Keanekaragaman Mikrob Endofit dan Pengendalian Hayati Penyakit Kanker Batang (Neoscytalidium dimidiatum Penz.) pada Buah Naga Merah (Hylocereus costaricensis Britt. Et R.)

Abstract

Penyakit kanker batang buah naga yang disebabkan oleh cendawan patogen Neoscytalidium dimidiatum merupakan salah satu faktor penyebab penurunan produksi nasional tanaman buah naga di Indonesia. Strategi pengendalian yang tepat diperlukan untuk mencegah dan meminimalisir serangan dari patogen N. dimidiatum agar produksi nasional tanaman buah naga dapat meningkat dan stabil. Terdapat beberapa pengendalian yang telah dilakukan untuk mengendalikan penyakit kanker batang buah naga, yaitu secara kultur teknis dengan sanitasi lahan, secara mekanis melalui pemangkasan bagian tanaman terinfeksi, aplikasi garam dapur (NaCl) dengan konsentrasi 5%, fungisida kimia sintetik dengan bahan aktif azoksistrobin dan difenokonazol, kombinasi bahan aktif fluopyram dan tebukonazol, serta cyprodinil dan fludioxonil. Selain itu, pengendalian penyakit kanker batang buah naga dapat dilakukan secara hayati dengan memanfaatkan mikrob yang berpotensi sebagai agens biokontrol terhadap N. dimidiatum. Mikrob potensial baik cendawan maupun bakteri sebagai agens biokontrol terhadap patogen cendawan N. dimidiatum, dapat dibedakan menjadi tiga kelompok berdasarkan tempat hidupnya, yaitu mikrob rizosfer, mikrob filoplan, dan mikrob endofit. Keanekaragaman mikrob rizosfer, filoplan, dan endofit memainkan peran penting sebagai agens biokontrol patogen tanaman. Tingginya keanekaragaman suatu mikrob rizosfer mampu meningkatkan potensinya dalam menyediakan nutrisi untuk tanaman sehingga tanaman mampu bertahan dari ancaman patogen tanaman. Sementara itu, tingginya keanekaragaman mikrob filoplan mampu meningkatkan potensinya dalam mendominasi kompetisi ruang dan nutrisi untuk mencegah dan menghambat masuknya patogen, memacu pertumbuhan tanaman, serta membantu menyediakan unsur hara. Tingginya keanekaragaman mikrob endofit mampu meningkatkan potensinya dalam menginduksi ketahanan tanaman untuk menghambat perkembangan penyakit yang disebabkan oleh patogen tanaman. Penelusuran literatur ilmiah oleh penulis menunjukkan bahwa analisis keanekaragaman mikrob endofit asal tanaman buah naga dan potensi mikrob asal tanaman buah naga dalam mengendalikan penyakit kanker batang di Indonesia belum banyak dilakukan. Oleh karena itu, penelitian ini berperan dalam memberikan informasi terkait keanekaragaman mikrob endofit dan potensi mikrob asal tanaman buah naga dalam mengendalikan penyakit kanker batang buah naga. Penelitian dilakukan dengan beberapa metode, yaitu pengambilan sampel, isolasi mikrob endofit asal tanaman buah naga, analisis keanekaragaman mikrob endofit asal tanaman buah naga, pengambilan data pendukung, penyediaan isolat mikrob asal tanaman buah naga, uji keamanan hayati mikrob asal tanaman buah naga, uji potensi penghambatan in vitro mikrob asal tanaman buah naga, karakterisasi isolat terpilih, dan uji potensi penghambatan semi in vivo mikrob asal tanaman buah naga. Identifikasi morfologi isolat endofit asal daerah Banyuwangi dan Bukittinggi diperoleh enam genus, yaitu Aspergillus sp., Penicillium sp., Fusarium sp., Trichoderma sp., Bipolaris sp., dan Lasiodiplodia sp. Keanekaragaman cendawan endofit dari daerah Banyuwangi dan Bukittinggi tergolong moderat dengan indeks Shannon 1,64-2,08, populasi tiap spesies yang relatif merata dengan indeks Evenness 0,82-0,95, dan dominansi antar spesies dari rendah hingga moderat dengan indeks Simpson 0,13-0,31. Bakteri endofit pada daerah Banyuwangi dan Bukittinggi menghasilkan keanekaragaman dari rendah hingga moderat dengan indeks Shannon 0,46-1,32, populasi tiap spesies yang relatif merata dengan indeks Evenness 0,54-0,66, dan dominansi antar spesies dari moderat hingga tinggi dengan nilai indeks Simpson 0,35-0,71. Isolat cendawan dan bakteri endofit yang diperoleh dari wilayah Banyuwangi tidak ditemukan di wilayah Bukittinggi, begitu pula sebaliknya. Isolat cendawan endofit C4 dan Fusarium sp. C5 merupakan isolat yang memiliki frekuensi kemunculan tertinggi pada sampel daerah Banyuwangi. Isolat cendawan endofit C12 dan Aspergillus sp. C10 merupakan isolat yang memiliki frekuensi kemunculan tertinggi pada sampel daerah Bukittinggi. Isolat bakteri endofit B1 merupakan isolat yang memiliki frekuensi kemunculan paling banyak di sampel daerah Banyuwangi sedangkan isolat bakteri endofit B13 dan B12 merupakan isolat yang memiliki frekuensi kemunculan paling banyak ditemukan di daerah Bukittinggi. Sampel sulur asal Banyuwangi (S2) dan akar asal Bukittinggi (A5 dan A6) menghasilkan isolat cendawan endofit paling banyak diantara sampel lainnya, sementara sampel S1 (sulur asal Banyuwangi) dan sampel A4 (akar asal Bukittinggi) menghasilkan isolat bakteri endofit paling banyak diantara sampel lainnya. Isolat cendawan CR2, CR3, CF2, Trichoderma sp. C6, dan Trichoderma sp. C13, serta isolat bakteri BR8, B16, BR1, B2, dan B7 merupakan isolat mikrob asal tanaman buah naga yang berpotensi sebagai agens biokontrol terhadap N. dimidiatum berdasarkan uji potensi penghambatan in vitro dan kemampuannya dalam menghasilkan hormon auksin, enzim kitinase, dan glukanase. Hampir seluruh isolat cendawan dan bakteri, kecuali isolat cendawan CR2 yang diujikan mampu menghambat perkembangan lesio dengan nilai AUDPC yang tidak berbeda nyata dengan fungisida difenokonazol. Penelitian ini memberikan informasi terkait keanekaragaman mikrob endofit asal tanaman buah naga dan potensi mikrob rizosfer, filoplan, dan endofit sebagai agens hayati pengendalian cendawan N. dimidiatum penyebab penyakit kanker batang buah naga.

Stem canker disease of dragon fruit, caused by the pathogen fungi Neoscytalidium dimidiatum, is one of the major factors contributing to the decline of national dragon fruit production in Indonesia. Effective management strategies are required to prevent and minimize infections caused by N. dimidiatum in order to maintain high and stable national production levels. Several control measures have been implemented against stem canker disease, including cultural practices such as field sanitation, and mechanical approaches through pruning of infected plants parts. In addition, chemical control has been applied using salt sodium (NaCl) 5%, synthetic fungicides with active ingredients such as azoxystrobin and difenoconazole, fluopyram and tebuconazole, as well as cyprodinil and fludioxonil. Moreover, biological control can be employed by utilizing microorganisms with potential as biocontrol agents against N. dimidiatum. These potential biocontrol agents, consisting of both fungi and bacteria, can be classified into three groups based on their ecological niches: rhizosphere, phylloplane, and endophytic microbes. The diversity rhizosphere, phylloplane, and endophytic microorganisms plays a crucial role in their function as biocontrol agents against plant pathogens. High diversity within rizhosphere microbes enhances their potential to supply nutrients to plants, thereby enabling plants to withstand threats from plant pathogens. Similarly, greater diversity of phylloplane microbes dominate competition for space and nutrients, stimulate plant growth, and facilitate nutrient availability. Furthermore, a high diversity of endophytic microbes strengthens their potential to induce plant resistance, thereby inhibiting the development of diseases caused by plant pathogens. A review of the scientific literature conducted by the author indicates that studies analyzing the diversity of endophytic microbes originating from dragon fruit plants, as well as the potential of dragon fruit-associated microbes to control stem canker disease in Indonesia, remain limited. Therefore, this research contributes valuable information regarding the diversity of endophytic microbes and the biocontrol potential of microbes associated with dragon fruit plants against stem canker disease. The study was carried out using several methods, i.e: sample collection, isolation of endophytic microbes, analysis of endophytic microbial diversity, collection of supplementary data, biosafety testing of microbes from dragon fruit plants, in vitro inhibition potential assay of microbes from dragon fruit plants, characterization of selected isolates, and semi in vivo inhibition potential assay of microbes from dragon fruit plants. Morphological identification of the isolates from both regions revealed six genera: Aspergillus sp., Penicillium sp., Fusarium sp., Trichoderma sp., Bipolaris sp., and Lasiodiplodia sp. The diversity analysis of endophytic fungi both Banyuwangi and Bukittinggi indicates that the diversity is moderate (Shannon index ranged from 1,64 to 2,08), with relatively even species populations (Evenness index ranged from 0,82 to 0,95) and low to moderate species dominance (Simpson index ranged from 0,13 to 0,31). Endophytic bacteria from Banyuwangi and Bukittinggi exhibited from low to moderate diversity with Shannon index ranged from 0,46 to 1,32, the species populations remained relatively evenly distributed (Evenness index ranged from 0,54 to 0,66) and species dominance was moderate to high (Simpson index ranged from 0,35 to 0,71). The endophytic fungi and bacteria isolates obtained from Banyuwangi were not found in Bukittinggi, and vice versa. Among the Banyuwangi samples, the endophytic fungi isolates C4 and Fusarium sp. C5 exhibited the highest frequency of occurrence. In contrast, endophytic fungi isolates C12 and Aspergillus sp. C10 were the most frequently observed in Bukittinggi samples. For endophytic bacteria, isolate B1 was the most frequently found in Banyuwangi samples, whereas endophytic bacteria isolates B13 and B12 showed the highest frequency of occurrence in Bukittinggi samples. Cladode sample from Banyuwangi (S2) and root sample from Bukittinggi (A5 and A6) yielded the highest number of endophytic fungi isolates compared to other samples, whereas cladode sample S1 from Banyuwangi and root sample A4 from Bukittinggi produced the highest number of endophytic bacteria isolates. Five fungal isolates from dragon fruit plants were identified as the most promising: CR2, CR3, CF2, Trichoderma sp. C6, and Trichoderma sp. C13, while five bacterial isolates, such as BR8, B16, BR1, B2, and B7, were identified as the most promising bacterial isolates based on in vitro inhibition potential assay and their performance to produce chitinase, glucanase, and auxin. Several fungal and bacterial isolates (except for the fungal isolate CR2) were able to inhibit lesio development with AUDPC values that were not significantly different from those of the fungicide difenoconazole. This study provides information regarding the diversity of endophytic microbes from dragon fruit plants, as well as the potential of rhizosphere, phylloplane, and endophytic microbes as biological control agents against N. dimidiatum, the causal agent of dragon fruit stem canker disease.