Physiological and Biochemical Responses of Medicago sativa L. Infected by Cuscuta sp

This study aims to elucidate the physiological and biochemical alterations induced by parasitic Cuscuta sp. (dodder) in lucerne (Medicago sativa L.), a key forage crop. Comparative analyses between infected and healthy plants revealed that significant reductions in chlorophyll a, b, and total chlorophyll, and protein levels in the leaf and stem tissues of Cuscuta-infested plants were evident. The parasitic infection led to increased activities in antioxidant enzymes such as catalase (CAT) and peroxidase (POX) in stems, but not in leaves. Phenolic compounds were significantly lower both in leaves and stems of dodder-infected lucerne plants. No statistically significant changes were detected in jasmonic acid (JA) and salicylic acid (SA) levels in both plant parts, suggesting that classical defense signaling pathways may not be predominantly activated under Cuscuta-mediated stress. Possibly, host defense might be impaired. Histological examinations demonstrated active structural defense responses, including localized tissue remodeling and the formation of callose-like structures at haustorial penetration sites. DNA fragmentations showed that Cuscuta-infected M. sativa plants exhibited slightly higher instability. Collectively, these findings provide novel insights into the molecular and biochemical basis of the Cuscuta-lucerne interactions and highlight the need for further investigation into host defense mechanisms. We assume that active defense structural parts at early growth stages of lucerne or hypersensitive-type responses occurring in the early penetration phase might fend off the invading holoparasite. The results also offer a valuable foundation for the development of Cuscuta-resistant lucerne cultivars and support the design of integrated, sustainable weed management strategies to mitigate the detrimental effects of parasitic plants on forage production systems.