Abstract
BackgroundThe black pod disease affects cacao plantations worldwide; it is caused by the oomycete species of the genus Phytophthora. The resistance of cacao plants to the black pod is commonly evaluated by artificial inoculation of the pathogen and the monitoring of the disease symptoms. However, it is difficult to identify resistant plants because the commonly used methods for the inoculation of the pathogens produce inconsistent results. Therefore, this study aimed to develop an efficient and reliable method to evaluate the resistance of Theobroma cacao seedlings to the infection by Phytophthora palmivora.ResultsSeedlings of different cacao genotypes were inoculated with P. palmivora under greenhouse conditions using the previously reported inoculation methods and a newly proposed method, the agar–water solution method. While none of the previously reported methods was effective, the agar–water solution method ensured a 100% seedling infection under greenhouse conditions. The proposed agar–water methodology is fast, simple and reproducible. Furthermore, the evaluation of this method in susceptible (CCN-51) and tolerant (SCA-6) T. cacao genotypes produced the expected contrasting results.ConclusionsThe agar–water solution method presented in this study is an efficient alternative inoculation protocol for the identification of cacao genotypes that are resistant to black pod under greenhouse conditions.
Highlights
The black pod disease affects cacao plantations worldwide; it is caused by the oomycete species of the genus Phytophthora
Black pod is caused by four species of the genus Phytophthora: P. palmivora, P. megakarya, P. citrophthora and P
Initial evaluation of the inoculation methods Two susceptible genotypes of T. cacao, IMC-67 and CCN-51 were selected to evaluate the infection caused by P. palmivora using various inoculation techniques
Summary
The black pod disease affects cacao plantations worldwide; it is caused by the oomycete species of the genus Phytophthora. Phytophthora (Mont.) de Bary is a large genus of the oomycete class with more than 80 species [1] that attacks cultivated plant species [2, 3] This genus shares several biochemical and structural features with plants and algae. Phytophthora palmivora (Butler) infects more than 200 crops globally, including potato, durian, coconut, pineapple, rubber, citrus, papaya, oil palm and cacao [10,11,12]. It is a cosmopolitan species occurring in all cacao-producing countries and one of the most destructive Phytophthora species [11, 13]. The rapid decomposition of the infected tissues by P. palmivora is the main limitation in seedling production in tropical regions [14, 15], and in cacao bean production and its quality [16]
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