Judul: Eksplorasi Mikroba Rizosfer dan Hubungannya dengan Sifat Fisik & Kimia Tanah pada Tanaman Kelapa Sawit Terinfeksi Ganoderma boninense Pat.
Abstrak: Oil palm (Elaeis guineensis Jacq.) is one of the plantation crops which has a significance in contributing foreign exchange to the country from non-oil sector. One of the fence in development oil palm cultivation is the presence of stem rot disease caused by Ganoderma boninense. This research aims to explore the microbial rhizosphere surrounding to the oil palm plants, as well as its relationship to the condition of physical and chemical soil characteristics. The study was conducted by taking a surrounding soil of oil palm plantations as a sample and made its suspension. The suspension was made to serial dilutions to 10-8 dilution rate. In vitro antagonism test between antagonist candidate of actinomycetes to G. boninense conducted by using a dual culture methods. Observations were made by measuring the radial growth of pathogenic fungi and actinomycetes isolates were away from fingers pathogenic fungi actinomycetes isolates were approaching. The results of microbial isolation consist of 76.9% fungal isolates, 12.82% bacterial isolates, and 10.26% actinomycetes isolates. The content of chemical characteristics soil at the study was sited at pH 4.43 it is included in a slightly acid soil type and content of C/N ratio 8.78 is low. The results of in vitro experiments showed that isolate AK1 (actinomycetes 1), AK2 (actinomycetes 2), and AK3 (actinomycetes 3) have a significant effect on the growth of pathogenic G. boninense fungi on PDA at the fifth day.
Keyword: Ganoderma boninense, microbial rhizosphere, oil palm

Judul: Role of Arbusccular mycorrhizal fungi and mycorrhizal endosymbiotic bacteria in increasing oil palm (Elaeis guineensis Jacq) seedlings adaptation towards biotic stress of fungal pathogen ganoderma boninense Pat.
Abstrak: Basal stem rot caused by Ganoderma boninense is the most serious disease of oil palm (Elaeis guineensis) in Indonesia and it has caused major loss in palm oil production. Under natural conditions, oil palm is often colonized by arbuscular mycorrhizal (AM) fungi and together with mycorrhizosphere bacteria offer possible advantages in increasing plant adaptation against biotic stress of pathogen. This research comprised five interrelated experiments, namely: (1) Exploration, Isolation and Identification of Arbuscular Mycorrhizal Fungi (AMF) and Mycorrhizal Endosymbiotic Bacteria from Oil Palm Rhizosphere and Their Ability in Inducing Oil Palm Adaptation Towards Biotic Stress of Pathogen Ganoderma boninense Pat; (2) Selection of Mycorrhizal Endosymbiotic Bacteria on Spores Germination of AMF Gigaspora margarita and Their Inhibition Towards Fungal Pathogen G. boninense Pat; (3) Identification of Active Compounds from Mycorrhizal Endosymbiotic Bacteria B. subtilis B10 that Inhibit the Growth of Fungal Pathogen G. boninense Pat; (4) Adaptation of Oil Palm Seedlings Inoculated with AMF and Mycorrhizal Endosymbiotic Bacteria B. subtilis B10 Towards Biotic Stress of Pathogen G. boninense Pat; (5) Analyzing the Response of Oil Palm Seedlings Inoculated with AMF and Mycorrhizal Endosymbiotic Bacteria in the Form of Active Compound Profile as Expression of Oil Palm Adaptation Towards Biotic Stress of Pathogen G. boninense Pat. The soil sampels were used in this experiment came from Aek Pancur Plantation belong to Indonesian Oil Palm Research Institute, Medan. The results showed that twenty isolates of mycorrhizal endosymbiotic bacteria were obtained from spores of AMF isolated from oil palm rhizosphere and were dominated by genus of Bacillus sp. Among these isolates, isolate B10 identified based on 16S rDNA as Bacillus subtilis B10, had the highest activity against G. boninense in vitro by producing intracellular active compounds with molecular weight 255.39 and postulated as of 2-(4-aminophenoxy)-6-methyl-tetrahydro-2H-pyran-3,4,5- triol. Dual inoculation of AMF and B. subtilis B10 on oil palm seedlings resulted in the lowest basal stem rot disease incidence caused by G. boninese which indicated disease severity index was only 5% and necrotic area of roots just 10%. Application of AMF together with B. subtilis B10 also increased oil palm seedlings height, root dry weight and stem diameter at 52 weeks after planting. The adsorption of nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg) increased when seedlings were co-inoculated with AMF and bacteria B. subtilis B10 together. This finding is important in terms of recommendation for application of AMF and bacteria B. subtilis B10 as biocontrol of pathogen G. boninense causal agent of basal stem rot in oil palm.
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Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf