Wild mustard is one of the common and troublesome winter weeds of chickpea fields and a great competitor to reduce the chickpea productivity. Plant species (chickpeas cv. Saral and wild mustard) were compared at freezing temperatures (+4 as a control, 0, −4, −8, −12, −16, and −20°C) based on the morphophysiological traits and their recovery ability. Chickpea chlorophyll fluorescence was more sensitive to low temperatures than wild mustard. Chickpea and wild mustard Fv′/Fm′ (light-adapted maximum efficiency of photosystem II [PSII] photochemistry) decrease 33% and 11% exposed to −16°C, respectively, compared with +4°C. Particularly at lower temperatures, wild mustard electrolyte leakage was smaller than that of chickpea; the temperature drop had a greater impact on the stems than the leaves. Per temperature degree drop from −12 to −20°C, the survival probability decreased by 12.5%. Wild mustard had a greater root dry matter (RDM) compared with chickpea plants. 50% dry matter depression temperature (RDMT50) could better distinguish among the species freezing response; wild mustard RDMT50 was ~1°C higher than chickpea. Plant survival and Fv′/Fm′ correlation suggested the reliability of chlorophyll fluorescence measurements to assay plants freezing tolerance. The important contribution of a more powerful root system to wild mustard survival under adverse circumstances may be suggested by the positive association between plant survival and RDM. Higher tolerance of wild mustard to freezing stress ultimately leads to greater survival, regeneration, continued growth, and geographical distribution. Therefore, the wild mustard invasion will be possible in chickpea fields after freezing stress, especially in the cold climates and high-altitude regions.

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