Effects of drought stress on quantitative and qualitative characteristics, canopy ground cover and wilting score of sugar beet genotypes

Introduction Water stress is considered as one of the most widespread limitations to crop productivity and yield stability. In sugar beet, drought causes yield reductions between 10 and 30 %, which is increased in arid and semiarid regions. A solution is to improve the drought tolerance of sugar beet varieties and to identify sugar beet germplasm that is drought-tolerant and high yielding so that it can be included in future breeding programmes. Materials and methods To evaluate the effects of drought stress on qualitative characteristics of sugar beet including sugar content, Na, K, N, alkalinity coefficient, molasses sugar, root dry matter, canopy ground cover and wilting score of 36 sugar beet genotypes, a study was conducted in split plot based on randomized complete block design with three replications in Kamal-Abad station in Sugar Beet Seed Institute, Karaj in 2012. Main plots were allocated to two irrigation systems including normal and water stress and sub-plots were assigned to sugar beet genotypes including 29 o-type lines, developed from 7221, 110 and 111 seed bulks (BC1F2), as well as susceptible and resistant controls. Class A evaporation pan was used to measure evaporation. Irrigation was conducted after 80-90 and 270 mm evaporation from evaporation pan under normal and stress conditions. Each plot consisted of one planting raw with 8 m length and an interrow spacing of 0.5 m. During the growing season, number of plants after establishment, growth score, and growth uniformity were recorded. Canopy ground cover, wilting score and plant death were measured in three stages. Canopy ground cover was measured using a 0.25 m2 quadrat and wilting and senescence scores were measured at 11-13 am. Qualitative characteristics such as sugar content, white sugar content, sodium, potassium, nitrogen, alkalinity coefficient, molasses sugar and root dry matter were measured at harvest. Results Drought stress and genotype had significant effect (P< 0.01) on canopy ground covering. With increasing irrigation frequency from 90 to 270 mm evaporation, drought stress reduced canopy ground cover from 57 to 38% and accelerated the green ground cover reduction from 81 to 67 days after sowing. Drought stress, scoring time, and their interaction had significant effect on wilting score but no significant effect was observed among genotypes. Under normal condition, 116 days after planting, wilting score increased 97% compared with 87 days after planting. However, under stress condition, 87 days after planting, wilting score increased 51% compared with 116 days after planting. In addition, drought stress increased senescence score (1.90) as compared to normal conditions (1.54 and 1.50, respectively). Furthermore, sugar content and white sugar content were decreased by 33 and 43%, respectively whereas root Na content and molasses sugar were significantly increased by 23 and 13%, respectively. Conclusion With consideration of all qualitative indices including sugar content and white sugar content, root impurities, alkalinity coefficient and molasses sugar, genotypes 1 and 30 for all six traits, and genotypes 10, 28, 31 and 33 for five traits, and genotypes 8, 12, 27, 34, and 35 for four traits had more optimum level than the other genotypes.