Judul: Survey and Detection of Ringspot Disease on Papaya Plants in North Sumatra
Abstrak: Penyakit bercak bercincin merupakan salah satu penyakit penting pada pepaya yang disebabkan oleh Papaya ringspot virus (PRSV). Insidensi penyakit yang disebabkan infeksi PRSV pertama kali dilaporkan di Indonesia pada tahun 2012 di Nanggroe Aceh Darussalam dan sejak saat itu diketahui telah menyebar ke beberapa daerah di Sumatera, Jawa, Bali, dan Nusa Tenggara Barat. Penelitian ini bertujuan mengetahui insidensi penyakit bercak bercincin dan mengidentifikasi strain PRSV penyebab penyakit bercak bercincin tersebut. Pengamatan lapangan, wawancara petani, dan pengambilan sampel dilakukan di 2 lokasi, yaitu di Desa Namorih, Kabupaten Deli Serdang dan Kelurahan Bhakti Karya, Kota Binjai. Sampel daun, tangkai daun, dan buah yang diambil dari tanaman sakit di lapangan dibawa ke laboratorium untuk deteksi PRSV menggunakan metode DAS-ELISA dan RT-PCR yang dilanjutkan dengan analisis sekuens nukleotida. Variasi gejala yang teramati di lapangan berupa mosaik dan malformasi pada daun, mosaik bergaris pada tangkai daun, dan bercak bercincin pada buah. Insidensi penyakit mencapai 51,82% hingga 73,49%. Indikasi infeksi PRSV pertama kali ditunjukkan dengan reaksi positif sampel terhadap antibodi PRSV. Selanjutnya, infeksi PRSV terkonfirmasi melalui teramplifikasinya fragmen DNA spesifik PRSV. Analisis sekuens nukleotida juga menunjukkan bahwa isolat-isolat asal Sumatera Utara memiliki homologi yang tinggi (92,5-98,9%) terhadap isolat PRSV-P asal Genbank., Ringspot disease is one of the important diseases in papaya caused by Papaya ringspot virus (PRSV). Incidence of PRSV infection was first reported in Indonesia in 2012 in Nanggroe Aceh Darussalam and since then it has spread out to several regions in Sumatera, Java, Bali, and West Nusa Tenggara. This study aimed to determine the incidence of ringspot disease and identify the PRSV strain that caused the ringspot disease. Field observations, farmers interview, and samples collection was carried out in 2 locations, i.e. Namorih Village, Deli Serdang Regency and Bhakti Karya Village, Binjai City. Field samples of leaves, petioles, and fruit taken from diseased plants were brought to the laboratory for PRSV detection using DAS-ELISA and RT-PCR methods followed by DNA sequencing. Symptom variation was observed in the field involving mosaic and malformation of the leaves, striped mosaic on the petioles, and ringspot on the fruits. Disease incidence reached 51.82% to 73.49%. Infection of PRSV was first indicated by positive reaction of the samples to PRSV antibody. Furthermore, amplification of specific DNA fragment confirmed PRSV infection. Sequence analysis showed that the isolates from North Sumatra has high homology (92.5- 98.9%) to PRSV-P isolates from Genbank accession.
Keyword: DAS-ELISA, disease incidence, homology, RT-PCR, sequencing

Judul: Kisaran Inang Papaya ringspot virus Isolat  Bogor dan Medan
Abstrak: Papaya ringspot disease was first reported in Nanggroe Aceh Darussalam, Indonesia, in 2012. Since then, PRSV spread rapidly in papaya growing areas in Java, Sumatra and Bali. PRSV infection causes immediate yield loss due to the symptoms of ringed spots on the fruit which reduces the quality and quality of the fruit. This study aimed to evaluate the incidence, severity and symptoms of ring spot disease caused by two PRSV isolates, i.e. isolates Bogor and Medan on some varieties of papaya (“Callina”, “Miba”, “Sukma”, and “California) and plants from the family Cucurbitaceae, i.e. cucumber (Cucumis sativus), watermelon (Citrullus lanatus), bitter gourd (Momordica charantia), and melon (Cucumis melo). The source of virus isolates was taken from the collection of Plant Virology Laboratory, IPB. Virus inoculation was conducted mechanically using sap of virus inoculum. Disease symptoms was observed for 5 weeks and PRSV infection was confirmed by DAS-ELISA. Typical symptoms of PRSV infection was observed on papaya var. Callina, California, and Sukma, but did not appear on papaya var. Miba and all Cucurbitaceae. The types of symptoms that appeared on the leaves include mosaic, chlorotic spots, vein clearing, blisters, wrinkles, crunching, thickening of the lamina, and leaf malformations (“shoestring”). Disease incidence in var. Callina, California, and Sukma ranges from 33% to 100% while disease severity ranges from 6% to 86.11%. Infection of PRSV-Medan tends to cause higher severity than PRSV-Bogor
Keyword: Cucurbitaceae, DAS-ELISA, disease incidence, disease severity, mechanical inoculation, PRSV

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: