Identification of Susceptible Weed Hosts of Phytophthora spp. in Cocoa Trees in the Nawa Region, South-West of Côte d'Ivoire
Daniel Kouamé Kra
Plant Heath Unit, Université Nangui Abrogoua, UFR Sciences de la Nature, 02 BP 801 Abidjan 02, Côte d’Ivoire.
Yapi Richmond Baka *
Laboratory of Botany, Université Félix Houphouët-Boigny, UFR Biosciences, 22 BP 582 Abidjan 22, Côte d’Ivoire.
David Coulibaly N’golo
Pasteur Institute of Côte d'Ivoire, Adiopodoumé Molecular Biology Platform, 01 BP 490 Abidjan 01, Côte d’Ivoire.
Ipou Joseph Ipou
Laboratory of Botany, Université Félix Houphouët-Boigny, UFR Biosciences, 22 BP 582 Abidjan 22, Côte d’Ivoire.
*Author to whom correspondence should be addressed.
Abstract
The cocoa tree, the mainexport crop in Côte d'Ivoire is frequently attacked by a disease: brown pod rot, caused by Phytophthora spp. which causes a considerable drop in production. This soil-borne pathogen attacks on so-called weeds when environmental conditions are favourable. The presence of these susceptible weed hosts can amplify this scourge of brown rot by transmitting the pathogen to the crop plant. In order to improve the yield of this crop, a study was conducted in the Nawa region to identify the weed hosts through the characterization of the pathogen.
This study consisted first in the inventory of susceptible host weeds of Phytophthora spp. and second in the morphological characterization of the pathogen.
Concerning the host weeds inventory we procceeded determining all symptomatic weeds located within 3 m of the cocoa plants affected by brown rot.
We identified 48 susceptible host species, divided into 41 genera and 22 families and we observed brown spots on the leaves of Oplismenus burmannii and Laportea aestuans; on the leaves of Clerodendrum splendens and Xanthosoma mafaffa, brown necroses surrounded by a yellow halo were noticed. Oily brown spots were examined on the leaves of Ageratum conyzoides. On the proximal, lateral and distal parts of the pods symptoms of brown spots covered with whitish mycelia were observed. Phytophthora strains obtained from the pods and weeds on PDA culture medium were characterized by matted, white mycelial colonies with a cottony appearance. Microscopic features revealed the presence of sporocysts, oospores and chlamydospores of different shapes.