Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2012
Publication Date: November 1, 2012
Citation: Hoagland, R.E., Boyette, C.D., Vaughn, K.C., Teaster, N.D., Stetina, K.C. 2012. Effects of Myrothecium verrucaria on ultrastructural integrity of kudzu (Pueraria montana var. lobata) and phytotoxin implications. American Journal of Plant Sciences. 3:1513-1519. Interpretive Summary: The fungus Myrothecium verrucaria (MV) effectively controls several weeds, including kudzu. Aside from being a potent bioherbicide, MV produces mycotoxins (trichothecenes, e.g., roridin A). We previously explored various parameters of MV related to its development as a commercial product. Knowledge of disease progression, how the fungus kills plant tissues, and what organelles or plant constituents are affected could lead to major improvements in MV formulation and efficacy. Using ultrastructural analysis, we discovered for the first time, the early events that occur within kudzu tissues after application of roridin A or MV spores. These findings improve our understanding of the phytotoxicity of roridin and MV spores and suggest that phytotoxicity of MV spores is caused by factors other than the action of roridin.
Technical Abstract: The fungus Myrothecium verrucaria (Alb. & Schwein.) (MV), originally isolated from diseased sicklepod (Senna obtusifolia L.), has bioherbicial activity against kudzu and several other weeds when applied with low concentrations of the surfactant Silwet L-77. Ultrastructural investigations of MV effects on kudzu seedlings revealed a rapid (~ 1 h after treatment) detachment of the protoplast from the cell wall. Plasmodesmata appeared to be broken off and left in the wall. These ultrastructural symptoms occurred well in advance of the appearance of any fungal growth structures. Some fungal growth was observed after severe tissue degeneration (24 to 48h after treatment), but this occurred primarily extracellularly with respect to the kudzu tissues. Kudzu seedlings treated with roridin A, a trichothecene produced by the fungus, caused symptoms similar to those induced by the fungal spore formulations applied with surfactant. The overall results suggest that penetration of a phytotoxic substance(s) in the fungal formulation was facilitated by the surfactant, and that roridin A exerts phytotoxicity toward kudzu.