A balanced mineral nutrition is among the strategies for the control of Asian soybean rust. This work aimed to evaluate the severity of the soybean rust (Phakopsora pachyrhizi), the potential photosynthesis and the nutrition of soybean plants with different levels of K and Ca. The experiment was arranged in a randomized block design with 25 treatments, 4 repetitions and 2 plants per repetition. A 5 x 5 factorial scheme with 5 doses of K (4, 5, 6, 7, 8 mmol L-1) combined with 5 doses of Ca (3, 5, 7, 9, 11 mmol L-1) was used. Plants were inoculated at growth stage V4 and after nine days weekly evaluations of disease severity were carried out using percentage of injured tissues, which were transformed into area under the disease progress curve (AUDPCS). Potential photosynthesis and nutrient content in the root, stem and leaf dry matter were also evaluated. The supply of Ca reduced AUDPCS at all doses of K. The supply of K also reduced the AUDPCS at the doses of 5, 7 and 11 mmol L-1 of Ca. The smallest AUDPCS was observed at the combination 8 and 11 mmol L-1 of K and Ca, respectively, while the largest AUDPCS was observed at the doses of 4 and 5 mmol L-1 of K and Ca. The plants treated with 6 and 5 mmol L-1 of K and Ca and 5 and 5 mmol L-1 of K and Ca showed better photosynthetic response. Increasing doses of K in the solution promoted increase in K leaf contents and linear decrease in Ca leaf levels. Increasing the levels of Ca in nutrient solution promoted an increase in the content of this element and a linear reduction of K levels in the leaves.
Phakopsora pachyrhizi; mineral nutrition; photosynthesis
