Detecting Single Seeds of Small Broomrape (Orobanche minor) with a Polymerase Chain Reaction

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Abstract
The seeds of the federally-listed noxious weed and parasitic plant small broomrape (Orobanche minor Smith) are extremely small, averaging 200 to 300 μm in size. Because of its miniscule seed size, contamination of fields and seed lots by small broomrape seeds is difficult to detect and confirm via conventional methods. Complementary polymerase chain reaction (PCR) primers based upon unique sequences in the internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA (nrDNA) of small broomrape were developed. The PCR amplified small broomrape DNA and did not amplify DNA from other Orobanche species with similar host ranges found in Oregon. The primers also did not amplify the DNA of red and white clover (Trifolium pratense L. and T. repens L., respectively), two agricultural hosts for this parasite. The PCR-based assay was sensitive enough to detect a single small broomrape seed. Accepted for publication 14 October 2002. Published 18 October 2002.