Diallel Analysis of Cocoa (Theobroma cacao L.) Resistance to Phytophthora palmivora in Indonesia

Abstract

For the program towards the development of resistant cacao (Theobroma cacao L.) to the black pod rots disease caused by P. palmivora, the diallel crossing analysis is expected can be used to provide genetic parameters on quantitative traits. The objective of the present study was to determine genetic parameters of cacao resistance to the disease caused by P. palmivora, using half diallel crosses. The crosses used five cocoa clones as parental clones (ICCRI 3, TSH 858, DR 1, ICS 13, and Sca 6) having resistance levels from susceptible to resistant. The experiment was arranged in a Randomized Block Design with three replications. The treatments were 10 hybrids (F₁) and 5 parental clones. Observation was conducted 3 days after inoculation to the spot area caused by P. palmivora infection. The results showed that there was no interaction between genes in determining the resistance to black pod rots disease caused by P. palmivora. The resistance was more affected by the additive gene action. Characters of resistant to the disease were controlled by the recessive genes. The results in the present study also showed that the dominant genes were more in the parents. It is expected that the opportunity to produce cocoa hybrid owned by ICCRI 3 and Sca 6. Furthermore, the estimated value of broad sense heritability (h²BS) and narrow sense heritability (h²NS) was high for the spot area, while, based on the disease intensity it was moderate to high.

Keywords: Cocoa, genetic parameters, resistance, P. palmivora