Judul: Detection of Ethyl Stearate Compound Produced by Bacillus subtilis MN704394.1 Using GC-MS as Antifungal for Ganoderma boninense
Abstrak: G. boninense merupakan jamur penyebab penyakit busuk pangkal batang pada kelapa sawit yang salah satunya pengendaliannya dapat menggunakan agen biokontrol berupa bakteri B. subtilis karena ramah lingkungan dan kemampuan beradaptasi yang kuat. Penelitian ini bertujuan mendeteksi etil stearat yang dihasilkan oleh B. subtilis MN704394.1 sebagai senyawa bioaktif untuk menghambat pertumbuhan G. boninense pada tanaman kelapa sawit. Supernatan kultur B. subtilis diekstraksi pada 5 titik pengambilan, yaitu jam ke-8, ke-12, ke-16, ke-20, dan ke-24 dengan etanol. Ekstrak kasar diuji aktivitas penghambatannya terhadap G. boninense dengan metode simultan, preventif, dan kuratif. Senyawa bioaktif pada ekstrak yang berpotensi sebagai antijamur diidentifikasi menggunakan GC-MS. Hasil penelitian menunjukkan aktivitas penghambatan oleh ekstrak jam ke-8 dengan metode preventif paling tinggi persen penghambatannya, yaitu 96,44%. Salah satu senyawa bioaktif hasil analisis GC-MS yang terdapat pada semua titik jam dan memiliki konsentrasi yang tinggi, yaitu etil stearat. Etil stearat hasil GC-MS pada jam ke-8 memliki area sebesar 10,3018% dan waktu retensi pada 22,1221. Etil stearat termasuk asam lemak ester dan memiliki aktivitas penghambatan tehadap G. boninense., G. boninense is a pathogen that causes basal stem rot disease in oil palm which can be controlled by using biocontrol agents such as B. subtilis because it’s environmentally friendly and strong adaptability. This study aims to detect ethyl stearate produced by B. subtilis MN704394.1 as bioactive compound to inhibit the growth of G. boninense in oil palm. The supernatant of B. subtilis culture was extracted in 5 points cultivation 4th, 8th, 12th, 16th, 20th, and 24th hour using ethanol. The crude extracts activity was tested with simultant, preventive, and curative method. Analysis of bioactive compounds was conducted using GC-MS. Activity test of bacterial extract showed that the extract at 8th hour with preventive method had the highest inhibitor activity that is 96.44%. One of bioactive compounds from the GC-MS analysis that exists in all points of cultivation and has high concentration is ethyl stearate. Ethyl stearate at 8th hour has area 10,3018% and retention time 22,1221. Ethyl stearate is fatty acid ester and played role in inhibitory activity of G. boninense.
Keyword: antifungal, Bacillus subtilis, ethyl stearate, Ganoderma boninense

Judul: In vitro Screening of Dark Septate Endophytes (DSE) as Biocontrol Agents of Ganoderma boninense isolated from Oil Palm (Elaeis guinensis Jacq.)
Abstrak: Kelapa sawit merupakan komoditi perkebunan terbesar di Indonesia dengan salah satu permasalahan utama budidayanya adalah serangan Ganoderma boninense. Berbagai cara pengendalian telah dilakukan termasuk pengendalian hayati menggunakan cendawan. Namun, potensi cendawan dark septate endophytes (DSE) sebagai agen biokontrol G. boninense belum banyak diteliti. Uji tantang koloni DSE ̶ G. boninese dilakukan pada dua umur DSE yang berbeda, dan disertai dengan uji potensi penghambatan senyawa volatil DSE. Kultur DSE yang menunjukkan kemampuan antagonis tinggi dianalisis senyawa volatilnya menggunakan Pyrolisis Gas Chromatografi Mass Spectrometry. Hasil menunjukkan bahwa DSE TKC 2.2a memiliki persentase penghambatan G. boninense tertinggi dari 10 isolat DSE yang diujicobakan, masing-masing sebesar 26,38 % (DSE langsung dipasangkan dengan G. boninense) dan sebesar 67,32% (DSE berumur 7 hari ketika dipasangkan). Uji senyawa volatil DSE TKC 2.2a menunjukkan penghambatan sebesar 41,20%. Komponen senyawa volatil dari TKC 2.2a berumur 14 hari antara lain, 2H-1-Benzopyran-7-ol,3,4-dihydro-5-methoxy-6-methyl-2-phenyl (14,15%); 4-Allyl-2,6-dimethoxyphenol (11,37%); dan Hexadecanoic acid (10,70%). Kata kunci: antagonis, busuk pangkal batang, dark septate endophytes, kultur ganda, substansi volatil., Oil palm is the largest plantation commodities in Indonesia, with one of the main problems is the Ganoderma boninense. However, the potential of dark septate endophytes (DSE) as biocontrol agents for G. boninense has not been widely studied. The antagonistic capacity of DSE was determined in vitro based on growth inhibition percentage of G. boninense in dual culture at two difference age of DSE colonies and the potency of volatile DSE compounds testing against G. boninense. DSE cultures that showed high antagonistic ability will be analyzed for their volatile compounds using Pyrolysis Gas Chromatography Mass Spectrometry. The results showed that DSE TKC 2.2a had the highest percentage of G. boninense inhibition among 10 DSE isolates tested. G. boninense colony growth was inhibited about 26,38% (in direct DSE pairing) and 67,32% (7 days old DSE when pairing). Volatile compounds of DSE TKC 2.2a inhibited 41,20% of G. boninense colony growth. The volatile compound of 14 days old TKC 2.2a composed of 2H-1-Benzopyran-7-ol, 3,4-dihydro-5-methoxy-6-methyl-2-phenyl (14,15%); 4-Allyl-2,6-dimethoxyphenol (11,37%); and Hexadecanoic acid (10,70%). Keywords: antagonist, basal stem rot, dark septate endophytes, dual culture, volatile compounds.
Keyword: antagonis, busuk pangkal batang, dark septate endophytes, kultur ganda, substansi volatil, antagonist, basal stem rot, dark septate endophytes, dual culture, volatile compounds

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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