A comprehensive analysis of morphological and biochemical parameters of <i>Medicago sativa</i> during biotic stress

Background: Parasitism is an abiotic stress that significantly threatens plant growth and severely impacts crop productivity. Plants have developed complicated regulatory mechanisms to cope with stressful conditions, undergoing morphological and biochemical changes. Objective: The article presents the first comprehensive analysis of the Medicago sativa response to the penetration of flowering parasites Orobanche lutea and Cuscuta alba. The outcome of this study aim to enhance crop quality comprehend their bioactive properties and pinpoint optimal strategies for their utilization in preventing and treating human and animal health issues. Methods: Medicago sativa, Orobanche lutea and Cuscuta alba were collected in the Ararat province, located in southeastern Armenia. The plants’ morphological structures and leaf parameters were observed. The prooxidant activity was determined by the potentiometric method. The content of total phenols, flavonoids and catechins were determined by a spectrophotometric method. Pigments were separated and identified using thin layer chromatography and a spectrophotometric method. Results: The in-situ observations of M. sativa plant and ex-situ measurements of its leaves infected by O. lutea and C. alba reveal a significant negative impact on both the reproductive success and the vegetative aspects. Infected plants exhibited minimal inflorescence development, also, substantial reductions in leaf dimensions were observed. The analysis of prooxidant activity revealed that M. sativa exhibits inherent prooxidant properties, which are amplified in the presence of parasites. The influence of dodder on prooxidant activity is much more significant (14-38%) than that of broomrape (8-42%). The percentage changes in total phenolic content were more pronounced in the presence of C. alba, but flavonoid decline was more pronounced in the presence of O. lutea, suggesting a differential impact of the two parasites. Although catechin content was not affected, photosynthetic pigments of the host plant were significantly (28-57%) reduced by the parasites. Conclusion: Findings indicate a clear morphological alteration induced by parasitic infestation. The parasites, particularly O. lutea can cause temporal isolation and allochronic speciation in M. sativa populations. Biochemical analysis highlighted a complex interplay between the host and the parasite. The biochemical impact of the parasite is reflected on the host’s primary and secondary metabolism. The observed morphological and biochemical changes highlight the need for further research to explore potential mitigation strategies, selective herbicide development, and biocontrol measures against parasitic plant infestations in agricultural ecosystems. Keywords: alfalfa; Orobanche lutea; Cuscuta alba; parasites plants; morphophysiological observations; bioactivity.