Comparison of different priming methods of pumpkin (Cucurbita pepo) seeds in the early stages of growth in saline and sodic soils under irrigation with different water qualities
Introduction
Soil salinity in at least 20% of agricultural land will be a global problem and a serious threat to the human food supply in the coming years (Mukhopadhyay et al., 2021). Soils affected by salt are classified into three groups: saline, sodic and saline-sodic soils, but often the response to saline and sodic conditions is not differentiated enough and this can lead to inappropriate conclusions (Bui, 2017).
In saline soils, stress mostly occurs through osmotic stress, and in sodic soils through specific ion toxicity effects (Bui, 2017). In saline soils, a large amount of soluble salt reduces the osmotic potential of soil water and makes it difficult for seeds and seedlings to absorb water and nutrients (Singh, 2022). In sodic soils, a large amount of sodium, boron, and molybdenum ions causes toxicity to the seed embryo and disturbs the physiological processes of the seed and seedling (Kumar et al., 2022). Osmotic stress and ion toxicity cause oxidative stress and disrupt the physiological, molecular, and biochemical processes of the plant (Dos Santos et al., 2022).
Plants show different mechanisms to cope with ion toxicity in sodium-affected soils. In the pumpkin plant, sodium ion (Na+) accumulates more in the root and leaf veins, and as a result, the concentration of sodium ion (Na+) decreases in the leaf mesophyll cells, which is accompanied by an increase in potassium ion (K+) accumulation in the leaf mesophyll cells (Niu et al., 2018, 2017). This justifies the stability of the ratio of potassium to sodium (K+/Na+) in pumpkin seedlings with increasing salinity stress in the experiment of Kurum et al. (2013).
Plants show different mechanisms to deal with osmotic stress in soils affected by dissolved salts, the most important of which is an osmotic adjustment, which maintains cell turgor, and cell membrane stability prevents electrolytes from leaking out of the cell and improves stomatal conductance (Dourado et al., 2022). Osmotic adjustment occurs through the accumulation of organic osmolytes such as amino acids and soluble sugars as well as inorganic osmolytes such as nontoxic ions (calcium and potassium), which requires the expression of genes related to the activation of enzymes (amylases, proteases, and enzymes controlling ion pumps of cell membranes) and calcium signaling (Ghosh et al., 2021).
In salt-containing soils, osmotic stress and ionic toxicity of the soil are reduced by mechanisms such as osmotic regulation and maintenance of ionic balance in the soil. However, oxidative stress causes damage to the physiological, molecular, and biochemical processes of cells through the destruction of DNA, lipids, and protein structure, which will ultimately lead to a decrease in yield (Kerchev and Van Breusegem, 2022).
To reduce the effects of stress in salt-containing soils, low-cost and environmentally friendly methods such as seed priming have been the subject of much research in recent years (Johnson and Puthur, 2021). Seed priming is the exposure of seeds to a stimulus before germination that prepares plants for future stresses. Priming creates a defense to reduce the consequences of osmotic stress, ionic toxicity, oxidative stress, and the resulting injuries on plant growth and yield under salinity conditions (Zulfiqar, 2021). The mechanism of action of priming is to strengthen and facilitate the plant's natural defense systems, such as increasing the amount of cell soluble compounds (osmolytes), activating the enzymatic and non-enzymatic antioxidant system, as well as maintaining ion balance (Johnson and Puthur, 2021).
The noteworthy point is that reports show that the effect of priming on salinity tolerance in plants is highly dependent on the type of soil affected by salt (saline, sodic and saline-sodic). For example, osmopriming of corn seeds with zinc sulfate in saline and saline-sodic soils has increased the weight of aerial parts by 38 and 69% and the weight of roots by 22 and 48%, respectively, which indicates the greater usefulness of priming in saline-sodic soil compared to saline soil (Basit et al., 2020). While corn seed bio priming with Pseudomonas bacteria in saline soil has been more beneficial compared to saline-sodic soil (Singh et al., 2020).
Despite the numerous reports on the usefulness of priming for different crops under salinity stress conditions, little research has been done to compare the effectiveness of different priming methods and techniques to increase stress tolerance in salt-containing soils in Cucurbitaceae family plants.
The purpose of this study is to evaluate the effectiveness of different priming methods including hydro priming, osmo priming (halo priming), nano priming, hormone priming, and biopriming with microorganisms and plant extracts, and chemo priming to deal with osmotic stress and ionic toxicity on pumpkin plants in salt-containing soils. On the other hand, to compare different priming methods, molecular, biochemical, and physiological processes of the pumpkin plant under salinity stress and priming have been investigated. The behavior of the plant in saline and sodic soils are different and often the results related to salinity tolerance are not separated in different types of soil. This issue leads to confusing results, in this research, the effect of priming on salinity tolerance in pumpkin plants after sowing in different soils affected by salt is investigated separately.
Section snippets
Experimental design & treatments
This experiment was conducted in Golpayegan-Iran (33°45´67ʺ N, 50°28´87ʺ E, altitude 1814 m) in two separate 250 square–meter tunnel greenhouses (25 × 10), which have been used for planting various types of summer plants in previous years. Two greenhouses were 12 km apart, the soil of one greenhouse was sodic (SSO) and the other was saline (SSA). The complete soil characteristics of the two greenhouses are presented in Table 1. The greenhouses were covered with UV plastic (SunView™ 4 Mil Clear
Ionic adjustment
In saline soil (Ssa) irrigated with non-saline-sodic water (Wnss), the hydropriming treatment was superior only in terms of sodium reduction compared to the control (Table 2). But other priming methods compared to both the control and hydropriming treatments reduced sodium and increased potassium, potassium/sodium, and calcium, except for nanopriming, which did not decrease sodium compared to hydropriming as well as it did not increase potassium/sodium compared to control and hydropriming (
Hydro priming
Hydropriming is a cheap, simple, and environmentally friendly method to reduce the effect of osmotic stress and ion toxicity in saline and sodic soils. Hydropriming by increasing aquaporin gene expression improves water absorption by seeds and upregulates DNA repair and antioxidant genes (Matsunami et al., 2022; Forti et al., 2020). Hydropriming treatment did not increase the dry matter as well as gas exchange parameters in any of the water-soil conditions compared to the control (Table 2).
Conclusions
Research on the effect of different priming methods on salty soils usually leads to inappropriate recommendations, regardless of whether the soil is sodic or saline, which is considered in this research. Our results show that osmopriming as a cheap and regular method can be effective for saline soils that are irrigated with non-saline, non-sodic water, while hydropriming was not effective in these conditions. In both saline and sodic soil, chemopriming and nanopriming methods were the superior
CRediT authorship contribution statement
Ahad Madani: Conceptualization, Methodology, Writing – original draft. Mojtaba Hassanzadehdelouei: Conceptualization, Data curation, Formal analysis, Writing – review & editing. Ahlem Zrig: Writing – review & editing, Writing – original draft. Sami Ul-Allah: Conceptualization, Writing – original draft, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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