Judul: Bacterial Wilt Disease of Eucalyptus pellita: Disease Trigger Factors, Pathogen and Host Plants Diversity
Abstrak: The productivity of forest plantations such as Eucalyptus pellita in Indonesia is low, one of which is severely affected by bacterial wilt disease. The serious threat of this disease in Indonesia began in 2006, which attacked lowland eucalyptus plantations in Jambi. The disease has been widely spread in Riau, South Sumatra and East Kalimantan provinces. However, studies of bacterial wilt disease on E. pellita in Indonesia are still inadequate, particularly regarding to the integration of site and genetic factors; thus, a comprehensive study is required. The main objective of this study was to analyze the dominant variables of sylviculture, soil properties, and climate factors that can trigger bacterial wilt disease epidemics on eucalypts; identify and describe the phenotypic and genotypic diversity of the causal agent; characterize pathogen strains that have the highest virulence level based on phenotype and genotype diversity; evaluate the resistance of eucalyptus progenies and clones, and analysis SSR markers related to eucalyptus resistance to bacterial wilt disease. The surveys in four provinces in Indonesia showed that bacterial wilt incidence on E. pellita varied from 0–33.5% in plants aged 2–23 months. The initial disease symptoms are yellowing of the leaves followed by branches wilting and causing plant death. Color changes, turning blackish-brown, occurred in the inner cortex of the stem associated with bacterial ooze. Analysis of the triggering factors that contribute to the emergence of bacterial wilt disease was carried out on silvicultural factors (e.g. topography, site classification, diversity eucalyptus clones, seedling propagation technique, plant age, crop rotation, weed cover, incidence of root malformations, and expose to herbicide drift), soil properties (e.g. pH, C-org, N-total, P-available, S-total, Ca2+, Mg+, K+, Na+, and % soil texture) and climate variables (e.g. temperature, humidity, and rainfall). In silvicultural factors, three of the nine variables showed a significant correlation to disease incidence. The variables were plant age, eucalyptus clones, and root malformations incidence. The early growth of eucalyptus plants is a critical period of the disease epidemic, especially in susceptible. For the soil property factor, the soil texture variable is the dominant variable that partially associated with the disease incidence. The incidence of moderate and severe disease generally develops in clay loam soils. Meanwhile, for climatic factors, rainfall has a positive correlation with bacterial wilt incidence. Description of the diversity of pathogens that cause bacterial wilt is carried out by phenotypic and genotypic analyses. The phenotypic diversity analysis included biovar, exopolysaccharide quantification, and virulence tests, while genotypic diversity included phylotypes and sequevar determination based on egl gene sequences. A total of 35 strains were isolated from the field and nurseries. All isolates were confirmed as Ralstonia species complex based on morphological characteristics and molecular studies using species-specific primers. These pathogen strains were dominantly classified as biovar 3 and 4 and had a high variation in virulence and EPS production (0.13 - 8.38 g/mL). Based on the alignment of the egl gene sequences, 29 strains of Ralstonia originating from E. pellita belonged to Phylotype I and were grouped into four sequevars (sequevars 14, 17, 18, 30) and one new sequevar 58. New sequevars were identified
Keyword: epidemi, silvikultur, Ralstonia pseudosolanacearum, klon tahan, marka molekuler

Judul: The Role of Endophytic Bacteria and Mycorrhizal in Control of Bacterial Wilt in Eucalyptus pellita F. Muell.
Abstrak: Saat ini produktivitas tanaman eukaliptus (Eucalyptus pellita) Indonesia terkendala oleh penyakit layu bakteri (PLB). Penyebab PLB adalah bakteri Ralstonia solanacearum yang bersifat tular tanah. Pada area pembibitan maupun lapangan eukaliptus hutan tanaman industri (HTI) terjadi epidemik PLB yang sangat merugikan. Tanaman yang terinfeksi akan menunjukkan gejala daun menguning, mengering, dan layu. Batang yang terinfeksi dapat mengalami perubahan warna menjadi kehitaman. Hal ini terjadi karena xilem dihambat oleh senyawa ekstraseluler berupa exopolysaccharide (EPS). Senyawa EPS yang dihasilkan oleh R. solanacearum merupakan salah satu faktor penentu tingkat virulensi patogen. Beberapa taktik pengendalian PLB telah dilakukan diantaranya penggunaan agens hayati, penanaman eukaliptus secara multi klon, penanaman klon eukaliptus resisten, penggunaan bibit eukaliptus bebas patogen, penggunaan bakterisida sintetik, dan eradikasi tanaman sakit. Namun, upaya pengendalian yang dilakukan belum optimal yang ditunjukkan oleh tingginya populasi tanaman terinfeksi pada area HTI eukaliptus. Salah satu pendekatan yang berpotensi efektif mengendalikan PLB adalah pengendalian secara hayati. Strategi pengendalian hayati dengan memanfaatkan kombinasi bakteri endofit dan fungi mikoriza arbuskula (FMA) telah banyak dilaporkan mampu mengendalikan patogen terutama yang bersifat tular tanah. Kombinasi bakteri endofit dan FMA berpotensi efektif tinggi dalam pengendalian PLB melalui berbagai mekanisme, seperti meningkatkan ketersediaan nutrisi bagi tanaman, pertumbuhan optimum tanaman dan induksi ketahanan tanaman. Berdasarkan latar belakang tersebut diatas, maka dilakukan suatu penelitian yang bertujuan:1) Mendapatkan bakteri endofit asal eukaliptus yang berpotensi sebagai agens hayati R. solanacearum; (2) Memeroleh kombinasi isolat bakteri endofit dan FMA yang kompatibel dan tidak fitotoksik terhadap tanaman eukaliptus; dan (3) Memeroleh bakteri endofit dan FMA yang efektif dalam menekan perkembangan PLB pada bibit eukaliptus. Metode penelitian meliputi pengambilan sampel tanaman dan akar sehat dari 6 klon eukaliptus dan sampel tanaman dan akar sakit dari 5 klon diantara pertanaman eukaliptus terinfeksi PLB pada area milik PT Arara Abadi. Selanjutnya dilakukan isolasi bakteri, baik yang patogenik maupun yang bersifat endofitik. Isolat patogen diidentifikasi secara morfologi, fisiologi, molekuler dan uji patogenisitas serta virulensi. Isolat bakteri endofit yang berhasil diisolasi dilakukan penapisan yang meliputi uji hypersensitive response (HR), uji hemolisis, uji patogenisitas, dan uji pertumbuhan pada bibit eukaliptus. Bakteri endofit hasil penapisan dilakukan karakterisasi yang meliputi kemampuan antibiosis, aktivitas enzim protease, acyl homoserine lactonase (AHL), produksi hormon indole acetic acid (IAA), pelarut fosfat, dan penambat nitrogen. Selanjutnya dilakukan pemilihan isolat bakteri endofit potensial menggunakan metode analytical hierarchy process (AHP). Identifikasi bakteri endofit terpilih dilakukan secara molekuler. Berdasarkan hasil AHP diperoleh sepuluh bakteri endofit potensial. Selanjutnya sepuluh jenis bakteri endofit potensial dikombinasikan dengan tiga jenis FMA. Percobaan uji kompatibilitas bakteri endofit dengan FMA dilakukan di screen house dengan menggunakan rancangan faktorial acak kelompok. Faktor pertama adalah bakteri endofit yang terdiri atas sebelas taraf dan faktor kedua adalah FMA terdiri atas 4 taraf dengan 3 ulangan. Setiap unit percobaan terdiri dari 4 tanaman. Peubah yang diamati meliputi kolonisasi akar, jumlah spora FMA, tinggi tanaman dan diameter batang. Berdasarkan percobaan kompatibilitas, terpilih sepuluh kombinasi bakteri endofit dan FMA yang kompatibel. Selanjutnya dievaluasi keefektifan pengendalian terhadap R. solanacearum pada bibit eukaliptus yang berumur 4 bulan dalam growth chamber. Peubah pengamatan meliputi periode laten, laju infeksi, insidensi penyakit, tingkat kolonisasi bakteri R. solanacearum, dan produksi enzim pertahanan tanaman (fenol dan PAL).
Keyword: endophytic bacteria, AMF, R. solanacearum, PLB, ISR

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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