Evaluation of biochemical and molecular response of onion breeding lines to drought and salt stresses

•Response of onion breeding lines to abiotic stresses.•Biochemical functioning of onion to cope with stress conditions.•Role of antioxidant enzymes to alleviate reactive oxygen species.•Transcript changes in onion with the acclimatization to salt and drought stress. Onion is the most important crop in the Alliaceae family which is diversely used all over the world. Türkiye is the 5th largest onion producer with the production of 2.24 million tons, but onion production is under threat due to climatic changes especially in the Anatolia region. Therefore, in the present study, six onion breeding lines were investigated to quantify the biochemical and gene expressional changes under drought and salt stresses. Plants were divided into control, salt stress, and drought stress to apply stress treatment under semi-controlled greenhouse conditions. Current study showed that salt stress restricted the uptake of minerals from the soil. Study also revealed that under both stresses the chlorophyll a and b contents were stable in K41, U47 and U49 breeding lines. Moreover, gene expression for stress related genes showed that K41 and U47 breeding lines showed tolerance to drought and salt stress by adequately regulating their SOD, CAT, AOX, WRKY70 and NAC29 gene expressions, moreover highest antioxidant enzymatic activity was also observed in these breeding lines under drought and salt stress. The H2O2 concentration was highest in the sensitive breeding lines suggesting the sensitivity to both stresses. PCA analysis revealed that breeding lines K41, U47 and U49 showed tolerance to both stresses. These results can further used to understand onion stress tolerance mechanism and it may enable onion breeders for the development of abiotic stress resilient onion cultivars.