Spatial and temporal patterns of first
Phytophthora megakarya infections in newly established cacao plantations
By:
NDOUNGUE DJEUMEKOP Minette Mireille
Marie Ange NGO BIENG, Christian Gael NEMBOT, Sandrine PETCHAYO, Claire NEEMA, and Gerben Martijn ten HOOPEN
Where does chocolate come from……
Cacao tree and farmer Chocolate
Cacao pod
Cacao beans
www.worldcocoafoundation.org
90% global cacao production provided
by 4 millions of smallholder farmers
Cacao tree and P. megakarya
Black pod rot
(Mfegue, 2012; Akrofiet al., 2015)
Black pod rot due to Phytophthora spp
In Africa: P. palmivora and P. megakarya P. megakarya:
Most agressive species (80 to 100%
losses)
Only pods are infected Other hosts unknown
Free water, High humidity and low
temperature
Cacao tree and P. megakarya
Black pod rot
(Mfegue, 2012)
P. megakarya
Genetic diversity in Africa
Experimental plot Neighboring environment
Ants/Rodents (Evans et al, 1973)
Exogenous inoculum
Soil
Endogenous inoculum
Exogenous inoculum
Endogenous inoculum
Origin of inoculum
Human (Tjosvoldet al.,2002)
Run off water, river…
(Husson et al., 2006)
(Gregory et al, 1981; Griffin et al., 1981;)
Combined action of splash and wind splash
splash
Objective
Identify dispersal mechanisms of P. megakarya in newly established cacao plantations
Describe spatial and temporal dynamic of P. megakarya first infections in cacao plantations initially free of P.
megakarya inoculum
Experimental site
• Cacao plantations
established in 2006 on P.
megakarya soil‐free
• Cacao germplasm
developed by research team
• Associated with specific crops
(palm oil, fruit and coconut trees )Bokito
Yaoundé Nkolbisson
Bafia Nanga Eboko
Mbalmayo
Yoko
Tchad
Républiq ue centrafri
caine Nige
ria
Cong o Gab
on Guinée équatori
ale Océan atlanti que
DoualaYaoundé
Ngat Bakoa and Kedia
Savanna
Forest
Data collection
Farm monitoring from 2009 to 2016
Weekly observations on each tree on:
• Presence/absence of cacao pod
• Presence/absence of infection
Collection of P. megakarya strains
Isolation of P. megakarya on cacao pod, soil and water Genotyping with 14 microsatellites markers
Cacao tree status
• Healthy
• Infected
• Non productive
Mapping and Spatial analysis of infected trees
Ripley Analysis
Fonction K(r)=λ‐1E
Fonction L(r)=
; ;
K(r) <πr
2K(r) =πr
2K(r) >πr
2Mapping was doing in R Software
(Goreaud, 2000)
Results (Bakoa: savanna zone)
2010 2011 2013 2014 2015 2016
In BAC plot
Healthy cacao tree Infected cacao tree Non productive cacao tree
Results (Kedia in savanna zone)
2011 2013 2014 2015 2016
Healthy cacao tree Infected cacao tree Non productive cacao tree
In KEP plot
Results (P. megakarya genotypes in savanna)
Number of strains
Number of MLG
Dominant MLG
Number of strains
Number of MLG
Dominant MLG
2010 4 1 A No disease
2011 6 2 B 4 4 B
2013 4 2 B Loss of strains
2014 22 3 B 62 19 B
2015 14 6 B 14 5 B
BAC Plot KEP Plot
Conclusion and perspectives
Black pod rot propagation
• Agregated patterns in both savanna plots
• One P. megakarya clone is responsible of disease in both plots
Perspectives
• Analysis of data in forest plot
• Multivariate analysis of field survey data
• Virulence test of the main P. megakarya genotypes
Many thanks to …..
MartijnTen HOOPEN Marie A. NGO BIENG
Christian CILAS
Claire NEEMA Laurence BLONDIN
Claude HERAIL Michel DUCAMP
Salomon NYASSE Sandrine PETCHAYO
Christian NEMBOT
And FARMERS…
Reproduction and Infection cycle of P. megakarya
Reproduction cycle
Sexual (in vitro)
Asexual (in vivo)
Infection cycle Inoculum reservoir (soil)
secondary inoculum
(sporulation)
primary inoculum
Main dispersion mechanism: rain splashing
(Gregory et al, 1981; Griffin et al., 1981; Mfegue, 2012)
