Judul: First Report on powdery mildew on chili (Capsicum annuum L.) in Tegal Regency
Abstrak: Tanaman cabai merah di Kabupaten Tegal terjangkit penyakit langka dengan tingkat keparahan yang cukup tinggi. Akhir-akhir ini, sering dilaporkan adanya penyakit embun tepung di Kabupaten Tegal, Provinsi Jawa Tengah. Tujuan penelitian adalah untuk mendeskripsikan dan menganalisis keberadaan, gejala, dan keparahan penyakit embun tepung pada tanaman cabai di Kabupaten Tegal. Metode penelitian yang digunakan pada penelitian ini adalah pengamatan langsung di lahan, wawancara dengan petani terkait budidaya tanaman cabai, dan pengamatan laboratorium. Tanaman cabai merah dengan gejala klorotik pada permukaan daun bagian atas berwarna coklat kekuningan yang ditandai dengan adanya serbuk putih pada bagian bawah daun ditemukan di Kecamatan Bumijawa dan Kecamatan Margasari, Kabupaten Tegal pada bulan November 2020. Berdasarkan hasil pengamatan secara mikroskopis penyakit pada tanaman cabai merah dengan gejala tersebut berasosiasi dengan cendawan genus Leveillula taurica yang umum diketahui sebagai penyebab penyakit embun tepung.. Keparahan embun tepung pada cabai di Kecamatan Bumijawa lebih tinggi dibandingkan dengan Kecamatan Margasari., Red chili plants in Tegal Regency are infected with a rare disease with a fairly high severity. Recently, powdery mildew has been reported in Tegal Regency, Central Java Province. The purpose of this study was to describe and analyze the presence, symptoms, and severity of powdery mildew on chili peppers in Tegal Regency. The research method used in this study was direct observation in the field, interviews with farmers related to chili cultivation, and laboratory observations. Red chili plants with chlorotic symptoms on the upper leaf surface are yellowish brown which is characterized by the presence of white powder on the underside of the leaves found in Bumijawa Districts and Margasari Districts, Tegal Regency in November 2020. Based on microscopic observations of diseases in red chili plants with these symptoms associated with a fungus of the genus Leveillula taurica which is commonly known as the cause of powdery mildew. The severity of powdery mildew on chili peppers in Bumijawa District is higher than that of Margasari District.
Keyword: defoliasi, embun tepung, Leveillula taurica, defoliation, powdery mildew, Leveillula taurica

Judul: Insidensi Penyakit Daun Keriting Kuning Cabai di Bengkulu dan Penularannya Melalui Biji
Abstrak: Penyakit daun keriting kuning merupakan salah satu penyakit penting pada cabai di Indonesia yang disebabkan oleh Pepper yellow leaf curl virus (PYLCV) yang tergolong dalam genus Begomovirus dari famili Geminiviridae. Penularan dan penyebaran PYLCV di lapangan terjadi melalui vektor serangga kutukebul Bemisia tabaci. Potensi penularan benih PYLCV telah pernah dibahas. Penelitian dilakukan untuk mengetahui insidensi penyakit keriting kuning pada cabai di Kabupaten Kepahiang, Provinsi Bengkulu dan untuk memastikan virus tidak terbawa biji cabai. Pengamatan insidensi penyakit dilakukan di Desa Sumber Sari dan Desa Tangsi Duren. Sampel daun dan buah cabai dari lapangan dibawa ke laboratorium untuk penelitian lebih lanjut. Deteksi PYLCV dari sampel daun dilakukan dengan metode polymerase chain reaction (PCR) menggunakan primer universal Begomovirus SPG 1/2 dilanjutkan dengan sekuensing DNA. Biji cabai diekstraksi dari buah yang dikumpulkan dari lapangan, kemudian ditanam di rumah kaca. Pengamatan gejala penyakit dilakukan pada masing-masing tanaman dilanjutkan dengan deteksi PCR untuk memastikan adanya infeksi PYLCV. Insidensi penyakit di lapangan sangat tinggi, berkisar antara 62,69 sampai 100%. Gejala penyakitnya bermacam-macam, dari daun menguning, daun melengkung, hingga kerdil pada seluruh tanaman. Hasil deteksi PCR menunjukkan 8 dari 12 sampel positif terinfeksi Begomovirus. Berdasarkan analisis sekuens, isolat Begomovirus asal Kepahiang memiliki homologi 89,34-98,99% terhadap Pepper yellow leaf curl Indonesia virus. Sifat penyebaran penyakit keriting kuning cabai pada benih varietas cabai di Kepahiang perlu dikonfirmasi lebih lanjut., Yellow leaf curl disease is one of the most important diseases on chili pepper in Indonesia caused by Pepper yellow leaf curl virus (PYLCV), which belongs to the genus Begomovirus of the family Geminiviridae. Transmission and distribution of PYLCV in the field occurs through the insect vector, whitefly Bemisia tabaci. The potential for seed transmission of PYLCV has been discussed previously. Research was conducted to determine the incidence of yellow leaf curl disease of chili pepper in Kepahiang Regency, Bengkulu Province and to ensure that the virus is not seed transmitted. Observation of disease incidence was carried out in Sumber Sari and Tangsi Duren villages. Leaf and chili fruit samples from the field were taken to the laboratory for further studies. PYLCV detection from leaf samples was carried out by polymerase chain reaction (PCR) method using Begomovirus SPG1/2 universal primer followed by DNA sequencing. Chili seeds were extracted from fruit collected from the field, then grown in a greenhouse. Observation of disease symptoms was carried out on each plant followed by PCR detection to confirm PYLCV infection. Disease incidence in the field was very high, ranging from 62.69 to 100%. Disease symptoms varies, from leaf yellowing, leaf curling, to stunting of the whole plant. The result of PCR detection showed that 8 out of 12 samples were positively infected with Begomovirus. Based on sequence analysis, the Begomovirus isolates from Kepahiang has 89.34 to 98.99% homology to Pepper yellow leaf curl Indonesia virus. The seedborne nature of pepper yellow leaf curl disease on chili pepper varieties in Kepahiang needs further confirmation.
Keyword: disease incidence, disease symptom, Pepper yellow leaf curl Indonesia virus, polymerase chain reaction, whitefly

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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