Judul: Pengujian Bacillus thuringiensis galur SAHA 12.08 sebagai pengendali pertumbuhan cendawan penyebab bercak daun kelapa sawit
Abstrak: Oil palm (Elaeis guineensis Jacq.) is one of major agriculture commodities in Indonesia. The disease caused by pathogenic fungi such as Curvularia affinis and Colletotrichum gloeosporoides could inhibit the growth of oil palm seedling plants. Cell wall, mycelia cells, stalks, and conidium of fungi that composed by chitin, can be degraded by chitinolytic bacteria through its ability to produce the chitinase enzyme. This research was aimed to study the ability of Bacillus thuringiensis strain SAHA 12.08 in inhibiting C. affinis and C. gloeosporoides that attacked oil palm leaf through in vitro experiment. Bacillus thuringiensis strain SAHA 12.08 showed inhibitor activity to pathogenic fungi using 24 hour and 12 hour bacteria culture. Result of inhibition test using Detached-Leaf Assays method showed that capability of Bacillus thuringiensis as biocontrol activity against C. affinis was 85% and 90%, and against C. gloeosporoides was 96% and 59%. Inhibition of the strain against C. affinis and C. gloeosporoides using in vitro test were 27,8% and 28,2 % respectively. Bacillus thuringiensis strain SAHA 12.08 had antagonistic activity at in vitro test using leaf of oil palm and showed biocontrol activity against C. affinis and C. gloeosporoides
Keyword: Bogor Agricultural University (IPB), oil palm, C. gloeosporoides, C. affinis, Chitinolytic bacteria

Judul: Daya hambat Bacillus thuringiensis KAHN 15.39 terhadap cendawan patogen Curvularia affinis dan Colletotrichum gloeosporoides asal daun kelapa sawit
Abstrak: Some fungi caused disease on oil palm seedling so that it could be decrease seedling quality. Therefore, the aim of this research was to investigate activity of Bacillus thuringiensis KAHN 15.39 to inhibit pathogenic fungi Curvularia affinis and Colletotrichum gloeosporoides which were isolated from oil palm seedling. The bacteria ability to inhibit was examined with Leaf-pieces assays method. Bacteria culture medium was Nutrient Agar which was containing 1% Carboxy Methyl Celullose and medium for fungi used Potato Dextrose Agar added with 500 mg/L chloramphenicol. The results showed B. thuringiensis KAHN15.39 could inhibit Curvularia affinis which were the infestation areas 69 mm2 or biocontrol effectiveness 86% either, while to inhibit Colletotrichum gloeosporoides was the infestation areas 152 mm2 or biocontrol effectiveness by 45%. Inhibition of Bacillus thuringiensis KAHN15.39 against Curvularia affinis and Colletotrichum gloeosporoides have curative characteristic.
Keyword: Bogor Agricultural University (IPB), biocontrol effectiveness., Colletotrichum gloeosporoides, Curvularia affinis, Bacillus thuringiensis KAHN15.39, Oil palm

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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