Salinity and heavy metals in soil are dreadful hazards causing reduction in plant growth, development and yield values. Therefore a medicinal cucurbit weed Citrullus colocynthis L. was given exposure to a series of salt (NaCl), heavy metal (NiCl₂) and combined (NaCl and NiCl₂) levels prepared in Hoagland's solution. Germination and other growth parameters were promoted in low concentrations of NaCl (100mM), NiCl₂ (50 µM) and combined (100mM NaCl and 50 µM NiCl₂) while inhibited under separate and combined high level stresses 400mM NaCl, 200µM NiCl₂ and combined 400 mM NaCl and 200µM NiCl₂. Moderate levels (200mM of NaCl and 100µM of NiCl₂) slightly promoted growth parameters in all separate and combined treatments. In combined stresses, low salt concentration (100mM NaCl) mitigated the adverse effects of high level of heavy metal (200µM NiCl₂) and low heavy metal (50µM NiCl₂) also ameliorated the high salt complications (400mM NaCl). Variable results in morpho-physiological parameters were observed in the combined effect of salt and heavy metal. Growth parameters like length of shoot, root, fresh and dry weight, number of leaves, branches, flowers, leaf area index, total yield, rate of photosynthesis, chlorophylls, Ca²⁺, K⁺ and proteins were affected adversely with increasing stresses while some factors like free amino acids, free sugars, proline, antioxidants like superoxide dismutase and catalase, Na⁺ and Cl^- increased with increasing stress levels. It is concluded that Citrullus colocynth produces adaptive chemicals when exposed to salt and nickel stresses and can tolerate low and moderate levels of salt and nickel.

Index-terms; Salinity stress, , Combined stress, Citrullus, NaCl Stress, Nickel (NiCl₂ ) Stress,