Abstract
Comparative studies were conducted on mycelial preparations of the bioherbicide, Myrothecium verrucaria (MV) strain IMI 361690 and a recently discovered sector (MV-Sector BSH) of this fungus. The whitish sector was discovered, isolated, grown in pure culture on PDA and found to be a stable, non-spore producing mutant when cultured over several months under conditions that cause circadian sporulation during growth of its MV parent. Application of MV and MV-Sector BSH mycelial preparations to intact plants (hemp sesbania and sicklepod) and leaf discs (kudzu and glyphosate-resistant Palmer amaranth) showed that the sector efficacy was generally equal to, or slightly lower than MV. Bioassays of MV and this sector on seed germination and early growth of sicklepod and hemp sesbania seeds demonstrated that hemp sesbania seeds were slightly more sensitive to the fungus than sicklepod seeds and that the sector bioherbicidal activity was slightly less than that of MV. SDS-PAGE protein profiles of cellular extracts of MV and the sector and their respective culture supernatants showed several differences with respect to quantity and number of certain protein bands. Overall results showed that the isolate was a non-spore producing mutant with phytotoxicity to several weeds (including weeds tolerant or resistant to glyphosate), and that the phytotoxic effects were generally equivalent to those caused by MV treatment. Results of this first report of a non-sporulating MV mutant that suggest additional studies on protein analysis, and an extended weed host range under greenhouse and field conditions are needed in order to further evaluate its possible bioherbicidal potential.
Highlights
Bioherbicides may offer alternatives to the control of weeds with synthetic compounds including the use of plant pathogens as bioherbicides [1] [2] [3] [4]
A substantial portion of this research has been devoted to the potential of Myrothecium verrucaria (MV) to control several economically important weeds including, hemp sesbania [Sesbania herbacea (Mill.) McVaugh] [11], sicklepod (Senna obtusifolia) [12], kudzu (Pueraria lobata) [13] [14] [15] and glyphosate-resistant and -susceptible Palmer amaranth
MV-Sector BSH formed during routine maintenance culture of MV (Figure 1(a)) and the sector was isolated and grown on Potato dextrose agar (PDA) under the alternating light/dark regime as above (Figure 1(b))
Summary
Bioherbicides may offer alternatives to the control of weeds with synthetic compounds including the use of plant pathogens as bioherbicides [1] [2] [3] [4]. Widely distributed in the southeastern United States [26], this major weed has evolved resistance to several herbicides, including triazine, acetolactate-synthase inhibitor, and dinitroaniline herbicides use [27] It was controlled with glyphosate, but the first glyphosate-resistant Palmer amaranth population was reported in Georgia in 2006 [28]. Initial host range studies of MV indicated that some phytotoxicity to redroot pigweed (Amaranthus retroflexus) [29], and more recently tests on Palmer amaranth demonstrated bioherbicidal activity on plants that were sensitive or resistant to glyphosate [16]. Greenhouse and bioassay tests were performed on several weeds with demonstrated susceptibility to MV as outlined above, i.e., hemp sesbania, sicklepod, kudzu and glyphosate-resistant Palmer amaranth
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