INTRODUCTION

Chinese cabbage (Brassica rapa L.) is recognized an important commercial vegetable crop in East Asia, including South Korea, and they are also a major ingredient of traditional fermented foods like Kimchi (Kim et al., 2022). However, due to worldwide climate changes and the diversification of agricultural environments, it became significant to examine the adaptability and productivity of varieties of Chinese cabbages in different areas as it is a semi-temperate crop and more adoptable in high altitudes (Niña et al., 2024).

Bolivia has a wide range of altitudes and climate conditions, with its regions showing various environmental characteristics for agricultural production. In particular, the alpine regions at the Andes mountains can be an adequate location to test the suitability for cultivation of crops since the regions have unique traits in temperature, soil, the amount of sunshine, etc.

Chinese cabbage grows in cool temperatures, typically between 15∼20°C, which makes autumn the ideal planting season. It is reported that temperature is the most critical factor that influences their growth (Kim et al., 2022). While Chinese cabbages can tolerate relatively high temperatures at early growth stages, they become vulnerable to high temperatures when their head formations have started (Oh et al., 2014). Hot weather can cause delayed growth, yellowing and wilting leaves, and the emergence of insects and diseases, which may further threaten their qualities and yields (Yue et al., 2021). Additionally, it is reported that the expose to drought stress during cultivation can also lead to deterioration in qualities and yields, with the severity depending on the degree, duration, and timing of the stress (Jang et al., 2024).

If Korean varieties of Chinese cabbage can adapt to Bolivia’s agricultural environment, it will open the possibility of entering the Bolivian market for Korea and adopting a new high-value crop for Bolivian farmers. In addition, it will contribute to improving the productivity and diversity of Bolivian agriculture and expanding the Korean food culture and exports.

The aim of this study is to investigate how the Korean varieties of Chinese cabbage grow in the climate conditions in Bolivia. The cultivars that well adapted to the climate conditions in Bolivia were selected through a region-specific cultivation method. As a result, two varieties from five different Chinese cabbage varieties were considered to be desirable candidates. The experiments were conducted at the KOPIA Bolivia Center, where a drip irrigation system was provided for water control.

MATERIALS AND METHODS

1. Climate conditions and soil analysis at test field

In this research, we planted the seeds of Korean varieties of Chinese cabbage provided by the Korea Seed and Variety Service (KSVS) at the KOPIA Bolivia Center to evaluate the crop yields under Bolivia’s environmental conditions. The optimum growth temperature for the Chinese cabbages is 18∼20°C, the temperature required to induce head formation is 15∼18°C, and the critical minimum temperature for them is 3∼4°C (Park et al., 2019). It makes Sipe Sipe region in Cochabamba (Latitude: -17° 26’ S, Longitude: -66° 22’ W), where the KOPIA Bolivia Center is located, an appropriate test site since the temperature there between August and November satisfies the aforementioned conditions. Table 1 shows the average climate conditions at Sipe Sipe that we measured during cultivation. The test was conducted between August to November in 2024.

Table 2 show the soil analysis results of the soil collected at the test field. The analysis was conducted at August 8th, 2024. The soil from test field had low clay content and high silt content. It was slightly alkaline, which required pH control for some kinds of crops to grow. Furthermore, the contents of nitrogen, phosphorus, and potassium were comparatively low, which also needs adjustment.

2. Test Targets and Cultivation Method

In this research, four kinds of Korean-variety Chinese cabbage seeds provided by KSVS were tested based on the standard cultivation methods from the Rural Development Administration in Korea. Additional cultivation technologies suitable for the climates in Bolivia were also applied together.

The four Korean varieties of Chinese cabbage used in this study were KB913 (Dayi International Seed), 23s7179 (Dayi International Seed), RCC9 (Kwonnong), and RCC65 (Kwonnong). Both KB913 and 23s7179 can be grown all year round, while the former is large-sized and the latter is medium-sized. RCC9 contains anthocyanin suitable to crop in fall, and RCC65 contains anthocyanin suitable to crop in spring and fall. Additionally, we also grew the ZAMBO variety, which i s widely a vailable i n Korea, as a control group to compare the productivity and adaptability at the test site.

The seeding process for all kinds of seeds was conducted by first sowing them in pots and then transplanting seedlings to the experimental field. We planted 45 seedlings of KB913, 44 seedlings of 23s7179, 56 seedlings of RCC9, 57 seedlings of RCC65, and 51 seedlings of ZAMBO. We used lightweight soilless potting mixes, which mainly consisted of chaff charcoal, and planted one seedling per seeding hole. Later, we transplanted them to the experimental field when the number of their normal leaves became 3∼4. Also, we utilized plastic pots (8cm ^* 8cm) during the process.

The experimental field was divided into 15 areas where the seedlings from 5 different varieties, including the control group, were transplanted in a completely randomized manner with 3 repetitions. Each area consisted of two rows of flat furrows with an interval of 130cm between neighbors. In a row, we planted the crops at intervals of 30cm. The experiment for each variety was repeated in 3 areas, taking 8 weeks in total, of which 6 weeks were for after-transplanting observation. However, only for the 23s7179 variety, it took 4 weeks before transplanting and another 4 weeks for observation in each experiment. That was because of the lack of 23s7179 seeds and their low germination rates.

The fertilizer management during cultivation is listed in 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, whose altitude is 2,600m above sea level. For disease and pest control, we sprayed pesticides according to Table 4.

3. Investigation of Crop Growth

The investigation of crop growth for four target varieties and one control group includes 3 phases: investigation on seedlings, investigation after transplanting, and investigation after harvest. The investigation on seedlings was conducted twice. We first measured germination rates at July 30th, which was 25 days after sowing. The germination status was judged by the emergence of cotyledons at that time. After that, we measured the number of leaves and plant height at August 7th. For the investigation after transplanting, we measured the plant height of the crops at 7-day intervals, starting 10 days after transplanting. Lastly, we measured crop weight, plant height, head circumference, leaf count, and the total yield for the investigation after harvest. The investigation after harvest was performed at November 6th and November 12th.

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 results of the germination rates and morphological characteristics of seedlings of five different Chinese cabbage varieties in Table 5 and Table 6, we observed that the seedlings of RCC65 and KB913 showed superior growth measurements to those of the others. They had larger values in plant heights, leaf counts, and germination rates. The ZAMBO variety also showed the highest germination rate, comparatively stable leaf count, and high plant height. The KB913 variety also showed a high germination rate and the highest leaf number. On the other hand, the germination rate and the leaf number of the RCC9 variety were not very notable. The 23s7179 variety, however, showed the lowest germination rate and the lowest leaf number, indicating its growth overall was poor.

As described in Table 7, the result of the investigation after transplanting confirmed that the RCC65 variety showed the best plant height and stable growth traits. Regarding the RCC9 variety, it showed the second-highest growth amount and stability. In the case of the KB913 variety, while it showed the fastest growing speed in the beginning, the final growth was low due to the slowdown of growth in the end. The ZAMBO variety also showed a steady growth in plant height, but the final growth was relatively low. Lastly, the 23s7179 variety showed the lowest growth most of the time.

Table 8 and Figure 2 present the result of the investigation after harvest. First, the ZAMBO variety was evaluated as the most suitable for the local climate, recording the highest individual weight and total yield. The KB913 variety was as outstanding as ZAMBO, characterized by its large crop size and stable quality. In contrast, the 23s7179 and RCC65 varieties showed weak growth and low total yield. The RCC9 variety also needed quality improvement, although there was an acceptable total yield.

Table 9 shows the photographs of actually harvested Chinese cabbages of each variety. In this experiment, the ZAMBO variety achieved high total yield and desirable head formation, but it suffered intensely from bacterial soft rot and diamondback moths due to monocropping. It was because the ZAMBO variety had been being cultivated continuously at the KOPIA Bolivia Center. The KB913 variety was observed to have strength in overall growth, to have leaves that were more vivid and glossy than those of ZAMBO, and to be more resistant to pests and diseases than ZAMBO. The 23s7179 variety, on the other hand, showed a l ow germination rate and weak g rowth, while i t still had better resistance to pests and diseases than ZAMBO. Lastly, the leaves of the RCC9 and RCC65 varieties were slightly purple due to anthocyanin, and the leaves were harder than the others.

DISCUSSION

The experiment was conducted in the Sipe Sipe region of Cochabamba which is an alpine region, 2,600m above sea level to evaluate the adaptability of four different Korean varieties of Chinese cabbage to the local climate of Bolivia.

As a result of the experiment, the ZAMBO variety showed its superior traits in the aspects of individual weight, leaf number, and total yield, confirming that it is suitable for the local climate conditions. Similarly, the KB913 variety, which was a type of large Chinese cabbage, adapted well to the environment with respect to individual weight and total yield. Regarding their adaptability and productivity, the two varieties are considered the best for local cultivation in Bolivia. However, the 23s7179 variety had problems in germination rate and growth in the early stages, representing the low adaptability in Bolivia’s environment.

Although prior studies (Liu et al., 2020;Lin et al., 2021;Kangatharalingam et al., 2002) have reported the resistance to disease and pest in crops containing anthocyanins, RCC65 and RCC9―both anthocyanin-containing varieties― did not perform well in terms of average weight and total yield, despite showing a relatively high number of surviving plants during growth.

This trial was the first attempt to evaluate the adaptability of Korean Chinese cabbage varieties in Bolivia, as far as we have checked. Given the diverse climates and ecological conditions across different regions of Bolivia (Seiler et al., 2013), further research in other areas is needed to conduct a more in-depth analysis of varietal adaptability and productivity. Additionally, considering the limited water availability (Canedo, 2019) and farmers’ insufficient knowledge of chemical pest control methods in general (Barrón et al., 2024), it is needed to develop Korean Chinese cabbage cultivation technologies suited to the Bolivian agricultural conditions.

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