Screening of Blackgram (Vigna mungo L.) Genotypes for Salt Tolerance at the Vegetative Stage

Soil salinity is a major global challenge, affecting over 20 percent of irrigated lands and threatening food security (FAO, 2021). Factors such as unsustainable irrigation, seawater intrusion, and climate change accelerate salt buildup in soils, thereby reducing crop productivity. Salinity causes both osmotic and ionic stress, restricting water uptake and disrupting nutrient balance through toxic ions such as Na⁺ and Cl⁻ (Munns and Tester, 2008). These effects lead to stunted growth, chlorosis, premature senescence, and severe yield losses (Parihar et al., 2015). Black gram (Vigna mungo L.), an important pulse crop for protein supplement and soil fertility improvement in Southeast Asia, suffers greatly under saline conditions. In India, especially in Tamil Nadu and Andhra Pradesh, salinity arising from rice-fallow systems and poor drainage limits productivity to 450–600 kg/ha, far below its potential (ICAR, 2019; DPD, 2020). The vegetative stage is highly sensitive to salt stress, affecting canopy development and yield. Therefore, screening genotypes based on plant height, biomass, leaf area, relative water content, chlorophyll content, and survival rate is crucial for identifying tolerance (Sairam and Tyagi, 2004). Exploring genetic variability among cultivars can provide valuable sources for breeding salt-tolerant varieties (Bansal et al., 2014). Considering these aspects, the present study aims to assess the effects of salinity on black gram and to identify salt-tolerant genotypes through morphological and physiological traits at the vegetative stage, thereby contributing to breeding strategies for sustainable productivity in saline-prone regions

The experiment was conducted during the Rabi season of 2025 at the Plant Breeding and Genetics Laboratory of Nalanda College of Agriculture, Tiruchirappalli, Tamil Nadu, India, located in a semi-arid tropical zone. A Randomized Complete Block Design (RCBD) with a factorial arrangement (Genotype × Salinity level) and three replications was adopted.
Seven black gram genotypes viz., Aduthurai (ADT) 6, Killikulam (KKM) 1, VBN 6, VBN 8, VBN 10, VBN 11, and VBN 12 were evaluated under three salinity levels imposed using NaCl solutions: T₀ (0 mM, control), T₁ (50 mM), and T₂ (100 mM), representing moderate to high field salinity (Rengasamy, 2010). Salinity stress was initiated 14 days after sowing and maintained for 21 days through regular irrigation with respective saline solutions. Plants were grown in 3-litre-capacity plastic pots filled with sterilized soil: sand: FYM (2:1:1). A single healthy seedling per pot was maintained, and uniform nutrient application was ensured. The data were recorded for morphological and physiological traits viz., plant height, number of leaves, shoot and root biomass, relative water content (Barrs and Weatherley, 1962), chlorophyll content (SPAD) (Ling et al., 2011), visual injury score (Ashraf and Harris, 2004), survival percentage. All data were analyzed using a two-way ANOVA with genotype (G), salinity (S), and the G × S interaction. Mean comparisons were made using Tukey’s HSD test (p ≤ 0.05) (Gomez and Gomez, 1984).

The study evaluated seven black gram (Vigna mungo L.) genotypes, viz., ADT 6, KKM 1, VBN 6, VBN 8, VBN 10, VBN 11, and VBN 12, under 0, 50, and 100 mM NaCl to assess genotypic variation in salinity tolerance at the vegetative stage. Plant height and leaf number declined significantly with increasing salinity (Table 1 and Figure 1). At 100 mM NaCl, reductions were highest in ADT 6 and KKM 1 (55–60 percent), while VBN 8 and VBN 10 recorded moderate declines (26–28 percent). Maintenance of vegetative growth under saline conditions indicates better osmotic adjustment and reduced ion toxicity (Munns and Tester, 2008).

Table 1. Effect of salinity on the plant height of black gram genotypes under salinity stress[Ka1] 

Figure 1. Effect of salinity on the plant height of black gram genotypes

Biomass accumulation was markedly affected, with shoot and root dry weights decreasing over 60 percent in susceptible genotypes, whereas tolerant lines (VBN 8, VBN 10) retained ~65 percent of control biomass (Table 2 and Figure 2). Higher biomass retention suggests efficient water uptake and photosynthetic performance under stress (Parida and Das, 2005). RWC declined with salinity, falling below 50 percent in ADT 6 and KKM 1 but remaining around 70 percent in VBN 8 and VBN 12. High RWC reflects superior osmotic adjustment through solute accumulation and improved maintenance of hydration (Sairam and Tyagi, 2004; Ashraf and Foolad, 2007). Chlorophyll content decreased across genotypes, with tolerant ones (VBN 8, VBN 10) maintaining higher readings (34–35) than susceptible ones (20–21) (Table 3 and Figure 3). Chlorophyll stability indicates stronger antioxidant protection and sustained photosynthetic activity (Parihar et al., 2015). Visual injury and survival percentage varied widely (Table 4 and Figure 4). At 100 mM NaCl, ADT 6 and KKM 1 showed severe leaf necrosis (injury score 8) and <45 percent survival, while VBN 8 recorded an injury score of 3 and 90 percent survival. Survival percentage integrates multiple tolerance mechanisms, including ion regulation and membrane stability (Munns and James, 2003). Overall, salinity stress significantly impaired black gram growth and physiology but marked genotypic variation was evident. VBN 8 and VBN 10 consistently outperformed other genotypes across all parameters, maintaining higher plant height, biomass, RWC, chlorophyll content, and survival percentage, indicating robust tolerance mechanisms. These results align with previous findings in black gram and other legumes (Manivannan et al., 2007; Shanthi et al., 2021). Traits such as RWC, SPAD value, biomass retention, and survival percentage proved reliable, simple, and cost-effective for screening. Hence, VBN 8 and VBN 10 can serve as promising donors in breeding programs to enhance salinity tolerance in black gram.

Table 2. Shoot dry weight under salinity stress

Figure 2. Effect of Salinity on Biomass

Table 3. Relative Water Content and SPAD values at 14 days after stress

Figure 3. Relative Water Content under Salinity

Table 4. Survival percentage and visual injury score at 100 mM

Figure 4. Survival percentage of black gram genotypes under salinity

The present study clearly demonstrated that salinity stress (50 and 100 mM NaCl) significantly impaired growth, biomass accumulation, physiological stability, and survival of black gram genotypes at the vegetative stage, with significant genotype, salinity, and G × S interaction effects. Marked genetic variability was observed among the seven genotypes tested, confirming the feasibility of selecting salt-tolerant lines at early growth stages. Among them, VBN 8 and VBN 10 consistently maintained higher plant height, biomass retention, relative water content, chlorophyll content, and survival percentage with lower injury scores under 100 mM NaCl, indicating superior osmotic adjustment and stress tolerance mechanisms. In contrast, ADT 6 and KKM 1 were highly susceptible, exhibiting severe reductions in growth and physiological performance. The findings establish that traits such as RWC, SPAD value, biomass retention, and survival percentage are reliable and practical screening indices for salinity tolerance in black gram. Overall, VBN 8 and VBN 10 can serve as promising donor parents for breeding salt-tolerant cultivars suited to salt-affected regions. Future work may focus on multi-location field validation, biochemical and ionic profiling, and molecular characterization to strengthen breeding applications.

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