Discerning morpho-physiological and quality traits contributing to salinity tolerance acquisition in sorghum [Sorghum bicolor (L.) Moench]

Abstract

Soil salinization has become a major constraint affecting crop production worldwide. Salinity induces complex metabolic processes that involves ion toxicity, osmotic stress, biochemical and physiological perturbations. Sorghum is a gluten-free cereal crop, well adapted to semi-arid tropics, highly biomass productive and water-efficient. Sorghum crop's growing is an efficient way to utilize saline soils. Therefore, the present study aimed to assess the tolerance behavior of sorghum genotypes under different salinity levels (60, 80, 100, 120, 140 mM NaCl) concerning the performance of physiological, biochemical, and quality traits. Amongst 23 screened sorghum genotypes and 300 lines of sorghum germplasm, SSG59–3 was identified as salt-tolerant and PC-5 as salt susceptible genotype based on germination studies. The photochemical quantum yield (PC-5: 39.1% and SSG59–3: 12.7% reduction), chlorophyll content (SPAD units), relative water content and chlorophyll stability index (PC-5: 65.3% and SSG59–3: 54.9%) were significantly higher in SSG59–3 (SSG59–3 was identified as salt tolerant). Similarly, significant percent reductions in plant height (SSG59–3: 76%, PC-5: 86%), fresh and dry weight were observed with increasing salinity levels from 60 to 140 mM NaCl. Total phenols and soluble sugars (SSG59–3: 62.5%, PC-5: 46.7%) exhibited an upward trend, while flavanoids and flavanols showed a reverse trend. Salinity also affected the nutritive value of sorghum adversely, but the effect was less pronounced in SSG59–3. Quality traits viz. crude protein (SSG59–3: 5.16% and PC-5: 3.22%) and in-vitro dry matter digestibility reduced with increasing salinity levels from 60 to 140 mM NaCl. Reversibly, HCN content increased with every increment of salt stress, from 121.12–133.55 μg/g but were under the threshold level. Based on the above results, it was concluded that SSG59–3 performed better by retaining higher plant water status, photosynthetic rate and phenolic compounds, thereby alleviating stress, which may be utilized as genetic resource to establish sorghum cultivars with improved quality in saline soils.