Breeding of cocoa (Theobroma cacao L.) genotypes tolerant/resistant to cocoa swollen shoot virus (CSSVs) in cocoa orchards infected by the disease in Côte d'Ivoire
Creators
- 1. Centre National de Recherche Agronomique (CNRA), Station de recherche de Divo, Programme Cacao, Divo, Côte d'Ivoire, brigo2008@yahoo.fr
- 2. Centre International pour la recherche Agronomique et le Développement (CIRAD), UMR Amélioration génétique et adaptation des plantes pérennes (AGAP), Montpellier, France.
- 3. Centre International pour la recherche Agronomique et le Développement (CIRAD), UMR Amélioration génétique et adaptation des plantes pérennes (AGAP), Montpellier, France
Description
The cocoa swollen shoot virus disease (CSSVD) has caused enormous production losses on Ivorian cocoa farms since 2003. In order to identify tolerant or resistant cocoa trees to CSSV, 320 farmers accessions of cocoa trees with good agronomic performances were collected in areas infected by the swollen shoot disease in Côte d'Ivoire. These genotypes were vegetatively propagated on Amelonado rootstocks, a cocoa variety known for its susceptibility to diseases. The agronomic data collected during one year on the plants propagated in the greenhouse mainly concern the presence or absence of CSSV symptoms on the scion and rootstock and the type of symptom.
Three phenotypic groups were identified in the greenhouse. The first group is composed of Potentially Tolerant Accessions to CSSVD (APT) and is composed of 255 cocoa trees that were asymptomatic both in the field and in the greenhouse. The second group called "Potentially Susceptible Accessions" (APS) is composed of 49 cocoa trees that were symptomatic both in the field and in the greenhouse and the third group (PSA/PSA) is composed of 16 cocoa trees that were asymptomatic in the field but symptomatic in the greenhouse The accessions of the three phenotypic groups were then subjected to a molecular diagnostic PCR and qPCR to search and quantify CSSV within them.
Results showed that 53.33% of APTs; 71.42% of APSs and 50% of APT/APSs were positive by PCR molecular diagnosis. By qPCR, 33.33% of the trees in the APT group showed almost zero viral concentration. On the other hand, 27.45% of the trees in the APT group were negative for CSSV by both PCR and qPCR techniques. These results would confirm the tolerance of trees in the APT group to swollen shoot and could also indicate resistance of the disease by these trees. These CSSVD tolerant or resistant cocoa trees could be introduced into multi-location trials in infected areas to confirm their performance against the disease. The use of genotypes having confirmed their resistance to CSSVD as progenitors in the recurrent selection scheme underway in Côte d'Ivoire is considered and discussed.
Key words: Breeding, cocoa trees, tolerant, swollen shoot, Côte d'Ivoire
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