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: Isolation, Identification, and Media Formulation of  Endophytic Bacteria to Limit Ganoderma Fungus Attacks on Oil Palm
Abstrak: Ganoderma boniense merupakan cendawan patogen yang menyebabkan penyakit busuk pangkal batang (BPB) pada tanaman kelapa sawit. Penelitian ini mengkaji suatu alternatif dalam mengendalikan G. boninense melalui pemanfaatan agens pengendali hayati (APH) yang lebih ramah lingkungan daripada penggunaan fungisida komersial. Seleksi bakteri endofit sebagai APH dilakukan melalui isolasi bakteri dari akar kelapa sawit, mengukur persen zona hambatan terhadap isolat G. boninense secara in vitro, dan uji hipersensitif pada tanaman tembakau. Isolat bakteri endofit terpilih A2 dan C5 memiliki daya hambat terhadap G. boninense berturut-turut sebesar 35% dan 47%. Kedua isolat tersebut teridentifikasi secara molekuler berturut-turut sebagai bakteri Lysinibacillus xylanilyticus (99,85%) dan bakteri Aeromonas hydrophila (99,64%). Bakteri endofit terpilih diformulasikan ke dalam formulasi kompos, tepung, dan cair. Ketiga jenis formula dapat mempertahankan viabilitas sel sampai dengan 106 cfu/ml serta lebih stabil dan adaptif pada formulasi cair dengan kepadatan berkisar (8,0–9,0)×106 cfu/ml pada akhir minggu pengamatan dibandingkan formulasi lainnya., Ganoderma boninense is a pathogenic fungus that causes basal stem rot (BSR) diseases in oil palm plantations. This research examined an alternative in controlling G. boninense through the use of biological control agents (BCAs) which was more environmentally friendly than the use of commercial fungicide. Endophytic bacteria as BCAs were selected by isolating bacteria from oil palm roots, measuring the percent zone of inhibition against G. boninense based on in vitro test, and presenting hypersensitivity test on tobacco plant. Selected endophytic bacterias namely A2 and C5 had inhibiton against G. boninense of 35% and 47%, respectively. Those isolates were identified molecularly as Lysinibacillus xylanilyticus (99,85%) and Aeromonas hydrophila (99,64%), respectively. The selected endophytic bacterias were formulated in compost, flour, and liquid formulation. Those three types of formula could maintain cell viability up to 106 cfu/ml and are more stable also adaptive in liquid formulation within a range of (8,0–9,0)×106 cfu/ml at the end of the observation compared to other formulations.
Keyword: basal stem rot (BSR), endophytic bacteria, Ganoderma boninense, media formulation, oil palm

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