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Abstract

Cuscuta is a parasitic plant that is increasingly becoming an ecological and management problem especially in urban and semi-arid areas. This paper examined the environmental factors and the host physiological reactions that resulted in Cuscuta campestris infestation in Conocarpus erectus in four ecologically different areas of Punjab, Pakistan (Faisalabad, Khanewal, Toba Tek Singh and Wah Cant). Incidence measurements in the field were correlated with laboratory analyses in order to measure growth, photosynthetic pigments, osmolytes, stress markers, and antioxidant enzymes between the infested and healthy hosts. Host-parasite-environmental interactions were deciphered using statistical modelling, such as multivariate analysis, principal component analysis (PCA) and multiple linear regressions (MLR). Findings showed that site-specific climatic conditions, especially humidity and temperatures, were highly affecting the Cuscuta infestation intensity, as well as the host physiological impairment. High infestation rates, oxidative stress and high antioxidant and phenolic defenses were observed in warm and moderately humid environments (Faisalabad, Khanewal) and low parasite success and milder host responses in mild or dry cooler sites (Wah Cant, Toba Tek Singh). PCA predicted 83.7 per cent of the total variance and set the difference between the stressed infested hosts that exhibited high activity of antioxidants and osmolytes and the healthy pigment rich individuals in cool and moist regions. The interactions of humidity the most important environments predicting Cuscuta spread and host mortality and the next important factor was temperature, whereas excessive rain and low temperatures decreased the potential infestation. These data support the idea that the Cuscuta-Conocarpus interactions are controlled by the synergistic climatic controls and host metabolic adaptations. The infestation severity depended on environmental gradients which also interfere with the distribution of host defense between the resistance to growth and resistance to stress

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