Efficacy of Seed Treatments on Viability of Fusarium Oxysporum f. Sp. Vasinfectum Race 4 in Infected Cotton Seed

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 to 90°C) for various lengths of time (105 seconds to 20 min) was tested on seed of both Pima and Upland cultivars to determine the optimum combination to eliminate the pathogen from seed without reducing seed germination and vigor. In 2012, the incidence of FOV race 4 in seed was reduced by ~56% without reducing 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 seed was pretreated at 24°C and agitated on a shaker at 100 rpm for 1 hour in 1 L of sterile deionized water or sterile 30% potato dextrose broth (PDB). The seed was then immersed for 20 min at 60°C in 2 L in one of the following: water, 10% bleach (0.6% NaOCl, w/v), 0.5% sodium lauryl sulfate (SLS), fludioxonil (Cannonball® WP), thiabendazole (Mertect® 340-F), azoxystrobin (Quadris® Flowable), thiophanate (Topsin® M 70WP), or a fungicide bath containing all four fungicides. PDB or water pretreatments followed by a 20 minute immersion in a 60°C fungicide slurry containing all four fungicides or thiophanate alone were the most effective pretreatment-treatment combinations in reducing FOV in seed and avoiding loss of seed germination and vigor. The incidence of FOV in the seed was reduced by ~86% without reducing 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 pretreated at 24°C followed by a 20 minute immersion in a solution of thiophanate heated to 70°C. With this treatment, seed germination was reduced by 36% and vigor was reduced by 38%.