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

Abstract

Black pod disease, caused by Phytophthora species, is among the main limiting factors of cacao (Theobroma cacao L.) production. High incidence levels of black pod disease have been reported in Brazil, being induced by Phytophthora capsici, Phytophthora citrophthora, Phytophthora heveae, and Phytophthora palmivora. To assess the diversity of Phytophthora 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 P. citrophthora and P. palmivora 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 c oxidase I and II genes were PCR-amplified and Sanger-sequenced from the cacao-infecting Phytophthora isolates. The morphological characterization and evaluation of the mycelial growth rates for the Phytophthora isolates were performed in vitro. Based on the molecular analysis and morphological comparisons, 19 isolates were identified as P. palmivora (clade 4). Interestingly, 31 isolates grouped together in the phylogenetic tree and were placed apart from previously known species in Phytophthora clade 2. Therefore, these isolates are considered as a new species herein referred to as Phytophthora theobromicola sp. nov., which produced papillate, semipapillate, and persistent sporangia on simple sporangiophores. The P. palmivora isolates were identified as A1 mating type by pairing each isolate with known A1 and A2 tester strains of P. capsici, but no oogonia/antheridia were observed when P. theobromicola was paired with the different tester strains. The P. theobromicola and P. citrophthora isolates showed higher mycelial growth rates, when compared to P. palmivora, 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 Phytophthora species, with P. theobromicola inducing higher rates of necrotic lesion expansion, when compared to P. palmivora. Here, two Phytophthora species were found associated with black pod disease in the state of Bahia, Brazil, and the previously undescribed P. theobromicola seems to be prevalent in field conditions. This is the first report of P. theobromicola on T. cacao. Also, these findings are crucial to improve the disease control strategies, and for the development of cacao materials genetically resistant to Phytophthora.

Phylogeny and Pathogenicity of Phytophthora Species Associated with Artichoke Crown and Root Rot and Description of Phytophthora marrasii sp. nov.

“…This could be achieved through a combination of agronomic and phytosanitary practices, such as the selection of resistant varieties, adoption of proper irrigation practices, avoiding rotation with susceptible crops, and through the use of chemical treatments, although the oomycota fungicides currently available are very limited. The constant discovery of new Phytophthora diseases on crops [71][72][73] has exacerbated the problem of the correct management of these pathogens, emphasizing the need for new bioactive molecules [74].…”

Cacao agroforestry systems beyond the stigmas: Biotic and abiotic stress incidence impact

“…So far, seven species of Phytophthora have been reported related to the etiology of BPR disease in cacao cultivation, being P. palmivora the cosmopolitan species of the group ( Akrofi, 2015 ), with pantropical distribution ( Perrine-walker, 2020 ). The other species have only been found in specific countries or geographic regions such as South and Central America: P. capsici, P. citropthora, and P. tropicalis ( Barreto et al, 2015 ; de Bahia et al, 2015 ; Fernández Maura et al, 2018 ), Brazil: P. theobromicola ( Decloquement et al, 2021 ), Venezuela: P. megasperma ( Molina et al, 2016 ), West Africa: P. megakarya, and P. katsurae ( Guest, 2007 ; Liyanage and Wheeler, 2007 ). Among these species, P. megakarya is the most important economically in the world, since it is reported in the African countries with the highest cacao production ( FAOStat, 2021 ).…”

First report Calonectria hawksworthii as an aetiological agent of fruit rot of cocoa in Brazil

“…When considering the most significant pathogens inducing white rot, it is worth mentioning Phytophthora theobromicola , Phytophthora capsici and Phytophthora palmivora . Colletotrichum species have been reported to cause fruit rot, and the presence of Moniliophora perniciosa also leads to damage (Decloquement et al., 2021; Mendes et al., 2023).…”