Branched broomrape (Orobanche ramosa L.) is a chlorophyll-lacking, root parasitic plant that infects many crops and wild species (2). Plants are densely hairy with minute, glandular hairs, particularly on flowers and upper stems. Stems are erect, often branched just above the ground, and brown to straw yellow. Leaves are sparse, triangular, dark brown or purple, and arranged alternately mainly near the base of the stem. Flowers are numerous, arranged along an upright spike with a lance-shaped bract beneath the flower (about a third of the length of the flower). Petals are pale blue to purple and united into a slender tube approximately 15 mm long with two lips, the upper divided into two lobes and the lower into three lobes. The flowers have two short and two long stamens. During 2010 and 2011, a severe broomrape infection was found in an oilseed rape (Brassica napus L., cvs. Nelson and W31) crop on light-textured soil in northern Greece (Paralimnio-Serres, 41°01′N, 23°32′E, 40 m above sea level), where oriental tobacco (Nicotiana tabacum L.), a susceptible host of branched broomrape, was grown 20 years ago. The field had been cultivated with oilseed rape for three consecutive seasons in rotation with sunflower (Helianthus annuus L.). The infestation of the oilseed rape crop was confirmed in April by digging in the soil (25 to 30 cm deep) to verify attachment of the broomrape to roots of the crop plants. Density of the broomrape ranged from 20 to 120 stems per m2 and broomrape stems were 15 to 30 cm tall. Yield losses were estimated at 30 to 60%. In 2011, branched broomrape was found parasitizing wild mustard (Sinapis arvensis L.) growing as a weed in the oilseed rape field. Attachment of the broomrape was verified on a lateral root of the wild mustard plant near the soil surface, 0.95 m from the main root of the weed. Additionally, branched broomrape was found in April 2010 and 2011 parasitizing wild vetch (Vicia spp.) growing in field margins at the Cotton and Industrial Plants Institute-National Agricultural Research Foundation (Sindos, 40°41′N, 22°48′E, 17 m above sea level). The parasitized vetch plants were growing on light-textured soil. Attachment of the broomrape to roots of the host plants was verified at a 5-cm soil depth. Stems of the parasite were short (7 to 10 cm). The monthly mean air temperature for February (7.3°C), March (9.6°C), and April (14.1°C) and mean soil temperature at a 10-cm depth for February (7.0°C), March (9.5°C), and April (13.4°C), before verification of the broomrape infestation at Sindos, were much lower than the temperature range reported (18 to 23°C) for branched broomrape infestations (1). To our knowledge, this is the first report of O. ramosa on oilseed rape, wild mustard, and wild vetch in northern Greece. Since branched broomrape could be a significant parasite for oilseed rape, which was introduced to Greece as a commercial crop 5 years ago, measures should be taken to avoid significant yield losses from this parasitic plant.
References: (1) I. Faithfull and D. McLaren. Landcare Note LC0272. Department of Sustainability and Environment, State of Victoria, Melbourne, Australia, 2004. (2) C. Parker. Pest Manag. Sci. 65:453, 2009.