PENDUGAAN DAYA GABUNG DAN HETEROSIS KETAHANAN TANAMAN KAKAO (Theobroma cacao L.) TERHADAP PENYAKIT BUSUK BUAH (Phytophthora palmivora)
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High yielding and disease resistance of cacao clone needs to be developed through breeding program. Availability of genetic parameters for various agronomic importance characters in cacao would be very useful and beneficial for cacao breeding activities. Estimation of various genetic parameters could be done by analyzing F1 arrays generated from semi-diallele crosses among a number of parents. The objectives of this research were to estimate genetic parameters for resistance against P. palmivora infection in cacao using F1 arrays generated from semi-diallele crosses among five cacao clones. Five cacao clones (DR 1, TSH 858, ICS 13, ICCRI 3, and SCA 6), representing an arrays of clones with increased resistance against P. palmivora infection, were used as parents to generate 10 F1 hybrid arrays . This research was conducted at Kaliwining Experimental Station, Indonesian Coffee and Cacao Research Institute, Jember, Indonesia, during the period of 2008 to 2009. At most 20 seedlings were evaluated for each F1 hybrid and the evaluation was replicated 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 necrose response due to P. palmivora infection were observed during six days after inoculation and the disease intensity was calculated based on this recorded symptoms. 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, F1 hybrid originated from crosses between DR 1 x ICS I3, and TSH 858 x SCA 6 were the highest in specific combining ability (SCA) for resistance character. Therefore, this combination crosses might be used to develope new hybrid combinations resistance against P. palmivora infection. Combination crosses showing highest heterotic value for resistance against P. palmivora infection were DR 1 x ICS I3 , DR 1 x SCA 6, and ICS 13 x SCA 6.