عنوان مقاله [English]
In order to investigate the relationships of some morphological traits at the early stages of three sugar beet cultivars with final yield at varying levels of water regines, a field experiment was carried out in Karaj, and Mashhad, in 2001-2003. The objective of this study was to find the relation of some morphological traits of three sugar beet genotypes (7219-P.69, BP-Karaj and 7112) during the growing season with final yield traits such as root yield (RY), sugar content (SC) and white sugar yield (WSY) where plants were subjected to severe continuous water stress, moderate stress and nonstress conditions. The experimental design was split block with three replications. The continuous water stress gradient was applied from plant establishment onwards by using a line-source sprinkler irrigation system. Soil water content at the depth of 0-100 cm were determined byTDRand the amount of water received by each treatment recorded during the growing season. Morphological characteristics such as shoot dry weight (SDW), root dry weight (RDW), total dry weight (TDW) and SDW/ RDW ratio at three growth stages and yield and quality of sugar beet at final harvest were determined by destructive sampling. Total water used in nonstress, moderate stress and continuous stress conditions were 814, 635 and 363 mm, respectively. The results showed that RY reduced from 51 t ha-1 in normal irrigation by 24% and 57% in moderate and continuous water stresses, respectively. Similarly, WSY reduced from 6.73 t ha-1 in normal irrigation condition by 26% and 59% in moderate and continuous stresses, respectively. The response of RY and WSY of beet genotypes to water stress differed when the severity of water stress was changed. Thus, the intensity of water stress is a very important factor in the evaluation of sugar beet germplasm under drought stress conditions. There was a positive correlation (r= 0.91, P< 0.01) between the number of leaves and WSY and a negative correlation (r= -0.90, P< 0.01) between WSY and specific leaf weight. In terms of root characters, there were positive correlations (r= 0.86, P< 0.01) of root length and root diameter with WSY at final harvest. There was a negative correlation (r= -0.83, P< 0.01) between shoot: root ratio and final WSY. Thus, some morphological traits of sugar beet during the early growth stage may be useful for plant breeders to predict the genotypic productivity of sugar beet in a breeding program of drought tolerant variety. However, in order to obtain conclusive results additional studies with a larger number of genotypes are required.