An improved granular formulation for a mycoherbicidal strain of Fusarium oxysporum

• Published in: Weed science Vol. 47; no. 4; pp. 473 - 478
• Main Authors: Hebbar, K. P., Bailey, B. A., Poch, S. M., Lewis, J. A., Lumsden, R. D.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01-08-1999; Weed Science Society of America
• Subjects: Chlamydospores; Embryos; Fermentation; Fungal biomass; Fungi; Fusarium; Fusarium oxysporum; mycoherbicides; Rice flour; Room temperature; Soil fungi; Viability; Weed Management; biological control; Fusarium oxysporum Schlechtend: Fr. f. sp. erythroxyli; Fusarium oxysporum; formulation technology; Erythroxylum coca var. coca, coca; mycoherbicide
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1017/S0043174500092109

Modifications were investigated to improve shelf-life or long-term survival upon storage of an extruded Oryza sativa L. (rice) flour : gluten : clay: oil formulation (C7) of a mycoherbicide, Fusarium oxysporum Schlechtend: Fr. f. sp. erythroxyli strain EN4, that causes vascular wilt in Erythroxylum coca var. coca (coca). Fermentor-produced biomass, which contained abundant desiccation-resistant chlamydospores, was incorporated into various adaptations of C7 and stored at room temperature (22 to 25 C) under moderately high (50 to 60%) and low (0 to 5%) relative humidities (RHs). The effect of RH on shelf-life was not significant up to 4 mo of storage, while the presence of oil, added to improve its extrusion, reduced viability significantly. Addition of Gossypium hirsutum L. (cotton) embryo flour or complete elimination of oil from the formulation improved shelf-life from 3 mo to > 12 mo. Shelf-life was further improved by removing the binding agent gluten in the formulation and replacing it with autoclaved O. sativa flour. Ability of the formulations to produce secondary propagules, tested on 1% water agar, indicated that, while adding oil had no effect, G. hirsutum embryo flour increased desiccation-resistant chlamydospore counts but lowered macroconidial counts. Autoclaved rice flour (MR) significantly improved both macroconidial and microconidial counts without affecting chlamydospore counts. None of the formulations affected the total viable propagule counts. When compared with the original formulation (C7), the modification (MRRP7), with MR, G. hirsutum embryo flour, and without oil, was found to have improved shelf-life at higher temperature and RHs and enhanced potential for secondary chlamydospore formation. These characteristics are important for survival of the formulated F. oxysporum under less expensive storage conditions and, once applied, for survival in the soil.