Establishment of a semi-selective method for the detection of Sclerotinia sclerotiorum in dry bean and soybean seeds

Abstract

The objective in this work was to improve the existing methodology for the detection of Sclerotinia sclerotiorum in dry bean and soybean seeds through the use of water restrictors in place of 2,4-dichlorophenoxyacetic acid, in PDA substrate containing bromophenol blue and antibiotics (Neon-S). Firstly, the effects of the water restrictors mannitol, sodium chloride, and polyethyleneglycol (PEG6000) at different osmotic potentials were evaluated on the mycelial growth of S. sclerotiorum isolates and on the radicle protrusion of seeds of the species studied. The use of water restrictors with osmotic potentials of up to -0.5 MPa for PEG and -1.0 MPa for mannitol and sodium chloride did not affect the mycelial growth of the isolates tested, and proved to be satisfactory to inhibit the radicle protrusion of the seeds tested. In the second stage of this work, alternating light and continuous darkness were tested in the detection of fungus in the seeds of both species by the modified Neon method. The methodology composed by solid medium PDA, bromophenol blue (100 ppm), chloramphenicol (50 ppm) and water restrictor mannitol (-1.0 MPa) at a temperature of 20 °C with incubation in darkness, proved to be effective and reliable in the detection of that pathogen in routine analysis laboratory.