Evaluation of the Resistance of Bitter Cucumber (<i>Momordica charantia</i>) to Saline Stress through Physical, Biochemical, and Physiological Analysis

<i>Momordica charantia</i> is a climbing plant often used in traditional medicine to treat a large number of diseases, including diabetes. Salinity is one of the main stressors faced by plants, affecting almost half of irrigated agricultural land and constantly increasing. The aim of this study was to determine the resistance of some bitter cucumber genotypes to salt stress by means of dry matter analysis, chlorophyll <i>a</i>, chlorophyll <i>b</i>, malondialdehyde content, chlorophyll fluorescence, and potassium (K)/silicon (Si) and calcium (Ca)/silicon (Si) atomic ratios. Two varieties of bitter cucumber and three experimental lines were used for the experiment. Treatments with different saline solutions (100 mM of NaCl and 200 mM of NaCl) were applied and compared with an untreated control (0 mM of NaCl). The analyses revealed an increase in the dry matter content of the varieties subjected to salt stress. The Line 4 genotype showed an increase of up to 37.2% compared to the control when treated with 200 mM of NaCl. Following the analysis of the chlorophyll a content, a 38% decrease in its amount compared to the control was observed when treated with 100 mM of saline and 58.6% when treated with 200 mM of NaCl in genotype Line 4. Line 3 showed an increase in the chlorophyll a content compared to the control by 53% in the case of saline treatment with 200 mM. After the analysis of the chlorophyll b content, a 44% decrease was revealed in the case of Line 4 in the variant treated with 100 mM compared to the control and a 61% decrease in the 200 mM NaCl treatment. The highest increase in the concentration of malondialdehyde was recorded in the case of Line 4 in the variant treated with 200 mM of NaCl by 41% compared to the control. The maximum quantum yield of PS II decreased in the treated variants compared to the control plants. The most pronounced difference compared to the control was registered in the case of Line 4, where the treatment with 100 mM of NaCl caused a decrease of 16%, and the treatment with 200 mM caused a decrease of 25%. In the case of the atomic ratio, significant decreases in K and Ca were observed in the NaCl-treated variants. The observed differences between the values obtained for each studied genotype highlight the different degrees of their resistance to salinity.