The unsuccessful penetration of O. crenata seedlings into legume roots cannot be attributed to cell death in the host. It seems to be associated with lignification of host endodermis and pericycle cells at the penetration site. The accumulation of secretions at the infection site, may lead to the activation of xylem occlusion, another defence mechanism, which may cause further necrosis of established tubercles.

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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.

The effects of various temperature regimes in the range 29-17/21-9 degrees C day/night on each stage of the parasitism process of Orobanche cumana and O. aegyptiaca on sunflower were studied under controlled conditions in polyethylene bags. The response of the resistant sunflower variety 'Ambar' was expressed as the degeneration of the parasite tissues after its establishment in the plant roots, and this stage was found to be temperature dependent. The degeneration rate of Orobanche tubercles in the resistant sunflower variety was also found to be temperature dependent and was about five times as great as that in the sensitive variety in the highest temperature regime tested of 29/21 degrees C day/night. The ability to reject the parasite by causing its degeneration and death is the main factor that determines the resistance. As the temperature rises, more tubercles degenerate and die, that is the sunflower plant expresses higher levels of resistance.