Screening studies on the host range of branched broomrape (Orobanche ramosa).
Studies on the host range of Orobanche ramosa L., by screening different Summer and Winter crops, medicinal herbs, and a large number of weeds for possible attack by the parasite, revealed substantial variation among species in the number and vigour of parasites attached to their roots. The crops and medicinal herbs most affected were: Apium graveolens, Carthamus tinctorius, Carum carvi, and Trachyspermum ammi (with 36-214 Orobanche shoots per pot). Among the crops studied, Ammi visnaga, Brassica nigra, B. oleracea var. botrytis, Cucurbita moschata, Linum usitatissimum, Lupinus albus, and Raphanus sativus were least infected (with 1-2 Orobanche shoots per pot). Weeds, including Datura metel, Ferula communis, and Rumex acetosella were heavily infected (with 40-67 shoots per pot). In contrast, Antirrhinum orontium, Convolvulus arvensis, Diplotaxis erucoides, Polygonum aviculare and Solanum cornutum showed extremely low infection (with 1-2 shoots per pot). T. ammi is reported, for the first time, as a potential "trap species" for O. ramosa. Other plants tested are useful as "catch species" and both may be used effectively to manage infestation by the parasite by their inclusion in crop rotation or intercropping systems. Non-host species, or those that allowed very low parasite attachment may be grown in fields heavily-infested by the parasite. Control of highly-infected weed species is necessary to prevent parasite multiplication and spread. However, timing this operation after parasite attachment, or before emergence may be effective in exhausting the soil seed-bank, providing the weeds do not pose a serious competition with the crop plants. Many of the plant species tested were not attacked, suggesting a different mechanism of resistance, or lack of stimulants for O. ramosa seed germination. Of the species reported to be good "trap crops" for this parasite, L. usitatissimum showed very low infection, but B. campestris, C. frutescens, C. annuum, Coriandrum sativum, and T. foenum-graecum were heavily infected.