Estimation de la sensibilité et de la tolérance de différents génotypes de féverole (Vicia faba L. ) à la plante parasite Orobanche foetida Poiret : Impact du génotype hôte sur les particularités physiologiques et métaboliques du parasite

This work aim to evaluate some sensitivity and tolerance degrees of various faba bean genotypes to O. Foetida, to characterize mechanisms involved in resistance and finally to estimate the impact of the host genotype on the parasite sink strength which controls parasite development following attachment to the host roots. Cultures were performed under field, pot and in vitro conditions. The genotype Bachaar was used as the control of high sensitivity. Among the five tested genotypes, XBJ90. 03-16-1-1-1 was the less sensitive and the most productive under infestation in both field and pot assays. The root exudates of this genotype displayed low stimulatory activity for orobanche seed germination. Consequently, few tubercles developed on roots. The infection process of all these genotypes was followed in vitro. In comparison to Bachaar, the genotypes known as moderately resistant genotypes under field conditions limited growth of orobanche tubercles under in vitro conditions, especially the genotype XBJ90. 03-16-1-1-1. Growth of the parasite should be mediated by soluble invertase activities and restricted following attachment to XBJ90. 03-16-1-1-1 roots by the low osmotic potential of the infected roots in addition to the organic nitrogen deficiency of the host phloem sap. On the other hand, the faba bean genotype did not influence the osmoregulation process of O. Foetida. Potassium was by far the major osmotically active compound in orobanche. Among the organic solutes, hexoses were accumulated highly in the growing stems. In contrast, tubercles displayed higher contents in starch and free amino acids, mainly in asparagine and aspartate. In parallel, asparagine/aspartate, glutamine/glutamate, alanine, serine and gamma amino butyric acid were identified as the main nitrogen compounds in the host phloem exudates. The key role of the enzymes asparagine synthetase and aspartate oxaloglutarate aminotransferase in the utilization of these host-derived amino acids is proposed in O. Foetida parasitizing faba bean.