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McMahon P.J.,La Trobe University | Purwantara A.,Biotechnology Research Institute for Estate Crops | Wahab A.,BPTP SULTRA | Imron M.,BPTP SULTRA | And 3 more authors.
Australasian Plant Pathology | Year: 2010

Stem canker and Phytophthora pod rot (PPR) or black pod caused by Phytophthora palmivora are serious diseases of cocoa (Theobroma cacao L.) in Sulawesi, Indonesia, causing high yield losses for smallholders, possibly exceeded only by losses due to the cocoa pod borer (CPB), Conopomorpha cramerella. Potassium phosphonate (phosphite) applied by trunk injection has been demonstrated to effectively control canker and PPR in Papua New Guinea. The method was tested in a field trial in south-east Sulawesi. Fifty trees were injected with phosphonate, 50 with water and 50 were left untreated. Phosphonate was applied at a rate of ∼16 g active ingredient per tree per year, depending on the size of each tree. Trees were evaluated each month for canker severity, for PPR incidence and for CPB incidence and severity. From 4 months after the initial injection, trees treated with phosphonate had negligible levels of canker. Over a 2.5-year period, phosphonate significantly decreased PPR incidence. Cycles of PPR infection occurred in the wet season with PPR incidence fluctuating from less than 30% to greater than 75%. These fluctuations might have been due to variations in rainfall causing natural cycles of sporulation and infection. CPB incidence did not differ significantly between treatments. Since trunk injection of phosphonate effectively controls stem canker and decreases PPR in the long term it provides a valuable option for the management of these diseases for cocoa smallholders. © 2010 Australasian Plant Pathology Society.

McMahon P.,La Trobe University | Purwantara A.,Biotechnology Research Institute for Estate Crops | Susilo A.W.,Indonesian Coffee and Cocoa Research Institute | Sukamto S.,Indonesian Coffee and Cocoa Research Institute | And 8 more authors.
International Journal of Pest Management | Year: 2010

The cocoa industry in Sulawesi, the main region of cocoa production in Indonesia, is threatened by destructive diseases, including vascular-streak dieback (VSD) caused by the basidiomycete Oncobasidium theobromae and stem canker and Phytophthora pod rot (PPR) or black pod, caused by Phytophthora palmivora. Using the considerable genetic diversity of cocoa on farms, host resistance was identified and tested with the participation of farmers. Fortynine local and international cocoa selections with promising resistance characteristics (as well as susceptible controls) were side-grafted onto mature cocoa in a replicated trial with single-tree plots. Developing grafts were assessed in the dry season for severity of VSD infection, scored from 0 (no infection) to 4 (graft death). All of the 49 clones in the trial became infected with VSD in at least some replicates. Average severity varied from 0.2 to 1.6. Potential VSDresistance was found in eight clones, including DRC 15, KA2 106 and a local Sulawesi selection, VSD2Ldg. Some of the most susceptible clones were local Sulawesi selections from areas with a history of little or no VSD. Thirty-four pod-bearing clones were evaluated over a 2-year period for yield, quality and resistance to natural infections of PPR. Cumulative PPR incidence for all clones was 22% but varied from 8.6 to 43% among clones. Clones with less than 15% PPR incidence were designated as resistant, including DRC 16 and local Sulawesi selections, Aryadi 1, Aryadi 3 and VSD1Ldg. Scavina 12 was moderately resistant in the trial with a PPR incidence of 23%. Cumulative incidences of the mirid, Helopeltis spp., determined in the same evaluation period, indicated that DRC16 was the most susceptible clone with an incidence of 52% in ripe pods and 23% in immature pods. In comparison, KKM4 showed evidence of resistance to Helopeltis spp., with incidences of 34 and 0.8% in ripe and immature pods, respectively. The impact of diseases and pests (including cocoa pod borer) on bean losses and bean quality varied between clones but generally the bean size (or bean count) was affected more than the fat content or shell content. © 2010 Taylor & Francis.

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