Judul: The Potential of Yeast as a Biological Control Agent for Cordana Leaf Spot in Bananas
Abstrak: Pisang merupakan buah yang paling banyak dikonsumsi oleh masyarakat Indonesia serta mempunyai jumlah produksi yang meningkat dari waktu ke waktu. Meskipun begitu, secara umum produktivitas pisang yang dikembangkan oleh masyarakat Indonesia masih sangat rendah, yaitu hanya sekitar 10−15 ton ha-1, padahal potensi produktivitas pisang bisa mencapai 35−40 ton ha-1. Salah satu penyebab kesenjangan produktivitas adalah gangguan hama dan penyakit. Penyakit bercak daun Cordana yang disebabkan oleh Cordana musae telah diketahui dapat menjadi ancaman terhadap produksi pisang. Penyakit bercak daun Cordana dapat ditekan keberadaannya dengan menggunakan agens hayati, seperti pemanfaatan mikrob antagonis yang berada di tanaman pisang itu sendiri, salah satunya adalah khamir. Penelitian ini bertujuan untuk mengetahui keefektifan beberapa isolat khamir yang diisolasi dari permukaan daun pisang dalam menekan penyakit bercak daun Cordana. Efikasi isolat khamir diamati secara in vitro dengan menghitung persen perkecambahan konidia dan secara in planta dengan mengamati keparahan penyakit di lapangan. Isolat khamir yang didapat sebanyak 11, namun dua diantaranya positif uji agar darah sehingga hanya sembilan yang digunakan dalam pengujian. Isolat Kh10, Kh4, dan Kh5 merupakan isolat yang berpotensi sebagai agens antagonis terhadap penyakit bercak daun Cordana karena mampu menghambat perkecambahan Cordana musae secara in vitro dengan nilai efikasi sebesar 67,50%, 65,33%, dan 61,76%. Diantara tiga isolat yang diuji tersebut, Kh4 merupakan isolat khamir yang mampu menekan keparahan penyakit bercak daun Cordana dengan efikasi yang paling tinggi dalam pengujian di lapang, yaitu sebesar 40%., Bananas are the most consumed fruit by Indonesians and have an increasing amount of production from time to time. However, in general, the productivity of bananas developed by Indonesians still needs to be improved, which is only around 10−15 tons ha-1, even though the potential productivity of bananas can reach 35−40 tons ha-1. One of the causes of the productivity gap is pest and disease disturbance. Cordana leaf spot disease caused by Cordana musae is known to be a threat to banana production. Cordana leaf spot disease can be suppressed by using biological agents, such as using antagonistic microbes in the banana plant itself, one of which is yeast. This study aimed to determine the effectiveness of several yeast isolated from the surface of banana leaves in supressing Cordana leaf spot disease. The efficacy of yeast isolates was observed in vitro by calculating the germination percentage of conidia and in planta by observing the severity of the disease in the field. There were 11 yeast isolates obtained, but two of them were positive for the blood agar test, so only nine were used in the test. Isolates Kh10, Kh4, and Kh5 have the potential as antagonist agents against Cordana leaf spot disease because they could inhibit C. musae germination in vitro with efficacy values of 67,50%, 65,33%, and 61,76%, respectively. Among the three isolates tested, Kh4 was a yeast isolate that was able to suppress the severity of Cordana leaf spot disease with the highest efficacy in field test, namely 40%.
Keyword: antagonist agent, Cordana musae, yeast isolate

Judul: The potency of endophytic bacteria as biocontrol agents to control blood disease on banana
Abstrak: Blood disease of banana caused by blood disease bacterium (BDB) is an important disease of bananas in Indonesia. The available control techniques have not been able to solve the disease problem effectively. Therefore, the development of more effective control method is needed. Endophytic bacteria have potencies as candidates of biological control agents to blood disease, because the bacteria as reported to be associated with plant resistance to pathogens and plant growth promotion. The aim of the studies were to (1) explore, select and identify endophytic bacteria to control blood disease on banana; (2) determine the mechanisms of endophytic bacteria to control blood disease on banana; (3) evaluate endophytic bacterial colonization on banana plant and their effect on the effectiveness to control blood disease; and (4) analyse the effect of application method of endophytic bacteria to their effectiveness to control blood disease on banana. Ninety isolates of endophytic bacteria have been isolated from the root of banana. The average population densities of the bacteria varied between 6.0 x 103 and 4.2 x 105 cfu/g fresh weight of root. Twenty seven among the ninety isolates positively produced inhibition zone toward blood disease bacterium (BDB). However, only four isolates (EAL15, EKK10, EKK20, EKK22) were able to reduce the incidence of blood disease on banana with ranged from 66.67% to 83.33%. Based on the partial sequence of 16S rRNA, four isolates were identified as Serratia liquefaciens (EAL15), Bacillus megaterium (EKK10), Enterobacter cloacae (EKK20) and Pectobacterium cypripedii (EKK22). The mechanisms of endophytic bacteria to control blood disease on banana were induced resistance, based on their activities in increasing peroxidase, polyphenol oxidase and salicylic acid content. The endophytic bacteria EAL15-Rif colonized within roots and stem tissues of young banana trees at four weeks after inoculation. Histological analysis using Scanning Electron Microscopy showed that EAL15-Rif colonise within the root and stem tissues of banana. The colonization period of endophytic bacteria during the eight months suppressed the blood disease incidence on banana ‘Cavendish’ with ranged from 66.67% to 83.33%. Application of endophytic bacterial community K-AL3 and K-RB1 were able to suppress the blood disease incidence on ‘Kepok kuning’ cultivar as much as 75.00% and 83.33%.
Keyword: Pseudomonas solanacearum, Ralstonia solanacearum, Endophytic bacteria, Blood disease bacterium, Induce resistance, Banana

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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