Impact of nanosilicon and tebuconazole foliar application on some physiological traits, growth and white sugar yield of sugar beet under drought stress

There is ample evidence to illustrate the role of triazoles and silicon in mitigating the effects of abiotic stresses. However, the potential of nano-silicon and tebuconazole and their possible interactions in ameliorating the effects of drought stress and related mechanisms in sugar beet have not been investigated so far. Therefore, a split-plot factorial experiment based on randomized complete block design with four replications was carried out at Motahari Research Station of Sugar Beet Seed Institute (SBSI), Karaj, Iran over two seasons, 2016 and 2017. Three irrigation treatments including 100, 75, and 50% of plant evapotranspiration (normal, mild stress, and severe stress, respectively) were assigned to the main plots. Subplots were composed of a factorial combination of three nano-silicon doses of 0, 1 and 2 mM and two tebuconazole doses of 0 and 25 mg l-1. The results showed that under severe drought stress, the effect of nano-silicon on the studied traits was dose-dependent, so that the application of nano-silicon with 1mM concentration improved growth parameters as well as physiological traits and increased white sugar yield and the maximum dry matter by 20 % and 17%, respectively compared with severe drought stress treatment. Under severe drought stress condition (irrigation at 50% of plant evapotranspiration), the highest leaf area index, chlorophyll and relative water content were observed in 1 mM nano-silicon treatment. Under severe drought stress, foliar application of 2 mM nano silicon had an adverse effect on sugar yield. The combined application of nano-silicon and tebuconazole improved dry matter production and sugar yield by maintaining plant greenness and preventing leaf aging which may indicate an interaction between these two compounds. These results indicate that nano-silicon and tebuconazole can be used as a suitable tool to mitigate the effects of drought stress on sugar beet.