Evaluation of sugar beet monogerm O-type lines for salinity tolerance at vegetative stage

Abstract

Increased production of sugar beet under rainfed conditions on saline-sodic soils in the Iranian areas highlights the importance of salt tolerant varieties. Screening of genotypes for salinity tolerance is difficult in field due to heterogeneity of physical and chemical properties of soil. In order to evaluate the salinity tolerance of 21 sugar beet monogerm O-types lines, a pot experiment was conducted using a split plot design. The evaluation of plants was performed using 11 morphological and physiological traits at vegetative growth stage under severe salt stress (∼16 dS m-1) and control (0.3 dS m-1) for 8 weeks. Salinity stress significantly reduced weight related traits. The response of genotypes for total weights and stem weights was very similar under both conditions. But, ranking of O-type lines for root weights under normal and stress condition was different. Indeed, there was high significant genotype × treat interaction for two these traits. Cluster analysis by using STI index of all traits allowed the identification of tolerant, moderate tolerant and sensitive genotypes toward salinity. The four salttolerant genotypes, O-type 9669, O-type 1609, O-type 463-2, and O-type 463-5 identified in this study, could be used in the development of salt-tolerant sugar beet varieties. In the second part of this study in order to assess a simple, rapid, and nondestructive method to estimate chlorophyll content, the chlorophyll meter (SPAD 502) readings were recorded and the relation was determined. Regression analysis indicated that there was a significant linear regression between chlorophyll content and chlorophyll meter and about 74% of changes in chlorophyll meter based on chlorophyll content were predicted.

Salt and Drought Stress Responses in Cultivated Beets (Beta vulgaris L.) and Wild Beet (Beta maritima L.)

“…Capability of germination and seedling growth [17,22,25,30,38] Decline in the root weight and root length Higher root/shoot ratio Decline in the root weight and root length Higher root growth [8,34,38,61] Low water content and small leaf area The initial eight-weeks of growth associated with seedling vigor in sugar beet is considered to be the most crucial stage [79], which determines field emergence and stand establishment. Salt and drought stress negatively affect germination and seedling development in sugar beet [4,80] by affecting ionic balance, resulting in hyperosmotic stress and oxidative damage [25,70,81].…”

“…Although different physiological traits have been used to select salt-and droughttolerant beet cultivars, there are no established and universally accepted stress evaluation parameters except for root yield decrease [18,34,40]. Each research group selects the tolerant lines based on different parameters, including germination rate, root length [22,80], root yield, root/shoot ratio, white sugar yield, sugar content, and Na + and K + amounts in the roots [14,25,146].…”

“…So far, chlorophyll content, photosynthetic rate, and CO 2 assimilation have been used as selection criteria in beets [18,19,34,40,53], as it is known that stress conditions damage the most stress-sensitive organelles (chloroplasts) and impact PSII activity and CO 2 assimilation rate negatively [154]. In sugar beet, the decrease in chlorophyll levels caused by stress might be related to ROS production and osmotic stress, leading to pigment degradation, decrease in CO 2 influx, and photosynthesis [40].…”

“…maritima), they can be good sources of stressrelated studies in crops [28,29]. Moreover, isolation of highly salt-and drought-tolerant beet genotypes [16,30,31] and beets' capability of growing in reclaimed lands, which are adversely affected by salt, sodicity, and poor nutrient availability [32][33][34], will help plant breeders to develop stress-resistant traits and propagate the genetic variability in beets. By virtue of its salt stress tolerance, B. vulgaris is an excellent choice for ongoing cultivation in sub-tropical saline soils [35].…”