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Samuels G.J.,U.S. Department of Agriculture | Ismaiel A.,U.S. Department of Agriculture | Rosmana A.,Hasanuddin University | Junaid M.,Hasanuddin University | And 7 more authors.
Fungal Biology | Year: 2012

Vascular Streak Dieback (VSD) disease of cacao (Theobroma cacao) in Southeast Asia and Melanesia is caused by a basidiomycete (Ceratobasidiales) fungus Oncobasidium theobromae (syn = Thanatephorus theobromae). The most characteristic symptoms of the disease are green-spotted leaf chlorosis or, commonly since about 2004, necrotic blotches, followed by senescence of leaves beginning on the second or third flush behind the shoot apex, and blackening of infected xylem in the vascular traces at the leaf scars resulting from the abscission of infected leaves. Eventually the shoot apex is killed and infected branches die. In susceptible cacao the fungus may grow through the xylem down into the main stem and kill a mature cacao tree. Infections in the stem of young plants prior to the formation of the first 3-4 lateral branches usually kill the plant. Basidiospores released from corticioid basidiomata developed on leaf scars or along cracks in the main vein of infected leaves infect young leaves. The pathogen commonly infects cacao but there are rare reports from avocado. As both crops are introduced to the region, the pathogen is suspected to occur asymptomatically in native vegetation. The pathogen is readily isolated but cultures cannot be maintained. In this study, DNA was extracted from pure cultures of O. theobromae obtained from infected cacao plants sampled from Indonesia. The internal transcribed spacer region (ITS), consisting of ITS1, 5.8S ribosomal RNA and ITS2, and a portion of nuclear large subunit (LSU) were sequenced. Phylogenetic analysis of ITS sequences placed O. theobromae sister to Ceratobasidium anastomosis groups AG-A, AG-Bo, and AG-K with high posterior probability. Therefore the new combination Ceratobasidium theobromae is proposed. A PCR-based protocol was developed to detect and identify C. theobromae in plant tissue of cacao enabling early detection of the pathogen in plants. A second species of Ceratobasidium, Ceratobasidium ramicola, identified through ITS sequence analysis, was isolated from VSD-affected cacao plants in Java, and is widespread in diseased cacao collected from Indonesia. © 2011.


McMahon P.,La Trobe University | Purung H.B.,Mars Inc. | Lambert S.,Mars Inc. | Mulia S.,BPTP Sulsel | And 10 more authors.
Crop Protection | Year: 2015

Trials were established on smallholder cocoa farms in three provinces in Sulawesi to assess productivity and constitutive responses of local cocoa clones to cocoa pod borer (CPB) and Phytophthora pod rot (Ppr) in different environmental situations. Twelve clones per trial (local farmer-assisted selections or clones produced by hybridisation programs in East Java and Malaysia) were tested in the districts of Pinrang, Polewali-Mandar and North Kolaka, including four standards common to the trials: the Malaysian clone, PBC123, and three selections from Sulawesi farms. The clones were evaluated from the time they started fruiting in 2010 (about two years after planting) for two years during which time chemical pesticides were not applied. Otherwise farms were managed according to recommended practices, including harvesting each fortnight, fertiliser application and heavy and light pruning, depending on the season. Butter fat content was generally lower than 50% but was higher in three local selections in Pinrang, M04, RB and Panimbu Red. While strongly dependent on genotype, fat and shell content and pod values in the common standards showed some variation between sites. The bean size and fat content of PBC123 was low, but this clone yielded better than most of the clones tested. For the common standards, yield estimates obtained from average yield per tree were higher in Pinrang (735-1100 tons/ha/annum) than in N. Kolaka (342-894ton/ha/annum) or Polewali-Mandar (485-899tons/ha/annum) indicating a marked site-effect. The number of flowers produced was higher in the common standards in Pinrang. Soil parameters including pH and exchangeable calcium, magnesium and potassium were higher in Pinrang than in Polman, although both sites were deficient in soil nitrogen and organic carbon. Lower average CPB infestation rates in ripe pods for the two-year evaluation period occurred in Pinrang (48-66%) and Polewali-Mandar (19-68%) than in N. Kolaka (77-80%). In most of the clones, total and severe CPB incidence decreased during the high pod season but some selections, such as M04 and TR01, maintained a low total and severe CPB incidence in both the low and high pod seasons, indicating partial resistance. In the ripe pods of common standards, the highest average Ppr incidence (ranging from 10 to 14%) occurred in N. Kolaka, which had a higher annual rainfall than the other sites. In ripe pods in the Pinrang trial, Geni J, M06 and Panimbu Red had a low Ppr incidence (4.4-4.8%) while M04 was Ppr-susceptible (23%). Incidence of Helopeltis spp. was high in the immature pods of some clones (exceeding 30% of the total harvest in M01 and Geni J in Pinrang). The results show that the performance of clones is affected by the locality in which they are grown, as well as their genotype, indicating the importance of testing clones under different environmental conditions. While the trials confirmed the efficacy of farmer-assisted selection, they also indicated that clones resistant to CPB, were susceptible to Ppr or other pests/diseases, and vice versa. For example, local selection, M04, was highly susceptible to Ppr, yet resistant to CPB. Therefore, the results indicate the importance of efforts to screen the progeny of hybrid crosses that combine resistance and yield traits. © 2015 Elsevier Ltd.


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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