Abstract
Horseweed is traditionally considered a non-cropland weed. However, populations resistant to glyphosate have eventually become established in no-till agronomic cropping systems. Growth chamber and greenhouse experiments were conducted to compare selected biological and physi- ological parameters of glyphosate-resistant (GR) and -susceptible (GS) horseweed biotypes from Mississippi with a broader goal of fitness characterization in these biotypes. Vegetative growth parameters (number of leaves, rosette diameter and area, shoot and root fresh weights) were recorded weekly from 5 to 11 wk after emergence and reproductive attributes (days to bolting (production of a flowering stalk) and flowering) and senescence were measured for both GR and GS biotypes under high (24˚C/20˚C) and low (18˚C/12˚C) temperature regimes, both with a 13-h light period. Physiological traits such as net photosynthesis, phenolic content, and cell membrane thermostability, all in the presence and absence of glyphosate, and leaf content of divalent cations such as Ca 2+ and Mg 2+ were assayed in the two biotypes under the high temperature regime. All horseweed vegetative growth parameters except root fresh weight were higher in the high tem- perature regime compared to that in low temperature regime in both biotypes. Number of leaves, rosette diameter and area, shoot and root fresh weight were 40 vs. 35, 9.3 vs. 8.7 cm, 51 vs. 43 cm 2 , 3.7 vs. 3.2 g, and 3.5 vs. 4.2 g under high and low temperature conditions, respectively, when av- * Corresponding author.
Highlights
Horseweed, referred to as butterweed, coltstail, fleabane, or marestail, is an annual plant native to North America and Central America [1]
The two horseweed biotypes differed in all the variables evaluated
Both temperature and growth duration affected all aspects of horseweed plant growth and development
Summary
Referred to as butterweed, coltstail, fleabane, or marestail, is an annual plant native to North America and Central America [1]. Increasing adoption of herbicide-resistant crop technology, especially glyphosate-resistant crops, has encouraged reduced and no-till production practices. This switch in management strategy has encouraged traditionally noncropland weeds such as horseweed to migrate into and infest cropland. Koger and Reddy [9] reported 28% reduced translocation of 14C-glyphosate from the treated leaf of a GR biotype from Mississippi compared with a GS biotype. They suggest that reduced translocation of glyphosate to growing parts of the GR plant has a role in glyphosate resistance mechanism [9]. Potential differences between the GR and GS biotypes in common physiological traits could provide new insights into the glyphosate resistance mechanism
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