Standardization of pre-sowing treatments for enhanced seed germination and seedling growth in Prunus dulcis

Introduction

Almonds are members of the Rosaceae family, which includes roses. They belong to either the Amygdaloideae or Prunoideae sub-family. Since almonds belong to its own family (Prunaceae or Amygdalaceae), it is believed that prunus evolved from the Spiraeoidae subfamily (Bargah et al.,2024) [4] . Almond is a tiny deciduous tree with a trunk that is around 30 cm in diameter and a height of 4 to 10 meters (Netam et al., 2025) [32] . The immature twigs are initially green, but they turn purple when exposed to light. The leaves are three to five inches long (Singh et al.,2026) [21] . Nurseries provide the means to control moisture, light physical and chemical soil constituents in such a way as to produce healthy and uniform seedlings for planting (Singh et al.,2026) [27] . Several factors can influence seedling growth in the nursery (Nishad et al., 2025) [25] . The flowers have five petals and are pale pink. After five to six years of planting, the tree achieves maturity in the fall (Bargah et al., 2025) [5] . Javaid, T. (2019) [19] . The hard shell (endocarp) that surrounds almond seeds has a mechanical effect that affects gas exchange, prevents seed imbibition, and washes out the endocarp hormones (Yadu et al., 2026) [33] which can cause the germination rate to be low (García-Gusano et al., 2005) [15] . De-shelled (removal endocarp) seeds greatly speed up the germination process; this may be due to the removal of phenolic compounds and alkaloids from the seed coat, which inhibit the root to exit quickly and initiate the embryo's metabolic reactions (Chebouti-Meziou et al., 2014, Mishra et al.,2026) [10,23] . Acar et al. (2017), Chetouani et al. (2017) [11] , and Yasar and Acar (2019) [2] have conducted numerous investigations on the effects of cold stratification and the exogenous application of gibberellic acid in breaking seed dormancy and boosting germination (Bargah et al.,2024) [6] . Thus, the goal of this study was to assess how the germination percentage of bitter almond and seedling growth were affected by the interaction between cold stratification periods and various gibberellic acid concentrations (Bargah et al.,2025) [7] .

Seed germination

The first stage of a plant's life cycle is seed germination, which starts when a dry, dormant seed absorbs water and ends when the radicle protrudes from the seed coat (Aashutosh et al., 2024) [1] . According to (Chandra et al. 2024), seed germination is a complicated process that incorporates multiple signals and is impacted by both intrinsic and extrinsic variables.

Epigeal germination

This process involves the cotyledon being pushed out of the soil due to the rapid growth and elongation of the hypocotyl, as seen in species like Acacia, Adenanthera, Albizia, Cassia, www.extensionjournal.com Dipteryx, Diphysa, Erythrina, Gliricidia, Haematoxylum, Hymenaea, Hymenolobium, Parkia, Parkinsonia, Pterocarpus, Samaneasaman, Sclerolobium, Tamarindus, Casuarina, Annona, Cordia alliodora, Myrcia, Capparis, Cedrela, Melia, Zizyphus, Anacardium excelsum, Jacaranda, Ulmus, Ilex, and Elaeocarpus.

Hypogeal Germination

Germination in the hypogeal because of the epicotyl's quick elongation, cotyledons in this variety stay below the earth. This mostly affects monocotyledonous seeds, such as Terminalia catappa, Calophyllum, Swartzia, Syzygium, Swietenia, Prunus, and Sapindus. Prunus dulcis exhibits hypogeal germination because the stem grows upward and the epicotyl lengthens while the cotyledons stay below the earth.

The majority of species that live in regions with seasonally harsh weather exhibit dormancy, which allows the organism to survive as a seed when it may die as a seedling; even in moist tropical forests, pioneer, light-demanding genera like Macaranga and Trena go into hibernation (R. Umarani and K. Vannangamudi, 2004) [31] (Table 1). (Aashutosh et al., 2024) [1] Hypogeal Germination

In hypogeal germination, the epicotyl elongates while the cotyledons remain below the soil surface.

Cotyledons remain underground and function as storage organs while the shoot develops above the soil.

Terminalia catappa, Calophyllum, Swartzia, Syzygium, Swietenia, Prunus, and Sapindus. Prunus dulcis exhibits hypogeal germination.

(Aashutosh et al., 2024) [1] Types of dormancy 1.

Physiological dormancy

The majority of seeds undergo 'physiological dormancy,' a quiescence program beginning by. The embryo or the endosperm tissues that surround it. In the absence of the particular environmental stimuli that encourage germination, physiological dormancy uses hormones that restrict germination (Steven Penfield, 2017). There are three levels of physiological dormancy. Deep intermediate, and non deep (Baskin & Baskin, 2004) [9] . Newly developed seeds with shallow Physiological dormancy either prevents germination at any temperature or only allows germination in a very specific temperature range. This kind of dormancy is seen in species including eucalyptus, pine, and fagus. According to Baskin & Baskin (2004) [9] and Baskin et al. (2005), embryos removed from seeds that demonstrate deep physiological dormancy either do not grow or create aberrant seedlings. Additionally, embryos separated from seeds will develop into normal seedlings during intermediate physiological dormancy (R. Umarani and K. Vannangamudi, 2004) [31] . Physical dormancy increased from evergreen to savanna forests but dropped in montane forests, whereas physiological dormancy declined from evergreen to deciduous woods but somewhat increased in savanna and montane forests (Baskin & Baskin, 2005).Physiological dormancy occurred in 282 species in 57 families in evergreen forest, 147 species in 47 families in semi evergreen forests, 37 species in 15 families in deciduous forests, 63 species in 35 families in savannas, and 32 species in 15 families in montane forests (Baskin & Baskin, 2005).

Physical dormancy

This results from a layer of thick-walled, cutinized, palisade-like macroscleroid cells that make seed coverings impenetrable to water. The physical and chemical characteristics of the seed coat have been identified as the true source of hardseedness (Tran and Cavangh 1984, Egley 1989, Finch & Leubner 2006). Some seeds, such as Acacia nilotica and Albizzia lebbeck (R. Umarani and K. Vannangamudi, 2004) [31] , may have water impermeability due to the structure of the hilum (Gutterman, 1993). Several Anacardiaceae, Bixaceae, Bombacaceae, Cannaceae, Cistaceae, Cochlospermaceae, Convolvulaceae, and Cucurbitaceae members Dipterocarpaceae and Cusutaceae (subfamilies) Pakaraimoideae and Monotoieae, but not a subfamily. Because the seeds (or fruits) of Dipterocarpoideae, Fabaceae, Geraniaceae, Malvaceae, Nelumbonaceae, Rhamnaceae, Sarcolaenaceae, Sapindaceae, Sterculiaceae, and Tiliaceae are impermeable to water, the dispersion unit experiences physical dormancy (Baskin et al., 2000) [8] .

Combinational dormancy

It can be seen in seeds with physiological embryo dormancy and water-impermeable coverings, like PY (Baskin & Baskin, 2004) [9] . Trifolium and geranium are two examples. Many trees and shrubs experience dormancy as a result of the combined effects of the embryo, testa, and pericarp, which makes them difficult to reproduce. Several treatments may be required to disrupt this dormancy (Kumar 2015). Seeds must be treated prior to sowing in order to improve germination and solve the issue of seed dormancy. Pretreatment, often known as pre-sowing treatments, refers to a variety of treatments given to seeds before they are sown with the goal of accelerating or completing germination (L S Khanna 2021). Likewise, According to (Umarani R and Vanangamudi K, 2004) [31] , seed treatment is the application www.extensionjournal.com of any chemical, physical, or biological method to change how seeds germinate.

Morphological dormancy

According to Baskin and Baskin (1998), seeds that exhibit morphological dormancy (MD) have small, immature embryos but are highly differentiated into cotyledons and hypocotyls -radicles. The embryos only need time to finish; they are not physically inactive. The growth and subsequent germination of the embryo. According to Baskin and Baskin (2004) [9] , under the right conditions, embryos in recently matured seeds start to grow (elongate) within 1-2 weeks and begin germination within 30 days. For instance, seeds from Delphinium carolinianum and Anemone coronaria, among others.

Morpho-physiological dormancy

Underdeveloped embryos with a physiological component of dormancy are the hallmark of MPD. As a result, two factors are crucial before germination begins: the embryo must increase in size, and physiological dormancy necessitates a dormancy-breaking therapy, such as gibberelic acid administration or warm or cold stratification (Baskin & Baskin, 2000) [8] . For instance, Michelia yunnanensis, Magnolia grandis, and Manglietiastrum sinicum (Iralu et al., 2019) [18] (Table 2.). [9] Morphological Dormancy (MD)

Seeds contain underdeveloped embryos that require further growth before germination can occur.

Immature embryo at the time of seed dispersal.

Delphinium carolinianum, Anemone coronaria.

(Baskin & Baskin, 1998, 2004) [9] Morphophysiological Dormancy (MPD)

Seeds possess both an underdeveloped embryo and physiological dormancy. Embryo growth and dormancy-breaking treatments are required before germination.

Combination of immature embryo and physiological inhibition.

Michelia yunnanensis, Magnolia grandis, Manglietiastrum sinicum. 2019) [8,18] Wat to get rid of dormency Prunus species use seed dormancy as an adaptive strategy to shield temperate fruit trees from winter timee frost damage. [22] as two separate mechanisms: seed coat dormancy (external), which is hormonal in nature and manifests in the inhibition of germination, and embryo dormancy (internal), which is genetic in nature and primarily manifests in later plant growth. Grigorian (1972) and Kester et al. (1977) demonstrated how embryo dormancy affected almond seed germination.

Scarification

The term "mechanical treatment" describes the process of mechanically cutting or filling the hard, resistant seed coat to allow moisture to enter L.S. Khanna (2021). Before sowing, the seed coat can be sliced, drilled, or scraped to make it water-permeable. Scarification is another effective method of breaking seed dormancy (Dwivedi, 2006) [14] . Scarification was performed by spinning the handle of an instrument until the hard endocarps became thin and lustrous, but not punctured. The seeds were then soaked in fresh water for 10 hours and surface sterilized with 10% Clorox for 15 minutes. The seeds are then sown in beds after being treated with chemicals like potassium nitrate, thiourea, ethylene, and chlorohydrine to make the seed coats weak and soft (Jetti et al., 2017) [20] . Scarification can also be carried out using a concrete mixture with sharp gravel or sand; a special drum lined with abrasive materials, such as sand paper or cement with abrasive disks, may be made (Umarani R and Vanangamudi K, 2004) [31] .

Stratification

Depending on the species, it entails subjecting the seed to low temperatures of 3-5°C for two to three days to several months under stratified layers of wet sand, soil, or sawdust. In S. alnifolia species with deep physiological dormancy, cold stratification up to 150 days is efficient in breaking the dormancy and enhancing germination (Tang et al., 2019; Nautiyal et al., 2023) [30,24] .

Hormonal treatment

Growth hormones, such as gibberellic acid (GA), abscisic acid (ABA), auxin, and ethylene, have been found to be www.extensionjournal.com strictly regulated in germination (Han and Yang, 2015) [16] . Plant growth regulators are the chemical substances that control all the factors of development and growth within plants (B Desta and G Amare, 2021) [12] . Additionally, these PGRs aid in breaking dormancy and accelerating dormant seed germination. According to (Umarani R and Vanangamudi K, 2004) [31] , the following is a list of the most significant plant growth regulators.

Biological priming

Almond seed germination and seedling growth can be effectively improved by microbial priming, which is the inoculation of seeds with beneficial rhizospheric bacteria. By exposing seeds to a microbial wash from native plants like Pistacia lentiscus L., microbial priming may promote beneficial plant-microbe interactions that improve nutrient uptake, speed germination, and promote seedling development. Additionally, by boosting the population of beneficial bacteria that promote plant development, soil fertility, and nutrient cycling, microbial priming can enhance soil health (Schlatter et al., 2017) [26] . Its rhizosphere contains a variety of helpful bacteria and fungi that might enhance nutrient availability and promote plant resistance, according to studies. P.lentiscus L. was selected as a viable option for microbial priming in sustainable agriculture due to its capacity to foster beneficial plantmicrobe interactions. (Applebaum et al., 2022; Steinberger et al., 2024) [3,29] (Table 3). [26,3,29] Benefits of Seed Dormancy Natural adaptive mechanism that delays germination until favorable conditions occur.

Enhances seed survival and species persistence.

Prevents vivipary and reduces risk of seedling mortality under adverse conditions.

-(Sinha et al., 2017) [28] Drawbacks of Seed Dormancy Delays and reduces uniformity of germination.

Causes slow and uneven seedling emergence.

-Prolongs seed persistence in soil and complicates seed testing and cultivation practices.

(Sinha et al., 2017) [28] Benefits 1. In the event that unfavorable conditions kill the readily germinated seeds, it serves as a survival mechanism by lowering the likelihood of species extinction. 2. Prevents vivipary, or in situ germination, which aids in maintaining seed quality.

Drawbacks

1. Seed dormancy results in uneven and delayed germination. 2. It makes many species' seeds stay undisturbed in the soil for a longer period of time. These seeds show up in later crops as undesirable plants or weeds. 3. Impedes the process of assessing seeds (Sinha et al., 2017) [28] .

Process of Prunus dulcis seed germination www.extensionjournal.com [9] Seed Coat Permeability Seed coat/endocarp does not completely prevent water uptake. Rules out true physical dormancy.

Comparison

(García-Gusano et al., 2005) [15] Internal Regulation Germination is controlled by internal hormonal and biochemical mechanisms.

Conclusion

Prunus dulcis seeds predominantly exhibit physiological dormancy, which serves as an adaptive mechanism to ensure germination under favorable environmental conditions. Although the hard endocarp may slightly restrict water uptake and gas exchange, the primary barrier to germination is the internal physiological and hormonal regulation of the embryo. Various dormancy-breaking treatments, including scarification, cold stratification, hormonal treatments, chemical treatments, and biological priming, have been reported to enhance germination and seedling growth. Among these methods, cold stratification, particularly when combined with gibberellic acid (GA₃), is the most effective and widely recommended approach for overcoming dormancy and achieving higher germination percentages. Biological priming also offers a sustainable alternative by improving seedling vigor and promoting beneficial plantmicrobe interactions. Therefore, the adoption of appropriate pre-sowing treatments is essential for ensuring rapid, uniform, and successful germination, thereby improving the propagation and cultivation of Prunus dulcis.

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