AUTHOR=Decloquement Jennifer , Ramos-Sobrinho Roberto , Elias Samuel Galvão , Britto Dahyana Santos , Puig Alina Sandra , Reis Ailton , da Silva Rildo Alexandre Fernandes , Honorato-Júnior Jaime , Luz Edna Dora Martins Newman , Pinho Danilo Batista , Marelli Jean-Philippe 

TITLE=Phytophthora theobromicola sp. nov.: A New Species Causing Black Pod Disease on Cacao in Brazil

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.537399

DOI=10.3389/fmicb.2021.537399

ISSN=1664-302X

ABSTRACT=<p>Black pod disease, caused by <italic>Phytophthora</italic> species, is among the main limiting factors of cacao (<italic>Theobroma cacao</italic> L.) production. High incidence levels of black pod disease have been reported in Brazil, being induced by <italic>Phytophthora capsici</italic>, <italic>Phytophthora citrophthora</italic>, <italic>Phytophthora heveae</italic>, and <italic>Phytophthora palmivora</italic>. To assess the diversity of <italic>Phytophthora</italic> species affecting cacao in Brazil, 40 new isolates were obtained from cacao pods exhibiting symptoms of black pod disease collected in different smallholder farms in 2017. Further, ten cacao-infecting isolates morphologically identified as <italic>P. citrophthora</italic> and <italic>P. palmivora</italic> were molecularly characterized. The genomic regions beta-tubulin, elongation factor 1 alpha, heat shock protein 90, and internal transcribed spacer, and the mitochondrially encoded cytochrome <italic>c</italic> oxidase I and II genes were PCR-amplified and Sanger-sequenced from the cacao-infecting <italic>Phytophthora</italic> isolates. The morphological characterization and evaluation of the mycelial growth rates for the <italic>Phytophthora</italic> isolates were performed <italic>in vitro</italic>. Based on the molecular analysis and morphological comparisons, 19 isolates were identified as <italic>P. palmivora</italic> (clade 4). Interestingly, 31 isolates grouped together in the phylogenetic tree and were placed apart from previously known species in <italic>Phytophthora</italic> clade 2. Therefore, these isolates are considered as a new species herein referred to as <italic>Phytophthora theobromicola</italic> sp. nov., which produced papillate, semipapillate, and persistent sporangia on simple sporangiophores. The <italic>P. palmivora</italic> isolates were identified as A1 mating type by pairing each isolate with known A1 and A2 tester strains of <italic>P. capsici</italic>, but no oogonia/antheridia were observed when <italic>P. theobromicola</italic> was paired with the different tester strains. The <italic>P. theobromicola</italic> and <italic>P. citrophthora</italic> isolates showed higher mycelial growth rates, when compared to <italic>P. palmivora</italic>, on different media at 10, 15, and 20°C, but similar values were observed when grown on clarified CA media at 25 and 30°C. The pathogenicity tests carried out on pods of four cacao clones (CCN51, PS1319, Cepec2004, and CP49) showed significant variability among the isolates of both <italic>Phytophthora</italic> species, with <italic>P. theobromicola</italic> inducing higher rates of necrotic lesion expansion, when compared to <italic>P. palmivora</italic>. Here, two <italic>Phytophthora</italic> species were found associated with black pod disease in the state of Bahia, Brazil, and the previously undescribed <italic>P. theobromicola</italic> seems to be prevalent in field conditions. This is the first report of <italic>P. theobromicola</italic> on <italic>T. cacao</italic>. Also, these findings are crucial to improve the disease control strategies, and for the development of cacao materials genetically resistant to <italic>Phytophthora</italic>.</p>