Abstract
Previously we found two biotypes of Amaranthus palmeri (Palmer amaranth) in a population of this economically important weed that were resistant to glyphosate but differed with respect to pigmentation. One biotype was typically red-pigmented (betacyanin) while the other was green, with no visual appearance of red hue on any plant part at any growth stage. We have also reported that a strain of Myrothecium verrucaria (MV) exhibited bioherbicidal activity against several important weeds including glyphosate-resistant Palmer amaranth. In greenhouse tests, MV was applied to these two biotypes (red and green) at two ages (3-week- and 6-week-old) and effects of this fungus monitored over a 5-day time course. Initial symptoms of MV (16 to 24 h after inoculation) were: epinastic curvature, wilting and development of lesions on leaves and stems. Generally, the younger plants tended to be more sensitive to MV than older plants. Bioherbicidal damage increased with time leading to necrosis and plant mortality and increasing disease progress. Severe loss of fresh weight occurred in both biotypes as compared to untreated plants. Results indicated that MV was effective on both biotypes, but effects on growth reduction and disease progression were more rapid and generally greater in the green biotype, suggesting that compounds responsible for red pigmentation may be more potent as defense against pathogen attack.
Highlights
We have reported that a strain of Myrothecium verrucaria (MV) exhibited bioherbicidal activity against several important weeds including glyphosate-resistant Palmer amaranth
Glyphosate resistance in Palmer amaranth plants has been attributed to high copy numbers of the enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene, compared to glyphosate-susceptible plants [12] and high EPSPS copy numbers enable adequate EPSPS production and the concomitant synthesis of required aromatic amino acids even when high levels of glyphosate exist in the resistant plant tissues
Due to the involvement of plant pigments such as betalains in plant-pathogen interactions and the severe economic importance of Palmer amaranth and glyphosate-resistant Palmer amaranth, we wished to investigate the effects of the bioherbicidal fungus, Myrothecium verrucaria (MV) on our two biotypes
Summary
We found two biotypes of Palmer amaranth in a population of this economically important weed that were resistant to glyphosate but differed with respect to pigmentation [14]. Betalains are water-soluble nitrogen-containing compounds derived from tyrosine and have important functions in plants They are distributed among ten plant families belonging to the order, Caryophyllales (and in some fungi) and are divided into two groups: red betacyanins and yellow betaxanthins [15] [16] [17]. Due to the involvement of plant pigments such as betalains in plant-pathogen interactions and the severe economic importance of Palmer amaranth and glyphosate-resistant Palmer amaranth, we wished to investigate the effects of the bioherbicidal fungus, Myrothecium verrucaria (MV) on our two biotypes (red-pigmented and green-pigmented). This paper is the first report of the interactions of MV on these two differentially-pigmented Palmer amaranth biotypes
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