Infection of Phytophthora Palmivora From Soil in Cocoa Plantation

Phytophthora palmivora causes serious losses on cocoa in Indonesia and world-wide. The research aimed to assess the potential of soil as source of inocula for Phytophthora diseases in cocoa. Soil samples were baited using a healthy cocoa pod tissue, and the pathogen was isolated for morphological and molecular identification. Baiting technique was successfully used to detect the presence of P. palmivora in soil samples, and this was confirmed by morphological and molecular identification. P. palmivora can be detected in soil in all year around in wet areas indicating that soil is a massive and consistent source of inocula. Surveys conducted on the soil of Amazonian, Amelonado and Trinitario blocks of various ages showed that P. palmivora can be found in old and young cocoa blocks, even as young as 3 or 4 years. P. palmivora infection from soil to the pods appears to be mainly through contact or rain splash. Baiting with whole healthy pods exposed at different heights above undisturbed litter and above bare soil showed that the infection still occurred at 100 cm above the soil, even though it decreased gradually with the height. Infection from litter was not different to that from bare soil, indicating that the litter layer is not acting physically as a shield preventing rain from splashing the inocula up from wet soil to the pods. However, in tests for the possibility of P. palmivora carried through air convection, no pod was found to be infected, suggesting that the pathogen was not carried through convective accend of aerosol droplets from soil surface up to pods in the canopy

Chitinase and Peroxidase Activities, Stomatal Density and Resistance of CocoaAgainst Black Pod Disease

Research based on morphology which is related to structural resistance such as stomata density and chemical resistance involving chitinase and peroxidase enzymes needs to be conducted. Hereafter, cacao resistant mechanism against Phytophthora palmivora can be realized. Research took place in June 2008 till February 2009 in Plant Disease Laboratory and Experiment Station of Kaliwining, Indonesian Coffee and Cacao Research Institute, Jember, East Java. Research on chitinase and perxidase analysis took place in Inter University Center Laboratory of Bogor Agriculture University (IPB). Based on stomata observation of 10 clones, the stomata density in pod and leaf did not give high correlation to the resistance. Resistant cacao clone did not always low stomata density compared to susceptible ones. Cacao clone which was susceptible did not always have high stomata density in pod and leaf. The number of stomata did not give significant difference between resistant clones and susceptible ones. The activities of chitinase and peroxidase enzymes upon tested clones indicated that there was chitinase role in the resistance of cacao against the infection by P. palmivora fungi. The increase of chitinase activity fungus in resistant clones generally intensified consistently, and similiar with peroxidase enzyme

Cacao (Theobroma Cacao L.) Resistance Evaluation Againts Black Pod Diseaseand Effectiveness of Inoculation Methods

The general objective of this experiment was to standardize method of resistance evaluation of cacao germplasm against Phytophthora palmivora, the pathogen causing black pod disease in cacao. The sepecific objectives were to evaluate (1) effects of inoculum type and pod injury, (2) effects of inoculum type and seedling injury, and (3) effects of genetic background of cacao seedlings on infection of P. palmivora. In this experiment, effectiveness of either zoospora or mycellia was evaluated as inoculation sources for pod, leaf and stem of cacao clone GC 7 and Sca 12. Part of the tested cacao pods, leaves, and stems were injured prior to P. palmivora inoculation while the others were not. Observations were conducted on diameter of the necrosed symptoms on inoculated cacao pods, number of necrosed spot on inoculated leaf, and the length of necrosed symptoms on stem of tested cacao seedlings. Results of the experiment indicated inoculation using mycelia of P. palmivora was more effective than zoospora and injuring the tested cacao pods and seedlings before P. palmivora inoculation can be used to prediction the resistance of tested cacao clones against P. Palmivora infection. Results of resistance prediction using detached pod assay was similar to that of using seedling assay; therefore, seedling assay could be used as an alternattive method of resistance evaluation. Cacao F1 hybrids derived from TSH 858 x Sca 12 showed some resistance against P. palmivora and they might potentially result in high yielding lines