The biology of Cercospora leaf spot (Cercospora cf. alchemillicola) of Toona ciliata was examined in terms of the effects of temperature and duration of foliage wetting on the progress of disease and the mechanism of pathogen infection. To evaluate the effect of temperature on mycelial growth, cercosporin production and conidial germination, experiments were conducted in a 4 × 5 factorial design, with four isolates (HR01, HR02, HR03 and CML3059) at five temperatures (15, 19, 23, 26 and 30°C). The area under the disease progress curve (AUDPC) was calculated in a 3 × 5 factorial design at three temperatures (20, 23 and 29°C) and five leaf wetness durations (0, 12, 24, 48 and 72 hr). Penetration of C. cf. alchemillicola into leaves was examined by scanning electron microscopy. Maximum mycelial growth of all isolates occurred at 24.8°C. HR02 and HR01 produced higher quantities of cercosporin compared with CML3059 and HR03. Temperatures between 21.6 and 23.0°C favoured production of the toxin among isolates. Higher conidial germination rates occurred in isolates HR02 and HR01 compared with other isolates, with optimum germination occurring at 24.2–26.3°C. A leaf wetting period of 72 hr at 23.3°C gave the highest AUDPC value. No hyphal penetration was observed through natural openings. However, germ tubes grew inside wounds on the leaf epidermis. In addition, Phyllachora balansae (cause of tar spot) opened fissures on the leaf epidermis, thus creating wounds enabling C. cf. alchemillicola to infect.
The main control measure of Yellow Sigatoka (Pseudocercospora musae) in banana plants (Musa spp.) has been the planting of resistant varieties, and fungicide application. However, the use of adequately nourished plants is also emphasized as a complementary control method. This study evaluated the influence of interaction between potassium (K) and calcium (Ca) in nutrient solution on the severity of Yellow Sigatoka in banana. Evaluation included severity of disease, chlorophyll a and b contents, nutrient contents, and total dry weight (TDW). There was no interaction between concentrations of K and Ca for area under the disease severity progress curve (AUDSPC), although the AUDSPC increased in leaves 1 and 2 with increasing concentrations of K from 1 to 6 mmol L -1 . Increasing K led to a reduction in chlorophyll a and b contents, and in nutrients N, P, Mg, B, Cu, Zn, and Mn. TDW increased with increasing K. Therefore, high concentration of K causes nutritional imbalance in banana plants, and favors the severity of Yellow Sigatoka.
RESUMO O conhecimento da distribuição espacial da qualidade da água em uma bacia hidrográfica se torna fundamental na aplicação de medidas de planejamento e manejo. A geoestatística, por predizer sem tendência as variáveis em locais não amostrados, tem sido uma técnica apropriada no estudo de variáveis ambientais. Assim, objetivou-se com este trabalho mapear a distribuição espacial da qualidade da água, a precipitação e o uso e a ocupação do solo na Bacia Hidrográfica do Rio Pará, em Minas Gerais (MG), por meio da geoestatística. Os dados de qualidade e precipitação, amostrados em 25 pontos, entre 1997 e 2018, de 15 estações climatológicas, foram submetidos ao teste de coeficiente de Pearson. Para aquelas estações que apresentaram correlações forte e muito forte entre si, foram gerados mapas de krigagem ordinária. Também foram elaborados mapas de uso e ocupação do solo. Houve diferença na distribuição da precipitação entre os períodos seco e chuvoso, porém, em ambas as análises, o maior volume de chuva ocorreu na cabeceira da bacia. Como já esperado, os teores elevados das variáveis nitrogênio, fósforo, coliformes termotolerantes, demanda bioquímica de oxigênio, oxigênio dissolvido, sólidos dissolvidos totais e turbidez correlacionaram-se com as áreas dos centros urbanos da bacia. Portanto, por meio da krigagem ordinária, foi possível demonstrar o comportamento espacial das variáveis relacionadas à qualidade da água e ao uso e à ocupação do solo.
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