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Research Article
 

Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth



Gina Aliya Sopha and Shinta Hartanto
 
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ABSTRACT

Background and Objective: Shallot was reported with a high concentration of auxin, Indole Acetic Acid (IAA) and auxin's application might affect plant growth. However, the effect varies on plant species and genotype. This study aimed to determine the IAA concentration in shallot tissue and investigate the effect of exogenous IAA application on shallot vegetative growth, endogenous IAA and shallot bulb yield. Materials and Methods: The first study analyzed three different shallot tissues (root, bulb and leaf) from five different shallot cultivars (Bima, Mentes, Pancasona, Trisula and Maja). The second study was conducted using a randomized complete block design with two factors: Bima and Trisula cultivars and five exogenous IAA concentration levels. Results: The result showed that the bulb contains the highest IAA concentration and the application of exogenous IAA did not work significantly to affect shallot vegetative growth and bulb yield. However, the application of 10 mL L–1 of exogenous IAA increased the percentage of below-ground biomass and 5 mL L–1 of exogenous IAA increased total soluble solids and firmness. Conclusion: A high concentration of exogenous IAA altered biomass partitioning and a low concentration of exogenous IAA might improve shallot bulb yield quality.

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  How to cite this article:

Gina Aliya Sopha and Shinta Hartanto, 2021. Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth. Asian Journal of Crop Science, 13: 17-23.

DOI: 10.3923/ajcs.2021.17.23

URL: https://scialert.net/abstract/?doi=ajcs.2021.17.23
 
Copyright: © 2021. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

INTRODUCTION

Shallot (Allium cepa var aggregatum) is one of the most important vegetable crops in Indonesia. It is used in many Indonesian foods as an enhancer spice that makes Indonesian food tastier and aromatic. The quantity and quality of the shallot demand are increased due to the Indonesian population and Indonesian people's welfare. Several studies have been conducted to improve shallot growth and bulb yield through input production modification, including chemical fertilizer1,2, organic fertilizer3,4, soil amendments5 and phytohormone6 application. However, the results varied on the cultivar, location, season and treatments. One of the phytohormones that were used to improve shallot growth and bulb yield was auxin groups.

The application of 20 ppm Indole Acetic Acid (IAA) or Indole-3-Butyric Acid (IBA) on onion seedling roots increased vegetative onion growth and fresh bulb yield7. Moreover, the foliar application of IBA also positively impacted onion growth and bulb characteristics8. Furthermore, picloram application as an auxin source and 0.5 mg L–1 BA was increased seedling shoot onion meristem9. The IAA application positively impacted the growth, development and production of onions6. On the contrary, the minor effect was reported that NAA application did not significantly affect onion bulb dormancy10. Therefore, the shallot or onion response on auxin application might vary on the type of auxin, cultivar, concentration and plant stage.

The IAA is a common auxin form that participates in plant growth and development. Exogenous application of IAA may influence the role of auxin, for example, leaf abscission11, development of floral bud and fruit12, root growth13 and plant toxicity response14. The effect of IAA on plant physiological process varies, it might enhance some process and restricts others depending on its concentration, plant species, plant physiological age15 and environmental condition and IAA turns inactive when the IAA completes their roles16.

The sources of IAA can come from chemical or organic materials. The chemical sources might harm the environment. Therefore, the possible organic IAA sources would be investigated. Shallot was reported to contain a high of IAA. However, the concentration depends on the section and cultivar. To address this issue, the first trial of this study was an investigation of IAA concentration from three sections (root, bulb and leaf) of five shallot cultivars. Moreover, the application of IAA might involve shallot growth, yield and quality. Therefore, this second trial aimed to investigate the effect of shallot’s extract (contains exogenous IAA) concentration on shallot growth, bulb yield and bulb quality.

MATERIALS AND METHODS

Study area: The research was conducted from April-November, 2015 in the Indonesian Vegetable Research Institute (IVEGRI), located in Lembang, Bandung Barat, West Java, Indonesia (latitude: 6°48’S, longitude: 107°39’E, 120 m above sea level). The soil type is andisol with soil pH = 5.4 (acid), high of organic carbon 7.26%, total nitrogen 0.55%, the C/N ratio 13, low of available P (P-Bray = 12 mg P kg–1) and high of potassium (K-Morgan = 804 ppm).

The research consisted of two activities analysis and selection of endogenous auxin from shallot tissues and a pot experiment to determine the IAA application's effect on shallot growth and bulb yield.

Selection of IAA: This research was comprised of several steps: extraction, purification and determination of shallot tissues. Five different shallot cultivars were used: Bima, Mentes, Pancasona, Trisula and Maja. Three different tissues were used: roots, leaves and bulbs. About 150 plants per cultivar were grown in a greenhouse and were sampling at 30 days after planting. The method was used based on previous studies17.

Pot experiments: The pot trials were carried out using Randomized Complete Block Design with two factors and three replications were to determine the effect of auxin on shallot growth. The first factor being the cultivar, Bima and Trisula. Meanwhile, the sub-plot or second factor was the concentration of exogenous auxin, which were 0, 5, 7.5, 10 and 12.5 mL L–1. The exogenous auxin was made from the bulb of shallot cultivar Bima and Trisulaas, the highest IAA source.

The shallot cultivar Bima and Trisula from Indonesian Vegetable Research Institute (IVEGRI) were used. Bima is an established cultivar recognized for its resistance to Botrytis allii and its adaptability to lowland with a potential yield of 10 t ha–1. Similarly, Trisula is a dark red variety from IVEGRI adapted to the lowland with a higher potential yield of up to 23 t ha–1. Both cultivars had different genetic grouping based on molecular and morphological traits18.

The pot contained 2 kg of soils, with a single shallot plant per pot. The plants received a total of 1000 kg ha–1 of NPK over three stages, at planting time, 2 weeks after planting and 4 weeks after planting. Throughout the trial, the observations or measurements were plant height, number of leaves, number of tillers, endogenous auxin content, chlorophyll content, bulb yield and the bulb's quality (water content and texture).

RESULTS

IAA selection evaluation: In overview, bulb tissue contained the highest IAA concentration and leaf tissue contained the lowest concentration of IAA in Table 1. The highest concentration of IAA was gained by Bima’s bulb that 6.014 mg kg–1. In contrast, the lowest concentration of IAA was gained by Trisula’s leaf of 0.280 mg kg–1. On average, bulb tissue contained the highest IAA, 5.376 mg kg–1 that was 504% higher than leaf contained 1.066 mg kg–1. Moreover, Bima had the highest IAA concentration per plant, which was about 10.335 mg kg–1and the lowest cultivar was Pancasona, 6.208 mg kg–1.

Pot experiment observation: The exogenous IAA application did not significantly affect plant height, number of leaves and number of the tiller of shallot at 4 weeks after planting in Table 2. Control treatment (0 mL L–1) gave the highest height of Bima, 42.2 cm and 10 mL L–1 IAA for Trisula. The highest number of leaves, about 24.0, was achieved by application 12.5 mL L–1 in Bima cultivar and 5 mL L–1 gave the highest number of leaves of Trisula, 24.4 leaves. The highest number of tillers of Bima was gain by 12.5 mL L–1 of 4.2 tillers and the highest number of tillers of Trisula was achieved by 10.0 mL L–1, 4.0 tillers.

In overview, there was no significant difference between IAA exogenous levels on shallot biomass but there was a significant effect of IAA on the percentage of biomass or biomass partitioning in Table 3. The highest plant biomass of

Bima cultivar was achieved by applying 10 mL L–1 was about 2.00 g per plant that was not significantly different with the lowest plant biomass, control treatment about 1.35 g per plant. While the highest plant biomass of Trisula was gained by control treatment, 1.94 g per plant was not significantly different from the lowest plant biomass, 7.5 mL L–1 IAA about 1.25 g per plant.

The exogenous IAA application reduced the above-ground (leaves and stems) percentage and increased below-ground (roots and bulbs) biomass 4 weeks after planting. The highest percentage of below-ground biomass of Bima was achieved by application 7.5-12.5 mL L–1about 50%. At the same time, the highest percentage of below-ground biomass of Trisula was achieved by application 10 mL L–1, about 34%.

The exogenous IAA application did not significantly increase chlorophyll content but reduced endogenous IAA in Trisula’s bulb in Table 4. The highest concentration of Bima’s chlorophyll was gained by applying 12.5 mL L–1 IAA, which was about 2.20 mg g–1. While control treatments achieved the highest concentration of Trisula’s chlorophyll, 1.91 mg g-1 was not significantly different from other treatments.

The highest endogenous IAA contain was gained by controlling that 9.67 mg kg–1 and the lowest endogenous contain was achieved by applying 12.5 mL L–1 of IAA. There was a negative linear trend that increasing the rate of IAA reduced the endogenous IAA content.

In overview, ‘Bima’ had a better bulb yield than ‘Trisula’ and the application of exogenous IAA did not significantly affect shallot bulb yield in Table 5.

Table 1:Concentration of IAA from different tissues of five shallot cultivars
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth

Table 2:
Effect of exogenous IAA on plant height, number of leaves and number of tillers at 4 weeks after planting
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth
*Mean values within a column followed by the same letters are not significantly different at p<0.05 according to Duncan’s multiple range test, ns: Not significant

Table 3:
Effect of exogenous IAA on the plant biomass and percentage of biomass at 4 weeks after planting
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth
*Mean values within a column followed by the same letters are not significantly different at p<0.05 according to Duncan’s Multiple range test, ns: Not significant

Table 4:
Exogenous IAA's effects on chlorophyll content and endogenous IAA of ‘Bima’ and ‘Trisula’
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth
*Mean values within a column followed by the same letters are not significantly different at p<0.05 according to Duncan’s multiple range test, ns: Not significant

Table 5:Effect of exogenous IAA on shallot yield of ‘Bima’ and ‘Trisula’
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth
Mean values within a column followed by the same letters are not significantly different at p<0.05 according to Duncan’s multiple range test, ns: Not significant, wap: Weeks after planting, *Population per ha approximately 250.000 plants

Table 6:
Effect of exogenous IAA on water content, total soluble solids and texture of ‘Bima’ and ‘Trisula’
Image for - Exogenous Auxin Role on Shallot (Allium cepa Var Aggregatum) Growth
*Mean values within a column followed by the same letters are not significantly different at p<0.05 according to Duncan’s multiple range test, ns: Not significant, wap: Weeks after planting, TSS: Total soluble solids

Application of 5 mL L–1 IAA gave the highest fresh bulb yield for Bima cultivar, about 13.7 t ha–1. While the 10 mL L–1 IAA application gave the highest fresh bulb yield of Trisula, about 9.6 t ha–1, that was not significantly different from control and other treatments. On average, across the treatments, bulb yield of ‘Bima’ was 13.2 t ha–1, 47% higher than ‘Trisula’ was about 9.0 t ha–1.

There was a significant difference between treatments for shallot quality parameters, i.e., water content, total soluble solids and texture in Table 6. Application 12.5 mL L–1 IAA gave the lowest water content of Bima cultivar, 82.04% and 5 mL L–1 of IAA gave the lowest water content of Trisula, 82.13%. The highest percentage of total soluble solids of Bima was gained by control, 17.16%. In comparison, the highest percentage of total soluble solids of Trisula (16.64%) was gained by application 5 mL L–1 of IAA. The most firmness of Bima and Trisula was gained by application 5 mL L–1 of IAA.

DISCUSSION

Bulb of shallot contained the highest amount of IAA compared to other section and Bima and Trisula had the highest concentration of the IAA (Table 1). This result was in line with other findings that the endogenous concentration of IAA was massively transported from above ground to below ground section19. Therefore, the shallot bulb was used as the exogenous IAA source and applied in the following experiment. In this experiment, the concentration of IAA was higher than20 that found the total concentration of shallot IAA was 0.73-0.75 ppm. The higher result might occur due to the shallot section's separation, roots, bulb and leaf. In contrast, the previous experiment combined all sections (one shallot plant).

In overview, there was no effect of exogenous IAA application on shallot growth. However, the application of a high concentration of exogenous IAA altered biomass partitioning. About 10 and 12.5 mL L–1 of exogenous IAA increased the percentage of a below-ground section due to the exogenous IAA's effect on accelerating bulb formation. This effect was also reported on potato plants, that exogenous auxin stimulated root and tuber growth21. Auxin altered the leaves' cell wall permeability, resulting in photosynthate translocation to the below-ground section22.

Moreover, there was no significant effect of IAA levels on the total biomass of shallot. On the contrary, exogenous auxin significantly affected Zizania latifolia biomass23 and combined with cytokinin, improved the biomass and lipid of microalgae Desmodesmus sp24. A negative effect might occur when a high IAA concentration was applied that could inhibit cell propagation25 and reduced plant biomass. The different response might occur due to the difference in plants genotype21.

In this experiment, there was no significant effect of exogenous IAA application on shallot’s chlorophyll content. In contrast, exogenous IAA application increased the chlorophyll of green alga (Chlorella Vulgaris)25 and the exogenous auxin increased tomato’s chlorophyll contained only after 5-15 days after application26. The difference effect might occur due to the existence of other phytohormones that involve the chlorophyll content. The IAA increased the number of chloroplasts but the chlorophyll content increased when applied with kinetin but not on IAA application alone27.

A high concentration of exogenous IAA significantly reduced endogenous IAA concentration. Contrary to another study28, that the endogenous level IAA untreated was lower than IAA-treated cutting. IN this experiment, the 10 and 12.5 mL L–1 exogenous IAA application decreased the endogenous IAA concentration but did not affect the plant biomass per plant. This phenomenon might occur due to shallot metabolic pathways that control the number of phytohormones. In the high concentration of exogenous IAA condition, plants inactive conjugate auxin16. Therefore, the application of a high concentration of exogenous IAA reduced the concentration of endogenous IAA. The formation of endogenous IAA decreased because the plants regulate to maintain phytohormone balancing. Phytohormones are a self-synthesized compound within the plants that can be moved from one part to another and have physiological effects even in low amounts29.

Application 5 mL L–1 exogenous IAA improved shallot bulb yield quality that increased the total soluble solids and firmness and reduced water content percentage. Those characters might improve the shallot bulb's shelf life because total soluble solids and firmness affected the decay and weight loss during the storage duration30. Exogenous IAA did not terminate the onion bulb's dormancy but might involve the dormancy break22.

CONCLUSION

The 10 mL L–1 exogenous IAA application reduced endogenous IAA concentration but increased the percentage of below-ground biomass. All exogenous IAA levels did not significantly affect shallot vegetative growth, total shallot biomass and shallot bulb yield. However, an application of 5 mL L–1exogenous IAA might improve the shallot bulb's quality due to improving the bulb's total soluble solids and firmness.

SIGNIFICANCE STATEMENT

This study discovered exogenous IAA's effect on shallot physiology that can help understand phytohormone's role and improve shallot growth and bulb quality. This study will help the researcher uncover the critical areas of auxin on shallot that researchers could not explore.

ACKNOWLEDGMENT

The authors thank IVEGRI for funding the experiment under DIPA-BALITSA-2015.

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