Judul: Rhizobacteria of Bacillus sp. and Pseudomonas sp. growth promoter drought tolerant and their application on maize
Abstrak: Agricultural land in Indonesia was largely dominated by untapped dry land. Maize (Zea mays L.) is one of the staple crops that are known could be cultivated on dry land. The future of agricultural development strategy oriented to the application of biological fertilizers and optimize ecological function of each ecosystem component. Rhizosphere has been known to contain microorganisms that can improve the plant growth, both directly and indirectly. Those rhizobacteria was known as plant growth promoting rhizobacteria (PGPR), include genus of Bacillus and Pseudomonas. Rhizobacteria had adapted to drought conditions, one way by producing exopolysaccharide (EPS). Therefore, this research was aimed to screening of rhizobacteria of Bacillus and Pseudomonas drought tolerant as growth promoter of maize growth. Utilized of rhizobacteria could be alternative way that are effective and environmental friendly. Screening in vitro of rhizobacteria as growth promoter of 47 Bacillus CR and 34 Pseudomonas CRB resulted 24 and 9 isolates were able to stimulate the growth of maize sprouts, significantly. Further screening of those growth promoter of the rhizobacterial isolates to drought tolerance with PEG 6000 resulted 7 isolates of Bacillus CR and 6 isolates of Pseudomonas CRB that were able to grow on medium with osmotic pressure -1 MPa and -2 MPa, respectively. Rhizobacterial isolates of growth promoter and drought tolerance were tested for antagonist mechanisms which aims to determine ability to live together in one medium if to be made formulation. Both non antagonist rhizobacterial isolates were evaluated for their potential in producing EPS by Dubois method. CRB 19 and CR 90 exhibited the highest activity of EPS production up to 0.346 mg mL-1 on medium with -2.0 MPa and 0.107 mg mL-1 on medium with -0.73 MPa, respectively. Based on 16S rRNA sequence analysis revealed that CRB 19 and CR 90 belonged to Pseudomonas aeruginosa strain B2 and Brevibacillus brevis B33, respectively. Four of potential isolates of each genus to be made formulation using peat soil as carrier material (F1, F2, F3 and F4). In addition, CRB 19 and CR 90 as selected isolates of each genus also to be formulated. Formulation were selected based on the highest of OD and EPS value. Rhizobacterial formula were further applied in planta in greenhouse using a completely randomized design with two factors (water content and formula). Water content consists of two levels (field capacity and under of field capacity), and the formula consists of seven levels (six formulas+control). In planta test showed that formula CRB 19 and F3 (CR 83+CRB 10) were the best formula that could enhance plant growth parameters compared to other formula. Furthermore, those drought tolerant rhizobacteria had potency to be developed as inoculants of maize planted in dry land agriculture.
Keyword: growth promoter, rhizobacteria, maize, drought tolerant

Judul: Penapisan Komunitas Bakteri Rizosfer secara In Planta untuk Meningkatkan Pertumbuhan Jagung di Lahan Kering
Abstrak: Indonesia has wide proportion of dryland and its potential for the development of a variety of important crops, such as maize. Increment of the dryland capacity is still constrained by various problems, among others, drought and low soil fertility. Microbial applications to increase the dryland productivity have been carried out. However, effective microbial inoculum for specific problems in the dryland should continue to explore. In this study, in planta screening was done to obtain potential rhizosphere bacterial community for growth promoting of maize in dryland. The dominant bacterial group from selected bacterial community was also analysed for plant growth promoting characteristics and its potency and role in the growth of maize in greenhouse. A total of 11 rhizosphere soil samples (TR A, TR B, C TR, TR D, TR E, F TR, TR G, H TR, TR I, J TR, and TR K) were collected from selected maize grown in two farm of dryland development located in Lombok, West Nusa Tenggara. In green house screening, a 100 g of each rhizosphere soil sample was added to maize growth medium. The results showed that TR D gave the best growth performance of maize. In the 50% water content of growing media, TR D treatment generally showed increased fresh weight of upper biomass (47.1%), dry weight of upper biomass (45.2%) and highest increase of root dry weight (33.4%). Based on cultivation method using four culture media showed that at least 22 bacterial isolates and 5.72 x 107 cells g-1 of soil were found in the TR D. Those number of isolate was higher compared with the others rhizosphere soil samples. T-RFLP analysis of bacterial community inhabitant of TR D showed that 8 T-RFs were detected based on metagenomic approach and 7 T-RFs based on cultivation-dependent approach. Those number of T-RF based on metagenomic approach was higher compared with the others communities in this study. Based on Shannon index, the diversity level of bacterial community of TR D was 1.6 in metagenomic and 1.58 in cultivation-dependent approach. The diversity level in metagenomic approach was higher compared with the others communities. The bacterial community structure of TR D included Burkholderiales, Pseudomonas, Bacillus, Candidatus, Alphaproteobacteria, Betaproteobacteria, Rhizobiales, Sinobactera-ceae, and Acidobacteria. Burkholderiales is the dominant group in metagenomic approach with eveness value was 45.83%. Pseudomonas sp. strain L485 is the dominant group in cultivation-dependent approach with eveness value was 42.88%. Pseudomonas sp. strain L485 also detected in metagenomic with eveness value was 17.38%. Based on estimation of the dominance and existence in metagenomic and cultivation-dependent approaches, Pseudomonas sp. strain L485 was chosed to plant growth promoting characteristics and tested for its ability to promote the growth of maize in the greenhouse. Pseudomonas sp. L485 is the maize rhizosphere bacteria producing indole acetic acid (IAA) and exopolysaccharide (EPS). The amount of IAA produced by this strain in King's broth medium supplemented with 5 ppm L-tryptophan was about 4.97 ppm when the cell density reached 3.74 x 1010 cells ml-1 and 11.95 ppm when the strain reached the stationary phase of growth. Approximately 0.058 mg EPS per mg of cell
Keyword: bacterial community, in planta, rhizosphere, maize, dryland, T-RFLP

Judul: Closed Knight’s Tour pada Papan Catur Berbentuk Persegi Panjang dengan Ukuran Maksimal 8 × 8
Abstrak: Closed Knight’s Tour merupakan langkah kuda yang mengunjungi setiap kotak pada papan catur tepat satu kali dengan langkah kuda berawal dan berakhir pada kotak yang sama. Graf yang terbentuk dari closed knight’s tour dinotasikan sebagai graf G(m,n), dengan m adalah banyaknya baris dan n adalah banyaknya kolom. Graf tersebut memuat Hamiltonian cycle. Sebuah graf terhubung G adalah graf bipartite jika dan hanya jika graf tersebut tidak memiliki cycle dengan panjang ganjil. Papan catur yang memenuhi syarat cukup untuk memiliki closed knight’s tour adalah papan catur berukuran 5 × 6, 5 × 8, 6 × 6, 6 × 7, 6 × 8, 7 × 8, dan 8 × 8.
Keyword: bipartite, closed knight’s tour, hamiltonian cycle, knight’s tour, teori graf