Photoinactivation by cationic porphyrins reduces germination and severity of Phakopsora pachyrhizi, the cause of Asian Soybean rust
摘要
Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, is one of the most severe diseases of soybeans and is present in all major producing regions of the world. By causing premature defoliation, the disease compromises pod formation and filling. The loss of sensitivity in the pathogen populations to fungicides used to control this disease has rendered most fungicide control less effective. The aim of the present study was to evaluate the intervention by photodynamic inactivation (PDI) in P. pachyrhizi, using a mixture of cationic meso-(1-methyl-4-pyridinio) porphyrins, tested for the first time against this pathogen, as a photosensitizer (PS). The detached-leaf technique was performed with soybean leaves treated with PS at 50, 100 and 200 µg/mL, inoculated with the pathogen and exposed to an illuminance of 10.77 µmol m−2 s−1. Growth room experiments were performed with soybean plants grown in pots treated with PS, inoculated with P. pachyrhizi and exposed to an illuminance of 255 µmol m−2 s−1. Spore germination assays using the same PS concentrations were also performed. Significant reductions in disease severity compared to control were observed in detached-leaf assays: on average 86.4% with PS at 100 µg/mL and 97.9% with PS at 200 µg/mL, and in growth room experiments: about 93.7% with PS at 100 µg/mL and 97.7% with PS at 200 µg/mL. All PS concentrations tested reduced P. pachyrhizi spore germination by more than 95%. The results suggest that PDI has potential to be field tested and become an alternative to current control methods of Asian soybean rust.