Potassium Fertilization Reduces the Severity of Asian Soybean Rust Under High Disease Pressure

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.