In Indonesia, soybean is an important crop and the demand increases as population increases. Soybean production in 2011 was 851,286 tons (Badan Pusat Statistics (BPS), 2011), while the soybean demand reached 2.6 million tons. To fulfil the production shortage, the Indonesian goverment imports soybean in large quantity. Therefore, to decrease soybean import, the Indonesian government pushes to lift the domestic production through soybean selfsufficiency program (Kementan, 2011). Increasing soybean production through a breeding program for high yielding varieties is still the best choice (Mejaya et al., 2010), and this option becomes a priority because development of high yielding variety development is relatively more economical effort than environmental modifications. High yielding soybean varieties with broad adaptation are likely to be stable even though under different environment conditions. However high yielding varieties with narrow adaptation are also needed to develop varieties adaptive to the specific environmental conditions.

To obtain high yielding varieties, genetic materials should be selected for desired characters that affect plant growth and yield potential. Selection can be conducted on germplasm collection derived from wild species (Abdullah, 2006; Acosta-Gallegos et al., 2007), local varieties, and Indonesian and Korean varieties from other countries (Sumarno & Zuraida, 2008). Germplasm introduction is an attempt to increase genetic variability (Mursito, 2003) and allows to obtain genetic material having large characters and variability genetic distance. Therefore, germplasm exchange to obtain genetic material that potentially can be used for developing new variety is important .

Korean germplasm should be evaluated for growth and yield characters before it is used as hybriditation parent or a new variety (Malik et al., 2006; Mejaya et al., 2010). Evaluation of yield components as an indirect approach to selection criteria for seed yield tends to be more effective than direct selection. Growth character such as days to flowering, days to maturity, plant height, number of branches, number of pods per plant, number of seeds per plant, yield per plant and 100-seed weight can affect seed yield (Mangoendidjojo, 2003; Machikowa & Laosuwan, 2011; Sarutayophat, 2012). Every genetic material has different genetic structure and leads plants variability. In addition, environmental differences such as soil fertility, rainfall, altitude, soil structure, daylength, temperature and other climate factors can affect plants variability. Sitompul & Guritno (1995) stated that environmental conditions differ from one place to another place, and the needs of plants in a particular circumstances may lead to plants variability. Miladinovic et al. (2006) found differences on seed yield, plant height, seed weight, harvest index, period of vegetative and reproductive phase, protein content, and oil content of four tested varieties in different environments. Jiang et al. (2011) found that long daylength can delay flowering time in photoperiod-sensitive soybean. Differences of environmental conditions between Indonesia and its origin may lead different performance of plants grown on both areas.

Objective of this study was to evaluate the expression of agronomic characters of 20 Korean soybean varieties in Indonesia.

MATERIALS AND METHODS

This experiment was conducted in the Indonesian Legumes and Tuber Crops Research Institute, Malang, Indonesia during dry season from May to August 2012, located around 400 meters above sea level at the longitude 112° 7′ 12″E and the latitude 7° 8′ 48″S. The weather of the location had low rainfall and hot temperature. The materials were consisted of 20 Korean varieties and four Indonesian soybean varieties as check. The experimental design was a randomized completely block design with three replication. Each experimental unit consisted of four plants that grown in polybag with the size of diameter 20cm by height 25cm. NPK fertilizer (ratio 16:16:16) was applied at planting time with dosage of 2 g every polybag. Weedings were carried out at 14, 30, and 45 days after planting (DAP). Watering was conducted according to plant requirement. Observations were conducted for days to flowering and days to maturity, plant height, number of branches, number of reproductive nodes, number of filled and unfilled pods, number of seeds per plant, 100-seed weight, and seed yield per plant. Data were analyzed using honestly significant difference test (HSD) a 0.05. In addition, data were analyzed by correlation analysis that describes the relationship among observation variables.

RESULTS AND DISCUSSION

The results showed that there were differences among varieties on characters of days to flowering, days to maturity, plant height, number of branches, number of reproductive nodes, number of pods per plant, 100-seed weight, and seed yield per plant, while number of empty pods was not different. The differences among varieties on these characters indicated that each variety has a different genetic structure that leads to perfomance variability (Fig. 1 and Table 2). This result was supported by Mursito (2003) that different genotypes showed different performance when interacting with a particular environment. His study showed significant difference among 11 lines for characters of days to flowering, plant height, number of pods per plant, number of unfilled pods per plant, seed yield per plant, and 100-seed weight. Malik et al. (2006) also reported that there were differences on character of days to flowering and days to maturity, plant height and seed yield.

Soybean vegetative phase starts since plants emergence until flowers begin to appear. The tested varieties had vegetative phase varied between 25-35 DAP. The shortest vegetative phase was achieved by Geomjeongsaeol followed by Jangmikong and Pungsannamulkong i.e 25, 26, and 26 DAP, respectively (Fig. 1). The longest vegetative phase was achieved by Detam 1 and Cikuray, followed by Anjasmoro and Argomulyo i.e 35, 35, 34 and 33 DAP respectively (Fig. 1). Generally all Indonesian varieties had longer vegetative phase than the Korean varieties. The vegetative phase of the Korean varieties was shorter due to the plants responsed to the new conditions e.g. daylength and temperature. Indonesia has daylength 11.40 – 11.55 hours with average temperature 27 – 29 °C in Malang (Table 1), whereas South Korea has daylength 11.13 – 14.41 hours with average temperature 15 – 26 °C from the May to October in Suwon. Shorter daylength and higher temperature caused shorter vegetative phase. Cho et al. (2005) reported that days to flowering in South Korea was the range from 39 to 51 DAP. Levy & Dean (1998) and Jiang et al. (2011) stated that the difference in daylength could speed up the initiation of flowering. Other authors (Lawn & Byth, 1973; Major et al., 1975; Board & Hall, 1984) reported that soybean experiencing longer daylenght and lower temperatures would delay flowering initiation. Flowering phase will start earlier under normal or shorter daylength and higher temperature.

Reproductive phase starts from flowering initiation until plant maturity. The reproductive phase of tested varieties ranged from 39 to 56 days. The shortest reproductive phase was showed by Cikuray (only 39 days) while the longer was showed by Daemang 2, Daewonkong, Cheongja 3, Geomjeongkong 3, and Jangmikong i.e. 56, 55, 54, 54, and 54 days, respectively. Generally, Korean varieties had longer reproductive phase than the Indonesian varieties except Pungsannamulkong, Seonyu, Songhakkong, and Taekwangkong Pungsannamulkong and Songhakkong had the same reproductive phase with Anjasmoro, Argomulyo, and Detam 1 (45 days), while Seonyu and Taekwangkong were shorter (42 and 44 days, respectively) (Fig. 1). The length of vegetative and reproductive phase determines the days to maturity. Varieties that had longer days to flowering showed longer days to maturity although they had shorter reproductive phase. Lawn & Byth (1973) reported that the varieties with longer vegetative phase have the longer days to maturity. In this research, duration of reproductive phase lead to increase seed yield. It occurred because the photosyntate that was produced during the reproductive phase was primarily served in seed filling (Purnawati et al., 2010). Conversely, shorter reproductive phase varieties had less seed filling duration. Under normal growth, longer reproductive phase varieties had higher seed yield. For example, Daemang 2, Daewonkong, and Jangmikong produced higher seed yield while Cheongja 3, Geomjeongkong 3 and Cikuray produced lower seed yield (Table 2 and 3). Similar results also were reported by Machikowa & Laosuwan (2011) that the longger reproductive phase varieties produced higher seed yield. Generally plant age of Korean soybean was shorter than in the South Korea. Cho et al. (1999) stated that plant age of soybean in Korea varied with the range from 98 to 114 DAP, whereas in Indonesia were only with the range from 71 to 84 DAP in Malang. Plant age of Korean soybean varieties differs from Indonesia soybean variety.

Variability of plant height ranged from 18.2 to 64.0 cm. The shortest plant height was Pungsannamulkong whereas the highest was Detam 1 (Table 2). Generally, all tested Indonesian varieties had better performance than the Korean varieties. The plant height of the shorter Korean varieties might be due to the different environmental conditions between two countries such as temperate regions with tropical regions. The different environmental conditions from one location to another and the needs of plants in specific circumstances may lead to different plant perfomance (Sitompul & Guritno, 1995; Han et al., 2006). In different environmental conditions, Zhang & Du (1999) found that soybean plants receiving 16 hour daylength had a higher plant height than plants receiving 13.5 and 8 hour daylength, and Lee et al. (1988) found that soybean plants receiving 16 hour daylength had a broader range of days to flowering compared with the plants receiving 10 hours daylength and natural field experiment (longitude 126° 59′ E and the latitude 37° 16′ N). Agusta & Santosa (2005) reported that soybean plants receiving additional irradiation up to 24 hours had plant height up to 184 cm and an increase of 236% compared to the control (78 cm). Soybean is short-day plant which will bloom if it is grown under shorter daylength than the critical photoperiod. Soybean will terminate its vegetative phase and enter reproductive phase or start flowering if the plant undergos shorter daylength than 12 hours. Detam 1 and Cikuray with higher plant height also had the longest flowering age (35 DAP) while Geomjeongseol and Pungsannamulkong with the shortest plant height had the shortest days to flowering (25 and 26 DAP). Generally all the Indonesian varieties have the longer days to flowering than those of the Korean varieties (Fig. 1).

Number of branches varied among the varieties from 1 to 6 branches (Table 2). The fewest branching was produced by Pungsannamulkong and the most branching number was produced by Cikuray. Detam 1 and Cikuray had more branches than Korean varieties. There were 15 Korean varieties having branches equivalent to Anjasmoro. Number of branches is closely related to plant height of each variety. Varieties that had higher plant height also had more branches (Table 4). Similar results also reported by Hakim (2007) that the number of branches in mungbean was closely related to plant height.

Number of reproductive nodes varied from 7.8 to 26.1 (Table 2). The highest number of reproductive nodes was produced by Detam 1, while the least one was produced by Sodamkong. All of the Indonesian varieties except Argomulyo had more number of reproductive nodes than the Korean varieties. Among the Korean varieties, Songhakkong produced highest number of reproductive nodes. A higher plant height and number of branches might caused higher number of pods and reproductive nodes on Indonesian varieties. The less number of reproductive nodes among the Korean varieties was due to the shorter plant height.

Generally, number of filled pods of Korean varieties were less than Indonesian varieties (Table 3). Detam 1 and Cikuray produced the highest number of pods among all varieties. However, Songhakkong had the most number of filled pods after Detam 1 and Cikuray. Argomulyo, early maturing variety, had low number of filled pods such as some Korean varieties. Number of filled pods was affected by number of flower and ratio of pod setting. The number of flowers and ratio of pod setting were affected by the plants genotype (Zhang et al., 2004), plant physiology, and environmental factors such as daylength and temperature (Han et al., 2006; Lagercrantz, 2009).

Seed size (reflected to 100-seed weight) varied from 11.2 - 33.9 g. The highest 100-seed weight reached by Daehwangkong, Cheongja 3, and Sodamkong i.e. 33.9 g, 32.5 g, and 31.0 g while the lowest weight achieved by Cikuray, Pungsannamulkong, and Detam 1 i.e. 11.2 g, 13.4 g, and 15.1 g (Table 3). Usually, all-Korean varieties except Pungsannamulkong had higher 100-seed weight than the Indonesian varieties. Among Indonesian varieties, Argomulyo had the greatest 100-seed weight. Seed size was influenced by the plant genotype of each variety.

Seed yield is a result of photosyntate accumulation that is transferred from the photosyntetic organs. Plant having high vegetative organs will have low reproductive organ (Purnawati et al., 2010). Among the Korean varieties and all tested varieties, Daewonkong had the highest seed yield, while the lowest seed yield was showed by Taekwangkong. Detam 1 had the highest seed yield among the tested varieties. Seed yield per plant was influenced by the genotype of each plant (Mangoendidjojo, 2003; Machikowa & Laosuwan, 2011; Sarutayophat, 2012). The higher seed yield in some Korean varieties was caused by large seed size. This fact suggested that some varieties was potential parent to develop high yielding variety. The varieties with high seed yield had generally number of reproductive nodes, number of pods and number of seeds per plant (Table 4). Machikowa & Laosuwan (2011) reported that seed yield was affected by the number of pods and number of branches.

Higher plant height also had higher number of branches, number of reproductive nodes, number of pods, and number of seeds per plant (Table 4). The higher plant height had many reproductive nodes because every node has possibility to develop branches. Therefore, the formed branches were also higher on plant with higher plant height. Every branch will produce many nodes that allow the growth of flowers and pods. Therefore, more reproductive nodes lead more pods. Varieties producing smaller seed size lead to produce more pods. Detam 1 and Cikuray had the highest plant height, branches, reproductive nodes, pods and more seeds but had the smallest pods and seed sizes. Similar results also reported by Susanto & Adie (2005) stated that the 100-seed weight negatively correlated to days to flowering, plant height, number of branches and number of pods per plant.

Plant height variability had no relationship to maturity age (Table 4). Varieties that had longer maturity age, also had heavier 100-seed weight. Daemang 2, Cheongja 3, and Daehwangkong had days to maturity of 84, 80, and 80 DAP respectively, and also had heigher 100-seed weight. Similar result also reported by Malik et al. (2006) stated that the age of soybean maturity age varieties closely related to the 100-seed weight but had no relationship with plant height, number of branches and number of pods per plant. Maturity age of tested varieties varied from 71–84 DAP. The shortest maturity age was showed by Pungsannamulkong while the longest maturity age was produced by Daemang 2.

CONCLUSION AND SUGGESTIONS

The Korean varieties generally had shorter plant height, earlier days to flowering, longer reproductive phase, and larger seed size. Based on seed yield per plant, the best perfomance were showed by Daewonkong, Detam 1, Jangmikong, and Songhakkong, i.e. 12.8 g, 11.6 g, 11.4 g, and 11.3 g per plant in the polybag experiment, respectively. Some Korean varieties having high seed yield such as Daewonkong, Jangmikong, Songhakkong, and Daemang 2 can be used as a potential parent for developing a high yield variety, while some Korean varieties having large seed size such as Cheongja 3, Daehwangkong, Daemangkong, Geomjeongkong 3, Geomjeongsaeol, Ilmikong, Seonyu, and Sodamkong can be used as potential parents in breeding pragram for increasing seed size.