Study the Effect of Shade Stress on Indonesian Soybeans to Anticipate the Need for Breeding Superior Variety

. The need for superior soybeans which resistant against low light is a challenge for Indonesia that has large of soybean germplasms which potential for achieving national soybean self-sufficiency and sustainability. Unfortunately, research on this field still very lack. This study aims to investigate the responses of 28 soybean accessions to shade stress, and looking for potential candidates or basic material for the development of high-yielding varieties. The research was conducted in the Cikeumeuh-Bogor field using a randomized block factorial design with two treatments (genotype and percentage of shade), with three replications. Based on the results, all of the morph-agronomic characters significantly influenced by the treatments, except for the number of filled pods (p-value <0.001). There was interaction between genotypes and shade stress which influenced the plant height, number of branches, number of trifoliate leaves and flowering time. Based on this study, Kedelai Hijau (G-19) and Lokal Brebes (G-21) were potential to be candidate for breeding on shade-resistant varieties. G-19 had the best response to the number of branches and number of trifoliate leaves, while G-21 best on height and root length. This information becomes a novelty that contributes to breeding soybeans resistant to shade stress for food sustainability.


Introduction
The drastic change in global climate and implications for the increasingly limited carrying capacity of land that can be used for plant production media has implied the urgency of the need for more resilient plants, especially those that can adapt to conditions of higher cropping density while maintaining the productivity of individual plants [1].Agriculture is one of the sectors most vulnerable to climate change [2], [3].Climate change is expected to have a negative influence to crop production for food in areas of lower latitudes [4]which are currently experiencing food insecurity.It was also reported that yields are widely projected to fall the greatest.. Production of wheat, maize and sorghum and other cereals will experience an average yield loss of 8% in Africa and South Asia by 2050; even wheat in Africa, is predicted to undergo a -17% yield decrease [5].Climate change disruption to the recorded rainy season from 1966 to 2002 is estimated to have decreased rice yields by 4% in India [6].For other developing countries, this implication is very bad for rural and poor communities who depend on their agriculture income [7], including Indonesia.
Over the years Indonesia has become a net importer of soybeans as a result of the decline in soybean production caused by reduced soybean harvested areas [8], [9], whereas on the other hand the demand for soybeans continues to increase because soybeans are one of the strategic food commodities [10].Indonesia's soybean production is estimated to continue to decline from 2021 to 2024, where in 2021 it is projected that domestically produced soybeans will reach 613.3 thousand tons, which is down 3.01% from 2020 which reached 632.3 thousand tons [11].In 2022, it is estimated that it will decrease by 3.05% to 594.6 thousand tons; then fell again 3.09% to 576.3 thousand tons in 2023; and in 2024 the decrease will be 3.12% to 558.3 thousand tons [11].According to Agricluture Ministry, this downward trend in national soybean production is due to the intense competition for land use with other strategic commodities, such as corn and chilies, which resulted in a decrease in harvested area of around 5% per year [11].This is also further exacerbated by global climate change, which is detrimental to agriculture in general, including national soybean production.
The development of soybeans as intercrops under plantation stands, agroforestry environments, or intercropping with other food crops is a mainstay alternative to increase national soybean production which is still very low [8].This is also strategies to answer the challenges of the food system where there is an interest to reduce and adapt to climate change, prevent the desertification and land degradation, and achieve food security [12].Unfortunately, the realization of these efforts is constrained by the limited information on soybean varieties that are resistant to shade.
Currently in Indonesia, there are more than 114 soybean varieties existed but those with tolerance to shade are still limited.The previously released shade-tolerant soybean varieties were Dena-1 and Dena-2 created by researcher from Indonesian Agency for Agriculture Research and Development (IAARD) [13].Several other newly released varieties from universities mostly are not subject to tolerance against shade stress, for example, Devatra 1 and Devatra (released by Bengkulu University).We considered that now is the time to give large portion of efforts to increase our local soybean production through the expansion of planting shade-tolerant soybeans.Through optimization of agricultural land which more limited in size, production is expected to be increased significantly.In this regards, we therefore conducted research aimed to study the effect of shade stress against 28 varieties of soybean in Indonesia as a basic step for engineering an adaptive and high-yielding soybeans with tolerance against low-light.

Method
Research activities were carried out at the Cikeumeuh Experimental Station (Lat S -6'34"' Long E 106 o 47"') from March 2020 to September 2020.The average temperature in the field was 25 o Celsius with the lowest temperature reached 21 o Celsius, and highest temperature reached up to 31 o Celsius in the daytime, with the daily air humidity fall under the range of 60% to 20% (data not shown).Total of 28 accessions of soybeans mainly from local varieties of soybeans as tested materials (Table 1).
The study used a randomized block factorial design with two treatments i.e. shadeintensity and soybean genotype; with three replications each.The shade intensity consisted of 3 levels: no shade (0% shade), 50% shade, and 70% shade; while genotype of soybean was consisting of 28 levels from 28 accessions of soybean.
Observations on the morpho-agronomic characters were conducted at the vegetative stage, the generative stage, and at harvest time, depend on the characters.Plant height, number of branches, number of trifoliate leaves, and the diameter of the plant crown were observed during the vegetative stage of each accession when reached maximum.Flowering time were observed when plants entering the generative staged.Number of empty pods, number of filled pods, root length, and the weight of 100 seeds were observed after harvested.
The acquired data were examined using Analysis of variance (ANOVA) and if significant differences were found (pvalue < 0.05), the Duncan Multiple Range Test (DMRT) was used for further analyzed.We conduct data tabulation using Microsoft Excel, while data analysis was performed using Minitab version 19.

Results and Discussion
Based on visual observations, almost all soybean plant accessions in control plots (without shade) showed better growth and development than those with shading.Leaf development under conditions of 70% shading showed clear inhibition, where the leaf surface area was generally narrower and the stem diameter was also smaller when compared to the genotype of soybeans grown in 0% and 50% shading.According to Table 2, almost all variables (traits) are significantly influenced by genotype and shade treatment, except for the number of filled pods (at p value <0.001).Another point is, there is interaction between genotype and shading which influencing the plant height, number of branches, number of trifoliate leaves and flowering time.But there is no significant effect of the interaction to the number of clumps, number of filled pods and root length.The results of the analysis showed that the genotype had a significant effect on plant height, especially in plots without stress-shade treatment.The stress-shade treatment that has a significant effect on plant height is the 50% shade treatment (Table 3).The result showed that stress-shade treatment that has a significant effect on the number of branch is the 70% shade treatment, while the genotype which had significant effect are especially G1-G9 when combined with shading 70% and 0% ( Shading treatment had no significant effect on the number of clumps, as well as the effect of the soybean genotype (Table 5).
, There was a significant genotype effect on the number of pods in treatment plot N00 (without shade), especially genotypes G-1 to G-18, but almost all of the genotypes in the shaded plots did not show a significant effect on the number of pods ( The 70% shade treatment had a significant effect on the number of trifoliate leaves, as well as the genotype.However, the combination of genotype treatment with 70% shading had no significant effect on the number of trifoliate leaves ( Almost all genotype had no significant effect on the root lengths, except at G-1 -G9 when combined with 0% shading (N00).Meanwhile, the effect of 70% shade treatment was significant on the root length to all genotypes tested (Table 8).
, The significant effect of genotype on flowering time was shown by G1 -G18 and G21 -G28.In general, the effect of shade on flowering time was not significant, except for the combination of 70% shade treatment with genotypes G3, G14, G15, G22, G23 and G25 (Table 9).
It is known that in addition to provide the primary energy source for photosynthesis [14], light provides plants with important temporal and spatial information about their surrounding environment [15].An individual's ability to effectively tolerate or avoid shade will significantly increase competitiveness, and ultimately also increase the likelihood of reproductive success, in a rapidly growing population [1].The development of soybean as an inter-crop is faced with the main challenge in the form of tolerance of soybean varieties to low light intensity (shade)in this case, the shade of the main vegetation stand.
In shaded vegetation, plants generally experience a significant reduction in the quantity of light, particularly the red and blue bands, which are used by the canopy to support photosynthesis.Variation of plants to vegetative shade is thought to confer a selective advantage in different ecological habitats.Previous studies have shown that soybean morphological properties change significantly under shading conditions, resulting in increased plant height, decreased yield, and reduced root length [15,16,17].Leaf expansion was also suppressed when soybeans responded to shade stress [18,19].
Based on the results of the above research, to select potential accessions as breeding base material for assembling superior shade-tolerant varieties are available on genotypes that received 50% shade-stress treatment where almost all the tested soybean genotypes responded positively by showing good plant growth and development.In this case, information was also obtained that the 70% shade stress treatment was not recommended for soybean cultivation, because in general it causes plant death (low plant survival).
The genotype with the best plant height response was G21 (Lokal Brebes), the highest number of branches was G19 (Kedelai Hijau), the highest number of clumps was G12 (Lokal Hitam A), the highest number of filled pods was G26 (Merbabu), the highest number of trifoliate leaves was G19 (Kedelai Hijau) and the best root length is G21 (Lokal Brebes) Using these considerations, the potential genotype candidates as breeding material for assembling high yielding varieties of shade tolerant soybeans are G-19 (Kedelai Hijau) and G-21 (Lokal Brebes).

Conclusion
Almost of the morph-agronomic characters were significantly influenced by the genotype and shade-stress, except for the number of filled pods, root length and flowering time (pvalue <0.001).Interaction between genotypes and shade stress showed significant effect to plant height, number of branches, and number of trifoliate leaves.
Variety of G-19 (Kedelai Hijau) and G-21 (Lokal Brebes) were potential as candidate for breeding on shade-resistant varieties.The implication is that there needs to be further research to develop new superior varieties that are shade tolerant by utilizing this material. /doi.org/10.1051/e3sconf/202344404012444

Table 2 .
ANOVA on the influence of genotype, shading and their interactions towards traits ** Significant at value < 0.001

Table 3 .
Effect of genotype and shading to plant height Note : Value followed by capital letters indicates the effect of shading treatment to plant height.Values followed by lowercase letters indicate genotype influence on plant height.

Table 4 .
Effect of genotype and shading to the number of branches Note : Value followed by capital letters indicates the effect of shading treatment on the number of branch.Values followed by lowercase letters indicate genotype influence on the number of branch.

Table 5 .
Effect of genotype and shading to the number of clumps Note : Value followed by capital letters indicates the effect of shading treatment on the number of clumps.Values followed by lowercase letters indicate genotype influence on the number of clumps.

Table 6 .
Effect of genotype and shading to the number of pods Note : Value followed by capital letters indicates the effect of shading treatment on the number of pods.Values followed by lowercase letters indicate genotype influence on the number of pods.

Table 7 .
Effect of genotype and shading to the number of trifoliate leaves Note : Value followed by capital letters indicates the effect of shading treatment on the number of trifoliates leaves.Values followed by lowercase letters indicate genotype influence on the number of trifoliates leaves.

Table 8 .
Effect of genotype and shading to the root length Value followed by capital letters indicates the effect of shading treatment on the root lengths.Values followed by lowercase letters indicate genotype influence on the

Table 9 .
Effect of genotype and shading to the flowering time