ISOLASI DAN IDENTIFIKASI CENDAWAN TERBAWA BENIH KAKAO HIBRIDA

ABSTRAK Benih merupakan komponen dasar dalam menentukan produktivitas tanaman kakao. Benih yang sehat dapat merupakan faktor penting dalam menentukan keberhasilan produktivitas kakao. Benih kakao mempunyai kadar air cukup tinggi sehingga berpotensi terinfeksi cendawan, yang dapat menurunkan mutu benih dan produksi kakao. Penelitian bertujuan untuk mengisolasi dan mengidentifikasi beberapa cendawan terbawa benih pada kakao hibrida. Penelitian dilakukan di Kebun Induk Benih Pusat Penelitian Kopi dan Kakao Indonesia, Jember, Laboratorium Mikro- biologi, Balai Penelitian Bioteknologi Perkebunan Indonesia, dan Laboratorium Pengendalian Hayati IPB Bogor pada bulan Juni sampai Oktober 2008. Penelitian menggunakan benih kakao hibrida dari hasil persilangan buatan antar TSH 858 dengan Sca 6, dan percobaan disusun dengan rancangan acak lengkap dengan 3 ulangan. Benih ditumbuhkan pada 3 media, yaitu water agar (WA), potato dextrose agar (PDA), dan kertas saring (KS). Tingkat infeksi pada benih diamati setiap hari dan dianalisis dengan analisis sidik ragam dan dilanjutkan dengan uji selang berganda Duncan. Cendawan diisolasi, dibiakkan, dimurnikan, dan diidentifikasi dengan menggunakan buku kunci identifikasi. Tingkat infeksi cendawan terbawa benih kakao hibrida tertinggi terdapat pada hari keempat (35,00%) dan kelima (51,67%) pada media PDA. Sebanyak 13 spesies cendawan terbawa benih kakao hibrida berhasil diidentifikasi dengan menggunakan media WA dan PDA, serta 8 spesies cendawan dengan media KS. Ke-13 cendawan terbawa benih yang ditemukan sangat berpotensi menurunkan mutu fisiologis benih dan produktivitas kakao. Cendawan tersebut perlu diuji lebih lanjut karena masing-masing memiliki sifat-sifat patogenik, saprofitik, atau antagonistis terhadap cendawan lain pada benih kakao. Cendawan terbawa benih kakao hibrida paling dominan adalah Aspergillus spp., Penicillium chrysogenium, Coletotrichum acutatum, Curvularia geniculata, dan Fusarium spp. Cendawan-cendawan yang diduga berbahaya adalah Aspergillus spp., Coletotrichum acutatum, Curvularia  geniculata,  Fusarium  spp.,  Phoma  glomerata,  dan Macrophoma sp., dan yang diduga bersifat patogenik adalah Aspergillus flavus, Aspergillus ochraceus, Cladosporium herbanum, Curvularia geniculata, Fusarium oxysporum, Phoma glomerata, dan Macrophoma sp. Kata kunci : Theobroma cacao, benih hibrida, infeksi cendawan, media tanam Isolation and Identification of Fungi on Hybrid Cacao Seeds ABSTRACT Seed is the basic component influencing the productivity of cacao plantation. Healthy seed is the most important factor in determining the success of cacao productivity. Moisture content of cacao seeds is quite high potentially to cause fungi infection, which can further reduce seed quality and cacao production. The research aimed at isolating and identifying several seedborne fungi on hybrid cacao. The study was conducted at main nursery of Indonesian Coffee and Cocoa Research Institute Jember, Laboratory of Microbiology, Indonesian Biotechnology Research Institute for Estate Crops, and the Laboratory for Biological Control of IPB Bogor from June to October 2008. Research used hybrid cacao seeds derived from crossing between TSH 858 x SCA 6, and the experiment was arranged using completely randomized design with three replicates. Cacao seeds were grown on three media, i.e. water agar (WA), potato dextrose agar (PDA), and filter paper (KS). Infection rates on the seedlings were observed every day and analyzed using ANOVA followed by Duncan's multiple regression test (DMRT). Fungi were isolated, cultured, purified, and identified using the identification keys. The highest rate of seedborn fungal infection occured on fourth (35.00%) and fifth (51.67%) days on PDA media. A total of 13 species of seedborn fungi on hybrid cocoa were identified by using WA and PDA media, as well as 8 other species by using KS. The 13 seedborne fungi potentially reduce seed physiological quality and cacao productivity. These fungi need to be further tested because each has its own pathogenic, saprophytic, or antagonistic properties towards other fungi on cacao seeds. Predominant seedborn fungi on hybrid cacao were Aspergillus spp., Penicillium chrysogenium, Coletotrichum acutatum, Curvularia geniculata, and Fusarium spp. The fungi suspected harmful were Aspergillus spp., Coletotrichum acutatum, Curvularia geniculata, Fusarium spp., Phoma glomerata, and Macrophoma sp., and those suspected pathogenic were Aspergillus flavus, Aspergillus ochraceus, Cladosporium herbanum, Curvularia geniculata, Fusarium oxysporum, Phoma glomerata, and Macrophoma sp. Key words : Theobroma cacao, fungi infection, hybrid seed, growing media