Ⅰ. INTRODUCTION

Italian ryegrass (IRG, Lolium multiflorum Lam.) is a widely cultivated cool-season forage crop across the world, especially in temperate regions where it plays a vital role as a winter forage. This species is highly valued for its excellent palatability, high dry matter yield, and rapid growth rate, contributing significantly to improving livestock productivity. In the current agricultural environment, climate change and the need to enhance forage self-sufficiency have become critical challenges. IRG is receiving attention as a crop that can meet these demands.

In Korea, various IRG cultivars with different maturities have been developed, and a total of 25 cultivars have been registered to date. Starting with the country's first cultivar ‘Hwasan 101’ (Choi et al., 2000), late-maturing varieties such as ‘Hwasan 102’ (Choi et al., 2001a) and ‘Hwasan 103’ (Choi et al., 2001b) were developed first, followed by the early-maturing representative cultivar ‘Kowinearly’ (Choi et al., 2011). Early-maturing types have been favored in Korea, where IRG is mainly grown in paddy-upland double cropping systems. To ensure timely rice sowing, ultra-early cultivars such as ‘Greenfarm’ (Ji et al., 2011b), ‘Greenfarm 2ho’ (Ji et al., 2013), ‘Greenfarm 3ho’ (Ji et al., 2015), and ‘Greencall’ (Ji et al., 2018) were also developed. However, recent warming trends due to climate change have accelerated the growth stages of crops, leading to earlier heading in IRG. Although medium-maturing cultivars offer superior yield and forage quality compared to early-maturing ones, their late heading has limited their cultivation primarily to southern regions due to interference with subsequent rice cropping. Nevertheless, changes in growth patterns caused by climate change are shifting cultivar preferences, gradually expanding the suitable regions for medium-maturing varieties northward. Additionally, policies to increase forage production have diversified the production systems, and as rice cultivation is decreasing in paddy fields, there is less necessity to grow early-maturing types for double cropping with rice (MAFRA, 2024). As a result, farmer preference is increasingly shifting toward medium- and late-maturing cultivars that provide higher productivity and better forage quality than early-maturing types.

Given the limited area available for forage crop cultivation in Korea, it is essential to develop high-yielding IRG cultivars to compete with imported varieties. Particularly among mediummaturing types, there is a need to develop new cultivars with high productivity and abundant leaf biomass. Korea's forage industry faces increasing pressure as imported forages from countries like Canada (by 2024), the United States (by 2026), and Australia (by 2028) will enter duty-free due to multilateral Free Trade Agreements (FTAs). Under these circumstances, the development of high-yielding medium-maturing cultivars with superior forage quality is crucial to enhance the competitiveness of domestic forage and increase the self-sufficiency rate of locally developed varieties.

This study was conducted with the objective of developing a new medium-maturing IRG cultivar with high dry matter yield per unit area.

Ⅱ. MATERIALS AND METHODS

This study was conducted from 2011 to 2024 at the Forages Production Systems Division of the National Institute of Animal Science (NIAS) in Korea, with the objective of developing a new medium-maturing IRG cultivar.

1. Crossing combinations

From 2011 to 2013, five vegetative lines of IRG (13LmCb03, 13LmCb07, 13LmCb14, 13LmCb15, and 13LmCb17) were developed and used to generate crossing combinations.

2. Seed production of synthetic lines

In 2014, a synthetic plot was established using a triangular polycross design to produce seeds of the multi-parental crossing combinations. To prevent contamination by foreign pollen, rye was planted around the polycross block.

3. Experimental design

To evaluate the productivity and regional adaptability of IRG, Advanced yield trial (AYT) was conducted in Cheonan in 2021 using the synthetic lines. From 2022 to 2024, regional yield trials (RYT) were carried out at four locations—Cheonan, Pyeongchang, Jeongeup, and Jinju—as part of a collaborative research project for new variety development supported by the Rural Development Administration (RDA).

The medium-maturing cultivar ‘Kowinmaster’ was selected as the standard check variety. In all locations, sowing was carried out in late September. Phosphorus and potassium fertilizers were applied in two splits: half as basal fertilizer and the remaining half at the beginning of spring growth.

The experimental design was a randomized complete block design (RCBD) with three replications. Seeds were sown at a rate of 30 kg per hectare in rows spaced 20 cm apart. A total fertilizer application rate of N-P₂O₅-K₂O = 200-150-150 kg/ha was used. Nitrogen was applied in three splits: 20% as basal, 50% at early spring regrowth, and 30% after the first harvest to support regrowth for the second harvest.

The minimum temperature and precipitation data for January of each year were collected from each site using the Agricultural Weather Information Service (Agricultural Weather 365, http://weather.rda.go.kr) provided by the Rural Development Administration. Minimum temperatures and precipitation levels in 2022 and 2024 are presented in Table 1. The minimum temperature and precipitation in January are known to be the most influential factors affecting cold tolerance during the IRG growing season. In 2022, the average minimum temperature in January in Gangwon Province was –13.5°C, and the precipitation was only 0.5 mm. In 2023 and 2024, the average January minimum temperatures were –13.8°C and –10.6°C, and precipitation levels were 8.0 mm and 23.5 mm, respectively, showing a noticeable increase in precipitation in 2024 compared to the average year. Overall, a gradual increase in minimum temperatures was observed across all regions.

4. Growth characteristics analysis

Growth characteristics evaluated included winter hardiness, heading date, lodging, disease resistance, plant height, leafiness, and regrowth ability, based on the Standards for Research, Survey, and Analysis in Agricultural Science and Technology (RDA, 2012), and rated on a scale from 1 (strong) to 9 (weak).

5. Dry matter (DM) and dry matter yield (DMY) analysis

Dry matter yield was measured by harvesting and weighing the entire 6 m² plot. The yield of each cultivar was calculated by converting the harvested weight of the entire plot to a per-hectare basis. On the day of harvest, approximately 300–400 g of forage samples were collected from each plot, dried at 65°C for more than 72 hours in a forced-air drying oven, and weighed to determine the dry matter content. The following formulas were used to calculate dry matter rate and dry matter yield:

6. Evaluation of forage quality

Crude protein content was analyzed following the AOAC (1990) official method. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed using the methods of Goering and Van Soest (1970). The total digestible nutrient (TDN) was analyzed and calculated using the method of Menke and Huss (1980). Dry matter intake (DMI), digestible dry matter (DDM), and relative feed value (RFV) were calculated using the following formulas provided by Goering and Van Soest (1970).

7. Statistical analysis

Analysis of variance (ANOVA) was performed using SAS software (SAS, 2004), and differences among treatments were assessed using Duncan’s multiple range test.

Ⅲ. RESULTS AND DISCUSSION

1. Morphological characteristics

The major characteristics of the new IRG cultivar ‘Spider’ are summarized in Table 2.

‘Spider’ is a tetraploid cultivar with a semi-erect growth habit before winter and an erect growth habit in spring, similar to the check variety ‘Kowinmaster’. At the heading stage, the leaf width and leaf length of ‘Spider’ were 8 mm and 21.9 cm, respectively —1 mm thicker and 1.6 cm longer than those of ‘Kowinmaster’. The plant height at heading was 103 cm, approximately 5 cm taller than ‘Kowinmaster’. The spike length of ‘Spider’ was 30.7 cm, which was 5.9 cm longer than that of the check variety.

The leaf color of ‘Spider’ was classified as green, similar to ‘Kowinmaster’. The heading date of ‘Spider’ was May 13, which is 7 days later than that of ‘Kowinmaster’. Due to recent climate change and rising temperatures, phenological shifts have been observed, leading to an overall advancement in crop flowering time (Lee et al., 2020). As shown in Table 1, recent temperature increases due to climate change have led to earlier heading. As a result, the cultivation of medium-maturing cultivars is becoming more feasible, even in paddy-upland cropping systems, without negatively affecting the transplanting schedule of rice.

2. Cold tolerance

Table 1 presents the average minimum temperatures and precipitation in January, which are key factors affecting winter survival of IRG.

In 2022, although all test regions experienced higher-thanaverage temperatures but lower precipitation, which typically creates unfavorable overwintering conditions, no significant issues were observed in winter survival (Table 3).

The cold tolerance of the new cultivar ‘Spider’ tended to be relatively lower in Pyeongchang, but no statistically significant differences were detected among regions or years. These results indicate that ‘Spider’ is capable of overwintering stably in all tested regions, including Cheonan, Pyeongchang, Jeongeup, and Jinju (Table 3).

According to previous studies, the cold tolerance of IRG is determined by the genetic traits inherent in the germplasm and is affected by various factors such as tissue structure, moisture content, and freeze damage rate (Pfahler et al., 1984). To breed cold-tolerant cultivars, it is essential to repeatedly select individuals with strong cold tolerance. Therefore, the selection of cold-tolerant germplasm plays a crucial role in the development of cold-tolerant IRG varieties in Korea.

3. Dry matter yield

The dry matter yield of the new cultivar ‘Spider’ is shown in Table 4. Across the four test locations—Cheonan, Pyeongchang, Jeongeup, and Jinju—the average dry matter yield of ‘Spider’ was 10,169 kg/ha, which was significantly higher than the 8,696 kg/ha recorded for the check variety ‘Kowinmaster’. From 2022 to 2024, ‘Spider’ consistently outperformed ‘Kowinmaster’ in all regions except Pyeongchang, suggesting that it is well-suited for cultivation in both central and southern regions of Korea. In addition, when compared with previously reported mediummaturing cultivars IR 604 and IR 605, ‘Spider’ produced approximately 2,000 to 4,000 kg/ha more dry matter when grown in Cheonan, the same test location, where IR 604 and IR 605 had recorded 10,956 kg/ha and 9,252 kg/ha, respectively (Ji et al., 2023;Kim et al., 2020).

4. Feed value

Table 5 shows the forage quality characteristics of the new IRG cultivar ‘Spider’. The TDN of ‘Spider’ was 67.8%, which is comparable to the 68.0% of ‘Kowinmaster’. The ADF and NDF contents of ‘Spider’ were 26.6% and 49.5%, respectively. Notably, the NDF value was 2.1% lower than that of ‘Kowinmaster’. The relative feed value (RFV) of ‘Spider’ was 128, higher than the 123 of the check cultivar. This slightly higher forage quality of ‘Spider’ is likely due to its excellent leafiness, as described in Table 2.

Wilman and Altimimi (1982) reported that in both IRG and perennial ryegrass, the digestibility of stems decreases more rapidly than that of leaf sheaths. Additionally, Kim et al. (2020) found that among different parts of the corn plant, the leaves contained the highest crude protein levels. However, in the present study, there were no significant differences in crude protein content between ‘Spider’ and ‘Kowinmaster’ for IRG.

Ⅳ. CONCLUSION

This study was conducted from 2022 to 2024 at the Grassland and Forage Division of the National Institute of Animal Science, Rural Development Administration, with the aim of developing a high-yielding, medium-maturing IRG cultivar. The newly developed cultivar ‘Spider’ is a tetraploid type with green leaves. It exhibits a semi-erect growth habit before winter and an erect growth habit in spring. ‘Spider’ is a medium-maturing cultivar with a heading date around May 16, which is 7 days later than that of the check cultivar ‘Kowinmaster’. At the heading stage, its plant height was approximately 103 cm, about 5 cm taller than ‘Kowinmaster’. The flag leaf width and length at heading were 8 mm and 21.9 cm, respectively—1 mm thicker and 1.6 cm longer than those of ‘Kowinmaster’. In conclusion, although ‘Spider’ heads later than the check variety, it shows superior productivity and wider leaves, indicating its potential for high yields in the central and southern regions of Korea.