PATOGENISITAS BEBERAPA ISOLAT CENDAWAN TERBAWA BENIH KAKAO HIBRIDA

ABSTRAK Benih kakao hibrida diketahui dapat membawa beberapa mikroba yang bersifat patogenik dan menurunkan mutu benih. Penelitian bertujuan untuk mengetahui pengaruh beberapa isolat cendawan terbawa benih terhadap penurunan viabilitas benih dan vigor bibit kakao hibrida. Penelitian dilakukan di Kebun Benih Pusat Penelitian Kopi dan Kakao Indonesia, Jember, Laboratorium Mikrobiologi dan rumah kaca Balai Penelitian Bioteknologi Perkebunan Indonesia, Bogor, pada bulan Juli sampai November 2008. Penelitian menggunakan 13 cendawan terbawa benih kakao hibrida. Benih diperoleh dari persilangan buatan antara kakao TSH 858 dengan Sca 6. Penelitian menggunakan model Rancangan Acak Lengkap dengan 4 ulangan. Inokulasi patogen pada benih kakao dilakukan dengan cara merendam benih di dalam suspensi patogen dengan kerapatan 10 6 spora/ml selama 30 menit. Selanjutnya benih ditanam pada media pasir steril dalam boks plastik ukuran 30 x 30 cm, menurut rancangannya. Setiap perlakuan diulang 4 kali. Parameter yang diamati adalah daya berkecambah, indeks vigor, kecepatan tumbuh relatif, kecepatan berkecambah T 50 , laju pertumbuhan kecambah, jumlah daun, tinggi bibit, panjang akar, jumlah akar dan kematian benih. Data dianalisis dengan ANOVA dan dilanjutkan dengan uji Jarak Berganda Duncan. Hasil penelitian menunjukkan bahwa ke-13 spesies cendawan bersifat patogenik pada benih kakao hibrida. Cendawan patogen terbawa benih yang bersifat patogenik adalah Aspergillus flavus, A. ochraceus, Cladosporium herbanum,  Curvularia  geniculata,  Fusarium  oxysporum,  Phoma glomerata dan Macrophoma sp. Cendawan patogen tersebut dapat menurunkan daya berkecambah 20-40%, indeks vigor 30-47%, kecepatan tumbuh relatif 13-45%, dan meningkatkan kecepatan perkecambahan (T 50 menurun) dari 0,62-7,36 hari. Ke-13 isolat patogen dapat menyebabkan kematian benih 29-52% dibanding kontrol. Ke-13 isolat patogen juga menginfeksi bagian tanaman seperti kotiledon, daun, batang dan akar bibit kakao, namun hanya Phoma glomerata dan Macrophoma sp. yang menurunkan tinggi bibit, jumlah daun, jumlah dan panjang akar secara nyata. Tujuh dari 13 isolat cendawan patogen terbawa benih tidak hanya menurunkan viabilitas dan vigor benih kakao hibrida tetapi juga dapat berkembang pada bibit sehingga perlu penanganan benih secara dini. Kata kunci: benih hibrida, patogen terbawa benih, viabilitas, vigor benih, Theobroma cacao ABSTRACT In 2009 revitalization of cacao plantations in Indonesia required 168 million seeds. Distribution of low quality and infected seeds leads to huge losses and in a long term will destruct cultivation of cacao. Seed-borne pathogens of infected cacao hybrid seeds are dangerous because they may reduce physiological qualities of the seeds. The study aimed at determining the effect of several isolates of seed borne fungi on the viability and vigor of hybrid cacao seeds as well as growth of the seedlings. The study was conducted at the Seed Garden Indonesian Coffee and Cacao Research Center in Jember, Microbiology Laboratory and glass house of Biotechnology Research Institute for Estate Crops of Indonesia, Bogor, from July to November 2008. The study used 13 seed-borne fungi in hybrid cacao. The cacao seeds were obtained from hand pollinated crossing between TSH 858 with Sca 6. The experiment was arranged using Completely Randomized Design with four replicates. Cacao seeds were inoculated by immersing them for 30 minutes in the spore suspension of 13 isolates of seed-borne fungi CTB at a density of 10 6 spores/ml. After inoculation, the seeds were planted on sterile sand in a plastic box (30 x 30 cm). Parameters observed were germination rate, vigor index, KCT-R T 50 rate of seedling growth, leaf number, seedling height, root length, root number, and level of pathogenicity. Data were analyzed by ANOVA followed with Duncan's Multiple Test. The results showed that the 13 species of seed-borne pathogens were in hybrid cacao seeds with varying pathogenicity. The most pathogenic fungi were Aspergillus flavus, Aspergillus ochraceus, Cladosporium herbanum, Curvularia geniculata, Fusarium oxysporum, Phoma glomerata, and Macrophoma sp. Seed borne pathogenic fungi had the ability to reduce seed germination of 20-40%, vigor index of 30-47%, relative growth rate of 13-45%, and delayed germination speed (T 50 decreases) from 0.62 to 7.36 days. Seed borne pathogens caused (29-52%) death seed compared to control. All that 13 isolates of seed-borne pathogens infected plant tissues such as cotyledons, leaves, stems, and roots of cacao seedlings, but only isolates of Phoma glomerata and Macrophoma sp. which lowered the height of seedlings, leaf number, root number and length. The study indicated that infection of seed-borne pathogens on cacao seed hybrid can cause seed death. Therefore, seeds should be handled properly. Key words: hybrid seeds, seed borne pathogens, viability, seed vigor, Theobroma cacao