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Factors influencing the herbicidal activity of Nep1, a fungal protein that induces the hypersensitive response in Centaurea maculosa

Published online by Cambridge University Press:  20 January 2017

Ronald Collins
Affiliation:
Weed Science Laboratory, USDA/ARS, Beltsville Agricultural Research Center, Beltsville, MD 20705
James D. Anderson
Affiliation:
Weed Science Laboratory, USDA/ARS, Beltsville Agricultural Research Center, Beltsville, MD 20705

Abstract

The fungal protein Nep1, produced by Fusarium oxysporum f. sp. erythroxyli in liquid culture, caused extensive necrosis to Centaurea maculosa when water solutions of Nep1 (5 µg ml−1) and an organosilicone surfactant (1,1,1,3,5,5,5-heptamethyltrisiloxanyl propyl-methoxy-poly[ethylene oxide]) were applied as foliar sprays. Nep1 did not cause necrosis when applied with a nonionic surfactant or organosilicone surfactant plus unrefined corn oil. Plant age, protein concentration, organosilicone surfactant concentration, and the presence of a dew period influenced the amount of necrosis caused by Nep1. The addition of an 18-h dew period after treatment resulted in an increase of 10% or more in foliar necrosis at the 0.313 and 1.25 µg ml−1 (0.40 and 1.62 g ai ha−1) Nep1 concentrations. Increasing the spray volume from 129 ml m−2 (1,291.3 L ha−1) to 516 ml m−2 (5,165.2 L ha−1) more than doubled the amount of foliar necrosis caused by the 0.313 µg ml−1 (0.40 g ai ha−1 vs. 1.62 g ai ha−1) Nep1 concentration. A maximum necrosis rating of 95% was reached by 1.25 µg ml−1 Nep1 applied at 516 ml m−2 (6.46 g ai ha−1) followed by an 18-h dew period. Nep1 (6.46 g ai ha−1) remained active when coapplied to Centaurea maculosa with the herbicides 2,4-D or glyphosate (0.13 to 2.58 kg ai ha−1), causing foliar necrosis prior to the herbicides killing Centaurea maculosa. An increase in the organosilicone surfactant concentration from 1 to 2 ml ai L−1 was required to achieve levels of Nep1-induced necrosis on Centaurea maculosa acclimated to direct sun comparable to levels achieved on greenhouse-grown plants. Repeated application of Nep1 (6.48 g ai ha−1) 3 wk after an initial treatment (6.48 g ai ha−1) prevented the recovery of acclimated Centaurea maculosa. Greater damage was caused to acclimated Centaurea maculosa when Nep1 was applied near the middle of the day (80% necrosis at 10:00 A.M. and 85% necrosis at 2:00 P.M.) compared to early or late in the day (25% necrosis at 6:00 A.M. and 10% necrosis at 6:00 P.M.).

Type
Research Article
Copyright
Copyright © Weed Science Society of America 

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