Malaysian Journal of Sustainable Agriculture (MJSA)

An onion is a vegetable that is the most widely cultivated and used in Bangladesh like other countries of the world. However, the productivity of onion in Bangladesh is low as compared to other countries due to lack of high quality seed. Hence, a field research was conducted to assess the impact of plant biostimulant and plant growth regulators (GA3 and Florigen) on morphological and physiological traits, yield attributes, and quality seed production of onion. The experiment was laid out in a randomized complete block design with three replications. Three onion varieties like Lalteer King, Taherpuri, and BARI Piaz 1 and eleven treatments were included such as T0 (control); T1, T2, T3 and T4 (plant biostimulant of 1, 2, 4 and 8 gL-1 Goemar respectively); T5, T6 and T7 (Benzyl adenine of 10, 20, and 30 ppm of mg/L-1 of BA respectively); T8, T9, and T10 (Gibberellic acid of 25, 50, and 75 mg/L-1 GA3 respectively). The variety Lal teer king which was sprayed with 75 mgl-1 GA3 produced the highest length of scape, number of scape, number of flowers per umbel, number of fruits per umbel, photosynthesis rate (Fv/Fm), 100 seed weight, total seed weight per plot, yield per hectare, and PI value at 23.41 cm, 4.05, 166.66, 117.33, 0.96, 0.42g, 93.00g 620.24 kg and 3.35 respectively. However, the plant height including leaf was found to be profoundly superior 51.33 cm, 61.00 cm and 70.66 cm in Lal teer king variety at 30, 45 and 60 days after planting (DAP) when treated with 75 mg/L-1 GA3. At the same time, control treatment in BARI piaz 1 was produced the lowest plant height including leaf 37.00 cm, 43.00cm and 47.33 cm at 30, 45 and 60 DAP respectively. In turns, the maximum amount of CO2 assimilation was calculated in BARI piaz 1 under the treatment T10 (75 mg/L-1 GA3) at all measuring times. The highest number of shoot (5.60) per bulb was found in BARI piaz 1 under the treatment T4 (8 gL1 Goemar). The findings revealed that the application of 75 mgL-1 GA3 (T10 treatment) in Lal teer king onion variety exhibit a significant better performance in terms of the morpho-physiological characteristics, yield and best quality onion seed production compared to the use of other PGR and plant biostimulant.

Onion (Allium cepa L.) is one of the major cultivated bulb vegetable species used by the most people and the world onions were valued not only for their flavor but also for their medicinal properties. Research from the 20th century onwards has focused on enhancing seed quality and yield through genetic improvement and innovative agricultural practices (Jain, 2013). High-quality onion seeds are crucial for enhancing crop yields, improving plant health, and ensuring the overall success of onion production. Seeds can significantly increase productivity. FAO, reported that the improved seeds can boost yields by up to 20% Additionally, quality seeds are often bred for resistance to diseases like downy mildew and pests such as onion thrips, reducing the dependency on chemical treatments and lowering production costs for farmers (FAO, 2020; Smith and Johnson, 2018).

Thus, quality seed not only makes onion farming more efficient but also more environmentally sustainable. Farmers using high-quality, disease-resistant seeds can cut down on pesticide usage by up to 15%, resulting in lower production costs (FAO, 2022). Moreover, onions produced from quality seeds have better post-harvest qualities, such as improved texture, longer shelf life, and enhanced resistance to spoilage, reducing storage losses and ensuring that onions maintain their quality during transport and sale (Wang et al., 2017). Therefore, high-quality onion seeds are foundational to achieving higher productivity, economic gains, better crop quality, and sustainable agricultural practices.

In 2022, Bangladesh produced around 1,500 metric tons of onion seeds, contributing approximately 1.5% to the global market (FAO, 2022). This production is primarily focused on domestic needs, as the country continues to work towards self-sufficiency in onion cultivation, reducing its reliance on imports. Bangladesh currently imports a significant amount of onion seeds, particularly hybrid varieties. So, the ongoing efforts to improve seed breeding programs and local production capacity may increase its share in the coming years. The production of high-quality onion seeds in Bangladesh faces several significant challenges, hindering its ability to meet both domestic demand and compete globally. One major constraint is the lack of advanced breeding programs, which limits the development of hybrid, disease-resistant, and high-yielding varieties compared to leading producers like the Netherlands and the USA (Nair etal., 2020).

Climatic conditions, particularly the heavy monsoons and high humidity,also pose problems by increasing the risk of disease and reducing seedquality (Khan et al., 2021). Additionally, farmers struggle to access highqualityparent seeds, often relying on lower-quality, saved seeds that leadto poor crop performance (FAO, 2022). Inadequate infrastructure for seeddrying, storage, and testing, combined with a lack of modern technology,further hampers seed quality. Moreover, many farmers lack training inbest seed production practices, leading to inefficient irrigation, pestmanagement, and harvesting (Rahman et al., 2020). Market regulation andquality control are also weak, with unregulated and uncertified seedscommonly sold, resulting in inconsistent quality (Khan et al., 2021).Addressing these issues, including improving infrastructure, farmereducation, and market regulation, is essential for advancing Bangladesh’sonion seed industry.

On the other hand, the high humidity and frequent heavy rainfall duringthe monsoon season create an environment conducive to fungal diseasesand water logging, which can severely compromise seed quality andreduce yields. Implementing measures to mitigate the effects of climatechange and adopting advanced technologies for better irrigation and seedquality management are essential for ensuring sustainable and highqualityonion seed production in Bangladesh. Overcoming the constraintsin onion seed production in Bangladesh requires a comprehensiveapproach addressing several key areas. Advanced breeding programs areessential to develop high-yielding, disease-resistant onion varietiestailored to the local climate and soil conditions, in collaboration withagricultural research institutions (Nair et al., 2020).

Plant biostimulants (seaweed extracts trade name Goemar) and plantgrowth regulators like Benzyladenine (BA) and Gibberellic Acid (GA3)play significant roles in enhancing onion crop growth, yield, and seedquality. These substances contribute to improving various aspects of plantdevelopment through distinct mechanisms. Plant biostimulants are rich ina variety of bioactive compounds, including vitamins, minerals, aminoacids, and natural plant hormones. These components enhance plantgrowth and stress tolerance by promoting root development, improvingnutrient uptake, and increasing resistance to environmental stressors.Additionally, plant biostimulants boost photosynthesis by increasingchlorophyll content, which enhances energy production and contributesto better seed and bulb quality.

By stimulating enzymatic activity and soil microbial health, seaweedextracts also improve soil fertility and support sustainable agriculturalpractices (Rathore et al., 2009). Benzyladenine, a synthetic cytokinin,plays a crucial role in regulating plant growth by promoting cell divisionand differentiation. In onions, BA application encourages vigorous shootgrowth and delays leaf senescence, leading to increased photosyntheticactivity and enhanced nutrient mobilization which collectively producebetter bulb development and higher seed yield. BA also stimulates theproduction of side shoots, which can be beneficial for seed production, andregulates flowering processes, contributing to more uniform andproductive flowering (Sharma and Singh, 2018). By improving overallplant structure and function, BA enhances both the quantity and quality ofonion seeds. GA3 influences various developmental processes bystimulating cell elongation and division.

In onion cultivation, GA3 accelerates shoot and root growth, improvesplant height, and promotes early flowering, which is crucial for successfulseed production. The synergistic application of seaweed extracts, BA, andGA3 can significantly improve onion cultivation. Seaweed extracts enhancenutrient uptake and stress resilience, while BA and GA3 regulate growthprocesses and boost seed production. Together, these biostimulant andgrowth regulators lead to stronger plant growth, higher yields, andimproved seed quality, providing a sustainable approach to optimizingonion cultivation.

2. MATERIALS AND METHOD

2.1 Study site

The experiment was conducted in the research field of the Department ofAgricultural Botany. Analysis was done in Laboratory of plant physiologyunder the Department of Agricultural Botany, and Central Laboratory,Patuakhali Science and Technology University, Bangladesh.

2.2 Land preparation and fertilization

The land was ploughed followed by cross-ploughing to obtain good tilth,which was necessary to get better yield of the crop. All the weeds andstubbles were removed from the experimental field. The experimentalfield was divided into unit plot to maintaining the desired spacing; theplots were spaded one day before planting and Cowdung (10 tons/ha),TSP (275 kg/ha); MOP (150 kg/ ha); urea (250 kg/ha); gypsum (110 kg/ha) were applied in the main field. All the cowdung, TSP, MPO and 1/3of the urea were applied before transplanting, and rest urea were appliedin 3 instalments after 15, 30 and 45 days of transplanting respectively.Furadan 5G was used @ 8 kg/ha to protect the young plants from theattack of mole cricket, ants, and cutworms.

3. MATERIALS

Bulbs of Onion varieties such as BARI piazl 1, Taherpuri, and Lalteer Kingwas collected from BARI, Gazipur, Rajshahi, and Lal teer companyrespectively.

3.1 Experiment design

Three onion varieties and 11 treatments experiments were laid out in aRandomized Complete Block Design (RCBD) with three replications. Thus,there were 99 (treatment 11 x variety 3 x replication 3) unit plotsaltogether in the experiment. The size of each unit plot was 1.5 x1.2 m2thus the 1.8 m2 plot where line to line and plant to plant distance were 30and 15 cm respectively.

3.2 Plant biostimulant and PGRs Treatments

Different level of plant biostimulant “Goemar” (1 gL-1, 2 gL-1, 4 gL-1, and 8gL-1Goemar), Benzyl adenine (BA) (10 ppm, 20 ppm and 30 ppm), GA3 (25ppm, 50 ppm and 75 ppm) and control (water spray) treatments weresprayed at 20 DAS and 40 DAS respectively.

3.3 Transplanting and intercultural operation

Onion bulbs were transplanted in rows by hand. The distance betweenrow to row and plant to plant were 30 and 20 cm, respectively. Bulb wasplaced in each point at 2-3 cm depth from the soil surface. The plots wasalways kept under careful observation for getting better growth anddevelopment of plants and the intercultural operations is weeding,irrigation were done when it was necessary. Plants were infected bypurple leaf blotch disease and controlled by spraying Rovral 50 WP at therate of 0.2% at 15 days interval after 30 days of transplanting.

3.4 Data Collection

Different morpho-physiological and yield contributing characters wererecorded viz., plant height(cm), number of leaves plant-1, number of shootper bulb, Length of scape (cm), number of scape plant-1, number of flowersper umbel, number of fruit per umbel, 100 seed weight (g), chlorophyllcontent (mg/cm2) (Fv/Fm), CO2 assimilation, PI value, seed weight perplot (g), and yield hectare-1(kg).

3.5 Statistical Analysis

The data obtained for different characters were statistically analyzed toobserve the significant difference among the treatments by using theMinitab 2017. The mean values of all the characters were calculated andanalysis of variance was performed. The significance of the differenceamong the treatments means was estimated by the Tukey’s test at 5% levelof probability.

4. RESULT AND DISCUSSION

4.1 The effect of plant biostimulant (Goemar) and PGRs (BA andGA3) on growth of Onion

Plant biostimulant (PB) trade name “Goemar” and PGRs (BA and GA3)treatments influenced and reduced the plant height, number of leaves andnumber of shoot per bulb, Length of flower stalk, No of flower stalk perplant, No. of flowers per umbel, No. of fruits per umbel compared with acontrol (Table 1 and 2). The interaction between onion varieties and PB &PGRs were significant in plant height at 45 and 60 DAT, number of leaves,number of shoot per bulb, Length of flower stalk, No. of flowers per umbeland No. of fruits per umbel. The response of varieties to biostimulant andPGRs was also different under Goemar, Benzyle amine and GA3 treatments.At 30 DAT, interaction result was insignificant in plant height. The V1variety (Lalteer king) showed the highest plant height (51.33 cm) at 30DAT under T10 treatment (75mgL-1 GA3).

Similarly, all other interaction reported statistically similar plant height toV1T10 interaction (Table 1). A similar trend of plant height was recorded at45 and 60 DAT, with interaction V1T10 reporting significantly maximumplant height (61.00 cm) and (70.66) followed by V2T10 (59.83 cm) and(69.83 cm) at 45 and 60 DAT respectively. Internodes elongation is themost pronounced effects of gibberellins on plant growth. In many plantssuch as dwarf pea and maize, the genetic dwarfism can be overcome. Insub apical meristem region, GA3 speed up cell elongation and cell divisionresulting plant height increasing. This increase is the result of an increasein auxin in plant tissues by inducing the tryptophan conversion to IAApromoting cell division and cell elongation. Most of researchers reportedthe increase in plant height with the application of GA3 by increasing the length of internodes of marigold (Kanwar and Khandelwal, 2013; Singh, 2004).

The response of number of leaves was also treatment and variety dependent. At 30 DAT, V3 variety showed the maximum number of leaves (22.33) under T4 treatment and the minimum number of leaves (12.00) were found in same variety under the T0 (control) treatment. Similarly, treatments T10 (21.33) of V3 variety, T3 (22.33), T4 (22.66), T10 (22.00) of V2 variety and T3 (23.00), T4 (23.00), T10 (22.66) of V1 variety reported statistically similar numbers of leaves to V3 variety under T4 treatment. Among the interactions, the highest number of leaves was calculated from V1T10 (28.33) interaction and the lowest number of leaves was noted in V3T5 (9.66) combination at 45 DAT. In the same way, V1T9 (27.33) also reported statistically similar numbers of leaves to V1T10 (28.33) interaction. At 60 DAT, V1 variety showed the highest number of leaves (25.33) under T1 treatment and the least number of leaves (11.00) were initiated in V3 variety under the T7 treatment. Similarly, V1T10 (24.00) also reported statistically similar numbers of leaves to V1T1 (25.33) interaction. The above results indicate that the number of leaves of a plant might be controlled by genetical characteristics of a variety. Similar results were earlier reported (Kumar, 1996). A group researcher reported that GA 25 ppm exhibited maximum leaf number in grape plants (Bhat et al., 2011).

The application of plant bio stimulation and PGRs on onion varieties was found to have a significant effect on the number of shoot per onion bulb. The V3T4 interaction reported the maximum shoot (5.60) initiation per bulb followed by V1T4 (5.30), V1T10 (5.53), V2T3 (5.37), V2T4 (5.45), V2T10 (5.53), and V3T10 (5.53). Interaction V3T6 showed the least shoot production per bulb (3.44) in onion bulb to seed production (Table 1). These results may be due to the effect of plant biostimulant “Gomar” and GA3 on cell elongation, cell division which turn resulted increasing the number of shoot initiation per bulb and scape production of onion (Abou Elsalahein, 1990). The effect of gibberellic acid (GA3) appears essential for the induction of lateral shoots, when applied at an early development stage of onion plants.

V1= LaLtir king, V2=Taherpuri, V3=BARI piaz 1, T0=control, T1=1 g·L−1Goemar, T2=2 g·L−1Goemar, T3=4 g·L−1Goemar, T4=8 g·L−1Goemar, T5=10 mg L-1 BA, T6=20 mg L-1 BA, T7=30 mg L-1 BA, T8=25 mg L-1 GA3, T9=50 mg L-1 GA3, T10=75 mg L-1 GA3

DAT= Days After Transplanting

The interaction between variety and biostimulant and PGRs application was significant for length of flower stalk (scape) evaluated at 60 DAT (Table 2). The V1 variety treated with T10 (75 mgL-1 GA3) reporting significantly maximum length of flower stalk (23.41 cm) followed by V2T10 (22.28 cm). On the other hand, V3 variety treated with T5 (10 mgL-1 BA) showed the lowest length of flower stalk (11.49 cm). This finding correlated with (Jyoti et al., 2018). This result indicates that GA3 might be involved in cell division and elongation and BA might be involved in cell elongation barrier. In the growing portion, GA3 induced cell division and rapid cell elongation that helped increase flower stalk length. Auxins play an important role in cell division, vascular tissue differentiation, and apical dominance. Within plant metabolism GA3 play an important role in auxin production.

Number of flower stalk per bulb is very important for onion seed production. In this research, interaction effect was significant on number of flower stalk per bulb. The maximum number of flower stalk (4.50) was recorded in V1T10 interaction followed by V2T10 (4.27) and V3T10 (4.31). Conversely, the minimum number of flower stalk (2.14) was found in V3T0 interaction followed by V1T0, V2T0 and V3T6 interaction (Table 2). From the above result, we concluded that GA3 treatment influence the flower stalk production in onion bulb.

Table 2 showed that the marked influence of application of different treatments of plant biostimulant and PGRs on number of flower per umbel and number of fruits per umbel at different variety of onion. The maximum number of flower per umbel (166.66) was recorded in V1T10 interaction followed by V2T10 (164.00) and V3T10 (161.33) interaction. In contrast, the lowest number of flower (128.00) per umbel was noted in V3T0 followed by V3T1, V3T5 and V2T0 interaction. However, the highest number of fruit was observed in V1 variety under T10 treatment followed by V2 variety under T10 treatment. This result indicated that genetical factors of onion varieties and PGRs might be influence fruit production of onion. On the other hand, the lowest number of fruit (79.33) was detected in V3 variety under T0 treatment followed by V1T0 (81.66), V2T0 (81.66), V3T5 (81.66) and V3T6 (80.66) interaction.

4.2 The effect of plant biostimulant (Goemar) and PGRs (BA and GA3) on physiology of Onion

The interaction between variety and biostimulant & PGRs application was significant for CO2 assimilation evaluated at 30 DAT and 60 DAT (Table 2) but insignificant result was found at 45 DAT. At 30 DAT, the highest CO2 assimilation (578 ppm) was found in V3T10 interaction followed by V1T4 (470.33ppm), V1T9 (469.66ppm), V1T10 (469.00ppm), V2T4 (470.51ppm), V2T9 (470.83ppm), V2T10 (523.50ppm), V3T4 (470.66ppm), and V3T9 (472.00ppm). The lowest (427.34 ppm) CO2 assimilation was found in V1 variety under the T5 treatment. However, no statistical significant result was found at 45 DAT. The maximum CO2 assimilation (478.66 ppm) was calculated in V3 variety under the T10 treatment which was statistically similar with V1T10 interaction (478.00 ppm) at 60 DAT. On the other hand, the minimum CO2 assimilation (429.33 ppm) was noted in V1 variety under the T5 treatment.

V1= LaLtir king, V2=Taherpuri, V3=BARI piaz 1, T0=control, T1=1 g·L−1Goemar, T2=2 g·L−1Goemar, T3=4 g·L−1Goemar, T4=8 g·L−1Goemar, T5=10 mg L-1 BA, T6=20 mg L-1 BA, T7=30 mg L-1 BA, T8=25 mg L-1 GA3, T9=50 mg L-1 GA3, T10=75 mg L-1 GA3

DAT= Days After Transplanting

Chlorophyll Fluorescence, Fv/Fm reflects the maximum photochemical efficiency of the PSII. The experiment showed that there was significant difference in Fv/Fm among the varieties and treatments interaction indicating that varieties and treatments (Biostimulant, BA and GA3) application had effect on the maximum photochemical efficiency of PS (photo-systems) of onion (Table 3). At 30 DAT, the maximum photochemical efficiency (Fv/Fm) was estimated from V3 variety under the T10 treatment which was statistically similar with V1 variety under the T4 treatment, V1 variety under the T10 treatment, V2 variety under the T4 treatment, V2 variety under the T10 treatment and V3 variety under the T4 treatment (Table-3). On the other hand, V2 variety treated with control treatment produced minimum photochemical efficiency (Fv/Fm) which was statistically similar with V1 and V3 variety under the T0 treatment, This result indicates that PGRs and biostimulant can significantly influenced on chlorophyll contents of onion leaves.

The highest photochemical efficiency (Fv/Fm) was estimated from V1 and V3 variety under the T4 and T10 treatment respectively at 45 DAT followed by V1 variety under the T2 treatment, V1 variety under the T3 treatment, V1 variety under the T9 treatment, V1 variety under the T10 treatment, V2 variety under the T1 treatment, V2 variety under the T2 treatment, V2 variety under the T3 treatment, V2 variety under the T4 treatment, V2 variety under the T8 treatment, V2 variety under the T9 treatment, V2 variety under the T10 treatment, V3 variety under the T1 treatment, V3 variety under the T2 treatment, V3 variety under the T3 treatment, V3 variety under the T8 treatment, and V3 variety under the T9 treatment (Table-3). Conversely, the lowest chlorophyll content was calculated from V2 variety under the T0 treatment.

In the present research, it was observed that Chlorophyll fluorescence
parameters showed significant differences with the different PGRs and Biostimulant application levels. At 60 DAT, the maximum photochemical efficiency (Fv/Fm) was estimated from V1 variety under the T10 treatment which was statistically similar with V1 variety under the T9 treatment, V2 variety under the T4 treatment, V2 variety under the T10 treatment, V3 variety under the T4 treatment and V3 variety under the T10 treatment (Table-3). On the other hand, V2 variety treated with control (T0) treatment produced minimum photochemical efficiency (Fv/Fm). These results indicate that PGRs and biostimulant can significantly influence on chlorophyll contents of onion leaves and V1 and V3 varieties produced highest amount of chlorophyll content than V2 variety. However, a group researcher indicated the different results for sunflower where they found that Fm was significantly increased and Fv/Fm was not affected by N stress (Ciompi et al., 1996).

4.3 The effect of plant biostimulant (Goemar) and PGRs (BA and GA3) on seed yield of Onion

100 seed weight of onion varieties were not significantly influenced by combined effect of variety and PGRs & biostimulant in this study (Table 3). The highest 100 seed weight was calculated in V2T4 which was not statistically different with others interaction. Total seed weight per plot was significantly influenced by combined effect of variety and PGRs & biostimulant. The maximum seed weight (93.00 gm) per plot was found in V1T10 interaction which was statistically similar with V1T4, V2T4, V2T10 and V3T10 interactions. However, the minimum seed weight (57.66gm) per plot was calculated in V1T1 interaction which was statistically similar with V2T0 and V3T0 interactions.

Onion seed yield is directly depending on seed size and quality. Onion seed plays important role for onion production. In this research, seed yield per hectare was statistically significant according to different interactions. The highest seed yield was recorded in V1T10 interaction which was statistically similar with V1T4, V2T4, V2T10, V3T4 and V3T10 interactions (Table-3). In contrast, the lowest amount of seed yield per hectare was found in V1T0 followed by V2T0 interaction. These results were supported by where they showed that GA3 (50 ppm) increased the seed yield of coriander (Kumar et al., 2018). The same results were found by some researchers where they also observed that GA3 influenced growth, yield and quality parameters of chilli (Capsicum annum L.) (Singh and Singh, 2019). A group researcher showed that biostimulant applied in arid climates and vegetable cultivation had the highest impact on crop yield (Li et al., 2022). These results indicate that varieties and treatments (PGRs and Biostimulant) both are influenced the seed yield.

The germination results are presented in Table 3. The results showed that there were no significant differences found in varieties and treatments combination results. The seeds were not treated with PGRs and biostimulant. Some study showed the biostimulant stimulant influence germination of seed (Kalymbetov, et al., 2023; Makhaye, et al., 2021). They also used the biostimulant for seed treatment but we did not treated the seed.

V1= LaLtir king, V2=Taherpuri, V3=BARI piaz 1, T0=control, T1=1 g·L−1Goemar, T2=2 g·L−1Goemar, T3=4 g·L−1Goemar, T4=8 g·L−1Goemar, T5=10 mg L-1 BA, T6=20 mg L-1 BA, T7=30 mg L-1 BA, T8=25 mg L-1 GA3, T9=50 mg L-1 GA3, T10=75 mg L-1 GA3

DAT= Days After Transplanting

5.CONCLUSION

From the present study, it may concluded that GA3, BA and biostimulant has significant effect on seed production of Onion. Among the different concentration of GA3, BA and biostimulant, 75 mg L-1 GA3 was the best for onion seed production in most of the cases and 8 g·L−1 Biostimulant (Goemar) was also showed the best result among the concentration of PGRs and biostimulant except 75 mg L-1 GA3. Lalteer king onion variety showed the best result among the varieties. However, further studies are needed to investigate the effects of GA3 and biostimulant on onion seed production in different areas with different climatic conditions.

ACKNOWLEDGMENTS

The research work was supported by the University Grants Commission (UGC), Bangladesh for the Year 2022-2023.

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