RJOAS January 2025
by
Hemon A. Farid, Doctoral Program of Sustainable Agriculture, University of Mataram, Indonesia
Ujianto Lestari, Kisman, Master’s Study Program of Dry Land Agriculture, University of Mataram, Indonesia
Dewi Suprayanti Martia, Study Program of Agroecotechnology, Faculty of Agriculture, University of Mataram, Indonesia
Hemon Tufaila, Study Program of Soil Science, University of Halu Oleo Kendari, Indonesia
This study aimed to evaluate the performance of several local landraces of shallots grown from bulbs of different sizes under drought stress. The experimental design used was a Randomized Complete Block Design with Split Plot Design and 3 replications. The main plot treatment was the drought stress factor (C), and the subplot treatment was the bulb size (U) and shallot landrace (V). Factor C consisted of two levels: c0 = optimal conditions without drought stress and c1 = drought stress conditions. Factor U consisted of three levels: u1 = small size (1-2.5 g); u2 = medium size (2.6-4.1 g); and u3 = large size (4.2-5.7 g) per bulb. Factor V consisted of five levels: v1 = Sumenep; v2 = Brebes; v3 = Nganjuk Bauci; v4 = Keta Monca; and v5 = Super Philip. The results of the study showed that: 1) The performance of the five shallot landraces was dominated by genetic variation, with broad-sense heritability values ranging from 0.59 to 0.81 (high) for traits such as plant height, leaf number, tiller number, dry root weight, dry leaf weight, fresh bulb weight, and dry bulb weight. Traits such as bulb number, root length, and bulb diameter had moderate heritability values ranging from 0.33 to 0.41; 2) The Nganjuk Bauci landrace had the highest yield under drought stress, with the heaviest fresh bulb weight per clump (21.3 g per clump) and an average of 7.8 bulbs per clump; 3) Large-sized bulbs (4.2-5.7 g) produced higher yields, with 6.4 bulbs per clump, a fresh bulb weight of 21.98 g per clump, consumption bulb weight of 17.89 g per clump, and a bulb diameter of 14.59 mm per bulb; and 4) The Nganjuk Bauci and Keta Monca landraces showed drought-tolerant phenotypes (T), the Super Philip landrace was moderately tolerant, while the Sumenep and Brebes landraces exhibited drought-sensitive phenotypes (P).
Shallots (Allium ascalonicum L.) are a nutritious vegetable that is economically important and serve as a useful spice for cooking and medicine (Khorasgani and Pessarakli, 2019). This commodity is also a source of income and employment opportunities, making a significant contribution to the economic development of many regions in Indonesia (Hindarti et al., 2023; Parmawati et al., 2021), as well as in other developing countries (Calica and Dulay, 2018).
Consumer demand for shallots continues to rise over time. The Central Statistics Agency (BPS, 2020) reported that shallot production in Indonesia fluctuated, reaching 1.82 million tons in 2020 and 1.70 million tons in 2021. The consumption of shallots has steadily increased along with population growth and rising public awareness of healthy living.
Despite the high demand for shallots, production has not kept pace with demand, showing a declining trend in productivity. In 2015, the yield was 10.06 tons per hectare, but by 2016 it had decreased to 9.67 tons per hectare, and in 2017 it further dropped to 9.29 tons per hectare (Badan Pusat Statistik, 2019). The decline in shallot productivity is significantly influenced by the use of superior landraces, cultivation techniques, and environmental stress factors (https://www.scribd.com/document/84633990/).
Shallots are mostly grown on marginal lands, such as drylands, fallow lands, and rainfed lands. Dryland cultivation causes drought stress on plant growth. Drought stress affects all aspects of plant growth, including anatomical, morphological, physiological, and biochemical traits. Bulb yield in shallots has been directly linked to the availability of water. The extent of damage to the bulb yield depends on the landrace/genotype and the plant’s phenology in response to drought stress (Ghodke et al., 2018; Polakitan et al., 2022).
Shallots are predominantly cultivated during the dry season because they require a lot of sunlight, with a minimum light exposure of 70%, temperatures ranging from 25–32°C, and humidity levels between 50-70%. While shallots need plenty of water, they are sensitive to heavy rainfall and high rainfall intensity. High humidity can lead to rapid disease development (Moekasan et al., 2016). Shallots have an inefficient root system, with 90% of the roots concentrated within the top 40 cm of soil, and only 2-3% of the total roots found below 60 cm (Fanny et al., 2020). This limits their ability to absorb water, making them more vulnerable to drought stress.
Efforts to overcome drought stress in shallots may include the use of drought-tolerant landraces and the use of quality seeds. Drought-tolerant shallot landraces are expected to achieve maximum production according to their genetic potential when appropriate cultivation techniques are applied. One such cultivation technique that must be considered is bulb size. Several studies have shown that large bulb size (bulb diameter) can result in higher production (Putrasamedja, 2007).
Efficient seed use is essential, particularly by reducing bulb weight or size. The optimal bulb weight (size) is expected to reduce production costs, thereby impacting farmers' income. Seeds with bulbs that are too small can negatively affect plant production. Each landrace has different bulb sizes to achieve high-quality shallot production. The size of the seed bulb also influences drought tolerance (Azmi et al., 2011). Determining the appropriate bulb size in the cultivation of different shallot landraces under drought stress is an issue that needs to be researched. Therefore, this study aims to assess the performance of several local shallot landraces when grown from bulbs of different sizes under drought stress.
This study used a Randomized Complete Block-Split Plot Design with 3 replications. The main plot treatment (C) was the drought stress factor, and the subplot treatment was the bulb size factor (U) and the shallot landrace factor (V). Factor C consisted of two treatment levels: c0 = optimal conditions without drought stress and c1 = drought stress conditions. Factor U consisted of three levels: u1 = small size (1-2.5 g); u2 = medium size (2.6-4.1 g); and u3 = large size (4.2-5.7 g) per bulb. Factor V consisted of five levels: v1 = Sumenep; v2 = Brebes; v3 = Nganjuk Bauci; v4 = Keta Monca; and v5 = Super Philip. Each treatment was planted with 5 replications.
The experiment was carried out according to the following steps:
- Seed Preparation. The seed bulbs used should be sufficiently mature, ranging from 70-80 days after planting. The shallot seeds used were those stored for 2 months, healthy, shiny, not hollow, and with undamaged skins. The seeds were selected according to the treatment for bulb size (small, medium, and large) and the landrace used;
- Preparation of Planting Media. Polybags with a diameter of 15 cm and a height of 20 cm were filled with sieved soil weighing approximately 7 kg and placed inside a greenhouse. The planting media was fertilized with compost at a rate of 3.5 tons per hectare or 10.5 g per polybag;
- Shallot Seed Planting. Before planting, the shallot bulbs were cut by one-third of their size. Bulb cutting was done one day before planting. Planting was done with a spacing of 20 cm x 15 cm, with two bulbs per hole. The shallot bulbs were placed in planting holes previously made with a dibble. The planting hole was made to the depth of the bulb. Each planting hole was sprinkled with Furadan 3G. The bulbs were then inserted into the soil by twisting them in a corkscrew motion. Polybags were arranged to follow the planting distance of 20 x 15 cm;
- Irrigation was performed based on the plant’s age: days 1-10: 2 times a day (morning and evening); days 11-35: once a day (morning); days 36-50: once a day (morning or evening);
- Fertilization was done using NPK compound fertilizer (15-15-15) at a dose of 300 kg per hectare. Fertilizer was applied 3 times: basal fertilizer before planting, follow-up fertilization at 10-15 days after planting, and at 30-35 days after planting. Fertilizer was applied by spreading it evenly and mixing it into the soil to the depth of the cultivated layer;
- Pest and disease control was not carried out using pesticides;
- Drought stress treatment.
All plants were irrigated to field capacity from the start of planting until 10 days after planting. Field capacity was determined by irrigating the planting media until saturated. Saturation was indicated when water began to drip from the aeration holes at the base of the polybag. Drought stress treatment was applied starting from 10 days after planting (DAP) until harvest (70 DAP). At 10 DAP, some plants were not subjected to drought stress (plants maintained under field capacity conditions), while others were subjected to drought stress due to reduced water supply.
Plants under drought stress were irrigated to field capacity every 4-7 days (one day after 70% wilting symptoms appeared on the leaves). Wilting symptoms began when the soil water content fell below 60-70% of field capacity, calculated based on the weight difference between the amount of water applied to reach field capacity and when the plants began to show wilting symptoms (Hemon, 2006).
- Harvesting. Harvesting was done at 70 days after planting, or when the shallot plants showed signs that 60% of the necks had softened, the plants had fallen over, and the leaves had turned yellow;
- Estimation of heritability values (genetic variants);
- Identification of landrace tolerance to drought stress.
The drought tolerance of shallot landraces was calculated based on the Sensitivity Index (S) to drought stress for the parameters of dry bulb weight, bulb number, and dry root weight. The value of S was calculated using the formula by Fischer and Maurer (1978).
One of the efforts to increase shallot production on dryland is the use of drought-tolerant landraces. Drought-tolerant shallot landraces will be able to produce optimally according to their genetic potential when proper cultivation techniques are applied.
Water shortage is a major problem for the growth of shallots. Plant growth is disrupted when the water availability at the root surface decreases. Water deficit affects the agronomic traits of several shallot genotypes. The agronomic response of drought-tolerant shallot landraces to water deficit will vary. As long as the water deficit is within a level that the genotype can tolerate, it will not affect the growth and development of drought-tolerant landraces (Kambiranda et al., 2011).
One cultivation technique that must be considered is bulb size. Several studies have shown that larger bulb size (bulb diameter) can result in higher yields (Putrasamedja, 2007). The efficiency of seed use is also important and can be achieved by reducing the weight or size of bulbs. Seeds with very small bulbs will affect plant productivity. Each landrace has a different bulb size to achieve high-quality shallot production. The bulb size of the seed also influences its tolerance to drought stress (Azmi et al., 2011). The determination of bulb size in the cultivation techniques of several shallot landraces under drought stress conditions is a matter that requires further investigation.
This study aims to assess the genetic performance of several shallot landraces under drought stress. The genetic performance of shallots can be measured using broad-sense heritability. Heritability values indicate whether the phenotypic variation in shallots is influenced by genetic or environmental factors. High genetic variation, supported by high measurements of each parameter, indicates that a landrace has high genetic potential for the observed traits. The data in Table 1 show that the heritability values for several quantitative traits are high, except for the number of tillers at 60 days after planting (dap), bulb number, root length, and bulb diameter, which show moderate heritability values.
Specifically, for dry root weight and root length, genetic factors appear to influence the phenotype from moderate to high compared to environmental factors. Root growth under drought stress conditions is likely due to the plant’s mechanism for adjusting the root-to-shoot ratio. Under drought stress, plants reduce shoot growth by synthesizing retardant hormones that inhibit shoot growth, thereby promoting root growth. This mechanism helps the plant to prevent excessive water loss, as root elongation requires less water compared shooting elongation.
The heritability values for fresh and dry bulb weights are high (0.59-0.69). This suggests that these traits are more influenced by genetic factors than environmental factors. Genetic factors play an important role in drought tolerance, allowing drought-tolerant landraces to produce optimal yields due to their genetic potential.
The analysis of variance (ANOVA) showed that each treatment factor (drought stress, landrace, and bulb size) significantly influenced all parameters. Drought stress and shallot landraces interacted significantly with several quantitative parameters (number of leaves, number of tillers, root length, fresh bulb weight, and bulb diameter). However, the performance of the shallot landraces did not significantly interact with drought stress and bulb size (Table 2).
Table 3 shows that drought stress inhibited plant height growth at both 40 and 60 dap. The Sumenep landrace had the shortest plant height compared to the other landraces. Each landrace showed different plant height growth, with these differences attributed to genetic potential.
Drought stress also reduced the number of leaves in shallots, as shown in Table 4. Water deficit can induce changes in plant structure, starting from morphological adaptations (such as reduced growth rates), to physiological and metabolic responses (Hund et al., 2009). According to El Balla et al. (2013), drought stress reduces the growth of shallots, particularly affecting the number of leaves. The Brebes landrace produced the fewest leaves. At 60 dap, the number of leaves further decreased due to leaf senescence and wilting at this stage.
Table 5 shows that drought stress did not significantly affect the number of tillers. The water deficit did not have a strong enough impact on tiller formation to cause significant differences. The number of bulbs per cluster under drought stress was similar to that under no drought stress conditions.
Landraces, however, had a significant impact on the number of bulbs per cluster. The Brebes landrace produced the fewest bulbs, with an average of 4.3 bulbs per cluster at 60 DAP. On the other hand, Nganjuk Bauci had the highest bulb count, producing 7.7 bulbs per cluster, followed by Super Philip, Keta Monca, and Sumenep landraces. As mentioned by Tambak (2013), genetic differences are a key factor in plant variation. The genetic potential of each landrace influences phenotypic variation, such as the number of tillers per cluster.
Table 6 demonstrates that drought stress significantly affected both dry root and dry leaf weights, but had no significant impact on root length. Dry weight and root length are indicators of a plant's ability to withstand water scarcity. A higher number of roots and greater root length help the plant absorb more water for growth. According to Kusvuran (2011), drought stress can disturb the permeability of root cell membranes, which inhibits plant growth, particularly in the root system, and thus reduces dry root weight.
Regarding dry leaf weight, drought stress, landrace, and bulb size independently influenced the results (Table 6). Drought stress inhibited leaf growth, which is in line with findings that water stress leads to reduced biomass in leaves and pods, as seen in peanuts (Collino et al., 2000). In soybeans, water deficit reduces leaf area and chlorophyll content (Shimada et al., 1992), ultimately lowering yield. Bulb size did not have a significant effect on root growth but did have a significant impact on dry leaf weight. Larger bulbs contain more carbohydrates and water reserves than smaller ones, which likely contribute to better growth when used as seed.
The yield of shallots is determined by parameters such as the number of bulbs, fresh bulb weight, consumption bulb weight, and bulb diameter. Table 7 shows that drought stress affects the number of bulbs per cluster, fresh bulb weight, consumption bulb weight, and bulb diameter. Drought stress inhibits bulb development. In shallots, the critical period for water shortage occurs during bulb formation, which can reduce production (Sumarni and Hidayat, 2005). Irrigation is recommended to maintain soil moisture above -12.5 kPa. Onion production and profitability improve when the soil water potential is within the range of -17 kPa to -12.5 kPa at a soil depth of 20 cm (Shock et al., 1998).
Landraces of shallots show different effects on the number of bulbs, fresh bulb weight, consumption bulb weight, and bulb diameter. The Nganjuk Bauci landrace shows heavier bulb growth compared to the Sumenep and Brebes landraces (Table 7).
The table also shows that different bulb sizes lead to varying results for the number of bulbs, fresh bulb weight, consumption bulb weight, and bulb diameter. Medium-sized bulbs (2.6–4.1 g) and large-sized bulbs (4.2–5.7 g) tend to produce larger bulbs than small bulbs. Larger bulbs provide sufficient food reserves to support growth and development in the field. According to Sutono et al. (2007), large-sized seed bulbs grow better, resulting in longer leaves, larger leaf area, and higher bulb yields per plant.
Water deficit interacts significantly with landrace on fresh bulb weight, number of bulbs, root length, bulb diameter, and the number of leaves at 40 dap. Table 8 shows that all shallot landraces under water deficit conditions tend to have lighter fresh bulb weights compared to those grown under field capacity (control). Fresh bulb weight decreased in all landraces under drought stress, with the greatest decrease observed in the Super Philip landrace (42.4%). The Nganjuk Bauci landrace produced the heaviest fresh bulbs under water deficit compared to the other landraces. The fresh bulb weight of the Nganjuk Bauci landrace decreased by about 29%. Bulb yield in shallots has been reported to be directly related to water supply (Pranjali et al., 2021). A reduction in water supply inhibits bulb formation. Water deficit limits photosynthesis, thereby reducing the photosynthetic products that go into the bulbs.
Table 9 shows that the number of bulbs per cluster varies among shallot landraces under water deficit conditions. Reducing water availability interferes with the plant’s growth processes, including bulb formation. The Nganjuk Bauci landrace produced more bulbs under water deficit conditions. Drought stress in shallots disrupts physiological and biochemical processes within the plant, which impairs growth and reduces productivity. Drought stress interferes with plant metabolism, leading to decreased growth and yield (Fathi and Tari, 2016).
Table 10 and Table 11 show that the bulb diameter and number of leaves at 40 dap of several shallot landraces respond differently to water deficit. All landraces exhibited smaller bulb diameters and fewer leaves under water deficit conditions. However, for the Nganjuk Bauci landrace, the bulb diameter under drought stress was the same as under optimal conditions (no water deficit). Water deficit can induce changes in plant structure, including morphological adaptations (such as reduced growth rate), as well as physiological and metabolic responses (Hund et al., 2009). Furthermore, El Balla et al. (2013) explained that drought stress reduces the growth of shallots, including the number of leaves and bulb diameter.
Table 12 shows that several shallot landraces had longer root growth under water deficit conditions and shorter roots under optimal (field capacity) conditions. The Nganjuk Bauci landrace showed no significant difference in root length between drought stress and optimal conditions. Dry weight and root length are indicators of a plant's ability to survive under water deficit conditions. A large and long root system helps absorb water for plant growth. According to Kusvuran (2011), drought stress can affect the permeability of root cell membranes, which inhibits root growth, thereby reducing dry root weight due to water deficit.
Root elongation under drought stress may occur because plants have a mechanism to adjust the root-to-shoot ratio. Under drought stress, plants reduce the growth rate of the shoots by synthesizing retardant hormones that inhibit shoot growth, which in turn increases the rate of root growth. This mechanism helps the plant minimize water loss because elongating roots requires less water than shoot elongation, which would increase respiration and leaf formation. Root elongation also allows the plant to access a larger soil volume, thus improving water absorption (Levitt, 1980). A study by Djazuli (2010) showed that plants capable of surviving water deficits have roots that can grow even under water stress conditions.
The drought tolerance of shallot plants grown under drought stress was measured using the drought sensitivity index (S) to water deficit. The sensitivity index can categorize shallot plants into tolerant, moderately tolerant, and sensitive groups. The drought sensitivity index shows the extent of reduction in various observed parameters under drought stress conditions relative to optimal conditions.
Tolerance values were determined based on the number of bulbs and fresh bulb weight. Using the formula from Fischer and Maurer (1978), several shallot landraces were categorized as tolerant, moderately tolerant, and sensitive to drought stress. The tested shallot landraces exhibited the ability to withstand drought stress through morphological, anatomical, or physiological adaptations. The sensitivity index provides an indication that reductions in yield, fresh bulb weight, and the number of bulbs can be minimized from the negative effects of drought stress. Shallot plants experiencing drought stress will express genes that help them cope with the stress. The Nganjuk Bauci and Keta Monca landraces showed a tolerant (T) phenotype to drought stress, the Super Philip landrace was moderately tolerant (AT), while the Sumenep and Brebes landraces were sensitive (P) to drought stress.
The genetic performance of five (5) shallot landraces was dominated by genetic diversity, with broad-sense heritability values ranging from 0.59 to 0.81 (high) for traits such as plant height, number of leaves, number of tillers, dry root weight, dry leaf weight, fresh bulb weight, and dry bulb weight. Traits like number of bulbs, root length, and bulb diameter had moderate broad-sense heritability values, ranging from 0.33 to 0.41.
The shallot landrace with the highest yield under drought stress was Nganjuk Bauci, with the heaviest fresh bulb weight per cluster (21.3 g per cluster) and 7.8 bulbs per cluster.
The use of large-sized bulbs (4.2-5.7 g) resulted in high shallot yields, with an average of 6.4 bulbs per cluster, fresh bulb weight of 21.98 g per cluster, consumption bulb weight of 17.89 g per cluster, and bulb diameter of 14.59 mm per bulb.
The Nganjuk Bauci and Keta Monca landraces exhibited a tolerant (T) phenotype to drought stress, the Super Philip landrace was moderately tolerant (AT), while the Sumenep and Brebes landraces displayed a sensitive (P) phenotype to drought stress.
Original paper, i.e. Figures, Tables, References, and Authors' Contacts available at http://rjoas.com/issue-2025-01/article_12.pdf