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Abstract. Sunaryo W, Widoretno W, Nurhasanah, Sudarsono. 2016. Drought tolerance selection of soybean lines generated from somatic embryogenesis using osmotic stress simulation of poly-ethylene glycol (PEG). Nusantara Bioscience 8: 45-54. Somaclonal variation is an alternative source to create genetic variability including generating a novel character like drought tolerance. The objective of this research was to select the drought tolerant lines derived from somatic embryogenesis (somaclones) of 4 soybean genotypes using drought stress simulated by Polyethylene Glycol (PEG). Soybean seeds (R 1 generation) generated from 37 somaclones (R 0 generation) were grown on semi hydroponic system using Greenleaf as supporting medium. The seedlings were watered with half strength of liquid Murishage and Skoog nutrient. The PEG solution treatment of either 0% or 15% (PEG: w/v = -0.41 Mpa osmotic potential) was applied in the MS solution, from the seedlings of 14 days old until harvesting period. The vegetative growth, intensity of leaf firing, plant biomass, and drought sensitivity index variables were observed during the PEG application. The same procedure was applied to the seeds, propagated conventionally, from the same genotypes as controls. The results showed that somatic embryogenesis had altered the drought sensitivity of soybean genotypes under drought stress simulated by PEG. Interestingly, the different drought tolerance level was showed by the R 1 plants. Some lines were increased and the other lines were decreased compared to the control genotypes. From a total of 185 R 1 plants, 4 plants increased their tolerance against drought stress and grouped as tolerant genotype.

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When obtaining plantlets, embryo maturation and simultaneous germination are important steps in plant micropropagation via somatic embryogenesis. Several studies have shown that the use of carbohydrates as a carbon source plays a significant role in inducing somatic embryo development in certain plant species. This study aimed to establish a somatic embryo maturation protocol for Batu 55 Mandarin (C. reticulata Blanco.) by examining the effect of various types of sugar and concentrations. The results showed that the type and concentration of sugar added to the medium affect the somatic embryo maturation of Batu 55 Mandarin. Galactose and maltose enhance somatic embryo maturation more effectively than does sorbitol. The combination of galactose or maltose with sorbitol was able to improve somatic embryo maturation more effectively than galactose or maltose alone. The combination of galactose and sorbitol enhanced the maturation of somatic embryos more effectively than did change the concentrations of maltose or sorbitol. It can be concluded that sugar type and concentration had effects on citrus somatic embryo development. The combination of sorbitol (36.5 mM) with galactose 73 mM was able to augment citrus somatic embryo maturation more effectively than the other concentrations applied.

Citrus mandarin Batu 55 (Citrus reticulata Blanco.) is one of Indonesian fruits commodities that have high economic value and consumers demand. The propagation of citrus mandarin by plant tissue culture generally was carried out on solid medium. The liquid culture system could increase cell multiplication therefore it became alternative method of plant propagation through somatic embryogenesis. The effect of initial cell density and Benzyl Amino Purin (BAP) concentration in liquid media were investigated. The initial cells density and right concentration of BAP given in media can increase cell proliferation of somatic embryo in liquid culture. Globular somatic embryo were cultured on Murashige and Tucker media with initial cell density 4, 6, 8 and 10 mgL -1 and BAP 0, 0.25, 0.5, and 0.75 mgL -1. Growth evaluation of somatic embryo were obtained by weighing fresh and dry weight every 2 weeks for 8 weeks for initial cell density treatment and 6 weeks of BAP treatment. The result of the research showed that cell density affect the growth of somatic embryo of citrus mandarin. Somatic embryo with low cell density showed slower growth compared than high cell density. Peak growth occured in 6 th cultured with cell density 10 mgL -1. In addition to cell density, the growth of somatic embryo in liquid culture was affected by BAP. The growth of somatic embryo on the media containing BAP showed better results than without BAP. The highest BAP concentration on media showed fresh and dry weight of somatic embryo increased. In this research, growth of somatic embryo is not optimal yet because fresh and dry weights of somatic embryo still increase with high concentration 0.75 mgL -1 of BAP.

In soybeans, drought stress causes 50% yield losses. Breeding for drought tolerance in soybeans has been widely developed using various methods, among which is polyethylene glycol (PEG-6000) induction to simulate drought in vitro. In a previous experiment, three somaclones with different levels of tolerance were generated. The objectives of this research were to determine the RAPD patterns of those somaclones and to investigate the correlation of the RAPD patterns to the drought tolerance characteristics. The results showed eleven RAPD primers capable of amplifying the DNA genome of soybeans, among which four primers were monomorphic and seven were polymorphic. Two of the polymorphic primers, OPK7 and OPK12, are capable of differentiating medium tolerance traits from other traits. Bands that are specific for medium tolerance against drought were 450 bp and 650 bp in size, generated by the OPK7 primer, and the band of 2000 bp, generated by the OPK12 primer. However, there was no band capable of differentiating between sensitive and tolerance varieties/ lines, although some changing of the DNA sequence was detected in this research. This indicates that there are other factors responsible for the expression of drought tolerance.

This research was conducted to evaluate the yield potential of 19 somaclonal variants resulting from in vitro selection when planted under drought stress condition in the field. Field test was done by planting the variants, the parents, and checked varieties in the field during dry season, and was irrigated once a week for non-stress and once two weeks for drought stress treatment. Split-plot design arranged in a factorial (2 x 28) with three replications was used in this research. Observations were done on yield and yield components. Analysis of variance was used to see the difference between treatments and then it was continued with analysis using Honestly Significant Difference test to find out the best treatments. There was no interaction between genotype and drought stress on seed yield. Different genotypes showed a significant difference on this character. It indicated that the yield potential of selected variants was not affected by drought stress treatment. This research gave 10 variants having the potential to be developed as drought resistant genotypes. However, these ten potential genotypes need to be tested further in field trial to find out the yield adaptability and stability and their resistance to drought stress.