Electronic Theses and Dissertation

Aceh merupakan salah satu provinsi penghasil pala terbesar di Indonesia. Tanaman pala (Myristica fragrans H.) merupakan tanaman rempah bernilai ekonomi tinggi yang banyak dibudidayakan di Indonesia. Namun dalam budidaya pala, petani mengalami kendala berbagai ancaman penyakit tanaman, salah satunya penyakit mati meranggas yang disebabkan oleh cendawan patogen Lasiodiplodia theobromae. Serangan penyakit mati meranggas dapat menurunkan hasil hingga 70%. Upaya pengendalian konvensional seperti pemangkasan pada cabang pohon terinfeksi serta penggunaan fungisida telah dilakukan oleh petani, namun efektivitasnya masih terbatas karena kurangnya pemahaman petani terkait biologi patogen serta pengaruh lingkungan terhadap siklus hidup penyakit. Oleh karena itu dibutuhkan pengendalian yang mampu menekan populasi patogen secara spesifik seperti bakteri endofit. Penelitian ini bertujuan untuk mengevaluasi efektivitas bakteri endofit asal tanaman pala terhadap penyakit mati meranggas yang disebabkan oleh L. theobromae.
Penelitian ini dilaksanakan di Laboratorium Ilmu Penyakit Tumbuhan dan Rumah Kasa Fakultas Pertanian Universitas Syiah Kuala. Isolat bakteri endofit merupakan hasil eksplorasi dari tanaman pala, yang diduga merupakan Pasudomonas, Bacillus 1., Bacillus 2., dan Agrobacterium. Pengujian bakteri endofit dilakukan pada bibit pala berumur tiga bulan melalui metode perendaman perakaran bibit pala ke dalam suspensi bakteri endofit dengan kerapatan 108 CFU/ml selama tiga jam. Empat belas hari setelah aplikasi bakteri endofit, bibit pala diinokulasi dengan patogen L. theobromae dengan cara menempelkan potongan media agar isolat patogen pada pangkal batang bibit pala. Parameter yang diamati dalam penelitian ini meliputi masa inkubasi gejala layu akibat infeksi
L. theobromae, insidensi penyakit mati meranggas, bobot basah dan bobot kering tanaman, panjang diskolorasi pembuluh batang, serta aktivitas enzim peroksidase pada bibit pala.
Hasil penelitian menunjukkan bahwa aplikasi bakteri endofit berhasil menekan perkembangan patogen dan insidensi penyakit (0,00%), yang menandakan bahwa kolonisasi patogen berhasil ditekan secara efektif, sehingga layu sistemik tidak terjadi. Perlakuan Bacillus 2 memberikan respon pertumbuhan tertinggi dengan bobot basah 20,63 g, bobot kering 5,88 g, dan kadar air 72,76%, mencerminkan akumulasi biomassa yang optimal sebagai hasil kesimbangan fotosintesis dan respirasi. Bacillus 2 juga menunjukkan kemampuan terbaik dalam menekan diskolorasi pembuluh tanaman, yaitu 0,5 cm. Hal ini menunjukkan kemampuan mekanisme antagonisme langsung bakteri endofit dalam membatasi perkembangan patogen. Sementara itu, aktivitas peroksidase (POD) tertinggi ditunjukkan oleh tanaman dengan perlakuan Bacillus 1 dengan POD 0,915, yang menandakan bahwa isolat ini terbaik dalam memicu respon pertahanan alami tanaman.
Bakteri endofit asal tanaman pala efektif sebagai agens hayati terhadap Lasiodiplodia theobromae penyebab penyakit mati meranggas, yang ditunjukkan dengan insidensi penyakit 0,00% dan mencegah terjadinya layu sistemik. Meskipun isolat endofit tidak meningkatkan bobot tanaman secara signifikan, keberadaannya tetap berperan dalam melindungi tanaman dari perkembangan penyakit.

Aceh is one of the largest nutmeg-producing provinces in Indonesia. Nutmeg (Myristica fragrans H.) is a spice crop with high economic value and is widely cultivated in Indonesia. However, in nutmeg cultivation, farmers face various plant disease threats, one of which is dieback disease caused by the pathogenic fungus Lasiodiplodia theobromae. Dieback disease can reduce yield by up to 70%. Conventional control measures such as pruning infected branches and the use of fungicides have been applied by farmers; however, their effectiveness remains limited due to a lack of understanding of the pathogen’s biology and the influence of environmental factors on the disease life cycle. Therefore, a control strategy capable of specifically suppressing pathogen populations is needed, such as the use of endophytic bacteria. This study aimed to evaluate the effectiveness of nutmeg-derived endophytic bacteria against dieback disease caused by L. theobromae. This research was conducted at the Plant Pathology Laboratory and the Screen House of the Faculty of Agriculture, Syiah Kuala University. Endophytic bacterial isolates were obtained from exploratory sampling of nutmeg plants and were presumed to belong to Pseudomonas, Bacillus 1, Bacillus 2, and Agrobacterium. Endophytic bacteria were applied to three-month-old nutmeg seedlings using a root immersion method in a bacterial suspension with a density of 10⁸ CFU/mL for three hours. Fourteen days after the application of endophytic bacteria, nutmeg seedlings were inoculated with L. theobromae by attaching agar plugs containing the pathogen isolate to the basal stem of the seedlings. The parameters observed in this study included the incubation period of wilt symptoms caused by L. theobromae infection, disease incidence of dieback, fresh weight and dry weight of plants, length of vascular discoloration in the stem, and peroxidase enzyme activity in nutmeg seedlings. The results showed that the application of endophytic bacteria effectively suppressed pathogen development and disease incidence (0.00%), indicating that pathogen colonization was successfully inhibited, thereby preventing the occurrence of systemic wilt. The Bacillus 2 treatment resulted in the highest growth response, with a fresh weight of 20.63 g, a dry weight of 5.88 g, and a water content of 72.76%, reflecting optimal biomass accumulation as a result of balanced photosynthesis and respiration. Bacillus 2 also exhibited the greatest ability to suppress vascular discoloration, with a lesion length of 0.5 cm, indicating the effectiveness of direct antagonistic mechanisms of endophytic bacteria in limiting pathogen development. Meanwhile, the highest peroxidase (POD) activity was observed in plants treated with Bacillus 1 (POD 0.915), indicating that this isolate was the most effective in inducing the plant’s natural defense response. Endophytic bacteria derived from nutmeg plants were effective as biological control agents against Lasiodiplodia theobromae, the causal agent of dieback disease, as indicated by a disease incidence of 0.00% and the prevention of systemic wilt. Although endophytic isolates did not significantly increase plant biomass, their presence played an important role in protecting plants from disease development