Judul: Studi Kolonisasi Rizobakteria Pemacu Tumbuh Tanaman Pseudomonas sp. dan Bacillus sp. di Rizosfer Tanaman Kedelai
Abstrak: Rhizosphere is a portion of soil affected by substances released by roots (root exudates), which are substrates for microbial growth, thereby triggering a competition amongst various microorganisms to colonize the rhizosphere. The survival and colonization of Pseudomonas sp. Crb 17, Crb 64, and Bacillus sp. Cr 76 were tested in the rhizosphere of soybean grow on sterile and non-sterile soil for six weeks. A marker used to monitor the dynamic population of the isolates in the rhizosphere was rifampicin resistance marker. Based on the results obtained, the rhizosphere colonization ability of these three isolates in the sterile soil was not significantly different (α = 0.05) from that in non-sterile soil, although there was a tendency of higher population in sterile soil compared to non-sterile soil. Colonization ability amongst the isolates was also not significantly different (α = 0.05) both in sterile and non-sterile soil. However, in non-sterile soil, colonization ability of isolate Crb 64 was better than that of two isolates. Isolate Crb 64 is the most competitive isolate in colonizing soybean rhizosphere. In general, all isolates have high ability to colonize and survive in the soybean rhizosphere as shown by their high population numbers until the end of the observation period, i.e. around 6 to 7 log cells/g dry soil.
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Judul: Karakterisasi Rizobakteria Pemacu Tumbuh Tanaman dan Toleran Kekeringan
Abstrak: Plant Growth Promoting Rhizobacteria (PGPR) are a group of bacteria that have some ability to support plant growth. Two of those rhizobacteria are Bacillus and Pseudomonas. This study aimed to isolate and characterize indigenous rhizobacteria Bacillus and Pseudomonas isolated from soybean (Glycine max) rhizosphere from Nusa Tenggara Barat. Characterization included the ability to stimulate soybean sprouts growth, indole acetic acid (IAA) production, the ability to face drought stress, phosphate solubilizing ability, and chitinase enzyme production. There were 22 isolates of Pseudomonas and 29 of Bacillus were isolated using selective media King's B and NB. Sixteen isolates consisting seven Pseudomonas and nine Bacillus isolates could significantly stimulate soybean sprouts growth. With the addition of 0.2 mM tryptophan in liquid media, bacteria are able to produce IAA in the concentration range of 1.02 to 21.06 ppm for genus Pseudomonas and 4.59 to 5.44 ppm for genus Bacillus. The sixteen isolates were tested for their ability in facing drought stress, phosphate solubilizing, and chitinase enzymes production. Isolates pntb80 and bntb20 can survive up to -2.5 MPa osmotic pressure on the media with PEG 6000 added as osmotic pressure controller. The highest phosphate solubilizing index were shown by pntb18 on Pikovskaya agar with tricalcium phosphate. The highest chitinolytic index were shown by bntb22 on 1% chitin media.
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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