Field bindweed (Convolvulus arvensis L.): Mechanisms of differential glyphosate sensitivity among biotypes, and characterization and breakdown of self-incompatibility

James Harry Westwood, Purdue University

Abstract

Biotypes of field bindweed differing in their susceptibility to foliar applications of glyphosate were studied to understand the mechanisms involved in this response. Experiments included studies related to glyphosate uptake, translocation, and glyphosate effect on target enzyme (EPSPS) activity and were conducted using whole plants, hydroponically grown plants, in vitro shoot explants, and cell suspension cultures. Further experiments were conducted to overcome sexual reproduction barriers (self-incompatibility) to allow future research into the genetic factors involved in differential response of field bindweed to glyphosate. Experiments with whole plants indicated no differences between biotypes in the uptake and translocation of either foliar- or root-applied glyphosate. However, EPSPS activity increased in all tissues of the more tolerant biotype (biotype 4) within 7 days of glyphosate treatment, but not in the more susceptible biotype (biotype 1). Differences in levels of phenolic compounds and DAHPS activity in untreated shoot tips of the biotypes suggest that the shikimate pathway may be more active in biotype 4 than in biotype 1. In vitro cultured shoots of field bindweed biotypes also varied in glyphosate sensitivity and were used to further evaluate differences between biotypes. Shoots of the biotypes did not differ in the amount of glyphosate absorbed from the medium or in EPSPS activity following glyphosate treatment. In the absence of glyphosate, biotype 4 shoots accumulated more biomass than those of biotype 1, which may indicate greater potential for growth under all conditions. Cell suspension cultures of biotype 1 initially absorbed more glyphosate from the media than biotype 4 cells, though uptake was equal between the biotypes by 24 hours after starting exposure. Metabolism of glyphosate was greater in biotype 4 cells than in those of biotype 1 after 5 days growth in the presence of glyphosate. The self-incompatibility system of field bindweed was determined to be of the multiallelic, sporophytic type. The most effective method to overcome this barrier was by heating stigma tips with a hot soldering iron for 2-3 seconds, followed by self-pollination. This method resulted in production of viable, selfed-seed in amounts equal to that of outcrosses. These studies indicate that multiple mechanisms are involved in determining sensitivity to glyphosate in field bindweed biotypes. These may include activity of the shikimate pathway (or general metabolic vigor), cellular uptake of glyphosate, and metabolism of glyphosate. We now have the ability to genetically manipulate field bindweed to further study the role of these mechanisms in glyphosate sensitivity.

Degree

Ph.D.

Advisors

Weller, Purdue University.

Subject Area

Botany

COinS