<p>ABSTRAK</p><p>Klon kakao unggul berdaya hasil dan bermutu hasil tinggi sertaresisten terhadap penyakit utama perlu dikembangkan melalui pemuliaantanaman dan tersedianya informasi tentang parameter genetik diharapkandapat membantu memecahkan masalah tersebut. Pendugaan parametergenetik dapat dilakukan dengan analisis persilang dialel. Penelitianbertujuan untuk menduga parameter genetik ketahanan tanaman kakaoterhadap infeksi P. palmivora, menggunakan analisis persilangan setengahdialel. Bahan tanaman terdiri atas lima klon kakao (ICCRI 3, TSH 858,DR 1, ICS 13 dan Sca 6) yang tergolong rentan hingga tahan terhadapinfeksi P. palmivora yang digunakan sebagai tetua dan 10 galur hibrida F1hasil persilangan antar lima klon. Penelitian dilaksanakan di KebunPercobaan Kaliwining Pusat Penelitian Kopi dan Kakao Indonesia,Jember, Jawa Timur dari tahun 2008 hingga 2009. Untuk setiap kombinasipersilangan dievaluasi 20 bibit dan diulang tiga kali. Untuk mengetahuirespon bibit hibrida F1 terhadap infeksi P. palmivora, daunnya diinokulasidengan inokulum zoospora dan disungkup dengan plastik untuk menjagakelembapannya (>90%). Pengamatan luas bercak akibat infeksi P.palmivora dilakukan enam hari setelah inokulasi dan digunakan untukmenghitung intensitas penyakit. Hasil penelitian menunjukkan bahwakakao klon DR 1, ICS 13, dan ICCRI 3 mempunyai DGU yang palingtinggi dibandingkan dengan tetua lainnya. Selanjutnya, persilangan antarklon kakao DR 1 x ICS 13, dan TSH 858 x Sca 6 mempunyai DGKtertinggi sehingga kombinasi persilangan ini berpeluang untuk menjadipenghasil hibrida baru yang resisten terhadap P. palmivora. Kombinasipersilangan yang menunjukkan nilai heterosis tertinggi adalah DR1 x ICS13, DR1 x Sca 6, dan ICS 13 x Sca 6.</p><p>Kata kunci: Heterosis, hibrida F1, DGU, DGK, intensitas penyakit</p><p>ABSTRACT</p><p>Estimation of Heterosis and Combining Ability forResistance Against Black Pod Disease (Phytophthorapalmivora) in Cacao (Theobroma cacao L.)</p><p>High yielding and disease resistance of cacao clone needs to bedeveloped through breeding program. Availability of genetic parametersfor various agronomic importance characters in cacao would be veryuseful and beneficial for cacao breeding activities. Estimation of variousgenetic parameters could be done by analyzing F1 arrays generated fromsemi-diallele crosses among a number of parents. The objectives of thisresearch were to estimate genetic parameters for resistance against P.palmivora infection in cacao using F1 arrays generated from semi-diallelecrosses among five cacao clones. Five cacao clones (DR 1, TSH 858, ICS13, ICCRI 3, and Sca 6), representing an arrays of clones with increasedresistance against P. palmivora infection, were used as parents to generate10 F1 hybrid arrays. This research was conducted at KaliwiningExperimental Station, Indonesian Coffee and Cacao Research Institute,Jember, Indonesia, during the period of 2008 to 2009. At most 20seedlings were evaluated for each F1 hybrid and the evaluation wasreplicated three times. To evaluate the response of the seedlings against P.palmivora infection, their leaves were inoculated with zoospore of P.palmivora. Relative humidity around inoculated leaves was maintained at>90% by wrapping them with plastic bag. The sizes of leaf necroseresponse due to P. palmivora infection were observed during six days afterinoculation and the disease intensity was calculated based on this recordedsymptoms. Results of the experiments indicated that cacao clones (DR 1,ICS 13, and ICCRI 3) were the highest in general combining ability(GCA) for resistance character than the other two clones. Moreover, F1hybrid originated from crosses between DR 1 x ICS 13, and TSH 858 xSca 6 were the highest in specific combining ability (SCA) for resistancecharacter. Therefore, this combination crosses might be used to developenew hybrid combinations resistance against P. palmivora infection.Combination crosses showing highest heterotic value for resistance againstP. palmivora infection were DR 1 x ICS 13, DR1 x Sca 6, and ICS 13 xSca 6.</p><p>Key words : Heterotic effects, F1 hybrid array, GCA, SCA, diseaseintensity</p>
PENDUGAAN DAYA GABUNG DAN HETEROSIS KETAHANAN TANAMAN KAKAO (Theobroma cacao L.) TERHADAP PENYAKIT BUSUK BUAH (Phytophthora palmivora)