Abstract
The effect of planting density on producing quality seed tubers using shoot tip cuttings and conventional methods from tubers has not been studied in Ethiopia. An experiment was conducted to determine the effects of spacing on seed tuber yield and related traits of potato cultivars at Adet Agricultural Research Center in northwestern Ethiopia during the 2023 cropping season. The treatments consisted of two potato varieties (Belete and Gera) propagated by shoot tip cuttings at four inter-row spacings (30, 40, 50, and 60 cm) and intra-row spacing (15, 20, 25, and 30 cm). The two varieties propagated using seed tubers at 60 cm inter-row and 30 cm intra-row spacing. The experiment was laid out in a randomized complete block design with three replications. The results showed that the main effects of variety, inter-row spacing, intra-row spacing, propagation method, and the interactions of variety, inter-row spacing, and intra-row spacing significantly influenced the parameters considered. The earlier tuber initiation (43 days) and 50 % flowering (51 days), were recorded from Gera variety propagated using shoot tip cutting. The earlier maturity date (85 days) was recorded from Belete variety propagated using shoot tip cutting. Gera variety propagated using shoot tip cutting at 40 cm inter-row spacing and 25 cm intra-row spacing recorded the longest plant height (85 cm). Belete variety propagated using shoot tip cutting at 30 cm × 15 cm inter- and intra-row spacing produced the highest leaf area index (5.51). The highest seed tuber number per hill (3.96), the highest average seed tuber weight (63 g), and the highest seed tuber weight per hill (248 g) were recorded from propagation by seed tuber (control). Gera variety propagated using shoot tip cutting at 50 cm × 15 cm recorded the highest seed tuber yield (21.11 tons ha−1), which is 57.3 % seed tuber yield increment over seed tuber propagation (control). Based on the study findings, it is recommended to propagate potatoes by shoot tip cutting at a spacing of 50 cm inter-row and 15 cm intra-row for seed tuber production in the study area.
Keywords: Leaf area index, Plant spacing, Seed tubers, Shoot tip cuttings, Tuber yield
1. Introduction
Potato (Solanum tuberosum L.) is a crucial food crop worldwide, ranking fourth in production after wheat, maize, and rice. It is cultivated on 18.13 million hectares of land and yields 376.12 million metric tons annually [1]. Potato is a significant food security crop since it offers a high yield per unit input and has a shorter crop cycle [2]. It is a dietary staple for around 1.3 billion people worldwide [3]. In Ethiopia, where smallholder farmers produce most food and cash crops, potato is the most commonly produced and consumed root and tuber crop, followed by sweet potato and yam [4]. The northwestern region of Ethiopia contributes about 35 % of the national potato production, as reported by the Ethiopia Statistics Services [5] in 2022. However, potato productivity in Ethiopia is quite low compared to the global average, with 15 t ha−1 in Ethiopia and 14.9 t ha−1 in northwest Ethiopia [[5], [6], [7]].
Several challenges face potato production in Ethiopia, including scarcity and high costs of seed tubers, the lack of well-adapted varieties for different agroecological zones, inadequate agronomic practices, disease and pest infestations, and limited post-harvest storage facilities [[8], [9], [10]]. Among these key issues contributing to low productivity is the insufficient availability of healthy and quality seed tubers in the required quantities and at the right time [11].
In Ethiopia, a common propagation method for potatoes is using tubers, which can lead to the accumulation of pathogens in subsequent generations. It has a low multiplication rate, requires too much seed tuber per hectare, needs about 2 t ha−1, and is difficult to store and transport. Moreover, the seed tuber requires more time to break from dormancy. These conditions could contribute to low yield and inferior tuber quality over successive seasons [12,13].
Shoot tip cutting is a rapid multiplication technique that can produce 20 to 60 cuttings from each mother plant [14]. These cuttings can develop into new plantlets within three weeks, providing a continuous source for further propagation. Within six months, a single cutting potential to yield up to 100,000 progenies [15]. This method of propagation using shoot tip cuttings effectively cuts contact with tubers and soil-borne non-systemic diseases and nematodes, thereby eliminating diseases caused by pathogens such as Synchytrium endobioticum (Wart), Erwinia spp., and Rhizoctonia solani [14].
In Ethiopia, the common spacing for producing seed tubers is 60 cm inter-row spacing and 30 cm intra-row spacing for all varieties. However, conflicting findings from studies by Mamun et al. [16] indicate that a spacing of 50 cm inter-row and 15 cm intra-row results in better tuber quality and yield when using shoot tip-cutting propagation. On the other hand, Nikmatullah et al. [17] found that a spacing of 20 cm inter-row and 20 cm intra-row improves tuber quality and yield when using shoot tip cutting propagation. These inconsistencies point to the need for further research to clarify the impact of plant density on seed tuber production quality and yield.
Therefore, the study was initiated to determine the effects of spacing on seed tuber yield and related traits of potato cultivars propagated from shoot tip cuttings and seed tubers under field conditions. It is assumed that the spacing requirements for potato seed production using shoot tip cuttings may differ from those using tuber propagation methods. Hence, the study provides valuable information that could contribute to advancements in potato seed tuber production practices.
2. Materials and methods
2.1. Description of the study area
The study was conducted at the field experimental farm of Adet Agricultural Research Center in the northwestern highlands of Ethiopia. The center of location is at an altitude of 2240 m.a.s.l. with coordinates of 11°17′ N latitude and 37° 43′ E longitude. The soil is well-drained red-brown Cambisol, with a pH value of 5.43 and an organic matter content of 6.53 %. The climate in the area is conducive to potato production, with mean annual temperatures ranging from 8 to 25 °C, and annual rainfall of 1270.5 mm. The rain seasons are from May to October and the maximum rainfall received is from June to September [18]. The data on climatic parameters such as maximum and minimum temperature, and rainfall relative humidity were recorded from the National Meteorological Agency (NMA) during the experimental year and period are indicated in Fig. 1.
Fig. 1.
The environmental conditions (temperature, relative humidity, and rainfall) during the experimental year and period.
(Source: National Meteorology Agency [19].
2.2. Experimental materials
The study used two types of potato varieties: Belete, which had better-rooted shoot tip cuttings treated with Indole-3-butyric acid (IBA) rooting hormone, and Gera, which had better-rooted shoot tip cuttings without IBA treatment in a related study (unpublished manuscript). The seed tubers were obtained from Amhara Regional Agricultural Research Institute (ARARI) Tissue Culture mini tuber seed lots.
2.3. Treatments and experimental design
The treatments included two potato varieties (Belete and Gera), four inter-row spacing levels (30, 40, 50, and 60 cm), and four intra-row spacing levels (15, 20, 25, and 30 cm), resulting in a total of 32 treatments. Additionally, seed tubers of the two potato cultivars with common spacing (60 × 30 cm) were included in the experiment, thus making a total plot number of 34 per replication. These treatments were arranged in a randomized complete block design (RCBD) with three replications to control field variability. The plot sizes were 3.6 m × 3 m (10.8 m2), with 0.5 m between plots and 1 m between replications.
2.4. Experimental Procedures and Management
Mini-tubers obtained from Amhara Regional Agricultural Research Institute (ARARI) Tissue Culture were kept in diffused light storage (DLS) for three months to encourage proper sprouting. After sprouting, the tubers were planted in pots to raise mother plants. Around 45 days after planting, shoot tips were removed from the main stems to encourage the growth of lateral shoots from auxiliary buds. These lateral shoots typically take 15 days after the apical growing point removal to be ready for use as a source for cuttings.
Sharp sand with 1–2 mm grain size rooting media was used. Before planting, the sand was moisturized and compacted to prevent holes from collapsing. 12–15 cm lateral shoots were selected around 15 days after removing the apical growth point. A 4 to 5-cm stem was left below the first node, and the leaves were carefully removed with a sharp razor blade.
For Belete variety, shoot tip cuttings were treated with 6000 ppm of IBA plant growth regulator. Six grams of IBA powder were weighed and added to a 1-L container. To dissolve the powder, 20 ml of ethyl alcohol (EtOH) was added, and the volume was adjusted to 1 L with distilled water using volumetric containers. The shoot cuttings were dipped in the solution for 1 min and then planted on raised beds with the sand medium. After 2 h, the cuttings were watered to aid the translocation of the plant growth regulator to the cuttings' tissues [20]. Gera variety without IBA treatment was dipped in distilled water to prevent air from entering the lower part of the shoot tip cutting.
2.5. Field preparation and transplanting
The land used for cereal production in the previous season was used for the experiment. The selected plot of land was plowed and prepared to a fine tilth a month before the rooted cuttings were planted. The plots were prepared one day before the transplanting, with each plot carefully measured to ensure the correct spacing of treatments. The seed tubers and rooted shoot tip cuttings were planted in the field on the designed day. At the time of transplanting, the recommended NPS fertilizer was applied at a rate of 182 kg/ha, consisting of 19 % N, 38 % P, and 7 % S. Additionally, urea fertilizer was applied at a rate of 225 kg/ha (46 % nitrogen), which was split into three applications. One-third of the recommended nitrogen rate was applied at transplanting, another third two weeks after transplanting, and the final third during the flowering stage. To account for any non-established or dead transplanted roots, rooted cuttings were reserved and used to substitute for missing plants.
2.6. Field management and harvesting
Hand weeding was performed to eliminate weed competition and maintain a conducive environment for the transplanted plants and those grown from seed tubers. Pest and disease control measures were implemented according to recommended guidelines, with pesticides applied at appropriate rates and frequencies to combat potential threats in the field.
Hilling was performed three times. The first hilling was done two weeks after transplanting, coinciding with the first weeding session. The soil was carefully piled around the plant to create mounds. Subsequent hilling was carried out two to three weeks after the first, with the final mound reaching a height of around 30 cm.
Dehaulm was done about two weeks before harvesting when 95 % of the plants in a plot showed yellowing or senescence observed on the lower leaves (physiological maturity) by cutting the stem at the soil line to kill the potato plant and harden the skin, thus reducing bruising during handling and transport. Tuber harvesting was done after two weeks of dehaulm by digging the soil gently to avoid wounding the tubers.
2.7. Data Collection
2.7.1. Phenology traits
Days to Tuber Initiation: When the first flower that appeared in a plot was considered the tuber initiation date. Tuber initiation was predicted based on the date of the flowers' appearance.
Days to 50 % Flowering: The number of days from planting to when 50 % of the plants in each plot reached the flowering stage was recorded.
Days to 95 % Maturity: The number of days from planting to when 95 % of the plants in each plot showed yellowish haulms or senescence on the lower leaves was recorded.
2.7.2. Growth traits
Plant Height (cm): The height of 10 randomly selected plants was measured from the ground surface to the tip of the main stem, and the average height was calculated.
Leaf Area Index: To determine the leaf area index, 10 plants were randomly selected per plot. To obtain the average leaf length per plant, seven leaves from the bottom, seven from the middle, and seven from the top were taken from each plant. All the leaves of each selected plant were counted. The leaf area of each plant was estimated using a formula developed by Firman and Al (1989): Log10 (leaf area in cm2) = 2.06 x log10 (leaf length in cm) - 0.458. The leaf area index was calculated by dividing the total leaf area of a plant by the ground area covered by the plant.
2.7.3. The seed tuber components and quality parameters
Number of tubers per hill: At harvest, the number of seed tubers harvested from all experimental plants in each plot is recorded to calculate the average number of tubers per hill.
Average seed tuber weight (g/tuber): The average seed tuber weight is calculated, by dividing the total fresh tuber yield of each plot, by the corresponding total number of seed tubers, resulting in the average seed weight per tuber.
2.7.4. Seed tubers yield per plant and hectare
Tuber weight per hill (g/plant): At harvest, the actual weight of seed tubers (40–75 g) harvested from all experimental plants in each plot is divided by the corresponding total number of plants, resulting in seed tuber weight per plant.
Seed tuber yield (t ha−1): The seed tuber yield is determined by sorting healthy, medium-sized (40–75g) tubers suitable for planting from the harvested tubers in the net plot area and calculating the yield in tons per hectare.
2.8. Data analysis
Data collected for phenology, growth, and seed tuber yield propagated using shoot tip cuttings were subjected to analysis of variance (ANOVA) by using SAS (Statistical Analysis System) version 9.4 for RCBD, and the least significant difference (LSD) test at 5 % probability was used for mean separation of the treatments. A t-test was conducted to compare potato varieties under two propagation methods: seed tuber propagation versus shoot tip cutting propagation. Additionally, a comparison between Belete and Gera varieties, both propagation using seed tuber was conducted. The analysis was carried out using SPSS Statistics, version 22.
3. Results and DISCUSSION
3.1. Effects on phenology, growth, and seed tuber yield in potato attributes of shoot tip cutting
Table 1 presents an ANOVA for the effects of variety, inter-row, and intra-row on phenology, growth, and seed tuber yield in potato attributes of shoot tip cutting measured during the investigation.
Table 1.
Mean squires from analysis of variance (ANOVA) for phenology, growth, and seed tubers yield in potato attributes of shoot tip cutting.
| Variables | Replication | Variety(V) | Inter-row (IE) | Intra-row (IA) | V∗IE | V∗IA | IE∗IA | V x IE xIA | Error |
|---|---|---|---|---|---|---|---|---|---|
| Degrees of freedom | 2 | 1 | 3 | 3 | 3 | 3 | 9 | 9 | 62 |
| Tuber Initiation | 0.94 | 408.37∗∗ | 1.51ns | 1.37ns | 1.46ns | 1.49ns | 1.25ns | 1.05ns | 0.92 |
| 50 % flowering | 0.13 | 1600.66∗∗ | 1.25ns | 0.36ns | 0.53ns | 0.58ns | 0.42ns | 0.66ns | 0.49 |
| Maturity Date | 7.03 | 256.76∗∗ | 1.45ns | 14.09∗∗ | 1.29ns | 4.42ns | 1.03ns | 1.66ns | 2.81 |
| Plant height | 10.67 | 4606.51∗∗ | 8.81ns | 18.89ns | 13.43ns | 53.12ns | 37.31ns | 39.53∗ | 22.33 |
| Leaf Area Index | 0.22 | 13.1∗∗ | 10.32∗∗ | 12.3∗∗ | 0.20ns | 0.60ns | 0.25ns | 0.82∗∗ | 0.26 |
| seed tubers per hill | 0.04 | 6.5∗∗ | 0.74∗∗ | 0.69∗∗ | 0.11ns | 0.84∗∗ | 0.35∗ | 0.60∗∗ | 0.15 |
| Seed tuber weight | 32.41 | 524.55∗∗ | 818.25∗∗ | 313.85∗∗ | 119.23∗ | 168.95∗∗ | 61.89ns | 48.03ns | 33.17 |
| Seed tubers weight/plant | 5.2 | 37307.87∗∗ | 10514.08∗∗ | 5295.42∗∗ | 1573.49∗∗ | 2885.43∗∗ | 1570.34∗∗ | 2615.83∗∗ | 298.72 |
| Seed tubers yield per hectare | 0.59 | 422.46∗∗ | 71.29∗∗ | 140.27∗∗ | 7.05ns | 38.14∗∗ | 15.52∗∗ | 37.05∗∗ | 3.63 |
∗∗ Significant at P < 0.01; ∗significant at P < 0.05; ns = non-significant at 5 % probability level.
Potato varieties significantly influenced tuber initiation, 50 % flowering, maturity date, plant height, leaf area index, seed tubers per hill, seed tuber weight, seed tubers weight/plant, and seed tubers yield per hectare. Inter-row spacing significantly affected leaf area index, seed tubers per hill, seed tuber weight, seed tubers weight/plant, and seed tubers yield per hectare. Intra-row spacing significantly affected maturity date, leaf area index, seed tubers per hill, seed tuber weight, seed tubers weight/plant, and seed tubers yield per hectare.
Statistically significant variety by inter-row interaction effects were recorded for seed tuber weight and seed tuber weight/plant. Variety by intra-row interaction effects were significant for seed tubers per hill, seed tuber weight, seed tuber weight/plant, and seed tubers yield per hectare. Similarly, inter-row by intra-row interaction effects were significant for seed tubers per hill, seed tuber weight/plant, and seed tuber yield per hectare.
The three-way interaction among potato varieties, inter-row, and intra-row, was significant for plant height, leaf area index, seed tubers per hill, seed tubers weight/plant, and seed tubers yield per hectare.
3.2. Phenology traits
3.2.1. Tuber initiation
The main effects of variety significantly influenced tuber initiation propagated using shoot tip cutting (P < 0.01). While inter-row spacing, intra-row spacing, and their interaction with variety showed no significant effects (Table 1). A t-test analysis indicated a significant difference between Belete and Gera varieties propagated using seed tuber at the 5 % level. Additionally, a significant difference was observed between seed tuber and shoot tip cutting propagation at the 1 % level (Table 2).
Table 2.
Effects of variety, Inter-row spacing, and intra-row spacing on tuber initiation, 50 % flowering, and maturity date, and comparison of propagation methods on these variables.
| Shoot tip cutting |
Tuber Initiation | 50 % flowering | Maturity Date |
|---|---|---|---|
| Varieties | |||
| Belete | 47.54a | 58.91a | 85.08b |
| Gera | 43.41b | 50.75b | 88.35a |
| LSD (5 %) | 0.39 | 0.28 | 0.68 |
| Intra row | |||
| 15 cm | 45.2 | 54.95 | 86b |
| 20 cm | 45.45 | 54.91 | 86.12b |
| 25 cm | 45.45 | 54.75 | 87.25a |
| 30 cm | 45.79 | 54.7 | 87.50a |
| LSD (5 %) | 0.96 | ||
| CV | 2.11 | 1.28 | 1.93 |
| Tuber (Control) | |||
| Varieties | |||
| Belete | 48.6 | 59.6 | 96.6 |
| Gera | 50 | 58 | 99.3 |
| T-test | −2∗ | 2.5∗ | −2.41ns |
| Overall mean | |||
| Tuber | 49.33 | 58.83 | 96.71 |
| Shoot tip cutting | 45.48 | 54.83 | 86.72 |
| T-test | −4.05∗∗ | −2.33∗∗ | −11.41∗ |
Means followed by the same letter within a column are not significantly different at the 5 % significance level. LSD = least significant difference; CV (%) = coefficient of variation; ns = non-significant at 5 % probability level.
Among the varieties tested, the Gera variety propagated through seed tubers (control) showed a delay in tuber initiation, taking 50 days after planting. In contrast, the same variety propagated through shoot-tip cutting showed earlier tuber initiation, occurring 43.41 days after transplanting. Among the propagation methods, shoot tip cutting showed earlier in tuber initiation (45.48 days) compared to the seed tuber propagation method (49.33 days) (Table 2).
The difference in tuber initiation time could be due to genetic variations between the varieties, and the difference in tuber initiation times between the two propagation methods can be attributed to the different growth and development patterns associated with each material. Seed tuber propagation typically involves a slower initial growth phase as the tubers require time to establish roots and develop shoots before initiating tuber formation. On the other hand, shoot tip-cutting propagation enables quicker establishment of new plants with pre-existing roots and shoots, leading to earlier tuber initiation [21]. These findings align with previous research by Kacheyo et al. [22] regarding propagation methods influencing tuber initiation time.
3.2.2. 50 % flowering
The main effects of variety significantly influenced days to 50 % of flowering potato plants (P < 0.01), while inter-row spacing, intra-row spacing, and the interaction with variety showed no significant effects on days to 50 % of flowering propagated by shoot tip cutting (Table 1). T-test analysis revealed a significant mean difference between Belete and Gera varieties propagated by seed tuber at a 5 % level. Additionally, a significant difference was observed between seed tuber and shoot tip cutting propagation at a 1 % level (Table 2).
Among the varieties tested, Belete variety propagated through seed tubers (control) showed a delay in tuber initiation, taking 59.6 days after planting. In contrast, Gera variety propagated through shoot-tip cutting showed earlier days to 50 % flowering of potato plants, occurring 50.75 days after transplanting. Among the propagation methods, shoot tip cutting showed 50 % flowering of potato plants (54.83 days) compared to the seed tuber propagation method (58.83 days) (Table 2).
The difference in flowering time could be due to genetic variations between the varieties, and seed tuber propagation typically involves a slower initial growth phase as the tubers require time to establish roots and develop shoots before 50 % flowering. Conversely, shoot tip-cutting propagation resulted in early 50 % flowering because the rooted cuttings had roots and shoots before transplanting, resulting in rapid establishment in the field [23]. This observation is consistent with previous studies by Aarakit et al. [24]. Also, Satyanarayana et al. [25] reported genetic variation in flowering time among various potato varieties.
3.2.3. Maturity date
The main effects of variety and inter-row spacing significantly influenced (P < 0.01) the maturity date of potatoes, while intra-row spacing and their interactions showed no significant effects on shoot tip cutting. The t-test revealed no significant difference between Belete and Gera varieties under seed tuber, but a significant difference between the seed tuber and shoot tip cutting at a 5 % level for the maturity date.
Belete variety demonstrated an early maturity date of 85 days propagated by shoot tip cutting, while Gera variety took three days longer to mature using the same propagation method. Regarding inter-row spacing, 30 cm spacing matured early (86 days) compared to 60 cm spacing, which resulted in a slight delay in the maturity date. Among the propagation methods, shoot tip cutting showed an earlier maturity date (86.72 days) than the seed tuber propagation method (96.71 days). The accelerated maturity date observed in the Belete variety and the 30 cm spacing might be linked to genetic diversity and the closeness of plants. These conditions likely intensified competition among the plants for resources, encouraging quicker potato growth and development. Conversely, the slower maturity date of Gera variety and the wider 60-cm spacing could be attributed to the genetic characteristics of slower growth and reduced competition for resources among the plants. The earlier maturity date of shoot tip cutting could be associated with the early establishment of rooted cutting in the field, enabling faster growth and early maturity date compared to seed tuber [17].
This finding aligns with previous research by Regasa et al. [26], who noted that tight spacing and genetic differences in potato plants lead to earlier maturity. Similarly, it supports the idea that wider spacing and slower growth of varieties can delay the maturity of potato plants [27,28].
3.3. Growth traits
3.3.1. Plant height
The main effect of variety (P < 0.01) and its interaction with inter-row spacing and intra-row spacing (P < 0.05) significantly influenced potato plant height. However, the main effects of inter-row spacing and intra-row spacing alone showed no significant influence on plant height propagated by shoot tip cutting (Table 1). T-test analysis revealed a significant mean difference between Belete and Gera varieties propagated by seed tuber at a 1 % level. In comparison, no significant difference was between tuber and shoot tip-cutting propagation methods at the 5 % level (Table 3).
Table 3.
The interaction effect of variety, inter-row spacing, and intra-row spacing on plant height and leaf area index, and comparison of propagation methods on these variables.
| Shoot tip-cutting | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Variety | Plant height |
Leafe area index |
|||||||
| Intra-row |
Intra-row |
||||||||
| Inter-row | 15 cm | 20 cm | 25 cm | 30 cm | 15 cm | 20 cm | 25 cm | 30 cm | |
| Belete | 30 cm | 69f-j | 61.6jk | 64i-k | 68.6g-j | 5.51a | 3.40e-h | 3.18f-j | 3.03g-l |
| 40 cm | 65i-k | 59.3k | 65.3i-k | 67.3g-j | 4.18c-e | 3.16f-k | 2.43i-p | 2.56i-o | |
| 50 cm | 64.6i-k | 62.3jk | 66g-k | 64.6i-k | 3.40e-h | 2.72h-o | 2.44i-p | 2.30m-o | |
| 60 cm | 62jk | 65.6h-k | 69f-j | 67.6g-j | 2.86h-m | 2.34k-p | 2.43i-p | 1.94o | |
| Gera | 30 cm | 76.3c-f | 81a-c | 77.6c-e | 82a-c | 5.03ab | 4.64b-d | 4.47b-d | 4.39b-d |
| 40 cm | 79.3a-d | 77.6b-e | 85.3a | 79.3a-d | 4.78a-c | 3.86d-g | 3.81d-g | 2.79h-n | |
| 50 cm | 79.3a-d | 80a-d | 82.3a-c | 70.3e-i | 4.84a-c | 4.35b-d | 3.19f-j | 2.04no | |
| 60 cm | 84.3ab | 79.3a-d | 73.3d-g | 76.6c-e | 3.88d-f | 3.22f-i | 2.37j-p | 2.04no | |
| CV (%) | 6.55 | 15.3 | |||||||
| LSD (5 %) | 7.71 | 0.84 | |||||||
| Tuber (Control) | |||||||||
| Belete | 63.6 | 2.02 | |||||||
| Gera | 73.3 | 1.86 | |||||||
| T-test | −4.8∗∗ | 4ns | |||||||
| Overall mean | |||||||||
| Tuber | 68.3 | 1.95 | |||||||
| Shoot tip cutting | 72.07 | 3.37 | |||||||
| T-test | 1.04ns | 3.20∗∗ | |||||||
Means followed by the same letter(s) in rows and columns are not significantly different at the 5 % significance level. LSD = least significant difference; CV (%) = coefficient of variation; ∗∗ Significant at P < 0.01; ns = non-significant at 5 % probability level.
Gera variety recorded the longest plant height (85.3 cm) at 40 cm × 25 cm spacing for shoot tip-cutting propagation. Conversely, Belete variety recorded the shortest plant height (59.3 cm) at 40 cm × 20 cm spacing using shoot tip-cutting propagation (Table 3). This variation in plant height may be due to genetic differences between the varieties, leading to distinct responses to different spacing and propagation methods [16].
The findings are consistent with those of Bell and Sarker [29], who demonstrate varying responses of varieties to different spacing to plant height. Furthermore, Tessema et al. [30], also observed genetic variations in plant height among different potato varieties. Moreover, Masnenah et al. [32] and Thirupal et al. [31] highlighted the influence of spacing on plant height, aligning with the results of this study.
3.3.2. Leaf area index
The main effects of variety, inter-row spacing, and intra-row spacing, along with their interactions, significantly influenced the leaf area index propagated by shoot tip cutting (P < 0.01, Table 1). T-test analysis showed no significant mean difference between Belete and Gera varieties propagated using seed tuber at the 5 % level. However, a significant mean difference was observed between tuber and shoot tip cutting propagation methods at the 1 % level (Table 3).
The highest leaf area index (5.51) was recorded in Belete variety with a spacing of 30 cm inter-row and 15 cm intra-row for shoot tip-cutting propagation. On the other hand, the lowest leaf area index (1.86) was recorded in the control Gera variety (Table 3). This difference in leaf area index across different treatments may be because different potato varieties exhibit varying leaf area indexes due to their unique growth habits and responses to different spacing arrangements.
The results align with the findings of Derebe and Kola [33] and Thakur, who reported that the potato varieties showed varying responses to different spacing significantly influenced leaf area index due to their diverse growth characteristics. Furthermore, Derebe and Kola [33] also confirmed that plants grown with closer spacing tend to exhibit higher leaf area indexes, indicating that tighter spacing promotes a greater number of leaves per unit area compared to wider spacing arrangements.
3.4. The seed tuber components and quality parameters
3.4.1. Number of seed tubers per hill
The main effects of variety, inter-row spacing, intra-row spacing, and their interactions, significantly influenced seed tuber number per hill propagated by shoot tip cutting ((P < 0.01, Table 1). T-test analysis revealed no significant mean difference between Belete and Gera varieties propagated by seed tuber at the 5 % level. However, a significant mean difference was observed between seed tuber and shoot tip cutting propagation at the 1 % level (Table 4).
Table 4.
The interaction effect of variety, inter-row spacing, and intra-row spacing of on seed tubers per hill, and comparison of propagation methods on this variable.
| Shoot tip-cutting | |||||
|---|---|---|---|---|---|
| Variety | Seed tubers per hill |
||||
| Intra-row | |||||
| Inter-row | 15 cm | 20 cm | 25 cm | 30 cm | |
| Belete | 30 cm | 2.1f-l | 1.83j-l | 1.93i-l | 2.46c-j |
| 40 cm | 1.83j-l | 2.66b-g | 2.53b-i | 2.86a-d | |
| 50 cm | 2.03g-l | 1.53l | 2.4d-j | 2.73b-f | |
| 60 cm | 2.2e-k | 1.96h-l | 2.83a-e | 2.66b-g | |
| Gera | 30 cm | 1.63kl | 2.6b-h | 3.10a-c | 2.9a-d |
| 40 cm | 2.96a-d | 2.93a-d | 2.53b-i | 2.86a-d | |
| 50 cm | 3.16ab | 3.1a-c | 2.93a-d | 2.13f-l | |
| 60 cm | 3.03a-d | 2.83a-e | 3.40a | 2.8a-e | |
| CV (%) | 15.41 | ||||
| LSD (5 %) | 0.64 | ||||
| Tuber (Control) | |||||
| Belete | 3.70 | ||||
| Gera | 4.23 | ||||
| T-test | −2.1ns | ||||
| Overall mean | |||||
| Tuber | 3.96 | ||||
| Shoot tip cutting | 2.54 | ||||
| T-test | −5.81∗∗ | ||||
Means followed by the same letter(s) in rows and columns are not significantly different at the 5 % significance level. LSD = least significant difference; CV (%) = coefficient of variation; ∗∗ Significant at P < 0.01; ns = non-significant at 5 % probability level.
The highest seed tuber number per hill (3.96) was recorded from propagated by seed tuber (control). On the other hand, the lowest seed tuber number per hill (1.53) was recorded for Belete variety propagated by shoot tip cutting with a spacing of 50 cm × 20 cm (Table 4).
This difference may be due to genetic variations among potato varieties affecting tuber numbers. Additionally, wider spacing between plants provided more area per plant for growth and development, potentially allowing for higher tuber production. Furthermore, seed tuber propagation has more stems than shoot tip cutting which could have more seed tubers per hill.
This finding aligns with Chindi et al. [34], who reported significant variations in tuber number per hill among potato varieties. The results support the conclusion of Getaneh and Laekemariam (2021), who similarly observed that wider spacing between plants directly correlated with enhanced tuber production.
3.4.2. Seed tuber weight
The main effects of variety, inter-row spacing, intra-row spacing, and their interaction significantly influenced seed tuber weight propagated by shoot tip cutting (P < 0.01, Table 1). T-test analysis revealed no significant mean difference between Belete and Gera varieties propagated by seed tuber at the 5 % level. In comparison, a significant mean difference was between seed tuber and shoot tip cutting propagation methods at the 5 % level (Table 5).
Table 5.
Effects of variety, Inter-row spacing, and intra-row spacing on average seed tuber weight of potato, and comparison of propagation methods on this variable.
| Shoot tip cutting |
Average seed tuber weight |
|---|---|
| Varieties | |
| Belete | 50.72b |
| Gera | 55.40a |
| LSD (5 %) | 2.35 |
| Inter-row | |
| 30 cm | 45.97c |
| 40 cm | 50.58b |
| 50 cm | 57.69a |
| 60 cm | 58.00a |
| LSD (5 %) | 3.32 |
| Intra row | |
| 15 cm | 48.39c |
| 20 cm | 55.35a |
| 25 cm | 51.84b |
| 30 cm | 56.66a |
| LSD (5 %) | 3.32 |
| CV | 11.57 |
| Tuber (Control) | |
| Varieties | |
| Belete | 65.64 |
| Gera | 60.24 |
| T-test | 1.18ns |
| Overall mean | |
| Tuber | 62.94 |
| Shoot tip cutting | 53.06 |
| T-test | −2.31∗ |
Means followed by the same letter within a column are not significantly different at the 5 % significance level. LSD = least significant difference; CV (%) = coefficient of variation; ∗ Significant at P < 0.05; ns = non-significant at 5 % probability level.
Among the varieties propagated by shoot tip cutting, Gera variety produced the highest average seed tuber (54.50 g) compared to Belete (50.72 g). Among the propagated methods, seed tuber (control) recorded the highest average tuber weight (62.94 g) than propagated by shoot tip cutting (53.06 g). Regarding spacing, 60 cm inter-row and 30 cm intra-row spacing recorded the highest average seed tuber weight of 58 g and 56.66 g, respectively. In comparison, the lowest average seed tuber weight recorded the narrower inter-row and intra-row spacing of 45.97 g and 48.39 g, respectively (Table 5).
The variation in average seed tuber weight can be attributed to the unique genetic traits of each potato variety and their response to spacing and propagation methods. The wider spacing between plants could have facilitated better tuber development, by reducing competition among plants for essential resources.
The study findings align with the research conducted by Lemma et al. [35], emphasizing the significant differences in average tuber weight among various potato varieties. Moreover, the finding that greater spacing between plants results in increased average tuber weight aligns with the findings of Derebe and Kola [33].
3.5. Seed tubers yield per plant and hectare
3.5.1. Seed tubers weight per hill
The main effects of variety, inter-row spacing, intra-row spacing, and their interactions significantly influenced tuber weight per hill propagated by shoot tip cutting (P < 0.01). T-test analysis showed no significant mean difference between Belete and Gera varieties propagated by seed tuber at the 5 % level. In comparison, a significant mean difference was between seed tuber and shoot tip cutting propagation methods at the 1 % level (Table 6).
Table 6.
The interaction effect of variety, inter-row spacing, and intra-row spacing on seed tubers weight per hill and seed tubers yield per hectare, and comparison of propagation methods on these variables.
| Shoot tip-cutting | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Variety | Seed tubers weight per hill (g) |
Seed tubers yield per hectare |
|||||||
| Intra-row |
Intra-row |
||||||||
| Inter-row | 15 cm | 20 cm | 25 cm | 30 cm | 15 cm | 20 cm | 25 cm | 30 cm | |
| Belete | 30 cm | 85.00k-m | 74.50m | 84.16k-m | 106.83j-l | 18.49a-c | 12.15e-j | 10.69h-l | 11.59f-k |
| 40 cm | 81.00lm | 129.67h-j | 145.00e-h | 143.17f-h | 13.19d-i | 16.00b-d | 14.18d-g | 11.60f-k | |
| 50 cm | 110.17i-k | 92.00k-m | 124.00h-j | 168.83c-f | 14.22d-g | 8.77k-n | 9.60i-m | 10.99h-l | |
| 60 cm | 105.83j-l | 104.67j-l | 167.33c-f | 138.00g-i | 11.46g-l | 8.33lm | 10.86g-l | 7.4m | |
| Gera | 30 cm | 69.66m | 129.00h-j | 146.50e-h | 171.50b-e | 14.87de | 20.57a | 18.81ab | 18.32a-c |
| 40 cm | 128.00h-j | 163.67c-g | 109.17j-l | 178.00a-d | 20.74a | 19.27a | 10.50h-l | 14.59d-f | |
| 50 cm | 161.17c-g | 198.33ab | 150.83d-h | 131.83h-j | 21.11a | 19.29a | 11.70f-k | 8.47k-m | |
| 60 cm | 187.17a-c | 189.33a-c | 205.67a | 171.17b-f | 20.27a | 15.51cd | 13.06d-i | 9.14i-m | |
| CV (%) | 12.71 | 13.66 | |||||||
| LSD (5 %) | 28.21 | 3.11 | |||||||
| Tuber (Control) | |||||||||
| Belete | 241.83 | 13.04 | |||||||
| Gera | 254.00 | 13.80 | |||||||
| T-test | −1.7ns | −1.8ns | |||||||
| Overall mean | |||||||||
| Tuber | 247.91 | 13.42 | |||||||
| Shoot tip cutting | 135.75 | 13.95 | |||||||
| T-test | −6.76∗∗ | 0.28ns | |||||||
Means followed by the same letter(s) in rows and columns are not significantly different at a 5 % significance level. LSD = least significant difference; CV (%) = coefficient of variation; ∗∗ Significant at P < 0.01; ns = non-significant at 5 % probability level.
The highest seed tuber weight (248 g hill−1) was recorded from propagation by seed tubers (control). In contrast, the lowest tuber weight per hill (74.5 g) was observed for Belete variety propagated by shoot tip cutting with a closer inter-row spacing of 30 cm × 20 cm (Table 6).
This variation in tuber weight per hill can be attributed to genetic differences among potato varieties, wider spacing provided an opportunity for better tuber development by reducing competition for resources among plants, and the impact of the propagation method on the number of stems per hill. Propagation by seed tubers, for instance, can lead to a higher number of stems and stolons, resulting in an increased number of tubers and, consequently, greater tuber weight per hill.
These results are consistent with the study by Gemmechu [36], who found that the weight of potato tuber per hill was significantly affected by the interaction of variety, inter-row spacing, and intra-row spacing. Furthermore, Ozkaynak [37], also verified significant variations in tuber weight per hill among different potato varieties. Moreover, higher tuber weight per hill was recorded in the findings of Derebe and Kola [33] when the distance between potato plants was increased, leading to greater air circulation, better sunshine access, and less competition for nutrients among plants with wider spacing between them. Additionally, Çalışkan et al. [38], found a significant difference between aeroponic and conventional propagation methods on seed potato tuber weight.
3.5.2. Seed tubers yield per hectare
The main effects of variety, inter-row spacing, intra-row spacing, and their interactions significantly influenced seed tubers yield per hectare propagated by shoot tip cutting (P < 0.01). T-test analysis showed no significant difference between Belete and Gera varieties propagated by seed tuber at the 5 % level, while a significant between seed tuber and shoot tip cutting propagation at the 5 % level (Table 6).
Gera variety, propagated with shoot tip cutting at 50 inter-row cm and 15 cm intra-row spacing and closer intra-row spacing, produced the highest seed tuber yield (21.11 tons ha−1), while Belete variety, propagated with shoot tip cutting at 60 cm × 30 cm spacing and wider inter-row and intra-row spacing, the lowest yield of 7.4 tons ha−1 (Table 6).
The variation in seed tuber yield among different varieties and propagation methods may be due to genetic traits, spacing configurations, and propagation method efficiency. Gera variety exhibited a higher yield, potentially because of, its suitability for the narrower spacing configuration and closer intra-row spacing, creating optimal growing conditions for this specific variety. Conversely, Belete variety, propagated with wider spacing configurations and larger intra-row spacing, may have lacked the essential environmental conditions for optimal growth and yield.
The results of this study are in line with the findings of Mamun et al. [16] and Nikmatullah et al. [17], the interaction effect of variety and spacing significantly influenced seed tuber yield of potato propagated by shoot tip cutting. Furthermore, Ozkaynak [37], observed a significant impact of Cevher variety showing better seed tuber yield than other varieties. Van Dijk et al. [39] also emphasized the importance of spacing 20 cm between and 20 cm within rows to give the maximum seed tuber yield propagation using shoot tip cutting. Furthermore, Gadana [40] supports that suitable spacing is crucial for enhancing seed tuber yield.
3.6. Leaf area index on yield of seed tuber
The linear regression analysis revealed that the leaf area index was a significant independent factor influencing seed tuber yield in the field experiment. R-squared value of 59 %, indicating a good fit. The positive and statistically significant effects and positive correlation (r = 0.77) of the leaf area index on the yield of seed tubers were evident from the results presented in Fig. 2.
Fig. 2.
Relation between leaf area index and yield of seed tuber.
As a result, the regression analysis indicated that increasing the leaf area index from two (low) to five (high) led to a significant increase of 13 tons in seed tuber yield per hectare. This observation can be attributed to the greater utilization of solar radiation, increasing the net photosynthesis rate. These findings align with a study by Chala and Dechasa [41], which also reported a positive correlation between increasing leaf area index and seed tuber yield.
4. Conclusion
The results revealed that variety, spacing, and propagation methods significantly influenced potato growth and seed tuber yield. The result supports the hypothesis that variety, spacing, and propagation methods affect potato growth and seed tuber yield. Potato varieties propagated using shoot tip cutting at 50 cm inter-row spacing and 15 cm intra-row spacing archives significant yield increment, which is 57.3 % seed tuber yield increment over seed tuber propagation (control). Based on this finding, it is recommended to propagate potatoes using shoot tip cutting at 50 cm inter-row spacing and 15 cm intra-row spacing for seed tuber production in the study area.
CRediT authorship contribution statement
Shege Getu Yayeh: Writing – review & editing, Writing – original draft, Visualization, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Wassu Mohammed: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Investigation, Formal analysis, Data curation, Conceptualization. Kebede Woldetsadk: Writing – review & editing, Writing – original draft, Visualization, Supervision, Investigation, Formal analysis, Data curation, Conceptualization. Tewodros Bezu: Writing – review & editing, Writing – original draft, Visualization, Methodology, Investigation, Data curation, Conceptualization. Yigzaw Dessalegn: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Formal analysis, Data curation, Conceptualization. Semagn Asredie: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Data curation, Conceptualization.
Informed consent statement
Not applicable.
Data availability statement
The data supporting the findings of this study is available from the corresponding author upon reasonable request.
Institutional review board statement
Not applicable.
Funding statement
This research received no specific grant from funding agencies in public, commercial, or not-for-profit sectors.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank the Ministry of Education, Ethiopia for supporting this research and Adet Agricultural Research Center, Ethiopia for providing the experimental area and planting materials.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data supporting the findings of this study is available from the corresponding author upon reasonable request.