Physiological, biochemical, and molecular aspects of induced resistance in soybean against rust using a nitrogen-and calcium-polyphenols compound and a phosphite of nickel and potassium
Authors:   , Fontes Bianca Apolônio 
Published: February 2024

Soybean rust (SR), caused by Phakopsora pachyrhizi, is an aggressive disease that severely reduces the production of soybean crops worldwide. The SR control has been done by spraying fungicides and using cultural practices (e.g., early sowing dates, early detection of the rust symptoms development, cultivars of early maturing, and 60 to 90 days without growing soybean). However, sustainable control methods are preferred nowadays. In this point of view, induced resistance using biotic and abiotic defense elicitors plays an important role in plant disease management. The present study investigated the potential of Cautha® [calcium (11.01%) and nitrogen (3.3%) complexed with polyphenols (10%)] and Blindage Ni® [potassium (20% K2O, 280 g/L), nickel (0.5% Ni, 7 g/L), and phosphorous acid (500 g/L)] in displaying biochemical, molecular, and physiological resistance mechanisms against P. pachyrhizi. In the first study, plants were sprayed with water (control) or Cautha® (referred to as induced resistance [IR] stimulus after that) and inoculated or non-inoculated with P. pachyrhizi. The germination of urediniospores was reduced by 26% in vitro at the same dose of IR stimulus used to spray soybean plants. The rust severity and area under the disease progress curve lowered by 41% (at 15 days after inoculation) and 27%, respectively, for IR stimulus-sprayed plants compared to water-sprayed plants. The IR stimulus treatment greatly reduced the cellular damage caused by P. pachyrhizi infection in soybean tissues, maintained a great content of photosynthetic pigments, enhanced activities of defense-related enzymes, and built a robust antioxidative metabolism compared with the control treatment. In the second study, the factors investigated were water (control) or Blindage Ni® (referred to as induced resistance [IR] stimulus after that) inoculated or non-inoculated with P. pachyrhizi. In vitro, the urediniospores germination was reduced by 99% by IR stimulus. The soybean rust severity and area under the disease progress curve was decreased by 73% (at 15 days after inoculation) and 74%, respectively, in IR stimulus-sprayed plants compared to water-sprayed plants. The infected plants sprayed with IR stimulus maintain the proper functionality of photosynthetic apparatus and a good concentration of pigments. In addition, this treatment reduced the damage and lipid peroxidation in plant tissue, up-regulated the expression of several defense-related genes in plants infected by P. pachirhizi, kept a great concentration of potassium and nickel in soybean tissues, and increased the concentrations of phenolics and lignin in contrast with the control plants. The results of the present study highlighted the positive role of both IR stimuli in activating defense mechanisms against P. pachyrhizi in soybean crop and reducing disease severity. Keywords: Soybean rust. Glycine max. Plant defense mechanisms. Management of plant disease.