Iwaro, D., Sreenivasan, T.N. & Umaharan, P. 1997
Phytophthora resistance in cacao (Theobroma cacao): Influence of pod morphological characteristics. Plant Pathology 46: pp. 557-565
Notes
Trinidad - CRU, University of the West Indies Datafile: DIS_PHDS - Disease reaction to Phytophthora STOMA_DS - Leaf/Fruit Anatomical Characteristics Germplasm: Information on 12 clones grown in the ICG,T. Environment: See details given for TTO - ICG,T Descriptors. Descriptors: Characteristics of the stomata, surface wax, exocarp and mesocarp hardness, exocarp and endocarp thickness of the pod are described in relation to infection by Phytophthora. Experimental Conditions: Each clone was represented by 15 trees at the ICG,T. Fully grown unripe pods were used. The multiple point inoculation method was used to assess frequency of lesions. A drop of inoculum (4 micro litres) was applied using a micro pipette at 10 points along the ridges of the surface of detached pods, with a zoospore concentration of 30,000 per ml. The control treatments recieved sterile distilled water. The pods were arranged in a completely randomised design with 5 replications in plastic trays lined with moist paper towels and covered with another plastic tray. The trays were enclosed in plastic bags and incubated at 25 degrees C. After 72 hours frequency of lesions was assessed based on the mean of successful inoculation points observed. Four trials were conducted. For stab inoculation a standard injury was created on the pod surface using 20 pins penetrating to a depth of 3mm. Inoculation followed Sreenivasan (1985) placing a 4mm. diameter disc of filter paper immersed in a zoospore suspension 200,000 per ml on the wound and covering with a spot plaster. Controls were treated with sterile distilled water. Pods were arranged in completely randomised design with 5 replications per clone and incubated at 25 degrees C. in trays lined with moist tissue paper and covered with plastic film. After 5 days the area of the established lesion was determined by transcribing the outline of the lesion onto brown paper and the area of the cuttings determined by a leaf area meter. The experiment was conducted twice. Data collected was subjected to square root transformation and analysis of variance to determine significance. Character data: Immature pod, stomatal pore length: 10 pods were assessed at five points per pod for each clone. Mature pod, thickness of exocarp on ridge: each pod was measured at 5 points on the ridge. 10 pods were assessed per clone. Mature pod, thickness of exocarp on furrow: each pod was measured at 5 points on the furrow. 10 pods were assessed per clone. Mature pod, thickness of endocarp on ridge: each pod was measured at 5 points on the ridge. 10 pods were assessed per clone. Mature pod, thickness of endocarp on furrow: Each pod was measured at 5 points on the furrow. 10 pods were assessed per clone. Exocarp and mesocarp hardnes: tested at the equatior of the pods. 10 pods were assessed at 5 points per clone. Relative hardness was estimated in Newtons (N) per square mm. Pod wall moisture content: 5 pods were assessed for each clone. Wound: N=no, P=punch inoculation (4 mm hole), S3=stab inoculated to 3 mm depth, S9=stab inoculated to 9 mm depth. Morphological - Physiological Characteristics. Disease - Phytophthora palmivora, P. megakarya (Local Names: Black Pod, Podredumbre negra, Pourriture Brune, Podridao parda).
Disease