Role of Seed Treatments in Plant Competition Clarence Swanton University of Guelph

Aspects of competition (Bosnic and Swanton, 1997)

Crop-weed competition Can corn seedlings Detect their environment? Adjust quickly to environmental changes? Communicate with weeds? Photo: P. Smith

Shade Avoidance Light quality can be measured as R/FR Low R/FR light induces a shade avoidance response

Shade avoidance decreased anthocyanin and increased lignin content in stem tissue a b b a b b

Anthocyanin’s act as: 1) sunscreen for leaves 2) powerful antioxidants

Shade avoidance increased ethylene biosynthesis gene expression

Shade avoidance up-regulated the auxin transporter gene

Are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxidases (H 2 O 2 ) Naturally found in cells as a by product of oxygen metabolism Play an important role in cell signalling and homeostasis (maintenance of physiological stability) Environmental stress causes ROS levels to increase dramatically Reactive Oxygen Species

Damage DNA Damage proteins and lipids Inactivation of enzymes Alteration of plant metabolism Stomatal closure Oxidative damage caused by reactive oxygen species (e.g.H 2 O 2 ) include:

Shade avoidance increased H 2 O 2 content in corn seedlings a c b a a a a a a a

WF W FRF

Shade avoidance caused 3 times the amount of stomatal closure in corn seedlings Weed-freeFRFWeedy

Seed treatment sold as Cruiser ®, Syngenta Distributed systemically throughout the plant Thiamethoxam is a broad-spectrum neonictinoid insecticide

Anthocyanins H 2 O 2 We know the R:FR reflected from the leaf surface of weeds

1) Weed-free – untreated 2) Weed-free – seed treated 3) Weedy – untreated 4) Weedy – seed treated Experiment replicated 5 times Treatments:

Thiamethoxam increased percent germination and length of root radicle

Corn seedlings originating from seeds treated with thiamethoxam did not express typical morphological shade avoidance responses when exposed to above-ground neighbouring weeds

Seed TreatmentNo Seed Treatment Weed-FreeWeedyWeed-FreeWeedy

Phenotypic parameters Treatment UN-WFUN-WT-WFT-W Second leaf collar height (cm) 8.6 a 9.9 b 8.9 a 8.8 a Influence of thiamethoxam on corn height at the 4th leaf tip stage

Thiamethoxam as a seed treatment prevented the loss of anthocyanin caused by neighbouring weeds

Corn seedlings originating from seeds treated with thiamethoxam accumulated less H 2 O 2 when exposed to above-ground neighbouring weeds

Under non-limiting resource conditions thiamethoxam Enhanced seed germination Negated the anticipated morphological shade avoidance response Summary:

Maintained anthocyanin content Activated antioxidant systems that reduced accumulation of H 2 O 2

Seed treatments a component of Integrated Weed Management Agronomic implications- stress & ROS Role of seed treatments go beyond crop protection to include targeted gene activation for stress tolerance

Acknowledgements

Thank you