New Infestation of Branched Broomrape, Orobanche ramosa (Orobanchaceae), on Black Medic, (Medicago lupulina) (Fabaceae), in Virginia.

Abstract

Orobanche ramosa L. is arguably the most insidious of the major broomrapes, achlorophyllous root parasites of various row crops (4). It has a broad host range and is the most widely spread of any agronomically important broomrape. In the United States, California, Kentucky, and Texas have persistent populations. The California and Texas populations are carefully monitored. Isolated and ephemeral occurrences were reported from New Jersey and a New York greenhouse (1). In May 2006, remnants of capsules were found by a botany student in an urban area of Norfolk, VA. We visited the site during May 2007 and found a flowering population of approximately 100 plants parasitizing Medicago lupulina L. On the basis of size, color, and shape of the corolla and capsule and the branching pattern, the species was determined to be O. ramosa, part of a complex of closely related taxa that is currently undergoing revision. It differs from native broomrapes and the widely introduced O. minor because of its corolla color and branching habit (2). To our knowledge, this is the first record on M. lupulina although other species of Medicago are known hosts (L. J. Musselman, unpublished data). The site of the infestation is an approximately 230-m2 mowed area next to a carwash, suggesting that seeds could have come from trash removed from cars at the vacuuming station that vents onto the mowed area. Since the carwash is near a large naval base with a transient population, seeds could have come from anywhere in the world. This species exhibits little host specificity, and earlier studies have shown that numerous crops can be parasitized by plants grown from seed collected from broomrape on wild or ornamental hosts (3). Crops grown in the Middle Atlantic Region, which are especially susceptible to parasitism by O. ramosa, include potato (Solanum tuberosum), tobacco (Nicotiana tabacum), and tomato (Lycopersicon esculentum). Because of the broad host range and potential damage by this parasite, as well as its record of expanding distribution, agricultural workers should be aware of its presence in the Mid-Atlantic States. Voucher specimens from this infestation have been deposited at the following herbaria: ODU, NCU, and VPI ( http://sciweb.nybg.org/science2/IndexHerbariorum.asp ). At the time of this publication, the USDA APHIS has initiated a control program for this first documented population in Virginia (2).