O. cernua is a non-photosynthetic parasite producing erect, fleshy, leafless flowering stems 15-40 cm high bearing alternate scales less than 1 cm long. Although usually unbranched above ground, multiple stems sometimes arise from a single tubercle below ground. The plant is pale, completely lacking any chlorophyll. The base of the stem, below ground, is normally swollen and tuberous. The inflorescence, occupying up to half the length of the stems carries many acropetally developing flowers, arranged in spikes or racemes, each subtended by a bract 7-12 mm long (without the additional bracteoles present in O. ramosa). The calyx has four free segments, more-or-less bidentate, 7-12 mm long. The white corolla tube, 12-30 mm long, is inflated near the base, conspicuously down-curved, with narrow reflexed lips, up to 10 mm across. The tube is mainly white or pale while the lips are contrastingly blue or purple, without distinct venation. Filaments are inserted in the corolla tube, 4-6 mm above the base. A capsule develops up to 8-10 mm long and may contain several hundred seeds, each about 0.2 x 0.4 mm. A single plant carries 10-100 flowers and hence may produce over 100,000 seeds (Chater and Webb, 1972).
It is possible to determine the level of O. cernua seeds in the soil by sieving the lighter, organic matter and the portion between 0.1 and 0.5 mm studied under a dissecting microscope for the presence of the characteristically sculpted seeds. Jacobsohn and Marcus (1988) have developed a method to check for the contamination of crop seed stocks which involves washing and sieving material a number of times. The presence of Orobanche seeds can be determined on the surface of the lower sieve, with the help of a dissection microscope.
Molecular techniques have also been developed for the detection of O. cumana seeds and the results of this assay can be expressed in terms of the number of O. cumana seeds per kilogram of crop seeds and can help decisions regarding crop seed lot utilisation and commercialisation (Dongo et al., 2012).
Related invasive species
- Orobanche cernua
Related Farm Practice
- Drought
- Production
- Processing
- Breeding
- Fixation
- Hosts
- Work
O. cernua is an obligatory, non-photosynthetic root parasite which is native over a wide range across northeast Africa, southern Europe and western and southern Asia. In many of these areas it is a serious pest of Solanaceaeous crops such as Solanum lycopersicum (tomato) Nicotiana tabacum (tobacco) and S. melongena (aubergine) and occasionally S. tuberosum (potato). Species of Orobanche depend totally on their hosts for all nutrition and become an active sink for the host plant. This therefore results in a decrease in crop yield and as a result can have a major impact on the economy and livelihoods. Once established, the seed bank may last 10-20 years and there are no simple, economic control measures. Seeds of O. cernua are very small and inconspicuous and can be accidentally introduced into new areas as a contaminant of soil, seeds and machinery. There is potential for this species to invade many other areas of the world.
O. cernua does not cause very distinctive symptoms but may cause some wilting, yellowing and necrosis of the foliage and a general weakening of the plant, with reduced fruit production. Hibberd et al. (1998) have shown that the damaging effect on Nicotiana tabacum (tobacco) is proportional to the weight of the parasite, while surprisingly, the carbon fixation by the host was increased by 20%. Under drought conditions there may be more serious reduction of crop growth.
The weedy form of O. cernua (var. desertorum), with which this data sheet is primarily concerned normally parasitises Solanaceae, especially Solanum lycopersicum (tomato) Nicotiana tabacum (tobacco), S. melongena (aubergine) and occasionally S. tuberosum (potato). In very dense infestations, there can be occasional attachment of O. cernua to species of Xanthium but it is possible that this occurred after stimulation of germination by an adjacent crop. Other varieties of O. cernua are usually recorded on Asteraceae, especially species of Artemisia but are also recorded on species of Galinsoga and Senecio. Helianthus annuus (sunflower) is usually attacked by the closely related species O. cumana rather but O. cernua has been recorded on sunflower in China (Daniel M. Joel, Newe Ya'ar Research Center, Israel, personal communication, 2016). Other crops which are attacked by O. cernua locally include Olea europaea (olive) in Jordan (Qasem, 2011), species of Capsicum (pepper) in Kenya, (Mwangi, 1999), Prunus armeniaca and P. persica in Jordan (Qasem, 2009), Cuminum cyminum (cumin) and Plantago ovata in Rajasthan, India (Maharshi, 2001).
A study on the mitochondrial activity in O. cernua from different hosts recorded this species on Petunia hybrida, Solanum nigrum and Datura metel (Singh, 2007).