Reduction of negative effect of simulated pre-harvest rainfall on winter wheat yield and grain quality by proteolyse and alpha-amylase activity inhibitors

The aim of experiments was to verify the effect of potential inhibitors of a negative effect of simulated preharvest rainfall, totally 50-70 mm, on the yield and technological quality of grain of winter wheat variety Astella, including superoxide dismutase activity. Inhibitors were applied 48-72 h before simulated rainfall. Rainfall was applied in two different terms, at first from milk to wax grain ripeness with the following drought period till harvest and in the period with rainfall from wax ripeness nearly up to technological ripeness of grain, after the previous drought stress period in pot experiments in the years 2003 and 2005. Preharvest rainfall and drought stress significantly influenced the grain yield and quality. The negative effect of preharvest rainfall in the period between milk and wax ripeness, but even more negative effect of drought stress on the grain yield in this period were reduced by applied regulators. Mechanical-spectral treatment by the green adhesive Nitrafol A EKO diluted 1:23 with water in both years statistically highly significantly increased the grain yield, in the average of years by 32.6% as compared to the control A without growth regulators treatment (June), mainly because of a higher grain number in spike, in the average of years by 31.8%. Treatment by Avit 35 at milk ripeness was successful in both years, but less effective. Avit 35 statistically significantly increased the grain yield by 15.8%, as compared to the control A. Drought stress between milk and wax ripeness affected the grain yield very negatively. Tannin application in the stage of wax ripeness was in the average of years the most successful treatment from the viewpoint of reduction of the following rainfall negative effect, but it was not confirmed by a positive effect in both years. Avit 35 applied at the stage of wax ripeness successfully eliminated in both years the negative rainfall effect after grain wax ripeness and increased the yield in the average of years by 23.7%, as compared to the B (July) control (control without regulator treatment, but exposed to rainfall after wax ripeness). An unfavourable effect of rainfall on grain technological quality was more significantly inhibited after application of regulators at milk ripeness before the following rainfall till the stage of wax ripeness. The 98.6% level of the mean value of grain wet gluten content from the control without rainfall (treatment C), but maintained at the optimal full water capacity of soil, was reached after treatment with Avit 35. Similar, but a little bit lower, was the effect of water extract of dandelion root (96.3% of C level). This extract improved the elastic-viscous properties of flour in both years by 19.7% in the average, compared to the C variant. It had not only an inhibition effect on degradation of high molecular weight proteins, but more over a stimulation effect towards their formation by an unknown mechanism. After the drought stress in the period between milk and wax grain ripeness, the following treatment with growth regulators in the stage of wax ripeness before simulated rainfall had a positive effect on the grain yield quantity, but grain quality was not influenced significantly positively, except for the falling number. The regulators reducing waterlogging stress and the stress from wet of the above-ground mass during the whole period from the milk to wax ripeness reduced superoxide dismutase activity in grain. Response of plants to the regulators applied at wax ripeness was less flexible from the viewpoint of superoxide dismutase activity changes. On the contrary, mixture of salicylic acid and colamine phosphoric acid increased the grain stress level, what was connected with increasing superoxide dismutase activity and this was reflected more in a lower grain technological quality than in the yield quantity.