Phytophthora palmivora merupakan patogen utama pada tanaman kakao di seluruh dunia. Akibat serangan patogen ini menyebabkan kerugian sebesar 25-50%. Pengendalian patogen ini masih mengandalkan fungisida sintetik yang dikhawatirkan berbahaya bagi manusia dan lingkungan. Fungisida nabati yang mengandung minyak atsiri, merupakan alternatif pengendalian yang lebih ramah lingkungan. Penelitian bertujuan mengevaluasi pengaruh formula eugenol, sitronella, asam salisilat dan silikon terhadap pertumbuhan P. palmivora. Penelitian dilakukan di Laboratorium dan Rumah Kaca Balai Penelitian Tanaman Industri dan Penyegar dari Maret sampai Agustus 2012. Minyak cengkeh (CK), serai wangi (SW), asam salisilat (AS) dan silikon cair (SI) digunakan sebagai bahan utama pembuatan formula. Formula yang diuji, yaitu (1) Eugenol, (2) Sitronella, (3) CK+SW, (4) SW+SI, (5) SW+AS, (6) CK+SI, dan (7) CK+AS. Percobaan dirancang secara acak lengkap dengan 5 ulangan. Pengujian formula terhadap pertumbuhan P. palmivora in vitro dilakukan dengan menginokulasikan potongan agar berisi kultur jamur pada permukaan PDA yang mengandung formula, sedangkan pengujian formula pada buah dan bibit kakao diuji di rumah kaca. Kadar fenol dan lignin dalam jaringan daun bibit kakao dianalisis untuk mengetahui mekanisme pertahanan tanaman terhadap infeksi patogen. Hasil penelitian menunjukkan bahwa semua formula yang diuji menghambat pertumbuhan dan biomassa P. palmivora pada kondisi in vitro, dan perkembangan gejala penyakit pada buah serta bibit kakao. Formula eugenol + asam salisilat mampu menghambat total pertumbuhan dan bioassay patogen pada media PDA, menekan perkembangan penyakit 65,2% pada buah dan 66,25% pada bibit, serta meningkatkan kadar senyawa fenol dan lignin dalam jaringan daun.Kata Kunci: Kakao, Phytophthora palmivora, eugenol, sitronella, fungisida nabatiPhytophthora palmivora is a major pathogen of cacao plants on the world. This pathogen caused 25-50% losses. The pathogen is commonly controlled with synthetic fungicide uses which may hazard for human and environment if used unwisely. Botanical fungicides containing essential oils offer more environmentally friendly control method. The study aimed to evaluate the effects of seven botanical fungicide formulas containing clove oil and citronella oil on P. palmivora. The study was conducted in the Laboratory and Greenhouse of the Indonesian Research Institute for Industrial and Beverage Crops from March to August 2012. A randomized complete designed with five replicates was used. Seven formulas tested were: (1) eugenol (CK), (2) citronella (SW), (3) CK+SW, (4) SW+ silicone (SI), (5) SW+salycilic acid (AS), (6) CK+SI, dan (7) CK+AS. The effects of formulas on growth and biomass of P. palmivora in vitro were tested by culturing the pathogen on solid PDA medium whereas its effect on disease developments was tested by inoculating cacao pods on fruits and seedlings. In addition, the phenol and lignin contents in the inoculated seedlings were assessed to support disease inhibition mechanism. The results showed that all the formulas tested inhibited the growth and biomass of P. palmivora in vitro. The highest inhibition was shown by the formula of clove oil mixed with salicylic acid. Disease developments on inoculated cocoa pods and seedlings reduced of 66.25% and 65.2% respectively, and increased levels of lignin and phenol in the leaves.
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