Intriguing World of Weeds -The Broomrapes1

LARRY W. MIT1CH2

INTRODUCTION other early botanists. Broomrape first appeared in En!!­ , the broomrape family, comprises ap­ lish in Dodoens, "a new herbal or historie of " :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 ( 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 , 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.

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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. Its seed has long vitality in the soil (15). Hold­ it prevented or arrested the process of mortification" sworth and Nutman (5) observed that small broomrape and "arrested gangrenes" (13). Now cancer root is does not initiate flowers unless the host has reached the rarely used in medicine, probably because of its flowering state. However, flowering in several strains nauseating taste. of Orobanche occurs on purely vegetative hosts (10). Cancer root, a North American native, is found from Small faoomrape can infest clover 7 yr after the last Wisconsin, south to Florida and Louisiana. Despite its clover crop was grown (16). common name, the species was never actually consid­ ered a cancer cure. Another common name is beech­ A NATIVE BROOMRAPE drops, because it is parasitic on roots of European beech (Fagus sylvatica L.). During the 19th century it The native Louisiana broomrape, 0. ludoviciana was prescribed as "an eminent astringent") (13). Its Nutt., inhabits sandy soils, chiefly in the Mississippi smooth slender branched stems reach 30 to 50 cm tall, Valley (16). However, it has a wide range-Illinois to and in August and September produce small clusters of Saskatchewan, south to Texas, and west to California whitish or whitish-purple flowers. and Arizona. It is parasitic on several wild plants, but has also attacked tobacco. In general habit and appear­ ance it is similar to branched broomrape. Its flowers are INTRODUCED NEW WORLD WEEDS borne in a dense spike. Louisiana broomrape has a Branched broomrape (Orobanche ramosa, L.), an wider range than its immigrant relatives, but it is of introduction from Europe, is also known as tobacco economic importance only in tobacco growing areas broomrape and hemp broomrape. It bears erect, slender, (1). In spring and early summer the Pah Ute Indians ate many-branched brown or straw-colored stems, 10 to 20 the thick, white fleshy bases of Louisiana broomrape cm high, and produces yellow or pale blue flowers in a (13). spike. Its one-celled capsules are many seeded. Branched broomrape occurs primarily in Illinois, Ken­ PREVENTION tucky, Tennessee, North Carolina, and New Jersey. It is parasitic on tobacco and tomatoes (2). The best control remedy is prevention, i.e., sowing At times, branched broomrape causes severe yield clean seed. Broomrape seeds are among the tiniest in loss in tomatoes in California (9), where it originally existence, so they are easily removed from large-seeded spread in seed-infested soil retained on farm imple­ crops (1). ments. Its hosts include redroot pigweed (Amaranthus Cultural methods generally involve the use of a retroflexus L.), shepherd's-purse (Capsella bursa­ susceptible species called a "trap" crop, which is alter­ pastoris (L.) Medicus), nightshade (Solanum spp.), and nated in rotation with the desirable crop species (9). spiny cocklebur (Xanthium spinosum L.). These weeds Badly infested fields should be planted for 2 or 3 yr may ensure the survival of branched broomrape. This is with crops that are not parasitized by the weed (2). important in California, where the parasite often grows For centuries, clean cultivation followed by hand in abundance on weeds in harvested fields of cucumber weeding or hoeing broomrape plants before they (Cucumis sativus L.) and along unpaved roads separat­ produced and disseminated seeds was advocated for ing old sugarbeet (Beta vulgaris L.) fields-two non­ control. This was especially important with new infesta­ host crops, thus surviving from year to year (9). tions. The attachment with the host roots is not very Small broomrape, Orobanche minor, another Euro­ firm, and the whole parasite breaks away readily. It is pean introduction, also is known as lesser broomrape, necessary to grub broomrape plants systematically for choke weed, herb-bane, clover devil, devil's root, and several years until the dormant seeds have all devel-

534 Volume 7, Issue 2 (April-June) 1993 WEED TECHNOLOGY oped (15). The survival of only a very few plants is 9. King, L. J. 1966. Weeds of the World. Interscience Publishers, Inc., New Yorlc. sufficient to reinfest a large area. 10. Kribben, F. J. 1952. Die blutenbildung von Orobanche. Ber. Deutsch. Bot. Ges. 64:353-355. 11. Kuijt, J. 1969. The Biology of Parasitic Flowering Plants. Univ. of LITERATURE CITED California Press, Berkeley. 12. LeStrange, R. 1977. A History of Herbal Plants. Angus and Robertson, I. Brenchley, W. E. 1920. Weeds of Fann Land. Longman, Green and London. Co., London. 13. Marudarjan, D. 1950. Note on Orobanche cemua Loefl. Current Sci. 2. Georgia, A. E. 1942. A Manual of Weeds. The Macmillan Co., New 19(2):64-65. York. 14. Menscher, W. C. 1948. Weeds. The Macmillan Co., New York. 3. Giliarov. M. S. 1943. Orobanche ramosa on kok-saghyz in Russia. 15. Pamrnel, L. H. 1912. Weeds of the Fann and Garden. Orange Judd Co., Biol. Abstr. 17, 3021. New York. 4. Henslow, G. 1898. Orobanche speciosa. Gardener's Chron., Ser. 3, 24: 16. Passerini, N. 1910. Duration of vitality of seeds of Orobanche crenata. 89. Atti R. Accad. Econ. Agric. Georg. Firanze, Ser. 7, 5(1):1-7. 5. Holdsworth, M. and P. S. Nutman. 1947. Flowering responses in a 17. Radosevich, S. R. and J. S. Holt. 1984. Weed Ecology. John Wiley & strain of Orobanche minor. Nature 160:223-234. Sons, New York. 6. Jaeger, E. C. 1944. A Source-book of Biological Names and Terms 18. Rao, M. K. 1919. Orobanche in tobacco. J. Mysore Agric. Exp. Univ. (2nd Ed.). Charles C. Thomas, Springfield, IL. 1(3): 18-20. 7. Kardy, A.E.R. and H. Tewfic. 1956. Seed germination in Orobanche 19. Simpson, J. A. and E.S.C. Weiner. 1989. The Oxford English Diction­ crenata Forssk. Svensk Bot. Tidsk. 50:270-286. ary, 2nd Ed. Clarendon Press, Oxford. 8. King, L. J. 1952. Germination and chemical control of the giant foxtail 20. Thieret, J. W. 1971. The genera of Orobanchaceae in the southeastern grass. Contrib. Boyce Thompson Inst. 16:469-487. . J. Arnold Arboretum, 52:404-413.

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