Deciphering Physio-Biochemical Basis of Tolerance Mechanism for Sesame (Sesamum indicum L.) Genotypes under Waterlogging Stress at Early Vegetative Stage

Abstract

Waterlogging represents a substantial agricultural concern, inducing harmful impacts on crop development and productivity. In the present study, 142 diverse sesame genotypes were examined during the early vegetative phase to assess their response under waterlogging conditions. Based on the severity of symptoms observed, 2 genotypes were classified as highly tolerant, 66 as moderately tolerant, 69 as susceptible, and 5 as highly susceptible. Subsequent investigation focused on four genotypes, i.e., two highly tolerant (JLT-8 and GP-70) and two highly susceptible (R-III-F6 and EC-335003). These genotypes were subjected to incremental stress periods (0 h, 24 h, 48 h, 72 h, and 96 h) to elucidate the biochemical basis of tolerance mechanisms. Each experiment was conducted as a randomized split-plot design with three replications, and the statistical significance of the treatment differences was determined using the one-way analysis of variance (ANOVA) followed by the Fisher least significant difference (LSD) test at p ≤ 0.05. The influence of waterlogging stress on morphological growth was detrimental for both tolerant and susceptible genotypes, with more severe consequences observed in the latter. Although adventitious roots were observed in both sets of genotypes above flooding levels, the tolerant genotypes exhibited a more rapid and vigorous development of these roots after 48 h of stress exposure. Tolerant genotypes displayed higher tolerance coefficients compared to susceptible genotypes. Furthermore, tolerant genotypes maintained elevated antioxidant potential, thereby minimizing oxidative stress. Conversely, susceptible genotypes exhibited higher accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde content. Photosynthetic efficiency was reduced in all genotypes after 24 h of stress treatment, with a particularly drastic reduction in susceptible genotypes compared to their tolerant counterparts. Tolerant genotypes exhibited significantly higher activities of anaerobic metabolism enzymes, enabling prolonged survival under waterlogging conditions. Increase in proline content was observed in all the genotypes indicating the cellular osmotic balance adjustments in response to stress exposure. Consequently, the robust antioxidant potential and efficient anaerobic metabolism observed in the tolerant genotypes served as key mechanisms enabling their resilience to short-term waterlogging exposure. These findings underscore the promising potential of specific sesame genotypes in enhancing crop resilience against waterlogging stress, offering valuable insights for agricultural practices and breeding programs.

Keywords: antioxidant enzymes; ethanolic fermentation; reactive oxygen species; sesame; waterlogging.

Figure 1

(i) Screening experiment set up; (ii) waterlogging stress-induced symptoms showing yellowing, browning, and wilting of leaves used as phenotypic markers for screening; (iii) phenotypic status of plants under different categories at the end of the experiment; and (iv) adventitious roots formation in tolerant and susceptible genotypes.

Figure 2

Impact of incremental waterlogging stress on the activities of (i) root length, (ii) shoot length, (iii) seedling length, and (iv) WTC (seedling length) in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 3

Impact of incremental waterlogging stress on the activities of (i) fresh root weight, (ii) fresh shoot weight, (iii) fresh seedling weight, and (iv) WTC (fresh seedling weight) in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 4

Impact of incremental waterlogging stress on the activities of (i) dry root weight, (ii) fresh dry shoot weight, (iii) dry seedling weight, and (iv) WTC (dry seedling weight) in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 5

Impact of incremental waterlogging stress on the activities of (i) superoxide dismutase (SOD), (ii) peroxidase (POX), and (iii) Catalase (CAT) in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 6

Impact of incremental waterlogging stress on the activities of ascorbate–glutathione cycle enzymes in tolerant and susceptible sesame genotypes: (i) ascorbate peroxidase (APX); (ii) monodehydroascorbate reductase (MDHAR); (iii) dehydroascorbate reductase (DHAR); and (iv) Glutathione reductase (GR). Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 7

Impact of incremental waterlogging stress on the content of non-enzymatic antioxidants of the ascorbate–glutathione cycle in tolerant and susceptible sesame genotypes: (i) ascorbate (AsA); (ii) dehydroascorbate (DHA); (iii) ratio AsA/DHA (DHAR); (iv) reduced glutathione (GSH); (v) oxidized glutathione (GSSG); and (vi) ratio GSH/GSSG. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 8

Impact of incremental waterlogging stress on the (i) H₂O₂ and (ii) MDA equivalent TBARS content in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 9

Impact of incremental waterlogging stress on the chlorophyll content in tolerant and susceptible sesame genotypes: (i) Chl a; (ii) Chl b; (iii) Total Chl; and (iv) Chl a/b ratio. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 10

Impact of incremental waterlogging stress on the proline content in tolerant and susceptible sesame genotypes. Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 11

Impact of incremental waterlogging stress on the activities of anaerobic metabolism enzymes in tolerant and susceptible sesame genotypes: (i) alcohol dehydrogenase (ADH); (ii) aldehyde dehydrogenase (ALDH); and (iii) pyruvate decarboxylase (PDC). Values are mean ± SD of three replicates. Different letters depict significant differences between the genotypes at p ≤ 0.05 (Fisher LSD test).

Figure 12

Biplot of different characters of sesame genotypes under control conditions.

Figure 13

Biplot of different characters of sesame genotypes under waterlogging stress conditions.