A copper-polyphenolic compound as an alternative for the control of Asian soybean rust

Rust, caused by Phakopsora pachyrhizi , is an important disease affecting soybean production. Induced resistance, using an array of abiotic or biotic inducers of resistance, becomes a very promising alternative to minimize fungicide applications for rust control. This study investigated the potential of using Mantus® [copper (20%) and polyphenolic (10%)] to reduce rust symptoms by boosting defense reactions. A 2 × 2 factorial experiment was arranged in a completely randomized design with four replications per sampling time. The factors studied were plants sprayed with water (control) or Mantus® (referred to as induced resistance (IR) stimulus hereafter) that were non-inoculated or inoculated with P. pachyrhizi . Urediniospores germination was reduced by 97% by the IR stimulus in vitro . Meanwhile, rust severity and area under disease progress curve significantly decreased by 68 and 35%, respectively, for IR stimulus-sprayed plants compared to control. Defense-related genes ( PAL1.1 , PAL1.3 , PAL3.1 , CHIA1 , CHI1B1 , LOX , PR10 , ICS1 , and JAR1 ) were up-regulated for IR stimulus-sprayed plants compared to control plants during fungal infection. Diseased and IR stimulus-sprayed plants showed less impairment in their photosynthesis (moderate changes on both gas and chlorophyll a fluorescence parameters, linked to great concentrations of chlorophyll a + b and carotenoid) and a more robust antioxidative metabolism (lower concentrations of hydrogen peroxide and anion superoxide, higher superoxide dismutase activity, and lower ascorbate peroxidase, catalase, peroxidase, and glutathione reductase activities) in contrast to control plants infected by P. pachyrhizi . These results highlight the potential of using this IR stimulus for rust management considering its fungistatic effect to reduce urediniospores germination linked to increased resistance of soybean plants to cope with P. pachyrhizi infection more efficiently.