Investigation of varietal sensitivity to herbicides in winter wheat using a method of very fast fluorescence induction

The very fast fluorescence induction (vfFI) of chlorophyll a was used to te st sensitivity of eight winter wheat varieties to three herbicides [Bromotr il (a.i. bromoxynil), Bladex 50 SC (a.i. cyanazine), IPU Stefes (a.i. isopr oturon)]. The purpose of conducted experiments was to assess: 1) if a singl e application of herbicides affected the plant state during its further gro wth, 2) if individual varieties differed in responses to these substances, and 3) how the changes of vfFI parameters are related to potential changes of biometric parameters. A fluorometer PEA (Hansatech Instruments, Ltd., No rfolk, England) was used to measure the vfFI curve (O-J-I-P transient) (Str asser, Govindjee, 1992). Herbicides were applied by spraying at the growth stage 30 DC (stem elongation - erecting the secondary stem). Parameters Fo, Fv/Fp and rFj of vfFI curve were measured after 9, 48, 96 and 144 hours af ter spraying. While the effect of Bromotril was maximum on the 2nd to 4th d ay, the effects of Bladex 50 SC and IPU Stefes did not reach maximum even o n the 6th day after spraying (Fig. 1). Varieties were ranked according to e xtent of changes of fluorescence parameters (Tabs I, II, III). The greatest changes in both fluorescence and yield were caused by Bladex 50 SC (Figs 1 , 3, 5). The best consistency between the fluorescence response and yield l oss was found in the case of Bromotril (Figs 1, 3, 4). The consistency is s ubstantiated by a favourable time of measurements in the field of maximum e ffects of the herbicide and the only sensitive parameter rFj being out of t he saturation field. In the case of Bladex 50 SC and approximately IPU Stef es an inversion relationship between fluorescence response ton the 6th day) and yield loss was assessed. This relationship is interpreted by a differe nt kinetics of both herbicide effects and regeneration. Based on relationsh ips between fluorescence reaction and yield components (Fig. 3), three type s of variety reactions and their representatives were suggested. The most s ensitive varieties (Rexia) responded by lowering a number of productive ste ms quickly. Slower and less sensitive reactions exhibited by varieties of t he Samanta type led towards a decreasing grain number per ear. The slowest but significant reaction of varieties of the Alka type led to decreasing bo th the grain number per ear and the grain weight. The first and third type of varieties showed the greatest yield loss; Plant dry weight was reduced a fter the herbicide application but the rate of biomass increase was maintai ned up to anthesis (Fig. 2). It is concluded that the significance of diffe rence between fluorescence parameters (rFj, Fo) indicates the difference in the yield.