Effect of temperature and light on germination behavior of PSII inhibiting herbicide resistant and susceptible junglerice (Echinochloa colona) populations.

Repeated use of triazine herbicides have resulted in evolution of triazine resistant junglerice (Echinochloa colona) populations in southwestern Iran. Experiments were conducted under controlled conditions to investigate the effect of temperature and light on germination of two triazine-resistant (R2 and R3) and one susceptible (S) junglerice populations. The germination response was evaluated at nine constant temperatures of 10, 15, 20, 25, 30, 35, 40, 45 and 50 degreesC and two alternating temperature regimes of 20/10 and 30/20 degreesC. For each population, the cumulative germination over time was modeled using a Weibull model. The three-piece segmented model was also used to describe the cardinal temperatures for the germination rate of junglerice populations. The R2 population was greatest germination in both temperature regimes. The time taken to reach 50% germination (t50) decreased with the increasing temperature in all populations. Based on the three-piece segmented model outputs, the base, the lower optimum, the upper optimum and the maximum temperatures for the germination were estimated to be 9.65, 22.12, 34.05 and 45.25 degreesC for S population. Also, these values were 9.77, 20.48, 35.73 and 49.90 degreesC for R2 population and 9.89, 22.14, 30.33 and 46.08 degreesC for R3 population. Germination of all populations was stimulated after the transfer of seeds kept in darkness to the light. We suppose resistance to triazine and triazinone herbicides not only did not have created negative effect on germination characteristics of R-biotype but also had created competitive advantage in its germination behavior.