Interactive effects of Orobanche latisquama parasitism and drought stress in Salvia rosmarinus plants growing under Mediterranean field conditions.

Mediterranean-type ecosystems are recognized as critical hotspots for both biodiversity and climate change. Within these environments, plants often interact with diverse species, including holoparasitic plants, while simultaneously facing increasing episodes of precipitation shortages and rising temperatures. Here, we investigated the impact of Orobanche latisquama Reut. ex Boiss infestation on the Mediterranean shrub Salvia rosmarinus (L.) Spenn (rosemary) across three populations along an altitudinal gradient, focusing on its effects on host tolerance and resilience to severe summer drought in its natural habitat. Results showed no major physiological impact of the parasite on the host during spring but revealed an enhanced photo- and antioxidant-protective response during the summer drought in rosemary plants infested with O. latisquama. Infested plants showed elevated contents of α-tocopherol and a shift in the ascorbate ratio towards its oxidized state during the summer, particularly in upper and sun-exposed leaves. This was accompanied by elevated malondialdehyde content, indicating enhanced lipid peroxidation. However, despite the heightened photo-oxidative stress observed in leaves from infested plants, no damage to photosystem II was observed, indicating a good tolerance of rosemary to the interaction between parasitism and drought. By autumn, all plants displayed similar recovery patterns, and the differences between infested and non-infested plants disappeared, thus indicating a high resilience to the combination of these biotic and abiotic stresses. Overall, these findings underscore the great adaptive mechanisms S. rosmarinus plants have evolved to endure severe summer drought, even when challenged by holoparasitic plant infestation, and provide new insights into plant-parasite interactions in Mediterranean-type ecosystems.