INTRODUCTION

Radish (Raphanus sativus L.) is a globally significant root vegetable crop, classified as an annual or biennial dicot in the Brassicaceae family (Luo et al., 2020). Korean radish has been one of the major vegetable crops in Korea, where a wide range of varieties are being grown across various regions and seasons. Radish is a nutrient-rich vegetable, containing proteins, lipids, fiber, vitamins, and essential minerals like iron, magnesium, and calcium. It is widely valued for its high yield per unit area and is commonly used as a key ingredient in kimchi, a traditional Korean fermented dish (Yu et al., 2023). In particular, in South Korea, about 10 percent of the land used for growing vegetables is dedicated to radishes and the demand for sustainable radish cultivation is increasing (Park et al., 2024;Seiler et al., 2013).

Bolivia has various levels of altitudes and climate conditions from tropical to cold desert climate (Lee et al., 2013), and the highland regions, such as Cochabamba, present relatively stable temperatures and limited precipitation. The climate conditions of this region can potentially offer a favorable environment for the cultivation of Korean radish, but selection of suitable varieties and their evaluation should precede to ensure their successful adaptation to the local environment.

In this paper, we investigated and assessed the adaptivity of Korean radish varieties to the high-altitude environments in Bolivia. Through this experiment, we aimed to confirm the competence of Korean radish varieties in terms of growth, yield, and quality under the agricultural environment in Bolivia, thereby providing a data basis to enhance the productivity of local cultivation.

Furthermore, this study seeks to promote the diversification of local crops in Bolivia, explore the international expansion potential of Korean radish varieties, and strengthen agricultural technology cooperation between Korea and Bolivia to contribute to the continuous development of agriculture in Bolivia, ultimately.

Materials and Methods

1. Climate conditions and soil analysis at test field

The experiment of cultivating Korean radish varieties in Bolivia was conducted from August 23 to October 23, 2024, at the KOPIA Bolivia Center located at Sipe Sipe (Latitude: -17° 26’ S, Longitude: -66° 22’ W), Cochabamba. The altitude above sea level of the Sipe Sipe region is 2,600 m, and the region has dry weather. The average climate conditions of Sipe Sipe that we measured in 2024 are shown in Table 1.

Table 2 shows the soil analysis results at the test site in Sipe Sipe. The analysis was conducted by the laboratory of soil and water at San Simon university. It was reported that the soil had low clay content and high silt content. The soil was slightly alkaline, which required pH control for some of the crops to grow. In addition, the contents of nitrogen, phosphorus, and potassium were comparatively low, which also needed adjustment.

2. Test Targets and Cultivation Method

In this research, six kinds of Korean radish varieties provided by the Korea Seed & Variety Service (KSVS) were tested based on the standard cultivation methods from the Rural Development Administration in Korea. We also applied additional cultivation technologies suitable for the climate in Bolivia.

The six kinds of Korean radish varieties tested were NS1181 (Neo Seed), NS8196 (Neo Seed), Bravo2 (Kwonnong), Redking (Kwonnong), HB45 (Dayi International Seed), and DR-4 (Dayi International Seed). NS1181 and NS8196, whose upper roots are white, can grow between August and December. Both Bravo2 and Redking are suitable for cropping in the fall and have 55∼60 days of maturation period. Their colors are purple and red, respectively. Lastly, HB45 and DR-4 are white radishes suitable for cropping in April. Note that we also grew the Tongil variety, which is widely available in Korea, as a control group to compare the productivity and adaptability at the test site.

Regarding the seeding process, all the seeds were directly sown. We sowed 42 seeds in total per variety, only one seed per seeding hole, due to the lack of seeds. The distance between furrows was 130 cm, and the crops were placed at intervals of 30 cm in a furrow. After seeding, the seeds were covered by soil to a depth of 5 cm.

The experimental field was divided into 21 areas where the seeds from 7 different varieties, including the control group, were sown in a completely randomized manner. The seeds from each variety were planted in 3 different divisions, with each division having 14 of them. The placement was randomized to effectively offset the effects of surroundings. It took 12 weeks for the whole experiment, and the investigation was conducted for 7 weeks out of the 12 weeks.

The fertilizer management during cultivation followed Table 3. For watering, we supplied 170L of water per row of the ridge via 30 minutes of dripping irrigation once every two days. This kind of watering was needed to deal with the dry weather of the Sipe Sipe region. For disease and pest control, we sprayed pesticides and fungicides according to Table 4.

3. Morphological and Yield Measurements

The investigation of individual crops for six target varieties and a control group included two phases: investigation on growth and investigation after harvest. For the investigation on growth, we measured leaf length (cm) at 7-day intervals, starting 10 days after seeding. At this stage, the leaf length was measured as the length of the longest horizontal width of each radish when we spread out the leaves fully. For the investigation after harvest, we measured total length (cm), root length (cm), leaf length (cm), total weight (g), root weight (g), leaf weight (g), diameter (mm), and leaf count, respectively, which are the characteristics of individual crops. The measurements were conducted right after harvest. Together with the examination of individual traits, we also examined the total yield (kg), the occurrence rate of branch roots (%), and the rate of bolting (%) at last. When calculating the total yield, the crops that lost commercial value were excluded.

4. Data Analysis

For the analysis of certain data, the statistical program SAS Version 6.12 (SAS Institute Inc., Cary, USA), and the PROC GLM command was used when conducting an ANOVA based on the randomized complete block design (RCBD). The ANOVA was performed to effectively estimate the mean of each variable. Mean comparisons were made using Duncan's statistics.

In this study, we also adopted the area under disease progress curve (AUDPC) method, which is widely used in phytopathology research. We used the equation as a tool to compare the crop development between varieties.

Results

According to the result of the investigation on growth shown in Table 5, Redking, DR-4, HB45, and Tongil were evaluated to have superior size, regarding the final average leaf length. On the other hand, Bravo2 and NS8196 showed comparatively insufficient growth in terms of leaf length, with their growth slowed moderately in the later phase. Lastly, NS1181 grew weakly, and its final average leaf length was also small. However, note that the characteristics such as root length and root weight are not directly proportional to the value of leaf length.

Figure 1 compares the crop development of the seven varieties in terms of AUDPC which was calculated based on the leaf length measurements during cultivation period. In this method, the varieties that grew fast in the early stages are considered better, even though they record the same measurements with those of others at the end. The graph shows that Redking and DR-4 were more desirable than the others from the perspective of AUDPC.

The result of the investigation after harvest is described in Table 6, and the same information is also plotted as graphs in Figure 2, 3, 4, and 5. As in Figure 2, DR-4, HB45, NS8196, and Redking showed the longest total length compared to all others. For root length, the two longest ones were the NS8196 and DR-4, and the three shortest ones were the Brabo2, Tongil, and Redking. Concerning leaf length, the leaves of the Redking and HB45 were the longest, and the leaves of the NS1181 were the shortest.

Regarding weight, NS8196 and Tongil showed both the highest total weights and the highest root weights, as described in Figure 3. In contrast, NS1811, which recorded the lowest total weight, showed significantly low root weight and leaf weight at the same time. Interestingly, Redking had the lowest root weight but also had the highest leaf weight. In addition, HB45 also showed the second- highest leaf weight with better root weight than that of Redking.

As for the additional shape traits of the Korean radish, Tongil had the largest diameter among all (Figure 4). The varieties with the smallest diameters were NS1181, NS8196, and DR-4, making it notable that NS8196 was the one that recorded the highest total weight and the highest root weight. The variety with the largest leaf count was HB45, and the variety with the smallest leaf count was Redking (Figure 5). It is also remarkable that Redking recorded the highest leaf weight and the smallest leaf count at the same time.

In summary, based on the traits of individual crops which determine their commercial value, NS8196 and Tongil were evaluated as adequate varieties in the highland environment of Bolivia regarding their total weights and root weights. On the other hand, Redking and HB45 showed the strongest leaf development, where the root weight of HB45 was better than that of Redking. Lastly, NS1181 was evaluated to have low adaptability to the environment overall.

In Table 7, the actual photographs of each variety are shown. Redking had red-colored roots, and Brabo2 had purple-colored roots. NS8189, NS1181, and DR-4 had long and thin roots, and Tongil showed the thickest root compared to the others.

Table 8 describes the total yield and the total number of crops harvested for 7 different varieties. Particularly, DR-4, whose individual traits were moderate overall, recorded the highest total yield. The total yields of NS8196, Brabo2, and HB45 were also high, comparatively. However, the total yields of Tongil, Redking, and NS1181 were low, with that of NS1181 recording the lowest.

The physiological disorder during growth was also examined in terms of the occurrence of branch roots and floral axes. According to Table 8, Tongil showed the strongest resistance to the branch roots, making it probable to withstand environmental challenges in Bolivia. Brabo2 and Redking also had relatively strong resistance to the branch roots. NS8196, on the other hand, showed the highest occurrence rate of branch roots among them. For bolting, as in Table 8, Brabo2, DR-4, HB45, and Tongil all showed zero occurrence of flower axes. However, NS1181 and NS8196 had significantly high rates of bolting.

In summary, among the long-shaped radishes, NS8196 showed the best root weight per plant. However, considering the total yield and bolting rates altogether, DR-4 was the best choice for long-shaped radishes. Among the short-shaped radishes, on the other hand, Tongil was the best variety in terms of root weight per plant. However, considering the total yield, Bravo2 was the best choice for short-shaped radishes.

Discussion

In this study, we explored the adaptation of seven different Korean Radish variety in the Sipe Sipe region of Cochabamba which is an alpine region 2,600m above sea level. As radish exhibits a wide range of varieties, differing in leaf morphology, root color, size, shape, flavor, vernalization requirements, and maturity period (Singh, 2021), the experimental results showed that each variety had different characteristics and productivity.

Nonetheless, the biggest problems with overall productivity are believed to be bolting timing and branch roots. While flowering is essential for plant reproduction, it also serves as a key agronomic trait in radish, as an imbalance between vegetative and reproductive growth can affect both the yield and quality of its fleshy taproot (Wang et al., 2017). Previous studies have shown that bolting time tends to increase with latitude of origin, with Southeast Asia (lowest latitude) having the earliest bolting (Kang et al., 2016), which we believe may have influenced this

Conversely, environmental factors likely played a significant role in contributing to the branch root. For instance, heavy and compacted soils, or those containing clumps, stones, and undecomposed organic matter, can physically impede root development by causing root branching or forking. Additionally, excessively wet soil conditions during root growth may promote abnormal secondary root elongation, further contributing to root deformities (Manzoor et al., 2021).

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