Morphological, physiological, and biochemical responses of onion (Allium cepa L.) breeding lines to single and combined salt and drought stresses

Abiotic stresses deteriorate plant growth resulting in devastating yield losses. Salt stress solely cause ionic toxicity and disturbed homeostasis, whereas combined salt and drought stress has more pronounced effects on plants. This study aimed to screen 32 Turkish onion breeding lines and commercial cultivars based on their morpho-physiological and biochemical responses after exposure to drought, salt, and salt + drought stresses at the bulbification stage under greenhouse conditions. Physiological characteristics, such as gaseous exchange traits, chlorophyll index, leaf temperature, and morphological traits including the number of leaves, length, and diameter of leaf were measured during stress treatment, and yield response of the onions was quantified by measuring bulb length, bulb diameter, and bulb weight after harvest. Proline and malondialdehyde accumulation was estimated for the biochemical effect of stress on onion genotypes. All genotypes responded differentially to the applied single and combined stresses. Overall results revealed that in the breeding lines K25, U6, U17 and commercial cultivar K58, the bulb weight (41.71-47.93 g) was significantly (p <= 0.05) lower, therefore they were grouped as sensitive across all stresses; whereas in the breeding lines K41, U47, U49 and commercial cultivar K52, the bulb weight (96.75-106.31 g) was significantly (p <= 0.05) higher among all the tested breeding lines and commercial cultivars and therefore found to be the most stable upon stress. These resilient genotypes can be used as breeding material for future abiotic stress studies.