Photosynthetic Properties and Cross-Resistance to Some Urea Herbicides of Triazine-Resistant Conyza canadensis Cronq (L.)

Open Access
Publisher Website
Google Scholar
Abstract
A comparison of the photosynthetic activities, chloroplast ultrastructures and sensitivities to some urea herbicides of atrazine-resistant (R) and suspectible (S) biotypes of Conyza canadensis Cronq (L.) (horseweed) in the rosette stage showed that: I) The light-intensitv dependences of the rates of CO2 reduction in intact leaves of the R and S plants are very similar. 2) The rate of the Hill reaction of the R chloroplasts at 25 0C is 15 - 20% lower at all light intensities than that of the S chloroplasts. 3) The rates of the Hill reactions of the R and S chloroplasts exhibit different temperature-dependences. The activation energy for the S chloroplasts in the temperature range 10-40 0C was found to be 15.3 kJ mol-1. For the R chloroplasts. the discontinuity in the Arrhenius plot was found at around 20 °C: the activation energy was 20.1 kJ mol-1 at below 20 0C. and decreased to 8.2 kJ mol-1 at higher temperatures. 4) The R plants have a better adaptive capacity than the S plants at low temperatures. 5) The chloroplast ultrastructure in the R plants was not reminiscent of that of plants grown under low light intensity. 6) The R biotype exhibited cross- resistance to chlorbromuron and metobromuron. and tolerance to linuron. The R and S biotypes, however, were equally sensitive to diuron. The results permitted conclusions on the properties of the triazine-resistance and urea cross-resistance.

This publication has 0 references indexed in Scilit: