MEKANISME PENGENDALIAN PENYAKIT PASCAPANEN ANTRAKNOSA OLEH KITOSAN PADA BUAH PISANG AMBON CURUP

Tunjung Pamekas, Ir.,M.Sc., Prof. Dr. Ir. Christanti Sumardiyono, SU,

2012 | Disertasi | S3 Fitopatologi

Pisang ambon Curup merupakan buah khas dari Kabupaten Rejang Lebong Provinsi Bengkulu. Pisang ambon Curup sangat rentan terhadap infeksi Colletotrichum musae, patogen penting pada buah pisang. Pengendalian penyakit dengan pencelupan benomil dilaporkan tidak aman sehingga perlu adanya alternatif pengendalian lain, yaitu penggunaan kitosan. Provinsi Bengkulu sebagai daerah perikanan memiliki limbah perikanan yang melimpah yang dapat diproses menjadi kitosan. Tujuan dari penelitian ini adalah mengkaji asal bahan dan konsentrasi kitosan terbaik dan mengkaji mekanisme kerja kitosan dalam mengendalikan penyakit pascapanen antraknosa pada buah pisang ambon Curup. Kitosan diekstraksi dari cangkang kepiting, kulit udang, dan tulang cumi-cumi dengan metode Bastaman dan diamati bentuk, warna, bau, pH, dan derajat deasetilasinya dengan spektrofotometer infra merah. Tujuh isolat jamur Colletotrichum musae yang diisolasi dari tujuh jenis pisang diuji virulensinya pada buah pisang ambon Curup. Kitosan konsentrasi 0, 5, 10, 15, dan 20 mg/ml diuji pengaruhnya terhadap pertumbuhan C. musae in vitro dan dilanjutkan uji in vivo pada konsentrasi 0, EC50, 2x EC50, dan 3X EC50. Mekanisme kerja kitosan pada pertumbuhan C. musae in vitro dilakukan dengan menumbuhkan jamur pada selapis tipis agar air di atas gelas objek dengan penambahan kitosan atau akuades. Mekanisme kerja kitosan in vivo dilakukan dengan mencelupkan buah pisang ambon Curup ke dalam larutan kitosan, suspensi patogen atau larutan benomil, dan respons buah diamati. Laju pertumbuhan koloni tujuh isolat C. musae tidak berbeda nyata. Isolat pisang jantan (PJ) memiliki tingkat virulensi yang paling tinggi pada buah pisang ambon Curup. Derajat deasetilasi kitosan cangkang kepiting, kulit udang, tulang cumi-cumi, dan kitosan standar berturut-turut adalah 75,64%, 75,64%, 74,92%, dan 74,27%. Semua jenis kitosan mampu menghambat pertumbuhan vegetatif C. musae pada awal pertumbuhan, namun kitosan asal cangkang kepiting memiliki aktivitas antijamur paling besar. Makin tinggi konsentrasi kitosan yang diberikan (dari 0 hingga 20 mg/ml) maka penghambatan akan makin besar. Aplikasi kitosan cangkang kepiting pada 21,34 mg/ml paling baik dalam menghambat perkembangan penyakit antraknosa pada buah pisang ambon Curup. Mekanisme kerja kitosan terhadap pertumbuhan C. musae in vitro adalah menghambat panjang buluh kecambah, kelebatan hifa, panjang dan lebar hifa, serta melisis hifa. Kitosan mampu menghambat laju respirasi dan kadar etilen buah, memperpanjang umur simpan buah, menginduksi lignifikasi dan pembentukan kalose pada epidermis kulit buah, serta menginduksi peningkatan kadar senyawa fenol total dan kadar protein kasar total buah. Kitosan menunjukkan efek penghambatan yang lebih baik daripada benomil. Keberadaan enzim kitinase terdeteksi pada buah pisang yang diaplikasi kitosan pada 12 hsi.

Ambon Curup banana (Musa sapientum c.v. ambon Curup) is local banana fruit grown at the District of Rejang Lebong, Province of Bengkulu. The fruits are susceptible to the infection of Colletotrichum musae, an important postharvest pathogen on banana fruits. Controlling the disease with benomyl is considered to be environmentally unfriendly. An alternative method available for controlling the disease is by using chitosan. Chitosan may be extracted from fisheries waste, like crab shell, shrimp shell, and oligo pen skeleton, which are available abundantly in Bengkulu. The research objectives were to study the best source of local chitosan in controlling anthracnose on banana fruits and to evaluate the mode of action of chitosan in controlling anthracnose on ambon Curup banana fruit. Chitosan was extracted from crab shells, shrimp shells, and oligo pen using Bastaman method, characterized for the form, color, smell, pH, and deacetylated degree. Seven isolates of Colletotrichum musae isolated from seven cultivars of banana were tested for the virulence on ambon Curup banana. In vitro experiment was carried out to evaluate the growth of C. musae on agar plate mixed with chitosan at 0,5,10,15, and 20 mg/ml. In vivo experiment was also conducted to study the growth of pathogen on the banana fruit at 0, EC50, 2X EC50, and 3X EC50 of the chitosan concentration. The mode of action of the chitosan on C. musae was evaluated in vitro by growing the pathogen on artificial medium added with chitosan or distilled water. The mode of action of chitosan on the pathogen was also studied in vivo by dipping the banana fruit of ambon Curup in chitosan solution, pathogen suspension, or benomyl solution. The fruit responses to the treatment were measured. The results showed that all isolates had the same rate of colony growth. However, the pathogen isolated from pisang jantan was the most virulent isolate. The deacetylation of the chitosan sources showed that crab shells, shrimp shells, oligo pen, and standard chitosan had the deacetylation dregree of 75.64%, 75.64%, 74.92%, and 74.27%, respectively. All kind of chitosans demonstrated inhibiton effect on the vegetative growth of C. musae at early stage, and the best antifungal effect was found in crab shells chitosan, whose effect was more pronounced with the increase of chitosan concentration. The crab shell chitosan showed the best concentration of 21.34 mg/ml in controlling anthracnose disease on banana cv. ambon Curup. The mode of action of chitosan on the growth of C. musae in vitro was by reduction germ tube length, inhibition hyphal growth, reduction hyphal width, and reduction in the length of hyphal nodes, as well as lysis of hyphae. Chitosan reduced the respiration rate and ethylene production of banana fruits, lengthen the shelf life of banana fruits, induce lignification and callous formation on epidermis of banana peel, induce the production of total phenol compounds, and promote the production of total crude protein of the banana fruits. Compared to the benomyl application, the application of chitosan showed much greater effect on inhibiting the growth of pathogen and prolonging the shelf life of the banana. Chitinase was detected on banana peel after 12 days treatment with chitosan.

Kata Kunci : Kitosan, antraknosa, ambon Curup, Colletotrichum musae