Intensidade da ferrugem-asiática-da-soja, em função de boro e manganês

Abstract

Adequate levels of micronutrients for the soybean crop may reduce the severity of soybean rust. To check this hypothesis, plants of soybean ("Conquista" cultivar) were treated in nutrient solution, with two doses of boron (0.1 and 0.5 mg L-1) combined with four levels of manganese (0.08, 0.4, 0, 8; 1.2 mg L-1). The inoculation of plants with urediniospores of P. Pachyrhizi was held in the V3 phenological stage. The severity was assessed according to the scale of Bromfield (1984), in central leaflets of the middle third of the plants. Five evaluations were carried at weekly intervals. Then, the area under the disease progress curve (AUDPC) was estimated. Adequate dose of manganese (0.8 mg L-1) combined with adequate dose of boron (0.5 mgL-1), kept the severity of rust at lower levels than other treatments. The levels of pigments, total phenolics and lignin from five leaflets of the middle third of each plant were assessed at the end of the experiment. Significant interactions between doses of B and Mn were noted for the levels of total chlorophyll and chlorophyll a and b. The highest levels of a, b and total chlorophyll were observed at the dose 0.5 mg L-1 of B. No significant interaction between doses of B and Mn were noted regarding carotenoid content. In the same way, isolated effect for doses of B and Mn were not found. A significant positive correlation for carotenoids and AUDPC at the dose of 0.5 mg L-1 was also detected. For the content of lignin and total phenolics no significant interaction between doses of boron and manganese were noted, but the isolated effect for doses of B could be observed. The highest level of lignin was found at the dose of B (0.5 mg L-1). There was a significant negative correlation for lignin and AUDPC at the dose of 0.1 mg L-1.