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Potassium (K) is one of the essential nutrients for plants and is involved in many cellular processes which might influence the severity of diseases. There are few reports of the effect of increasing concentrations of K in the field on the severity of the Asian soybean rust (ASR) caused by Phakopsora pachyrhizi. In this context, the objective of this work was to verify the influence of increasing concentrations of K on ASR, in the absence and presence of chemical control, in conditions that highly favored the development of the disease. Two experiments were conducted under field conditions and two also in the field but in pots with a capacity of 100 L. Evaluated concentrations of K were 0.0, 100, 200, and 400 mg/dm³, respectively in a randomized complete block design. The application of the fungicide mixture azoxystrobin (200 g/L) + cyproconazol (80 g/L) was performed at 45, 60, and 75 days after emergence. The severity of the disease, area under the disease progress curve (AUDPC), rate of disease progression (r), soybean productivity, and contents of chlorophyll a, b and total were evaluated. The severity, AUDPC, and r decreased with the increase of the concentration of K and fungicide application, while the rate of disease control and soybean productivity increased. Contents of chlorophyll a, b and total also had higher values according to the increase in the concentration of K. Potassium fertilization reduced the severity of ASR and grain yield under high disease pressure with or without chemical control.

O objetivo com este trabalho foi avaliar o efeito da aplicação de diferentes concentrações de extrato de própolis sobre a qualidade sanitária e fisiológica de sementes de arroz e soja. O experimento foi conduzido no Laboratório de Microbiologia e Saúde da Universidade Estadual da Região Tocantina do Maranhão (UEMASUL), no período de Janeiro a Maio de 2019. O delineamento experimental utilizado foi inteiramente casualizado, com seis tratamentos e quatro repetições de lotes de 20 sementes. Os tratamentos testados foram: testemunha (água destilada), concentrações de 2,5%; 5%; 7,5% e 10% de extrato de própolis e o fungicida Maxim (controle positivo). As sementes com as dosagens de própolis foram homogeneizadas em sacos plásticos e secas à temperatura ambiente sob papel absorvente. Na sequência, foram plaqueadas em placas de Petri, contendo três folhas de papel germitest previamente umedecidas e incubadas em BOD com fotoperíodo, à temperatura média de 26±1 ºC durante sete dias. Foram avaliados os parâmetros: incidência fúngica nas sementes tratadas, germinação de sementes, comprimento da raiz e altura da plântula. Todas as concentrações de extrato de própolis apresentaram eficiência na redução de incidência fúngica nas sementes de arroz e soja, sendo identificados os gêneros Aspergillus sp., Fusarium sp., Penicillium sp., Cercospora sp., Phomopsis sp. e Rhizopus sp. A qualidade fisiológica das sementes, quanto aos parâmetros de germinação, comprimento de raiz de plântulas de soja e altura de plântulas de arroz, não foram influenciadas pelas concentrações de extrato de própolis.

Mineral nutrition of plants is a strategy that can be used in the management of plant diseases. Therefore, the objective of this work is to determine which phosphorus dose reduces the severity of Asian soybean rust (Phakopsora pachyrhizi) with or without chemical control. Two trials were conducted under field conditions with six P doses (0, 25, 50, 100, 200 and 400 mg/dm³), and two trials in 100 L pots at P doses 0, 100, 200 and 400 mg/dm3. The inoculation of border rows and inoculation directly on plants in pots was performed with 105/mL of fungus urediniospores 15 days before the application of fungicide to increase the disease pressure. The application of fungicide (azoxystrobin + ciproconazole) was carried out at the R1 stage, and afterwards the mixture was reapplied three times in chemical control treatments. The results showed that the application of triazol + strobilurin fungicides in the presence of P decreased the severity of the disease (area under disease progress curve and disease infection rate) greater than in the absence of the fungicides. The productivity and levels of chlorophyll a, b and total also increased with chemical control in the presence of P. The dose 400 mg/dm3 of P was the most efficient in a soil with a low fertility, and 200 mg/dm³ was efficient in a soil with a high fertility. In conclusion the application of the fungicides triazol + strobilurin was very important to get good control of Asian soybean rust; phosphate fertilization contributed to the amelioration of Asian soybean rust.