Evaluating soybean germplasm from USA, China, and Brazil for tolerance to acidic soils in Indonesia

Soybean is a valuable grain crop in Indonesia mainly as a source of protein and a cash crop. The soybean production increases more slowly than the demand within the country. The opportunity to increase soybean production exists by planting soybean in the lands available outside the Java island, on acidic Ultisol soils. However, the number of soybean accessions that are tolerant to acidic soils is limited and these accessions do not have desirable traits to meet the market demands. The objective of the first study was to test the adaptability of selected soybean germplasm to acidic soils under greenhouse conditions. A total of 706 soybean accessions originating from the USA, China, and Brazil, were screened to select 20 best performing genotypes from each country through two phases of greenhouse trials. In Phase 1, 20 best performing soybean genotypes from each of the three countries were selected in a Peat moss medium at pH 5.0 using plant height and number of days taken for each line to reach V2 stage as the selection criteria. In phase 2, these 60 soybean genotypes were subjected to three low pH regimes; 4.5, 5.0 and 5.5 to select the best 20 performing genotypes in acidic soils using plant height and root length 55 days after planting as the selection criteria. Of the 60 genotypes, the 20 selected lines from the USA and the 20 selected lines from China reached the V2 stage in 12 - 24 days after planting while the 20 selected lines from Brazil took slightly longer to reach the V2 stage with 16 - 30 days after planting. In the second screening, 20 best performing lines out of the previous 60 were selected based on their performance on acidic soils with a pH of 4.5. The goal of the second study was to evaluate the 20 selected lines from the previous study for tolerance to aluminum toxicity, a major concern in Indonesian low pH soils. We used the same medium, Peat moss, but added aluminum hydroxide to the medium since Peat moss does not contain aluminum (Al). We conducted a greenhouse study where the previously selected 20 soybean lines were subjected to two levels of Al; 0.0% and 5% Al (by weight). Root length, number of root nodules, and plant height were taken as the dependent variables 35 days after planting as criteria for selection. All data were analyzed using ANOVA and LSD. All 20 selected lines survived and grew well at the 5% Al treatment. The measured variables were significantly different at P < 0.0001. Plant height and root length of the 20 lines were higher in the medium with 5% Al compared to the control with 0.0% aluminum. Of the 20 lines tested, PI628871 accession had the longest root length and PI567643 accession was the tallest plant. When comparing the initial and final pH levels of the growth medium, we observed a positive effect of adding Al to the growth medium as it increased the pH of the medium from an initial pH of 4.30 to a final pH of 5.23 - 5.34. The results indicated that the 20 selected lines would be tolerant to soils with low pH and Al3+ levels up to 5% by weight and could perform well under Indonesian acidic soils. The third study was intended to evaluate the 20 selected lines for tolerance to acidic soils in Indonesia and select promising lines for use that can be grown by farmers and/or used as parents in a soybean breeding program in Indonesia. To achieve our goals, we designed a field research for two seasons in 2017 and 2018, in two locations. To select the best performing out of the 20 lines under current farmer practices, a split-split plot design with three factors was used with lime as the main plot, organic fertilizer as the subplot, and soybean genotypes as the sub-subplot. Two farmer preferred varieties, ANJASMORO and DERING, were used as standards or check varieties. Plant height, root length, number of root nodules, number of pods, and yield were used to evaluate the performance of the 20 lines. All data were analyzed using ANOVA and LSD. In 2017 season, the best four genotypes of the 20 lines tested with the highest yields were PI675661 with 3.08 tons/ha (for farmers who applied lime, but did not apply organic fertilizer), PI628880 with 2.46 tons/ha and PI628929 with 2.41 tons/ha (both: for farmers who did not apply lime, but applied only organic fertilizer), PI628880 with 2.03 tons/ha (for farmers who do not apply lime or organic fertilizer), and PI628871 with 2.32 tons/ha and PI628929 with 2.28 tons/ha (both: for farmers who applied a combination of both lime and organic fertilizer). In the 2018 season, the yield reported was the highest in PI628925 with 2.38 tons/ha (for farmers who applied a combination of lime and organic fertilizer), and PI675661 with 2.17 tons/ha and PI628929 with 2.03 tons/ha (both: for farmers who did not apply lime, but applied only organic fertilizer). The yields of these lines in both seasons were higher than the two standards/check varieties. PI675661 and PI628929 can be considered as the promising lines with superior traits: number of pods, yield, and larger seed size.