Judul: Identification and Disease Severity of Dieback Disease on Sengon Seedlings in Persemaian Permanen Dramaga Bogor
Abstrak: Sengon merupakan salah satu komoditas tanaman kehutanan yang digemari masyarakat. Sehingga pengadaan semai sehat di persemaian sangat penting dilakukan dalam upaya mencapai keberhasilan tanam. Namun, sengon sangat rentan terhadap beberapa penyakit. Salah satu penyakitnya yaitu penyakit mati pucuk di persemaian. Penelitian ini bertujuan menghitung kejadian penyakit dan keparahan penyakit mati pucuk pada semai sengon di Persemaian Permanen Dramaga Bogorserta mengidentifikasi jenis patogen penyebab penyakit mati pucuk pada semai sengon. Metode pengambilan data dilakukan menggunakan metode sensus dan skoring. Selain itu, proses identifikasi dilakukan di bawah mikroskop cahaya dengan perbesaran 40x10. Analisis data dilakukan menggunakan analisis deskriptif. Persentase kejadian penyakit dan keparahan penyakit mati pucuk pada semai sengon berturut-turut sebesar 10,809% dan 73,764% yang mana keparahan penyakit dinyatakan berat. Berdasarkan hasil identifikasi, cendawan Rhizoctonia sp. diduga sebagai penyebab penyakit mati pucuk pada semai sengon., Sengon is one of the forestry plant commodities favored by the community. So that the provision of healthy seedlings in the nursery is significant to achieve successful planting. However, sengon is very susceptible to several diseases. One of the diseases is dieback in the nursery. This study aims to calculate the incidence and severity of shoot death in sengon seedlings in Persemaian Permanen Dramaga Bogor and identify the types of pathogens that cause dieback in sengon seedlings. Methods of data collection carried out using the census and scoring methods. In addition, the identification process carried out under a light microscope with a magnification of 40x10. Data analysis performed using descriptive analysis. The percentage of disease incidence and dieback severity in sengon seedlings were 10.809% and 73.764%, where the severity of the disease is declared as severe. Based on the identification results, the fungus Rhizoctonia sp. is suspect as the cause of dieback in sengon seedlings.
Keyword: dieback, disease severity, nursery, Rhizoctonia sp., sengon

Judul: Fungus Pathogenicity Test and Identification that causes Leaf Disease on Sengon in Dramaga Bogor Permanent Nursery
Abstrak: Sengon (Paraserianthes falcataria (L.) Nielsen) merupakan jenis pohon cepat tumbuh (fast-growing species) dan mudah didapat karena sudah banyak dibudidayakan di Indonesia. Usaha perbanyakan sengon melalui kegiatan pembibitan di persemaian banyak menemui kendala penyakit. Penelitian ini bertujuan mengidentifikasi cendawan penyebab penyakit daun pada tanaman sengon, serta menghitung luas dan intensitas serangan cendawan penyebab penyakit daun pada sengon di Persemaian Permanen Dramaga Bogor. Metode penelitian ini adalah rangkaian uji patogenisitas meliputi pengamatan lapang, postulat Koch, dan identifikasi jenis cendawan. Penelitian menggunakan Rancangan Acak Lengkap Faktorial (RALF). Gejala penyakit yang ditemukan pada daun sengon umur sekitar dua bulan yang ada di lokasi pengamatan adalah penyakit gugur daun, bercak daun, dan hawar daun. Hasil identifikasi cendawan penyebab gugur daun adalah Rhizoctonia sp., cendawan penyebab bercak daun adalah Colletotrichum sp., dan cendawan penyebab hawar daun adalah Fusarium sp.. Fusarium sp. menghasilkan persentase serangan tertinggi dengan luas serangan sebesar 67,34% dan intensitas serangan sebesar 57,28%., Sengon (Paraserianthes falcataria (L.) Nielsen) is a fast-growing tree species and easy to obtain because it has been widely cultivated in Indonesia. Sengon plant propagation is carried out through nursery activities in nurseries. The study aimed to identify the fungus that causes leaf disease on sengon plants and calculate the extent and intensity of attacks by the fungus that causes leaf disease on sengon in the Dramaga Bogor Permanent Nursery. This research method carried out pathogenicity test activities, including field observations, Koch's postulates, and the identification of fungal species. The study used a Completely Randomized Factorial Design (RALF). The disease symptoms found on around two months of sengon leaves old at the observation site were leaf fall, leaf spot, and leaf blight. The results of identifying the fungus that causes leaf fall were Rhizoctonia sp.. This fungus that causes leaf spots is Colletotrichum sp., and the fungus that causes leaf blight is Fusarium sp.. Fusarium sp. resulted in the highest percentage of attacks, with a disease incidence of 67,34% and disease severity of 57,28%.
Keyword: characteristics, identification, Koch's postulates, morphology

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: