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Adjuvant and Refined Corn Oil Formulation Effects on Conidial Germination, Appressorial Formation and Virulence of the Bioherbicide, Colletotrichum truncatum

C. Douglas Boyette, Robert E. Hoagland
Plant Pathology Journal 2013 v.12 no.2 pp. 50-60
Colletotrichum truncatum, Sesbania exaltata, adjuvants, appressoria, biopesticides, conidia, corn oil, dew, emulsions, fatty acids, germination, hemp, herbicidal properties, hosts, pathogens, pesticide formulations, plant extracts, seedlings, surfactants, virulence, weeds
Several surfactants, plant extracts, and fatty acids were tested for stimulation of conidial germination and appressorial formation of Colletotrichum truncatum, a bioherbicide of the weed, hemp sesbania (Sesbania exaltata). The commercial surfactants (Tweens® 40, 60, 80, 85 and Myvatex® 60) at concentrations of 0.25 to 1.0 % (v/v), stimulated germination, but these effects were not exclusively related to their hydrophylic-lipophylic balance values. The stimulatory surfactants were also tested for germination and virulence of C. truncatum when formulated with the conidia and applied to hemp sesbania seedlings. Conidia formulated in either water, a surfactant or, an emulsion of refined corn oil were ineffective on the plant in the absence of dew or when dew was delayed. However, formulations of conidia combined with surfactant in emulsified refined corn oil did exhibit bioherbicidal activity when adequate dew or free-moisture was unavailable. This is important since previous reports indicated that refined corn oil did not enhance bioherbicidal activity, whereas unrefined corn oil promoted pathogen germination and efficacy of C. truncatum. The fatty acids tested had little or no effect on conidial germination but, aqueous extracts of several plant species including pathogen hosts and non-hosts, stimulated germination. Appressorial formation influenced by the surfactants did not necessarily reflect the disease rating on hemp sesbania seedlings. Overall, results show that formulations containing an emulsion of conidia, a surfactant and refined corn oil have potential for enhancement of the efficacy of C. truncatum.