Effect of application of growth regulators on the physiological and yield parameters of winter wheat under water deficit

The objective of this study was to evaluate the effect of growth regulator applications on yield and physiological parameters of winter wheat (Triticum aestivum L.) under water deficit. Water deficit was induced artificially by using rain-out shelters in period between booting and late milk ripeness. The effect of growth regulators was evaluated in two contrast years in terms of yield formation (2014-2015). In both years the water deficit caused a significant reduction of grain yield. The negative effect of water deficit was partly alleviated by application of growth regulators. However, the effect of individual growth regulators varied depending on year. In favourable conditions for grain filling (2014) the alleviating effect was more pronounced in application of azoxystrobin which slows down the leaf senescence. On the contrary, in the year with suitable conditions for tillering (2015), the alleviating effect was most apparent in application of chlormequate-chloride. The applications of trinexapac-ethyl and ethephon showed small reduction of negative effect of water deficit consistently in both years. The CO2 assimilation rate and stomatal conductance were recovered particularly by applications of chlormequate-chloride and azoxystrobin. Chlorophyll content and chlorophyll fluorescence parameters were more affected by water deficit in 2014, and the alleviating effect of growth regulators corresponded with yield response.