Pathogenic Diversity of Xanthomonas sp. Infecting Cashew (Anacardium occidentale L.) and Susceptibility of Genotypes Released in Côte d'Ivoire

Abenan Natacha Kouman, Amoa Tehua, Nakpalo Silué, Klinnanga Koné, N’Dri N’Goran, Sibirina Soro, Eric-Olivier Tienebo, Kouabenan Abo and Daouda Koné

Background and Objective: Bacterial blight caused by the genus Xanthomonas is one of the main biotic constraints of cashews in Côte d'Ivoire. The aim of this study was to evaluate the susceptibility of cashew genotypes to various isolates of Xanthomonas sp. in Côte d'Ivoire. Materials and Methods: Cashew tree nurseries, consisting on the one hand of “all-round” genotypes and the other hand of high-producer genotypes A24, A27 and A30, arranged in a greenhouse, were used as plant material for the various inoculations. A total of 44 Xanthomonas sp. isolates were used for pathogenicity testing. The inoculation was carried out using a 1 mL syringe topped with gum. A bacterial inoculum of 0.5 mL of each isolate, with a concentration of 10⁸ CFU mL^–1, was infiltrated into young cashew leaves. At the same time, control was set up with plants whose leaves were infiltrated with sterile distilled water. Inoculation tests were repeated three times. Results: This experiment evaluated symptom onset time, incidence and severity index. The 44 Xanthomonas sp., isolates tested showed their pathogenicity in the marking zones where infiltrations were made on the different cashew genotypes tested after 30 days of incubation. Multivariate analysis generated four pathogenicity groups for the 44 isolates and two susceptibility groups for the cashew genotypes tested. Conclusion: These results suggested that these genotypes are susceptible to cashew bacterial blight in Côte d'Ivoire and that there is variability in the expression of pathogenicity among isolates of the causal agent.

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