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.
The objective of this work was to identify the time of the thermal shock that promotes the greater release of zoospores/sporangia. The experiments were carried out with five treatments, varying the thermal variation time (20', 30', 40', 50' and 60') of sporangia suspension of 7.105 sporangia mL-1 under 5 °C temperature. The incidence of sporangia germinated by 20 times whose It was evaluated100 units at random, using an optical microscope at 40 times magnification. The F and Tukey test were used to compare the means. The sexual phase (presence of oospores) was identified in the isolate derived from purslane. In purslane leaves (infected by Albugo portulacae) the time of 20-30' promoted a greater number of zoospores released, whereas for the isolate from amarantus (infected by A. bliti) the time of 30’ promoted statistically the highest release of zoospores; for the isolate from leaves of “jetirana” (infected by A. ipomoeae-panduratae) the time of 30-50’ promoted greater release of zoospores; and finally the isolate from “onze-horas” leaves (infected by A. portulacae) the time of 30-40’ statistically promoted the highest percentage of release of zoospores, It was demonstrating a differential behavior per host in the release of zoospores. The thermal shock time that promoted the highest amount of released zoospores (38 %) was observed for the purslane-Albugo portulacae and “onze horas”-A. portulacae pathosystem.
Orelha-de-rato (Dichondra repens – Convolvulaceae) é uma planta perene de baixo crescimento, considerada como forrageira. O trabalho teve como objetivo a identificação da ferrugem da orelha-de-rato causada por Puccinia sp. Amostras de folhas de orelha-de-rato foram coletadas no município de Bento Gonçalves, RS, exsicatadas e depositadas na coleção micológica de referência do IF Goiano Câmpus Urutaí e, posteriormente, analisadas em microscópio estereoscópico. Lâminas semi-permanentes e cortes histológicos foram realizados. Para registro dos sintomas e sinais do patógeno fez-se macro e microfotografias. A morfometria das estruturas reprodutivas foi realizada utilizando microscópio óptico. O fitopatógeno apresentou télia de coloração marrom avermelhado, hipófila e subepidérmica encontrada na face abaxial da folha, com dimensões 180-260 x 210-340 µm. Teliósporos lisos, bicelulares, com dimensões de 32,1 - (27,1) - 22,2 x 19,4 - (14,8) - 11,3 µm de coloração pardo a marrom avermelhado com papila de comprimento 7,5 - (5,0) - 2,6 µm, hialina e pedicelos filiformes e hialinos, com comprimento de 24,7 - (12,6) - 6,7 µm. Inicialmente os teliósporos jovens apresentaram-se hialinos e quando maduros se tornaram melanizados. Com base nas características descritivas da fase telial o isolado oriundo de Bento Gonçalves, RS, (2011) foi identificado como Puccinia dichondrae.
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