On-farm selection for quality and resistance to pest/diseases of cocoa in Sulawesi: (ii) quality and performance of selections against Phytophthora pod rot and vascular-streak dieback

Abstract

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.

Implementation of Biopesticides to Control Phytophthora palmivora Butl. and Conopomorpha cramerella Snell. on Cacao in South Halmahera

“…Control of IPM involves components of biological agents, resistant planting materials, and environmental management based on the ecological, economic, and sociological considerations to support environmentally friendly farming systems [19,20,21,22,23]. CPB control strategies can be done through technical culture approach, mechanical, chemical, as well as the use of resistant clones [24].…”

Interaction of vascular streak dieback disease of cocoa with soil nutrient status in Indonesia

“…The method has proven to be effective for disease transmission, as reflected in the percentage of infected trees, 78% for the tolerant genotype and 97% for the susceptible genotype. Efron et al (2002) and McMahon et al (2010) used the same disease transmission method to select for resistant genotypes.…”

“…Hence, a detailed study on VSD resistance is difficult to undertake. Based on current knowledge, the selection of resistant or tolerant genotypes is carried out under field conditions and relies on natural infection, as reported in Efron et al (2002) and McMahon et al (2010). Further research on the biology of the fungus is required as a starting point for a study of nutrient and disease interactions under more controlled conditions.…”

“…Spores are not always available in the plantation and the pathogen, Oncobasidium theobromae, is an obligate parasite which does not survive in dead tissue and therefore cannot be cultured (Guest & Keane 2007). McMahon et al (2010) selected cocoa clones for VSD resistance from farmer plantations in Sulawesi, Indonesia. There was variation in resistance to VSD and pod production.…”

“…In Indonesia, Vascular Streak Dieback (VSD) is one of the most significant diseases (McMahon et al 2010). VSD disease is caused by a fungus, Oncobasidium theobromae, which infects the cocoa leaf during the early formation period, and then develops into an infection in the xylem vessels (Keane 1981).…”