Judul: Intensity of Leaf Blight Disease on Trembesi (Samanea saman (Jacq.) Merr.) in the Nursery of PT Indominco Mandiri
Abstrak: Kegiatan pertambangan harus melakukan reklamasi untuk memulihkan kerusakan akibat kerusakan lingkungan. Reklamasi memerlukan bibit bermutu baik, yang diperoleh di persemaian. Bibit di persemaian sering menghadapi masalah yaitu munculnya penyakit pada bibit. Oleh karena itu diperlukan tindakan pencegahan dan pengendalian yang tepat. Penelitian ini bertujuan untuk mengetahui intensitas serangan penyebab penyakit hawar daun pada semai trembesi di persemaian PT Indominco Mandiri. Metode penelitian meliputi survei penyakit hawar daun pada bibit trembesi berumur 4, 8, dan 10 bulan dengan menggunakan metode sampling diagonal dengan intensitas sampling 10% untuk mengamati kejadian dan intensitas penyakit. Sampel daun yang bergejala hawar daun diambil untuk diisolasi untuk mengetahui penyebab penyakitnya, kemudian dilakukan uji patogenisitas. Kejadian dan intensitas penyakit tertinggi yaitu pada petak 1 sebesar 71,00% dan 37,67%. Intensitas penyakit termasuk kedalam kategori rusak sedang (RS). Tidak ada perbedaan yang nyata dalam kejadian dan intensitas penyakit hawar daun antara petak-petak yang berbeda di persemaian. Uji patogenisitas menunjukkan semua isolat menyebabkan gejala penyakit dengan masa inkubasi 2-4 hari. Cendawan penyebab patogen hawar daun yang diisolasi dari daun trembesi mempunyai karakteristik seperti cendawan Diaporthe sp. Sa-1, Rhizoctonia sp. Sa-2, Cercospora sp. Sa-3, dan Colletotrichum sp. Sa-4., Mining activities must carry out reclamation to restore damage caused by environmental damage. Reclamation requires good quality seeds, which are obtained in nurseries. Germination in nurseries often faces obstacles, namely the emergence of diseases in seedlings. Therefore, appropriate preventive and control measures are needed. This study aims to determine the intensity of attacks that cause leaf blight disease on trembesi seedlings in PT Indominco Mandiri nursery. The research method includes a survey of leaf blight disease on trembesi seedlings aged 4, 8, and 10 months using the diagonal sampling method with sampling intensity of 10% to observe the incidence and intensity of the disease. Infected leaves were isolated to identify pathogens. The highest disease incidence (71,00%) and intensity (37.67%) were found in plot 1. The intensity of the disease is categorized as moderate damage (MD). There was no significant difference in the incidence and intensity of leaf blight disease between different plots in the nursery. The pathogenicity test showed that all isolates caused disease symptoms with an incubation period of 2-4 days. The fungi causing leaf spot disease isolated from trembesi leaves have characteristics such as Diaporthe sp. Sa-1, Rhizoctonia sp. Sa-2, Cercospora sp. Sa-3, and Colletotrichum sp. Sa-4.
Keyword: uji patogenisitas, hawar daun, trembesi, masa inkubasi

Judul: Evaluasi Penyakit Bercak Daun Pada Bibit Johar (Cassia siamea Lamk.) di Nursery PT Indominco Mandiri, Kalimantan Timur
Abstrak: Salah satu jenis tanaman yang terserang penyakit bercak daun di nursery PT Indominco Mandiri adalah johar (Cassia siamea Lamk.). Tanaman yang berada di nursery rentan terserang penyakit bercak daun karena jenis tanaman yang seragam serta memiliki jarak tanam yang terlalu rapat sehingga penyakit lebih mudah menular. Tujuan penelitian ini adalah melakukan deteksi penyakit bercak daun serta menghitung insidensi dan keparahan penyakit bercak daun johar di nursery PT Indominco Mandiri. Metode penelitian yang dilakukan meliputi pembuatan blok dan pengamatan gejala bercak daun, evaluasi penyakit, isolasi, pemurnian patogen, dan uji patogenisitas. Hasil penelitian menunjukkan bahwa gejala penyakit bercak daun johar di nursery PT Indominco Mandiri berupa bintik cokelat kehitaman tidak beraturan. Insidensi penyakit bercak daun johar mencapai 100% dan tingkat keparahan penyakit pada blok 1 sebesar 82% (parah), blok 2 sebesar 89% (sangat parah), dan blok 3 sebesar 90% (sangat parah)., One of the plants affected by leaf spot disease in the PT Indominco Mandiri nursery is johar (Cassia siamea Lamk.). The plants in this nursery are particularly vulnerable to leaf spot disease due to their uniform types and close planting distances, which facilitate the spread of the disease. This study aimed to detect the presence of leaf spot disease and to measure its incidence and severity in johar plants at the PT Indominco Mandiri nursery. The research methods included creating observation blocks, monitoring leaf spot symptoms, evaluating the disease, isolating and purifying pathogens, and conducting pathogenicity tests. The findings indicated that the symptoms of leaf spot disease on johar plants were irregular blackish-brown spots. The incidence of the disease was 100%, with severity levels in block 1 at 82% (severe), block 2 at 89% (very severe), and block 3 at 90% (very severe).
Keyword: bercak daun, insidensi penyakit, tingkat keparahan, uji patogenisitas

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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