Standardization of seed enhancement techniques for healthy production of radish microgreens

Introduction

The increasing incidence of lifestyle-related disorders such as cancer, diabetes, and obesity has accelerated the demand for functional and nutraceutical foods. In this context, microgreens have emerged as a promising natural dietary source due to their high nutritional value and health-promoting properties. Microgreens are tender, edible seedlings of vegetables and herbs harvested at the cotyledon stage, typically within 7-21 days after germination, and are known to contain higher concentrations of phytonutrients such as ascorbic acid, β-carotene, phylloquinone and tocopherols compared to their mature counterparts (Sharma et al., 2020) [9] . Their short growth cycle, minimal input requirement, and suitability for urban and peri-urban cultivation have increased their commercial importance. Microgreens can be grown in soilless media such as cocopeat, peat and vermicompost, with cocopeat being widely preferred due to its superior water-holding capacity and aeration, resulting in improved germination and yield (Ramya et al., 2022) [6] . Among various crops, radish (Raphanus sativus L.) microgreens are particularly popular due to their rapid growth, ease of cultivation, desirable flavor, and rich nutritional profile. Despite their advantages, the success of microgreen production largely depends on seed quality, as seeds represent a major production cost and directly influence germination, uniformity, and seedling vigor. Moreover, ensuring seed health is critical, as contaminated seeds may harbor pathogenic microorganisms. Therefore, appropriate seed sanitation and enhancement techniques are essential, especially under organic and chemical-free production systems. Seed enhancement techniques such as hydropriming, matrix priming, and pre-germination treatments have been reported to improve germination rate, uniformity, and early seedling growth, thereby reducing the production cycle and enhancing crop performance (Lee et al., 2004) [4] . However, standardization of these techniques for microgreens, particularly in radish, remains limited. Hence, the present study was undertaken to standardize seed enhancement techniques for improving seed performance and ensuring healthy production of radish microgreens.

Material and Methods

The experiment was conducted at AICRP on Seed (Crops), UAS, GKVK, Bengaluru, using a Completely Randomized Design (CRD) with 16 treatments and 3 replications. The seeds of radish are collected from Ravi hybrid seeds, Bangalore used for the present study. The collected seeds of radish were fresh and untreated, stored under ambient conditions and recorded 85.0 percent and 6.0 percent of initial germination and moisture content respectively. Seeds were sown in trays (15 × 10.5 inches) filled with cocopeat at a seed rate of 20 g per tray.

Priming: Seeds were surface sterilized by dipping the seeds in sodium hypochlorite (5%) solution for 5 minutes and dried on filter paper. Priming solutions are prepared according to the dosage specific for the treatment. The duration of priming varies with the priming material used for the treatment.

During priming, the seeds were kept in dark condition @ 25±2 °C. After respective priming treatments for specific period, seeds were washed with distilled water thoroughly. Then primed seeds were dried at room temperature on filter paper for 24 hours, later to their original moisture contents. Dried seeds were then packed in polythene bags and stored for further use.

Treatment details

Seeds of were primed with following treatments and laboratory and microgreen tray observation were recorded. Priming with cow urine (30% for 6hrs), T 13 -Priming with α Tocopherol (100 mg/litre with 0.1% tween-20 for 4 hrs soaking), T 14 -Priming with beejamrutha (2% for 6 hrs), T 15 -Seed coating with red soil (5 g/kg of slurry treatment), T 16 -Seed coating with kaolinite (5 g/kg slurry treatment)

Observations recorded

Seed germination was assessed using the between paper method as per International Seed Testing Association rules (Anon., 2019), with 400 seeds (100 seeds × 4 replications) incubated at 25 °C and counts recorded on the 5 th and 14 th day; germination percentage was expressed based on normal seedlings. Speed of emergence was calculated by daily counting of emerged seedlings up to the 8 th day using Maguire's index (Maguire, 1962). Tray emergence (%) was recorded on the 8 th day using 1000 seeds per treatment and expressed on emerged seedling basis (Anon., 2019). Growth parameters such as mean seedling height, shoot mass and seedling mass were measured from ten randomly selected seedlings on 8 days after sowing (DAS). Microgreen yield was recorded at harvest (appearance of first true leaves) by cutting seedlings above the media surface and measuring fresh weight using a digital balance.

Results and Discussion

Different seed enhancement treatment was carried out to know its effect on seed and radish microgreen quality parameters. The results showed that different seed enhancement technique had significantly different effects on tray emergence, speed of emergence, seedling height, shoot mass, seedling mass and microgreen yield. Among 16 different seed enhancement techniques, by considering microgreen quality parameters tested, the best three seed enhancement treatments are hydropriming for 6 hours, priming with H 2 O 2 (0.3%) for 12 hours and priming with beejamrutha for 6 hours. Table 1 shows that hydropriming of radish seeds for 6 hours showed improved seed germination (94.0%), tray emergence (90.0%), speed of emergence (34.0) and seedling height (21.6 cm) of radish microgreens compared to control. Significantly highest radish seed germination in primed seeds (90.0%) compared to control (84%) might be due to soaking of radish seeds which increases enzyme activation, translocation and utilization of reserve food materials. Amylase and lipase are the storage-activating enzymes that are stimulated and produced by soaking. Soaking also mobilizes anti-oxidant enzymes that inhibit oxidation in seeds, maintaining seed vigour and causing early emergence. While rehydration affects pre-germinative germination processes, which in turn induces early emergence (Farooq et al., 2006) [1] . Rapid and synchronized germination by an activation of pre germinative process that induce quantitative and qualitative biochemical changes such as membrane repair, a strong synthesis and activation of the enzymes involved in the degradation and mobilization of reserves might be the reason for significantly increased tray emergence percentage (90.9%) of radish microgreens compared to control (85.0%).

In comparison to unprimed seeds, hydroprimed seeds causes early emergence and seedling establishment, which speeds up emergence and results in a much greater overall tray emergence. These similar results were also observed by Singh et al. (2014) [10] . Increased speed of emergence (34.0) of radish microgreens in primed seeds compared to control (28.4) attributed to the completion of pre-germination processes like DNA replication, increased RNA and protein synthesis, increased ATP availability, quicker embryo growth, repair of damaged seed parts, reduced leakage of metabolites, decreased lipid peroxidation and increased antioxidant activities by enhancing all these activities it increases the speed of germination. Increased germination and speed of emergence of primed seeds are caused by metabolic repair.

Early germination and emergence of seedling from hydroprimed seeds causes radish microgreens to grow quickly and become taller. Radish microgreens grown from primed seeds grow more quickly than those grown from unprimed seeds, resulting in taller seedlings (21.6 cm) compared to control (14.9 cm).The present results were in tune with the findings of Junpatiw and Sangpituk, 2019different soaking treatments had significantly enhanced the germination percentage, microgreen height and fresh weight of chia microgreens. Increased seedling height by primed seeds also observed by Shakuntala et al. (2020) [8] . Table 2 shows that hydropriming of radish seeds for 6 hours showed improved shoot mass (368.3 mg), seedling mass (412.2 mg) and yield (162.0 g/tray) of radish microgreens compared to control. Priming speed up the germination process and increasing the rate and synchronization, as well as the lengths of the shoots and roots so hydropriming increases the fresh and dry mass of radish microgreens.

Early emergence and seedling establishment in treated seeds might be the reason for increased shoot mass (368.3 mg) and seedling mass (412.2 mg) of radish microgreens compared to control 358.1 mg and 393.0 mg respectively. These results are in same line with Lee et al. (2005) [3] who revealed that 'primed-germinated' treatment increased shoot dry weights by 49, 20 and 84 percent for kale, radish and amaranth respectively, compared to those from non-treated seeds.

Primed seedlings showed a two-fold increase in sucrose phosphate synthase-specific activity in their cotyledons. Amylase activity was shown to be greater in the shoots of hydroprimed seedlings, which accelerated the shoot's rapid hydrolysis of transient starch. This hydrolysis increases the quantity of glucose that is available for the growth of the microgreen shoot and resulting in an increase radish microgreen yield (162.0 g/tray) compared to control (156 g/tray).These results are in agreement with Li et al. (2021) [5] that seed soaking increase the dry weight percentage in daikon radish, broccoli, cabbage and kohlrabi microgreens as compared with the unsoaked treatment. Hydroprimed seeds reported to be effective in early germination, better establishment and increased yield in barley (Rashid et al., 2006) [7] . Beejamrutha for 6 hours showed improved tray emergence (90.0%), speed of emergence (33.5), seedling height (20.0 cm), shoot mass (363.2 mg), seedling mass (406.2 mg) and microgreen yield (161.6 g/tray).The reason behind the better performance of Beejamrutha treatment might be due to presence of macro as well as micro nutrients, many vitamins, essential amino acids, growth promoting factors like Indole Acetic Acid (IAA), gibberellic acid (GA) and beneficial microorganisms in it. Swaminathan (2005) [11] showed that naturally occurring beneficial microorganisms mainly bacteria, yeasts, actinomycetes, photosynthetic bacteria and certain fungi were detected in cow dung which is one of component of Beejamrutha.

Conclusion

Results conclude that hydropriming for 6 hour seed enhancement technique showed improved seed and microgreen quality parameters in radish. Among 16 different seed enhancement techniques, by considering microgreen quality parameters tested, the best three seed enhancement treatments are hydropriming for 6 hours, priming with H 2 O 2 (0.3%) for 12 hours and priming with beejamrutha for 6 hours. Hydropriming of radish seeds for 6 hours showed improved tray emergence (90.0%), speed of emergence (34.0), seedling height (21.6 cm), shoot mass (368.3 mg), seedling mass (412.2 mg) and microgreen yield (162.0 g/tray).Highest seed germination in primed seeds might be due to soaking of radish seeds which increases enzyme activation, translocation and utilization of reserve food materials. Rapid and synchronized germination by an activation of pre germinative process that induce quantitative and qualitative biochemical changes such as membrane repair, a strong synthesis and activation of the enzymes involved in the degradation and mobilization of reserves might be the reason for increased tray emergence percentage of radish microgreens. Primed seedlings showed a two-fold increase in sucrose phosphate synthase-specific activity in their cotyledons.

References

1. Farooq M, Basra SMA & Wahid A, Priming of fieldsown rice seed enhances germination, seedling establishment, allometry, and yield. Plant Growth Regulation, 2006; 49: 285-294.
2. Junpatiw A & Sangpituk A, Effects of seed preparation, sowing media, seed sowing rate, and harvesting period on the production of chia microgreens. International Journal, 2019: 17(61); 80-85.
3. Lee JS & Pill WG, Advancing greenhouse establishment of radish, kale, and amaranth microgreens through seed treatments. Horticulture, Environment, and Biotechnology, 2005; 46(6): 363368.
4. Lee JS, Pill WG, Cobb BB & Olszewski M, Seed treatments to advance greenhouse establishment of beet and chard microgreens. Journal of Horticultural Science & Biotechnology, 2004; 79(4): 565-570.
5. Li T, Lalk GT & Bi G, Fertilization and pre-sowing seed soaking affect yield and mineral nutrients of ten microgreen species. Journal of Horticulture, 2021: 7(2): 14.
6. Ramya S, Sood M, Lingaiah HB, RL, RR & Rajesh AM, Microgreens: A nourishment bootstrapper. Journal of Pharmaceutical Innovation, 2022: 11(2): 2601-2607.
7. Shakuntala NM, Kavya KP, Macha SI, Kurnalliker V & Patil M, Studies on standardization of water soaking duration on seed quality in cucumber (Cucumis sativus L.) seeds. Research Journal of Phytochemistry, 2020; 9(4): 1400-1404.
8. Sharma S, Dhingra P & Koranne S, Microgreens: Exciting new food for the 21 st century. Ecology, Environment and Conservation, 2020; 26: 248-251.
9. Singh A, Dahiru R, Musa M & Haliru BS, Effect of osmopriming duration on germination, emergence, and early growth of cowpea (Vigna unguiculata L.) in the Sudan Savanna of Nigeria. Journal of Agronomy, 2014; 1-4.
10. Swaminathan C, Food production through vrkshayurvedic way: Technologies for natural farming. Agriculture College and Research Institute, 2005; 1822, Madurai, Tamil Nadu, India.