3.1 The biopriming concentration on the seed germination and root growth performance
Based on the results, biopriming concentration and biopriming duration had no significant interaction (p > 0.05) on all the parameters. Similarly, biopriming of Brassica rapa had no significant interaction between concentration and biopriming duration (Chin et al., 2021). There is no significant effect on seed biopriming duration and salinity level on seed germination percentage and speed (Seyed and Mahjoobeh, 2016). In contrast, chemical priming and duration had a significant interaction effect on seed germination and root growth performance (Mohajeri et al., 2016). No significant difference in Bokashi leachate concentration was shown in the seed germination performance. The concentration of Bokashi leachate to soak seeds had no significant effect on the germination percentage (p = 0.6284). In contrast, different concentrations of chitosan seed priming significantly affect the germination index and mean germination time but germination percentage (Guan et al., 2009).
Root growth characteristics, including taproot and lateral root in the early phase of plant growth, were improved by seed priming (Blunk et al., 2019). Seed priming with 0.2% of Bokashi leachate showed a significant improvement in root length (p = 0.0127012), root projection area (p = 0.0173353), root volume (p = 0.039321) and root surface area (p = 0.0173335) compared to others during the early growth (Fig. 3). Tomato seeds soaked in 0.2% Bokashi leachate for 30 minutes significantly affect stem diameter (Olle, 2020). The nutrient concentration does not show a significant difference in shoot nutrient content (Imran et al., 2013). However, the effect of biopriming concentration on root growth was unknown (Singh et al., 2016). EM in the leachate allow the connection between plant soil for nutrient mobility and auxin synthesis for rooting (Kumar Pandey et al., 2017; Ngoma et al., 2013; Sutariati et al., 2019). However, the other concentration of leachate (< 0.2%) may be too low for the connection building.
Biopriming also had a positive effect on plant growth and development, not only in initial plant growth. Biopriming with Piriformospora indica, a plant growth promoter and abiotic stress alleviator, improved the survival of rice under Cd stress (0.1 mM) as it had the potential to sequester the Cd, decrease the reactive oxygen species (ROS) generation, and cell death in rice roots (Dabral et al., 2019). Therefore, the root-shoot length and biomass had significantly improved after inoculation (Dabral et al., 2019). Besides, biopriming with cyanobacterial extract strengthened the plant from Pythium ultimum attack (Toribio et al., 2021).
Food waste Bokashi leachate is believed rich in nutrients and may consider as nutri priming also. Nonetheless, the nutrient analysis should be carried out in advance. Nutri priming has significantly enhanced early seed development and root growth, and nutrients content. For instance, seed priming with Fe and Zn + Mn significantly increased maize plants' biomass production and total root length (Imran et al., 2013), which lined with the studied results. Chitosan seed priming with 0.5% showed significant improvement in shoot and root length and dry weight (Guan et al., 2009).
A low concentration of landfill leachate had the potential to promote the growth of maize. For instance, 10% of landfill leachate to soak seed improved the yield of maize; however, 50% had a deleterious effect on the seed germination due to the phytotoxicity of the leachate (Li et al., 2017). Not all leachate showed a positive effect on plant growth and development. The cigarette butt and ash leachate have suppressed the germination rate and root development in all concentrations (200, 100, 50, 25, 12.5, and 6.25 pc/L) (Mansouri et al., 2020).
The treatment enhanced the root allowed the root for nutrient and water-seeking; however, the results showed that seedling vigour index had no significant difference between the concentration of Bokashi leachate. EM enhanced the seed germination and vigour in carrot, cucumber, pea, beet, and tomato (Alderson, J. Charles & Wall, 1992; Olle and Williams, 2013). Vermicompost and its leachate improved the leaf and root biomass (Kaur et al., 2018).
3.2 The biopriming duration on the seed germination and root growth performance
Seed priming accelerated germination due to the higher initial water concentration, and the seeds were dried back to their original moisture concentration (Pace et al., 2012). Hence, it is crucial to enhanced seed vigour and germination (Paparella et al., 2015). Acid and urea seed treatment eliminates the physical dormancy by infusing and cracking the hard coat and thus enhanced the water absorption into the embryo (Harsha et al., 2012). The germination percentage of bitter ground is significantly reduced in a longer priming duration (16 hours) (Saleem et al., 2016). In contrast, long priming duration (48 hours) and high concentration of Gibberellin (200 ppm) have a positive effect on the germination percentage in Christmas Palm (Ruminta et al., 2017). The possible reason was that the osmotic potential in seed was reduced, and the toxic effect occurred (Mohajeri et al., 2016).
The 12 hours seed priming duration have significantly enhanced the mean germination time (p = 0.0005747). However, 6 hours of seed priming duration were significantly improved the mean germination rate (time− 1) (p = 0.000768), germination speed accumulated (%) (p = 0.03024) and coefficient of germination velocity (% day− 1) (p = 0.000768) (Fig. 4). The long priming duration was prone to imbibition injury (Monalisa et al., 2017). In contrast, 12 hours of priming duration significantly reduce the mean germination time in “Badami” pistachio (Esmaeilpour and Van Damme, 2016). Coefficient of germination velocity in 12 hours priming duration significantly higher than 6 hours one. In bread wheat, 12 and 36 hours priming time of coefficient of germination velocity had significantly higher than 24 hours (Liela et al., 2010). The enhanced coefficient of germination velocity may be due to the cell division increase in the seeds (Ruan et al., 2002). Stress-resistant cultivars depend on cell elongation rather than cell division. Therefore, it does not require DNA duplication for the first germination steps (Pace et al., 2012).
Germination of Withania somnifera enhanced by priming in vermicompost leachate or tea with phytohormone and phenolic compounds (Aremu et al., 2015) for 12 hours (Kaur et al., 2018). Also, the combined treatment of vermicompost in seed and growing treatment enhanced germination and seedling growth up to 80% (Kaur et al., 2018). However, plant growth regulators treated with seeds did not significantly increase the germination percentage but aid in the breaking seed dormancy and early radical emergence at day 7 (Small et al., 2019). Gibberellins have the capacity to elongate the cell and stem internode. For instance, gibberellins enhance the shoot growth for the grasses and forb species (Small et al., 2019). Sesame seed soaks with GA3 for 12 hours increased the germination to nearly 99% (Kyauk et al., 1995). Sesame seed priming for 12 to 14 hours improves the proximate composition and functional properties (Kajihausa et al., 2014).
The stem leachate of Sonchus arvensis L. in the ratio of 1:20 (w/v) inhibits maize's seedling emergence and growth (Bashir et al., 2018). Besides, the saltgrass seed soaked with plant growth-promoting bacterial consortium for 2 hours had no significant effect on the germination performance (Xia et al., 2020). The slightly acidic electrolyzed water decontaminates the Enterobacteriaceae in alfalfa seeds growth (Zhang et al., 2021).
Seed priming with 6 hours showed a significant improvement in root length (p = 0.0006091), root projection area (p = 0.0008063), root volume (p = 0.002258) and root surface area (p = 0.0008062) compared to others during the early growth (Fig. 5). Long priming duration (12 hours) negatively affected the root growth performance and mean germination time. Comparably, 12 hours priming duration of pistachio was reduced the root dry weight (Esmaeilpour and Van Damme, 2016). The seed may cause loss of desiccation tolerance in long priming duration (Paparella et al., 2015). Priming should prevent the seed from fully germinating since it is triggered by ‘pre-germinative metabolism’ (Paparella et al., 2015). In contrast, long priming duration (12 and 36 hours) significantly increases bread wheat's radicle length (Liela et al., 2010).