosis, lower fruit production, and numerous abortions. The infestation of the celeriac crop was confirmed by verifying the attachment of branched broomrape to the celeriac roots. Broomrape plant heights were between 4.5 and 21 cm. The stems were erect, branched, frail, rather hairy, and bulging. Scale leaves were limited to 4 to 10 mm long, thick, acuminate, alternate scales. The flowers were numerous (between 4 and 51) and were 8.3 to 14.5 mm long. They were borne in the axils of scaly bracts. They had an irregular, curved shape, and a light mauve color. They did not have distinct peduncles and were grouped in rather long floral scapes during advanced flowering. The corolla tube was 10 to 15 mm long and its restricted part stood higher than the divisions of the calyx. It had ciliate, if not hairy, lobes. The calyx was more or less hairy, zygomorphous, with four lobes, and 6 to 8 mm long. Two bracteoles were situated on either side of the calyx. The four stamens observed were didynamous and borne 4 to 5 mm above the corolla base. The dorsifixed bilocularis, longitudinally dehiscent anthers were glabrous or covered with a fine down along sutures. Georges Sallé, (retired) Professor of Botanics at the University Pierre et Marie Curie, Paris, confirmed the identity of P. ramosa based on morphological characteristics (1). Celeriac infection by branched broomrape was confirmed using a developed assay (2). P. ramosa infecting celeriac roots was described by counting the numbers of individuals having reached ontogenic stages according to Gibot-Leclerc et al. (2). To our knowledge, this is the first study reporting P. ramosa infection on celeriac in eastern France. Since celeriac is produced in rotation with lentils, branched broomrape could pose a serious threat to production of these crops.
References: (1) M. Blamey and C. Grey-Wilson. La Flore d'Europe Occidentale. Edition Flammarion, Paris, 2003. (2) S. Gibot-Leclerc et al. Flora 207:512, 2012. (3) M. C. Press and G. K. Phoenix. New Phytol. 166:737, 2005.
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