Growth Responses in Sorghum and Wheat Induced by Glyphosate

Abstract

Foliar application of 2.8 μg/plant of glyphosate [N-(phosphonomethyl)glycine] to greenhouse grown sorghum [Sorghum bicolor (L.) Moench ‘Tophand’] seedlings resulted in increased fresh weight. As glyphosate levels were increased to 11.2 μg/plant, diameter of the basal growth zone increased while fresh weight decreased. In growth chamber studies with sorghum and wheat [Triticum aestivum (L.) ‘Era’] seedlings, glyphosate caused the greatest reduction in fresh weight at the optimum growth temperatures for both species. Glyphosate inhibited normal production of basal buds in wheat at the optimum growth temperature and stimulated bud production at temperatures above the optimum. Under normal growth conditions, basal buds in sorghum do not develop; however, application of glyphosate stimulated basal bud development under normal and above-normal temperature conditions. Histochemical analysis of malate dehydrogenase activity in apical meristem tissue of treated sorghum seedlings indicated that growth of the apex was normal and viable.

Effects of Pre-Harvest Glyphosate Application on Spring Wheat Quality Characteristics

“…Zollinger et al [23] and Darwent, Kirkland, Baig and Lefkovitch [14] also reported that an application of glyphosate prior to the hard dough stage or physiological maturity caused decreases in kernel weight and kernel size. Similar observations, where harvest aids caused negative effects on grain quality, were found in other crops such as dry bean [24], sorghum seed [25], soybean [26], peas [27] and rice [28]. However, contrary to the findings of the current study, He et al [29], who studied the impact of the harvest aids, such as diquat, paraquat and ethephan on rice quality, reported that pre-harvest application of these herbicides did not affect the TKW of rice.…”

The Influence of Glyphosate on Bud Dormancy in Leafy Spurge (Euphorbia esula)

“…Growth inhibition was measured by stem counts (Table 1). When new shoots did appear midway through the growing season, shoot growth and branching from buds were observed, a characteristic of sublethal rates of glyphosate observed on other species (5,7,18,19). These observations indicate that glyphosate may have the ability to interfere with correlative inhibition, which is dormancy enforced by the main shoot, and facilitate prolific shoot bud growth from previously inhibited buds on leafy spurge plants.…”

“…Glyphosate at sublethal concentrations causes tillering, axillary bud, and root bud growth in other species (5,7,18,19). These results indicate that glyphosate can temporarily overcome apical dominance either directly or indirectly and cause uncharacteristic stem and shoot growth.…”

Nicosulfuron tolerance and population dynamics of woolly cupgrass (Eriochloa villosa)

“…further demonstrated that main shoot apical dominance limited imazametbabenz translocation to lateral shoots, rendering tillers less susceptible to growth inhibition by the herbicide. The release of apical dominance has also been demonstrated with glyphosate on Cvnodon dactvlon (Fernandez and Bayer 1977), wheat (Triticum aestivum^ and sorghum (Baur et al 1977). Shieh et al (1993) reported that the sink activity of various buds along old rhizomes of quackgrass increased, thus competing strongly with other nearby buds, which consequently received little assimilates and glyphosate.…”

“…Sublethal doses of glyphosate (iV^hosphonomethyl)glycine) applied to the foliage of quackgrass (Agropyron repens^ stopped the growth of shoots and caused prolific tillering . Under normal growth conditions, basal buds in sorghum (Sorghum bicolor^ do not develop; however, application of glyphosate stimulated basal bud development (Baur et al 1977). (Setaria faberi^ .…”