Intriguing World of Weeds Orobanche-The Broomrapes1 LARRY W. MIT1CH2 INTRODUCTION other early botanists. Broomrape first appeared in En!!­ Orobanchaceae, the broomrape family, comprises ap­ lish in Dodoens, "a new herbal or historie of plants" :is proximately 150 species in. 17 genera. Four genera translated from the French by Henry Lyte (1529?-1607) represented by four species occur in and published in 1578. Wrote he, "That excrescence the southeastern U.S. (21). A comming from the roote of Broome is called in Latine majority of the genera and about Ragum Genistae, that is to say Broome Rape" (20). 90% of the species in Oroban­ Cattle and sheep graze broomrape shoots with impu­ chaceae are Old World natives. The nity. However, the seeds pass unharmed through their family is primarily'one of the north­ alimentary tracts and can infest tobacco plants (9). ern warm and temperate zones. Indiscriminate grazing in infested fields disseminates the parasite. Only about 10% of the species oc­ cur in the tropics; only one species reaches the arctic (21). ECONOMIC IMPORTANCE A few species in Orobanchaceae are used in folk Broomrape-infested crops result in great economi-: medicine (21). Several Old World species are widely losses in southern Europe, particularly to beans distributed weeds. The genus Orobanche accommodates (Phaseolus sp.) in Italy. In the U.S., broomrape causes about 60 species of unbranched parasitic herbs, without considerable yield losses in tobacco, clover, tomatoes chlorophyll (21). The broomrapes are variable in color, (Lycopersicon esculentum Mill.), sunflowers (Helian­ ranging from yellowish-brown and reddish-violet to thus annuus L.), and broad beans (Vicia faba L.). purple, blue, and orange (13). Species are found over Heavy infestations occur in beans in Egypt, where the much of the world, including most of Europe, Asia, and parasite's stalks grow 3.3 m high (4). In India, nodding North America, and the majority of species grow only broomrape (Orobanche cemua Loeffl.) causes a "near­ on one or two host plants (13). wilt" appearance in tobacco and affects yield and qual­ The parasitic broomrapes live directly on their hosts ity (14). It also parasitizes large numbers of wild sola­ by attaching strong haustoria to their roots, penetrating naceous plants (9). Heavily parasitized host plants of the tissues, and absorbing the food gathered by the host Datura fastuosa var. alba may have up to 500 nodules plants for their own development. The chief weedy (places of infection). species in the U.S. were imported in clover (Trifolium In studying the effects of broomrape on tobacco in spp.), hemp (Cannabis sativa L.), and tobacco (Nico­ India, Rao ( 19) observed that Orobanche seeds are so tiana tabacum L.) seed, and in like manner, spread to minute that they readily mix with tobacco seed, and several states (1). indeed look like tobacco seed. Severe infestations de­ In 1753, Linnaeus erected the genus Orobanche in stroy 25% of the crop. his Species Plantarum. He derived the name from the In Russia during August branched broomrape infests Greek orobos, a vetch, and ancho, to strangle, referring 48% of Russian dandelion (Taraxacum kok-saghyz to the effect the plants have on their hosts (6). Rodin), grown for rubber (3). Up to five individuals The name broomrape is a rendering of medieval were counted on one host plant, even on lateral roots 4 Latin Rapum genistea, broom knob or tuber; rapum to 5 cm away from the main root. The rubber content of being a knob or lump formed by the roots of trees, and parasitized plants was reduced 66%. genista, a broom. Therefore this name is not of popular In Egypt, Kardy and Tewfic (7) researched the ger­ origin (20). It was first applied to great broomrape, mination of crenat~ broomrape ( Orobanche crenata Orobanche major, the Rapum genistae of Lobel and Forsk.) seeds on broadbean. This weed causes great economic losses in broad beans, one of the country's main crops. They found that a broomrape plant produces about 40 000 seeds (0.35 mm long and 0.26 1No. 40 of the series "Intriguing World of Weeds." 2Ext. Weed Sci., Dep. Bot., Univ. Calif., Davis. CA 95616. mm wide), which remain viable for more than a decade. 532 Weed Technology. 1993. Volume 7:532-535 WEED TECHNOLOGY Crenate broomrape seeds require about a week of Upon germination, broomrape seed develops a small stimulation to start germination, which occurs about radicle which penetrates a fine rootlet of the host and one week before the host plant flowers. A substance becomes firmly connected with it. The radicle immedi­ produced by the roots of mature host plants encourages ately begins using nutrients from the host, and stores broomrape seed germination (7). Consequently, seeds these as a starchy reserve in the upper part of the may germinate at a distance up to 1 cm from the host radicle, causing it to become distended. It gradually plant, but only those at a distance of 2 to 3 mm actually forms a nodule on the host root (1). As the nodule cause infection. increases in size, small prominences emerge on its surface. The prominences develop into roots, which SEED SIZE AND LONGEVITY surround the nodule closely, and penetrate the host roots in other places, thus becoming attached at several Most weeds have seed weights ranging from about points. The large swelling develops into a shoot, which 0.1 g per 1000 seeds to about 3.0 g per 1000 seeds, and ultimately elongates to form the above-ground portion the lighter seeds are considered to have a decided of the plant. The greater part of the broomrape's life is advantage in dissemination (9). On this basis, broom­ spent below ground, as nodule development into a fair rape is a colossus. Some species bear seeds in prodi­ sized bulb-like structure, necessary for the development gious numbers and of near-microscopic size; e.g., seeds of aerial shoots, requires .several weeks (1). of small broomrape (Orobanche minor Sm.) are 0.2 to A few host plants stimulate the germination of 0.3 mm long and 0.2 mm wide, and 0.1 thick (9). broomrape seeds without themselves being parasitized, Additionally, 1000 seeds of 0. elatior weigh 0.0049 g including chili and bell peppers (Capsicum annuum L.), and one plant produces 270 000 seeds. 0. picridis coat buttons (Tridax procumbens L.), and hairy beggar­ produces from 94 000 to 116 000 seeds per plant and ticks (Bidens pilosa L.) (9). When broomrape seed 1000 seeds weigh 0.0029 g (8). occurs close to the roots of such species, 13 to 15% of Broomrape seeds are widely disseminated by the its seeds germinate but do not d;;:.velop haustorial con­ winds and, though minute, are very long-lived, having nections. Peppers grown in rotation with tobacco tend to reduce broomrape seed infestations in the soil (9). been known to survive in the soil for 13 yr (1). They are capable of lying dormant for several years and germinating in succession. Greenhouse experiments THERAPEUTIC USES OF BROOMRAPE conducted for 14 yr showed that broomrape seeds retain During the 16th and 17th centu­ their vitality when buried in soil for 8 yr. Other ries, great broomrape ( 0. major, researchers report the time as at least 10 yr, the varia­ synonym 0. rapum-genistae) of tion probably resulting from different conditions (17). Europe and Russia was prescribed For survival, parasitic plant seedlings must quickly as a medicinal herb throughout find a suitable host plant (12). To germinate, broomrape most of Europe "as a remover of seed requires exposure to a biochemical exudate stone in the bladder and kidneys­ produced by the root of the host plant, a phenomenon and as a provoker of lustry urine" highly advantageous to the parasite. The radicle of and was usually administered Orobanche species grows chemotropically toward host decocted in wine. Reportedly plant roots. This germination feature probably is highly it was bitter tasting and very astringent (13). Applied evolved and acts to enhance seeding survival (18). externally, the juice was regarded as "a singular remedy" in the treatment of "old green wounds-the SEEDLING DEVELOPMENT runnings of ulcers and sores-malignant and scabby ulcers, those that be hollow also" and "for fretting Broomrape seedlings are trivial, light-colored, nearly sores." The decocted flower spikes were used as a wash transparent threads, lacking roots and chlorophyll. Al­ for "cleansing the skin" and "for freckles, black or blue though they have no difficulty in penetrating the soil, spots or pushes thereof' (13). they are unable to draw sustenance from it (11). If a Great broomrape generally attaches itself to the roots suitable host is not found soon after germinating, the of broom (Cytissus sp.) or gorse (Ulex europaeus L.). seedlings shrivel and die. This stout leafless club-like perennial grows 70 to 100 Volume 7, Issue 2 (April-June) 1.993 533 MmCH: INTRIGUING WORLD OF WEEDS cm tall. Its honey-brown stems produce a dense spike hellroot. It ranges from New Jersey southward to North of yellowish, purple-tinged flowers from May to July. Carolina, and is found locally in a few places in interior Although very distasteful, the entire plant of cancer states. It inhabits clover fields but it also parasitic on root (0... virginiana L.), after "yielding its virtues" to tomato and tobacco (16). water or alcohol. was administered "with benefit in Small broomrape was brought inadvertently to the fluxes and diarrhea and certain afflictions to the bowl," U.S. in clover seed. The parasite grows larger than its and as a useful "application to obstinate ulcers, host and its presence in any abundance destroys the aphthous ulcerations," while locally "applied to wounds crop.