PATOGENISITAS BEBERAPA ISOLAT CENDAWAN TERBAWA BENIH KAKAO HIBRIDA
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2013-03-03
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Pusat Penelitian dan Pengembangan Perkebunan
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ABSTRAKBenih kakao hibrida diketahui dapat membawa beberapa mikrobayang bersifat patogenik dan menurunkan mutu benih. Penelitian bertujuanuntuk mengetahui pengaruh beberapa isolat cendawan terbawa benihterhadap penurunan viabilitas benih dan vigor bibit kakao hibrida.Penelitian dilakukan di Kebun Benih Pusat Penelitian Kopi dan KakaoIndonesia, Jember, Laboratorium Mikrobiologi dan rumah kaca BalaiPenelitian Bioteknologi Perkebunan Indonesia, Bogor, pada bulan Julisampai November 2008. Penelitian menggunakan 13 cendawan terbawabenih kakao hibrida. Benih diperoleh dari persilangan buatan antara kakaoTSH 858 dengan Sca 6. Penelitian menggunakan model Rancangan AcakLengkap dengan 4 ulangan. Inokulasi patogen pada benih kakao dilakukandengan cara merendam benih di dalam suspensi patogen dengan kerapatan10 6 spora/ml selama 30 menit. Selanjutnya benih ditanam pada media pasirsteril dalam boks plastik ukuran 30 x 30 cm, menurut rancangannya.Setiap perlakuan diulang 4 kali. Parameter yang diamati adalah dayaberkecambah, indeks vigor, kecepatan tumbuh relatif, kecepatanberkecambah T 50 , laju pertumbuhan kecambah, jumlah daun, tinggi bibit,panjang akar, jumlah akar dan kematian benih. Data dianalisis denganANOVA dan dilanjutkan dengan uji Jarak Berganda Duncan. Hasilpenelitian menunjukkan bahwa ke-13 spesies cendawan bersifat patogenikpada benih kakao hibrida. Cendawan patogen terbawa benih yang bersifatpatogenik adalah Aspergillus flavus, A. ochraceus, Cladosporiumherbanum, Curvularia geniculata, Fusarium oxysporum, Phomaglomerata dan Macrophoma sp. Cendawan patogen tersebut dapatmenurunkan daya berkecambah 20-40%, indeks vigor 30-47%, kecepatantumbuh relatif 13-45%, dan meningkatkan kecepatan perkecambahan(T 50 menurun) dari 0,62-7,36 hari. Ke-13 isolat patogen dapatmenyebabkan kematian benih 29-52% dibanding kontrol. Ke-13 isolatpatogen juga menginfeksi bagian tanaman seperti kotiledon, daun, batangdan akar bibit kakao, namun hanya Phoma glomerata dan Macrophomasp. yang menurunkan tinggi bibit, jumlah daun, jumlah dan panjang akarsecara nyata. Tujuh dari 13 isolat cendawan patogen terbawa benih tidakhanya menurunkan viabilitas dan vigor benih kakao hibrida tetapi jugadapat berkembang pada bibit sehingga perlu penanganan benih secara dini.Kata kunci: benih hibrida, patogen terbawa benih, viabilitas, vigor benih,Theobroma cacaoABSTRACTIn 2009 revitalization of cacao plantations in Indonesia required 168million seeds. Distribution of low quality and infected seeds leads to hugelosses and in a long term will destruct cultivation of cacao. Seed-bornepathogens of infected cacao hybrid seeds are dangerous because they mayreduce physiological qualities of the seeds. The study aimed atdetermining the effect of several isolates of seed borne fungi on theviability and vigor of hybrid cacao seeds as well as growth of theseedlings. The study was conducted at the Seed Garden Indonesian Coffeeand Cacao Research Center in Jember, Microbiology Laboratory and glasshouse of Biotechnology Research Institute for Estate Crops of Indonesia,Bogor, from July to November 2008. The study used 13 seed-borne fungiin hybrid cacao. The cacao seeds were obtained from hand pollinatedcrossing between TSH 858 with Sca 6. The experiment was arranged usingCompletely Randomized Design with four replicates. Cacao seeds wereinoculated by immersing them for 30 minutes in the spore suspension of13 isolates of seed-borne fungi CTB at a density of 10 6 spores/ml. Afterinoculation, the seeds were planted on sterile sand in a plastic box (30 x 30cm). Parameters observed were germination rate, vigor index, KCT-R T 50rate of seedling growth, leaf number, seedling height, root length, rootnumber, and level of pathogenicity. Data were analyzed by ANOVAfollowed with Duncan's Multiple Test. The results showed that the 13species of seed-borne pathogens were in hybrid cacao seeds with varyingpathogenicity. The most pathogenic fungi were Aspergillus flavus,Aspergillus ochraceus, Cladosporium herbanum, Curvularia geniculata,Fusarium oxysporum, Phoma glomerata, and Macrophoma sp. Seed bornepathogenic fungi had the ability to reduce seed germination of 20-40%,vigor index of 30-47%, relative growth rate of 13-45%, and delayedgermination speed (T 50 decreases) from 0.62 to 7.36 days. Seed bornepathogens caused (29-52%) death seed compared to control. All that 13isolates of seed-borne pathogens infected plant tissues such as cotyledons,leaves, stems, and roots of cacao seedlings, but only isolates of Phomaglomerata and Macrophoma sp. which lowered the height of seedlings,leaf number, root number and length. The study indicated that infection ofseed-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