Effect of Salinity on Seed Germination and Seedling Development of Soybean Genotypes
Ourania I Pavli*, Chrysanthi Foti, Georgia Skoufogianni, Georgia Karastergiou, Asimo Panagou and Ebrahim M Khah
Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Greece
Submission: February 08, 2021;Published: March 01, 2021
*Corresponding author: Ourania I Pavli, Department of Agriculture, Crop Production and Rural Environment, School of Agricultural Sciences, University of Thessaly, Volos, Greece
How to cite this article: Pavli OI, Foti C, Skoufogianni G, Karastergiou G, Panagou A, et al. Effect of Salinity on Seed Germination and Seedling Development of Soybean Genotypes. Int J Environ Sci Nat Res. 2021; 27(2): 556210. DOI:10.19080/IJESNR.2021.27.556210
Abstract
Soybean is one of the most important staple legume crops worldwide due to its high protein and oil content as well as its nitrogen fixing ability. Soybean is classified as moderate salt sensitive crop, with salinity causing adverse effects on all developmental stages, including seed germination and post-germinative growth. This study aimed at determining seed germination and seedling growth potential under salt stress conditions as a short-cut approach to identify salt tolerant genotypes at early growth stages. To this direction, nine commercial and pre-commercial varieties, whose adaptation to increased soil salinity is unknown, were imposed to salt stress using solutions differing in NaCl concentration (50, 100, 200mM NaCl), while non-stressed plants served as controls. Evaluation of tolerance was performed on the basis of germination percentage, seed water absorbance, seedling water content, root and shoot length and number of seedlings with abnormal phenotype. Overall findings revealed that stress substantially affects all traits associated to seed germination and seedling growth, with the effects being analogous to the stress level applied, yet genotypes exhibited varying response to increased salinity. Overall data suggest that seed germination and seedling growth potential may be readily employed to reveal genetic variability related to salt tolerance in soybean germplasm. Such screening approach may serve for selecting suitable germplasm material at early growth stages, thus upgrading all relevant breeding procedures.
Keywords: Abiotic stress; Early selection; NaCl-induced salt stress; Salt tolerance; Screening method; Screening criteria
Introduction
Soybean (Glycine max L.) is among the most important legume crops, providing considerable amounts of protein and oil for human consumption, while improving soil properties through establishment of symbiotic associations with N-fixing bacteria. Its cultivation, however, is often restricted by the crop’s high input demands and the fact that the achievement of its yield potential is subjected to optimum agroclimatic conditions. Such limitations are further strengthened by the gradual reduction of available natural resources and degradation of agricultural land worldwide [1]. In view of the obvious need to conform with the criteria posed by sustainable agriculture, requiring the reduction of inputs, the development of soybean varieties with genetic resistance and yield stability under suboptimal agroclimatic conditions is the most efficient and cost-effective strategy to address an economic crop viability.
Abiotic stresses pose serious constraints to agricultural crop production worldwide, with salinity viewed as one of the most important both in terms of effects on plant growth and crop productivity [2]. The adverse effects of salinity primarily reflect the result of an extremely reduced osmotic potential and ion toxicity around the rhizosphere, leading to inhibition of water uptake by hairy roots and increased uptake of sodium (Na+) and chloride (Cl−) ions by plant cells, ultimately evidenced as ion imbalance and secondary oxidative stress [3-6]. Consequently, salinity stress hampers plant growth and development by altering essential metabolic processes such as CO2 assimilation, protein and oil synthesis [7,8]. It is worth noting however, that plant species vary tremendously in their ability to cope with salinity stress, with soybean being classified as moderately salt sensitive crop [9] with a salinity threshold of 5.0dS/m [10-12].
Routinely, crops’ response to salinity stress is estimated on the basis of yield potential under salinity stress, while the emphasis is placed on determining the yield penalties attributed to soil salinity. Such an approach is rather laborious, time-consuming and often ineffective, mainly due to the complex genetic nature of salt tolerance traits as well as the limitations arising from obtaining homogeneous stress conditions in field trials. As an alternative, it has been proposed that salt tolerance at early growth stages is a heritable trait which, at the same time, provides an accurate estimation of growth and yield potential under salt conditions [13]. Recent studies underline that salinity stress during germination and early growth crucially affect crop growth [14], while inhibition and/or delay of seed germination and seedling growth due to salt stress is correlated with decreased yield in soybean [15-18]. In this context, this study aimed at determining seed germination and seedling growth potential under salinity stress conditions as a short-cut approach to identify salt tolerant soybean genotypes at early growth stages.
Material and Methods
Plant material
The genetic material consisted of nine commercial and precommercial soybean varieties, whose adaptation to increased soil salinity is not clarified. The germplasm under study included the varieties: PR92B63, PR92M35, PR92M22, PR91M10, ZORA, NEOPLANTA, P21T45, CELINA and ADONAI.
rowth conditions and experimental design
Seeds were initially surface-sterilized in 20% hypochlorite/ dH2O solution, containing Tween-20, while gently mixing for 5min, and washed (4x) with sterile dH2O. Sterilized seeds were allowed to germinate in plastic trays containing solutions differing in NaCl concentration: i) 0mM NaCl, ii) 50mM NaCl, iii) 100mM NaCl and iv) 200mM NaCl. Plants grown in distilled H2O (0mM NaCl) were included as controls. Plants were grown under controlled conditions (25˚C, 16h light/8h dark) for a period of 20 days.
The experimental layout was that of a completely random design with four replications, each consisting of 30 seeds. The experimental plots consisted of four rows, of which the two middle provided the material for the measurements.
Measurements
Variety performance was assessed on the basis of seed germination and seedling growth potential under salinity stress conditions. As evaluation criteria served the following parameters: germination percentage, seed water uptake, seedling water content, root and shoot length and number of seedlings with abnormal phenotype. All measurements were conducted when the radicle had a length of at least 2mm.
Germination Percentage (GP %) was estimated at five time intervals (3rd-7th day), according to the formula GP = seeds germinated / total seeds x 100. Seed water absorbance (WU%) was calculated at 5th and 7th day, following the formula WU (%) = (W2 - W1) / W1 × 100, where W1 = initial seed weight and W2 = seed weight after water absorbance [19]. Seedling water content (WC %) was determined at 7th and 12th day, according to the formula WC (%) = (FW-DW / FW) x 100, where FW = fresh weight and DW = dry weight [20]. Measurements for shoot and root length (cm) were conducted at 5th, 8th, 11th and 15th day. The number of seedlings with abnormal genotype, mainly referring to sprouts with spiral hypocotyl and dwarf primary root [21], was recorded throughout the period of observations.
For estimation of WU, the weight of twenty seeds (five per replication) was taken into account, while for shoot and root length as well as for FW and DW twenty seedlings (five from each replication) were used. DW was determined following incubation at 70 oC, for 48 hours.
Statistical analysis
Data were analyzed by ANOVA according to the experimental design. The performance of genotypes was comparatively assessed within stress levels but also across stress levels, while the effect of salinity stress was comparatively assessed across genotypes. Differences between pair of means were assessed using the Student’s LSD test (p ≤ 0.05). All statistical analyses were performed using JMP software v.8 (SAS, Cary, NC, USA).
Results
Overall findings revealed that all traits related to germination and seedling growth were severely affected by salt stress, with the effects of stress gradually intensifying as salt concentration increased. It is worth noting however, that genotypes under study exhibited varying response to increased salinity.
Although germination potential was significantly affected at all stress levels in the entire set of genotypes, the reduction was in general analogous to the stress level applied (Table 1, Figure 1). The onset of germination was at the 3rd day and was accompanied by significant variation both at treatment and genotype level. In the absence of stress, the higher GP was noted in varieties Neoplanta and Adonai, followed by PR92M22, Celina and Zora. At this time point, PR92B63, PR92M35, PR91M10 and P21T45 showed very low or zero GP values. Upon stress, a gradual decrease in GP was observed as NaCl concentration increased, thus leading to most profound decrease at 200mM NaCl. At all stress levels, varieties Neoplanta and Adonai presented the highest values for GP. Although initially (3rd day) presented a significant decrease both at 100 and 200mM NaCl, from the 4th day onwards Neoplanta and Adonai maintained a relatively high GP, yet even these varieties exhibited a significant decrease in GP at 200 mM NaCl. In contrast, varieties PR92M22, Celina and Zora performed satisfactorily at 50mM NaCl but showed a drastic decrease in GP at 100 and 200mM NaCl. On the other hand, varieties PR92B63, PR92M35, PR91M10 and P21T45 presented low values for GP both under control and stress conditions. Collectively, Neoplanta and Adonai appeared as the most tolerant varieties, with their superiority being evidenced both by their mean response across stress levels and their final GP (Neoplanta: GP=75% (50mM and 100mM) and 45% (200mM), Adonai: GP=69,17% (50mM), 64,17% (100 mM) and 27,50% (200mM) at the 7th day). Neoplanta’s ability to retain a high GP even at 200 mM NaCl, during the entire period of observation, is indicative of its potential to cope with severe salt stress conditions.
* At each time interval (days), values followed by the same letter, within each factor, are not significantly different according to LSD (P ≤ 0.05).
references
- Small C, Nicholls R (2003) A Global Analysis of Human Settlement in Coastal Zones. Journal of Coastal Research 19(3): 584-599.
- Nicholls RJ, Hanson S, Herweijer C, Patmore N, Hallegatte S, et al. (2008) Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes: Exposure Estimates. OECD Environment Directorate, Working Papers.
- Nicholls R (2002) Analysis of global impacts of sea-level rise: A case study of flooding. Physics and Chemistry of the Earth, Parts A/B/C 27(32-34): 1455-1466.
- Wolman A (1965) The metabolism of cities. Scientific American 213(3): e179-e
- Pash HS, Ebadi T, Pourahmadi A, Parhizkar Y (2017) Analysis of Most Important Indices in Environmental Impacts Assessment of Ports. Civil Engineering Journal 3(10).
- Konstantzos GE, Saharidis GKD, Loizidou M (2017) Development of a model for assessing Greenhouse Gas (GHG) emissions from terminal and drayage operations. Operational Research 17: 807-819.
- Chen J, Huang T, Xie X, Lee PTW, Hua C (2019) Constructing governance framework of a green and smartport. Journal of Marine Science and Engineering 7(4): 83.
- Kabisch N, Frantzeskaki N, Pauleit S, Naumann S, Davis M, et al. (2016) Nature-based solutions to climate change mitigation and adaptation in urban areas: Perspectives on indicators, knowledge gaps, barriers, and opportunities for action. Ecology and Society 21(2): 39.
- ESPO – European Sea Ports Organisation (2020) Environmental Report 2020.
- Wilmsmeier G (2020) Climate change adaptation and mitigation in ports: Advances in Colombiain. In: Ng AKY, Monios J, Jiang C (Eds.), Maritime Transport and Regional Sustainability, Elsevier, pp. 133-150.
- Serre D, Barroca B, Balsells M, Becue V (2018) Contributing to Urban Resilience to Floods with Neighbourhood Design: The Case of Am Sandtorkai/Dalmannkai in Hamburg. Journal of Flood Risk Management 11(S1): 69-83.
- Gonzva M, Barroca B, Gautier PE, Diab Y (2017) Modeling disruptions causing domino effects in urban guided transport systems faced by flood hazards. Natural Hazards 86: 183-201.
- Clemente María Á, Yubero E, Galindo N, Crespo J, Nicolás J, et al. (2021) Quantification of the impact of port activities on PM10 levels at the port-city boundary of a Mediterranean city. Journal of Environmental Management 281: 111842.
- Yang Z, Ng AKY, Lee PTW, Wang T, Qu Z, et al. (2018) Risk and cost evaluation of port adaptation measures to climate change impacts. Transportation Research Part D: Transport and Environment 61(Part B): 444-458.
- Demuzere M, Orru K, Heidrich O, Olazabal E, Geneletti D, et al. (2014) Mitigating and adapting to climate change: Multi-functional and multi-scale assessment of green urban infrastructure. Journal of Environmental Management 146: 107-115.
- Lee ACK, Maheswaran R (2011) The health benefits of urban green spaces: a review of the evidence. Journal of Public Health 33(2): 212-222.
- Port de Alicante (2019) Reports.
- Aregall MG, Bergqvist R (2019) Port green hinterland initiatives for a more sustainable port-city interaction: The case study of Barcelona. Maritime Transport and Regional Sustainability, pp. 109-132.
- Port de Barcelona (2020) Atmospheric environment.