Influência do fósforo e do potássio na severidade da ferrugem da soja Phakopsora pachyrhizi

Abstract

Mineral nutrition on soybean might reduce the severity of Phakopsora pachyrhizi. "Embrapa 48" showed higher level of partial resistance than "Al 83" cultivars. Both cultivars were utilized in the trials. The cultivars were planted in plastic pots with sandy soil, clay and unburned rice husks (3:1:2). The treatments added to the substract were different levels of phosphorus and potassium. The plants were inoculated with uredospores of P. pachyrhizi at V2 and R5 stages, and rust severity evaluated at 14, 17, 21 and 25 days after inoculation. The disease progress rate was calculated. The results showed significant influence of plant nutrition, reducing both the final severity and disease progress rate as P and K level increased. The greatest reduction was observed at V2 stage. Greater disease reduction was observed at lower levels of K. The expression of partial resistance of both cultivars was influenced due to variation of P and K levels. Lower doses of P and K induced a greater difference in the latent period of the pathogen. The association of genetic cultivar background to mineral nutrition might result in an integrated management disease program, along with evasion and chemical protection strategies.