Bong, C.L., Lee, M.T. & Yahya, M.N. 1996
Interaction between cocoa clones and isolates of Oncobasidium theobromae causal pathogen of Vascular Streak Dieback. In: Proceedings of the 12th International Cocoa Research Conference, Salvador, Brazil, 1996. Cocoa Producers' Alliance. (in press).
Notes
Malaysia - Malaysian Cocoa Board, Sabah Datafile: DIS_VSDS - Disease reaction to VSD Experiemental Conditions: The interaction between 11 isolates of Oncobasidium theobromae and 11 cocoa clones was studied using a dual culture method. Clones were selected based on origin of selection and locality: DESA 1, DESA 2, RP 3 - local selections from SAFIMA Plantations, Sandakan; PBC 123 - Golden Hope Plantations, from Peninsular Malaysia; K 20 - Trinitario type, Papuan New Guinea selection; BAL 209 - selection of BAL Plantations; BR 25 - Trinitario selected by a grower in Tawau; ICS 95, NA 33, PA 7 and NA 32 - primary clones. Pathogen isolates originated from 3 localities: high disease pressure areas at SAFIMA Plantations and Ulu Dusun Agriculture Research Station in Sandakan; low disease pressure area at the Agriculture Research Centre, Turan, Sabah. The dual culture system cultured together the callus of the cocoa clone and the pathogen isolate. 7-10 days old inoculum freshly isolated on 1.0% water from infected twigs of the various clones was used. Callus initiated from stem tissue was maintained on Murashige and Skoog medium supplemented with kinetin (0.05mg/l) and indole-3-acetic acid (10mg/l). The callus was subcultured once to eliminate explant tissue. Pieces of callus 2x5x5mm were placed into 50ml aliquots of MS medium (which had been autoclaved at 121°C for 15 minutes). 5mm mycelial disks were placed on top of the callus. There were 5 replicates per treatment. Growth in diameter of the colony was measured every 2/3 days for 3 weeks. Character Data: Reaction types are as follows: A - growth of the pathogen was good while that of the callus was reduced; indicative of virulence of the pathogen and susceptibly of the host. B - growth of both the pathogen and the host was good; virulence of the pathogen ineffective and the host relatively resistant. C - growth of both the pathogen and the host was poor; suggestive of a hypersensitive reaction. D - growth of the pathogen was poor while that of the callus was comparative to the control; indicative of virulence being overcome and resistance of the host. E - pathogen isolate grew poorly on the callus and the callus showed enhanced growth; indicative of an interaction where defence mechanism operated may have triggered off compensatory growth and inhibition of the pathogen. Dry weight of mycelium: determined after removal from cocoa callus. Calluses were harvested after dark incubation at 25°C for four weeks. Fungal colonisation of callus: mean of three replicates scored at the end of the experiment. 1,2 = little or negligible growth of the mycelium on the callus, callus apparently healthy; 3,4 = extensive mycelial colonisation but sparse, callus wholly visible, slightly inhibited, some parts discoloured; 5 = extensive colonisation, some parts of the callus enveloped by mycelium, exposed parts discoloured; 6,7 = callus almost completely enveloped by dense mycelium, new growth not visible, callus discoloured.
Disease