Dry heat and hot water treatments for disinfesting cottonseed of Fusarium oxysporum f. sp. vasinfectum

Authors: Bennett, Rebecca; COLYER, PATRICK - Louisiana State Experiment Station

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2010
Publication Date: 11/5/2010
Citation: Bennett, R., Colyer, P.D. 2010. Dry heat and hot water treatments for disinfesting cottonseed of Fusarium oxysporum f. sp. vasinfectum. Plant Dis. 94:1469-1475.

Interpretive Summary: Fusarium wilt is a major disease of cotton around the world caused by the fungus Fusarium oxysporum f. sp. vasinfectum. This fungus is able to infect cottonseed and spread to uninfested areas if infected seed are planted. In laboratory tests, cottonseeds immersed in water heated to 90 degrees C were less often infected with Fusarium than untreated seed. There was no difference in the frequency of Fusarium infection in seed immersed for durations ranging from 75 seconds to 3 minutes. Germination was not reduced relative to untreated seed if immersion times in 90 degree C water were 120 seconds or less for seeds of Pima cotton, or 150 seconds or less for seeds of Upland cotton. Incubating seeds in low- (30-40 degrees C) or high-temperature (60-80 degrees C) dry heat did not eliminate Fusarium from the seed, but seed infection declined more rapidly with higher treatment temperatures. Some high-temperature dry heat treatments effectively reduced Fusarium infection, but these treatments also decreased seed germination. These results suggest that hot water treatments may be used on cottonseed to reduce the risk of disseminating the Fusarium wilt pathogen by infected seed.

Technical Abstract: The potential of low- and high-temperature dry heat, and hot water treatments, for disinfesting cottonseed of Fusarium oxysporum f. sp. vasinfectum was investigated. Naturally infected seeds from Louisiana were air-heated in incubators set at temperatures of 30, 35, and 40 degrees C for up to 24 weeks. Seed harvested from bolls inoculated with race 4 of F. oxysporum f. sp. vasinfectum were incubated at dry heat temperatures of 60, 70, and 80 degrees C for 2 to 14 days, or were immersed in 90 degree C water from 45 s to 3 min. The effects on seed germination and vigor of hot water treatment and a subset of the high-temperature dry heat treatments were also examined in seeds of a Pima (Gossypium barbadense L.) and an Upland (G. hirsutum L.) cultivar. Low- or high-temperature dry heat did not eliminate Fusarium spp. from the seed, though seed infection declined more rapidly with higher incubation temperatures. High-temperature dry heat treatments effective in eliminating fusaria also significantly reduced seed vigor in both the Pima and Upland cultivars. Seed from all times of immersion in hot water were less frequently infected with Fusarium spp. than untreated seed. Incidence of seed infection did not differ significantly among immersion times ranging from 75 s to 3 min. Immersion in 90 degree C water did not reduce germination or vigor at exposure times 120 s or less for seeds of Pima cotton, and 150 s or less for seeds of Upland cotton. Results from the hot water treatments suggest that thermotherapy may be optimized to provide a tactic to prevent the spread of virulent F. oxysporum f. sp. vasinfectum races into uninfested areas through infected seed.