Orobanche aegyptiaca is a chlorophyll-lacking holoparasite that subsists on the roots of plants, inflicting severe damage to legumes and other crops in the Mediterranean region. Common vetch and purple vetch are important legume forage crops in Israel and the Middle East. Experiments in pots containing soil inoculated with O. aegyptiaca seeds have shown that common vetch genotypes ‘Yovel’ and ‘473-A’ are susceptible to the parasite, whereas purple vetch genotypes ‘Popany’ and ‘Sadot’ are resistant. When grown in association with O. aegyptiaca in polyethene bags, purple vetch genotypes stimulated a significantly higher rate of parasite seed germination than that stimulated by common vetch genotypes. However, the number of successful Orobanche attachments developed on the host root was lower on resistant genotypes compared to susceptible ones. This differential response between purple and common vetch genotypes was evident at diverse temperature regimes (17/12, 22/17, and 27/22 C day/night). Microscopic observations revealed that resistant genotypes rapidly developed necrotic lesions surrounding the contact point of the parasite radicle (germ tube) with the host root, hence preventing further development of the parasite. In the sensitive genotypes, attachments developed without necrotic lesions. These data may indicate involvement of host defense mechanisms induced by the parasite attachment.

Geostatistical techniques were used to describe and map the spatial distribution of crenate broomrape populations parasitizing broad bean over 6 yr (from 1985 to 1990). In the first year, the spatial distribution was random, but from 1986 to 1989, crenate broomrape populations were clearly aggregated. The crenate broomrape infection severity (IS: number of emerged broomrape m−2) increased every year, from an average of 0.45 in 1985 to 29.4 in 1989, with a slight decrease the following year (IS = 27.4). Spherical functions provided the best fit because the cross-validation criteria were accomplished in all study cases. Kriged estimates were used to draw contour maps of the populations. About 34.3, 43.3, and 74.3% of the field plot surface exhibited an IS ≥ 1 (economic threshold) in 1985, 1986, and 1987, respectively, and nearly 100% of the area exceeded the economic threshold from 1988 to 1990; 1985 and 1986 were key years for control of the parasitic weed population. The percentage of infested area at different IS intervals in each year's map obtained by kriging was used to estimate the percentage of yield losses in each infested area (YA) with the equation: YA = A ∗ Ymax ∗ (1 − IS ∗ 0.124), where A is the infested area at a given IS interval and Ymax is the expected broomrape-free broad bean yield. Yield losses under different IS intervals were compared with yield loss attributable to a uniform distribution of crenate broomrape. Results showed that yield loss assuming a uniform distribution of crenate broomrape was clearly overestimated, which is important to avoid overuse of herbicides.

Crenate broomrape is a major constraint for legume production in Mediterranean and East Asian countries. Resistance to this parasitic weed is scarce in many legumes but is common in chickpea germ plasm. A detailed in vitro study has shown that resistance in chickpea is the result of the combination of at least two mechanisms. First, and most importantly, the two chickpea lines studied have been identified with low rates of stimulant production. Once germination is induced by exogenous applications of the synthetic germination stimulant GR24, thus overcoming the primary resistance mechanism in these lines, a second resistance mechanism is apparent. This is evidenced by a darkening of host cell tissue in contact with the broomrape radicle, leading to failure of establishment, which was frequently observed in the chickpea accessions. Anatomical studies have shown that this apparently “hypersensitive” response does not correspond with the death of host cells in contact with the parasite cells but corresponds to blocking and death of the penetration structures of the parasite.