Phytotoxicity assay for seed production using Brassica rapa L

Area of Science:

• Agricultural Science
• Environmental Toxicology
• Plant Science

Background:

• Current plant testing for herbicide effects primarily assesses vegetative growth, potentially overlooking impacts on reproductive yield.
• Pesticide drift at low field application rates (FAR) can adversely affect crop yield, necessitating sensitive detection methods.

Purpose of the Study:

• To evaluate the efficacy of Brassica rapa L. Wisconsin Fast Plants®, a short-cycle species, in detecting herbicide-induced reductions in seed production.
• To determine if B. rapa can serve as a bioindicator for herbicide effects on seed yield at sub-lethal application rates.

Main Methods:

• Brassica rapa plants were treated with varying concentrations (≤0.1× FAR) of five herbicides (aminopyralid, cloransulam, glyphosate, primisulfuron, sulfometuron) 14 days after emergence.
• Effects on seed dry weight were quantified using nonlinear regression to determine the effective concentration causing a 25% reduction (EC25).
• Results were compared to effects on shoot dry weight to assess sensitivity differences.

Main Results:

• Sulfometuron, primisulfuron, cloransulam, glyphosate, and aminopyralid all reduced B. rapa seed dry weight at EC25 values below 0.1× FAR.
• Reduced seed production occurred at lower herbicide concentrations than those affecting shoot dry weight for sulfometuron and primisulfuron.
• Aminopyralid, cloransulam, and glyphosate did not significantly reduce shoot dry weight, highlighting seed production as a more sensitive endpoint.

Conclusions:

• A short-cycle Brassica rapa model can effectively indicate potential reductions in seed production due to herbicide drift at low application rates.
• This bioassay provides a more sensitive measure of herbicide impact than traditional vegetative growth assessments.
• Extending the growth period slightly beyond current vegetative vigor tests allows for the assessment of crucial seed production effects.