Efficacy of seed treatments on viability of Fusarium oxysporum f. sp. vasinfectum race 4 in infected cotton seed

Abstract

Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 is a seedborne pathogen of cotton. A series of seed treatments using hot water at various temperatures (55–90 °C) for various lengths of time (105 s–20 min) was tested on seed of both Pima (Gossypium barbadense) and Upland (G. hirsutum) cultivars to determine the optimum combination to eliminate the pathogen from seed without reducing seed germination or vigor. In 2012, the incidence of FOV race 4 in an Upland seed lot was reduced by ∼56% without reducing seed germination and vigor when FOV race 4-infected cotton seed was immersed in a hot water bath for 20 min at 60 °C. In 2013, infected Upland seed was pretreated at 23 °C and agitated on a shaker at 100 rpm for 1 h in sterile deionized water or sterile 30% potato dextrose broth (PDB). The seed was then immersed for 20 min at 60 °C in one of the following: water, 10% solution of household bleach (0.8% NaOCl, w/v), 0.5% sodium lauryl sulfate, azoxystrobin (0.24 g a.i.), fludioxonil (0.50 g a.i.), thiabendazole (0.42 g a.i.), thiophanate-methyl (0.70 g a.i.), or a fungicide bath containing all four fungicides. A pretreatment immersion in PDB or water followed by a 20 min immersion in a 60 °C fungicide slurry containing all four fungicides or thiophanate-methyl alone were the most effective pretreatment–treatment combinations in reducing FOV (by ∼85%) in seed and avoiding loss of seed germination and vigor based on recovery of the fungus on petri plates and greenhouse grow-out assays. FOV was completely eliminated from infected seed when the seed was immersed in water at 23 °C for 1 h at 100 rpm followed by a 20 min immersion in a solution of thiophanate-methyl heated to 70 °C, but seed germination was reduced by 36% and vigor was reduced by 38%.