Iwaro, D., Umaharan, P., Sreenivasan, T. & Warren, J. 1995
Anatomical and morphological determinants of leaf resistance to Phytophthora palmivora in cocoa. In: Proceedings of the 11th International Cocoa Research Conference, Yammoussoukro, Cote d'Ivoire, 1993. Cocoa Producers' Alliance, Lagos, Nigeria. pp. 247-251.
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 and leaf cuticle are described. ABSTRACT This study investigates some anatomical and morphological characteristics of the cocoa leaf and their relationship with resistance to Phytophthora palmivora. Three experiments were performed with the objective of identifying anatomical and morphological differences associated with resistance to P. palmivora at penetration stage. The experiments were carried out on detached leaves from interflush-2 with newly formed green leaves. Stomatal frequency and pore length were assessed based on stomatal impressions examined with a microscope. The cuticle thickness on both surfaces of the leaf was assessed using hand sections of fresh leaves while surface wax was determined gravimetrically after extraction in chloroform. In assessing the relationship between the characters examined and resistance, leaves of 12 clones (CATONGO, ICS 1,6,8,40,95, IMC 67, MXC 67, PA 30, SCA 6,12, SPEC 138-8) were inoculated with a spore suspension of P. palmivora and the number of necrotic lesions formed was correlated against surface wax, cuticle thickness (adaxial), stomatal frequency and pore length. A multiple regression analysis showed a higher correlation for the combined effect of stomatal density, stomatal pore length and cuticle thickness (abaxial) on resistance than the effect on individual characters. The addition of surface wax did not improve the regression model. Rapid assessment of resistance could therefore be based on stomatal density and pore length to complement inoculation tests. In general, leaves were less susceptible at the adaxial surface. METHODS Three experiments were performed with the objective of identifying anatomical and morphological differences associated with resistance to P. palmivora at penetration stage. The experiments were carried out on detached leaves from interflush-2 with newly formed green leaves. Stomatal frequency and pore length were assessed based on stomatal impressions examined with a microscope. The cuticle thickness on both surfaces of the leaf was assessed using hand sections of fresh leaves while surface wax was determined gravimetrically after extraction in chloroform. In assessing the relationship between the characters examined and resistance, leaves of 12 clones (CATONGO, ICS 1,6,8,40,95, IMC 67, MXC 67, PA 30, SCA 6,12, SPEC 138-8) were inoculated with a spore suspension of P. palmivora and the number of necrotic lesions formed was correlated against surface wax, cuticle thickness (adaxial), stomatal frequency and pore length. Both adaxial and abaxial surfaces were inoculated using 400,000 and 150,000 zoospores/ml inocula respectively. A 0.30 ml drop was placed on the leaf surface and then a piece of tissue paper was placed on top of the drop to allow uniform spread of the inoculum on the leaf surface. Inoculated leaves were spread in trays lined with moist tissue paper and kept at 25'C. Number of lesions was scored after 72 hours. Morphological - Physiological Characteristics. Disease - Phytophthora palmivora, P. megakarya (Local Names: Black Pod, Podredumbre negra, Pourriture Brune, Podridao parda).
Disease