Evaluation of water stress at different growth stages on yield, its components, cell membrane stability and leaf relative water content of grain sorghum (Sorghum bicolor L. Moench) genotypes

Crop yield, including sorghum, is limited under drought conditions, as one of the most important abiotic stresses. Although sorghum can be able to deal with a lot of stress like heat, drought and salinity, but in arid and semiarid areas is usually affected by water stress in the reproductive stage and after the flowering and its yield is reduced. There are significant differences between sorghum genotypes about tolerant to periods of drought stress and reactions to these periods. Some researchers emphasize on the characteristics of flag leaf water relations, especially because of its remarkable interaction with resistance to drought stress. Morphophysiological traits including leaf relative water content widely were used as selection parameter in addition to grain yield for drought tolerance in various crops. In this study, some traits such as cell membrane stability and relative water content and the response of yield and yield components of sorghum genotypes under drought stress treatments (irrigation cut off at vegetative and reproductive growth stage and normal irrigation) were evaluated in field conditions.
In order to evaluate the effect of water stress on grain yield and its components, cell membrane stability and relative water content of leaf (RWC) in sorghum (Sorghum bicolor L.), a field experiment as a split plot design was carried out with 3 replications in 2014 at the research farm of the southern khorassan Agriculture and natural resources research and education center. Water stress treatments including normal irrigation (control), irrigation cut off in vegetative growth stage(emergence of terminal leaf as rolled) and irrigation cut off in generative growth stage(50% of plants in start of flowering) as the main plot and 10 genotypes of sorghum including KGS29, MGS2, Sepideh, KGFS27, MGS5, KGFS5, KGFS17, KGF13 and KGFS30 was considered as sub plots. To determine the yield components, half a meter in length of each plot was harvested and the number of plants, number of panicle, grain weight, and number of seeds per panicle were recorded. To determine the yield and biological yield and harvest index after the removal of 2 and a half meter of margin line and beginning and end of each plot, plants was harvested from the surface of 3 square meters, after drying, biological yield of each plot was determined. To calculate the relative water content (RWC), flag leaf samples were taken from each plot and the samples were weighed immediately and then refrigerated for 24 hours in distilled water untill their full swelling, then the excess water was taken by tissue paper and then put into the oven at 72 ° C for 48 hours. After drying, the samples are weighed and leaf relative water content was calculated through wetherley formula (wetherley). To calculate the amount of damage to the membrane or membrane permeability, three plants of each plot were randomly selected and their flag leaf were removed. Then 4 discs of the leaves prepared was puted in distilled water for 24 hours at refrigerator temperature (4 ° C). Electrical conductivity of water in wich leaves had been laid was measured by the electrical conductivity meter (EC meter) and resulting values were used for calculations. After collecting data on yield and its components, simple analysis of variance was done using SAS software. The means comparison was done using LSD test at the 5% probability level.
Results showed that water stress had significantly effect on grain yield, biological yield, harvest index, 1000 seed weight and seed number per panicle, cell membrane permeability and Relative water content of leaf and caused to decrement of Them. The grain yield reduction was about 42% at the highest level of water stress in comparison with the control. Also the genotypes were significantly different about all above characteristics. The genotype KGFS13 had the highest grain yield, biological yield and harvest index. Interaction between water stress and genotype showed significant effect on all traits except for 1000 seed weight and cell membrane permeability. The highest value for (RWC) was belonging to severe water stress. Also with increase of water stress, cell membrane leakage increased, as the lowest value of cell membrane leakage and therefore the highest membrane stability was belong to normal irrigation and the lowest membrane stability was commonly belong to medium and severe water stress.
There are significant differences between sorghum genotypes about tolerant to periods of drought stress and reactions to these periods, also grain yield and its components, biological yield, harvest index, relative water content and cell membrane stability were different between genotypes and water stress treatments. Generally, water relations in flag leaf and cell membrane permeability can be used as criteria for assessment of drought tolerance as well as grain yield.