Analysis of the resistance to Phytophthora pod rot within local selections of cacao (Theobroma cacao L.) for breeding purpose in Cameroon


M. I. B. Efombagn, S. Nyassé, D. Bieysse, and O. Sounigo

The level of resistance against Phytophthora pod rot (PPR) was assessed among locally-selected accessions of cacao, the so-called selection of Nkoemvone (SNK), in Cameroon. The evaluation approaches have included four tests: Leaf disc inoculation (LDT); detached pod inoculation (DPT); artificial inoculation of pods and counting of successful infections (%SI); and field observations of the disease incidence (FI). The studied accessions were classified into four groups according to their genetic origin: SNK; SNK600-Tr (SNK*ICS); SNK600-Tr*UA (UPA*ICS); SNK600-Tr*UA (UPA*SNK). In all four testing methods, the groups UPA*ICS and SNK appeared respectively as the least and the most susceptible accession groups. Four resistance classes were defined for each testing method. A great part of the accessions were found in the intermediary resistance classes, based on DPT, LDT and %SI. Few accessions have displayed a significant level of PPR resistance in all testing methods. Rank correlation of the different accessions groups based on their performance in the four tests have shown that all correlation coefficients were positive (r = 0.37 – 0.87) and significant (p ≤ 0.06). The best correlation was registered between %SI and FI with r = 0.87 (p = 0.01). Subsequently, a unique classification of all accessions was done according to the scores recorded in all the testing methods. The use of locally-selected accessions (SNK) in the varietal development as well as in the cacao seed production is discussed.


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