Tolerance of some sugar beet varieties to water stress

Tolerance of three of sugar beet multigerm varieties: Zwanpoly, England; Halawa, Germany and Heba, Denmark, and two monogerm varieties: Xanadu and Marathon, Denmark to water stress levels of 30, 50 and 70% of field capacity (F.C) which were studied during 2013/2014 and 2014/2015 seasons in the experimental station, Faculty of Agriculture, Cairo Univ., Giza, Egypt. The variety Xanadu produced the highest values of the studied growth traits as dry matter accumulation, chlorophyll content, leaf area index (LAI), relative growth rate (RGR) and net assimilation rate (NAR) at 125, 150, 175 and 200 days post planting as well as root, top and sugar yield, and were of the most tolerant variety according to stress tolerance index (STI), followed by Zwanpoly, Halawa, Heba and Marathon variety in a descending order. Whereas, Marathon was of the highest variety in sucrose, purity and sugar recovery (SR) percentages. Increasing water stress level from 30 up to 70% from F.C was significantly decreased beet growth throughout the growing season. Juice quality (sucrose, purity and SR%) significantly increased as water stress increased up to 70%, while juice impurities and sucrose loss to molasses% (SLM) decreased. A reduction in root yield of 13.6 and 15.6%, sugar yield was obtained by 7.5 and 11.5% and top yield by 14.9 and 36.5% in the 1st and 2nd seasons, respectively which were recorded as water stress levels increased from 30 up to 70%. The highest value of WUE for root and sugar yield where obtained for Xanadu variety at 70% of water stress level.