Judul: Potential Inhibition of Phyllosphere Bacteria from Cabbage (Brassica oleracea var. capitata) towards Black Rot Disease (Xanthomonas campestris pv. campestris).
Abstrak: Busuk hitam yang disebabkan oleh Xanthomonas campestris pv. campestris merupakan salah satu penyakit penting pada tanaman kubis (Brassica oleracea var. capitata). Serangan busuk hitam pada tanaman kubis di lapangan dapat menyebabkan gagal panen karena dapat menyerang bagian krop yang bernilai ekonomi tinggi hingga 61%. Agens hayati seperti bakteri filosfer telah dilaporkan dapat menghambat pertumbuhan bakteri patogen tanaman. Bakteri filosfer merupakan jenis bakteri yang umumnya ditemukan di permukaan bagian tanaman terutama bagian daun. Penelitian ini bertujuan memperoleh bakteri filosfer asal tanaman kubis yang berpotensi menghambat pertumbuhan penyakit busuk hitam. Bakteri filosfer diisolasi dari pertanaman kubis di Cianjur, Bogor, dan Tegal sedangkan bakteri patogen busuk hitam diisolasi dari pertanaman kubis di Cianjur. Bakteri filosfer dan patogen busuk hitam yang berhasil diisolasi kemudian diremajakan untuk digunakan pada uji selanjutnya yaitu uji hipersensitifitas, uji hemolisis, uji antagonisme secara in vitro, uji antagonisme secara in vivo, dan diidentifikasi menggunakan teknik Polymerase Chain Reaction. Hasil uji antagonisme secara in vitro menunjukkan 6 isolat (dari total 187 isolat) mampu menghasilkan zona hambatan terhadap Xanthomonas campestris pv. campestris. Keenam isolat tersebut juga memiliki kemampuan yang berbeda-beda dalam menghambat keparahan penyakit busuk hitam secara in vivo serta memiliki kemampuan dalam memacu pertumbuhan bibit tanaman kubis. Daya hambatan tertinggi sebesar 62.83% dan keparahan penyakit terendah sebesar 33.90% dihasilkan oleh isolat CA27. Isolat CA27 juga mampu meningkatkan tinggi tanaman hingga 4.18 cm, panjang akar hingga 2.63 cm, serta jumlah daun hingga 2.12 dan nyata lebih tinggi dibandingkan dengan kontrol pada fase pembibitan. Berdasarkan uji Gram dengan larutan KOH 3%, isolat CA27 teridentifikasi sebagai bakteri Gram negatif. Identifikasi lengkap bakteri filosfer sebagai agens biokontrol secara molekuler tidak dilakukan karena adanya pandemi Covid-19.
Keyword: biological control agents, Gram negative bacteria, Integrated Pest Management, PGPR

Judul: Keefektifan ekstrak empat jenis tumbuhan dan kitosan terhadap xanthomonas campestris pv.campestris penyebab penyakit busuk hitam pada kubis
Abstrak: The aims of this study were to detect of X. campestris pv. campestris from five cabbage cultivars, to test the effectiveness of plant extracts and chitosan in inhibiting the growth of X. campestris pv. campestris, to test the effectiveness of seed treatment using plant extracts and chitosan to control X. campestris pv. campestris in infected cabbage seeds, and to evaluate the effect of seed treatment to seed viability. The results of this research showed that betel extract, clove extract, and chitosan had ability to inhibit X. campestris pv. campestris growth, while binahong and turmeric extracts did not show inhibitory effect. Cabbage seed cultivar Green Hero was positively infected by X. campestris pv. campestris. X. campestris pv. campestris developed yellowish green colonies on SX medium. DNA fragment of 535 bp was successfully amplified using PCR with spesific primer for hrpF gene of X. campestris pv. campestris, i.e. XCF and XCR. The treatment with 2% betel extract, 3% clove extract, and 0.5% chitosan totally inhibited bacterial growth in NB medium and suppressed over 99% inoculum density after 50 minutes soaking seed. Betel and clove extracts suppressed the infection rate on seed by 84% and 97.33%, respectively. Chitosan did not reduce the level of infection due to the high initial infection of seeds. The treatments did not decrease seed viability as indicated by seed germination rates (95%). It was evidenced that betel extract, clove extract, and chitosan have the potential to be developed as quarantine treatment techniques to suppress infection of X. campestris pv. campestris in cabbage seeds.
Keyword: 

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.
Keyword: