General Commission for Scientific Agricultural Research- Administration of Crop Research
Damascus University, Faculty of Agricultural
Forty genetically different sorghum [Sorghum bicolor (L.) Moench] genotypes were screened for salinity stress tolerance at early growth stage, using a rapid and efficient screening tool, which has been established under laboratory conditions.
Based on that suitable screening technique, five sorghum genotypes (IZRAA-15, IZRAA-18, LOCAL-26, LOCAL-29, GIZA-123) were highly salt tolerant, and three (IZRAA-14, IZRAA-19, ICSV-115) were highly salt susceptible in order to study the mechanism of salt stress impact on sorghum genotypes, and evaluate the response of such genotypes based on some morphological, physiological, and biochemical parameters, during four phynological plant stages (germination, early seedling /48h/, early plant growth /49 days old/, and adult plant stage under field conditions).
Germination and early seedling studies were conducted in petri dishes, under controlled condition, whereas hydroponic culture for early plant growth stage was carried out under greenhouse condition in plastic containers using Hoagland solution, to which different salt (NaCl) concentrations 0, 50, 100, 150 mm were added.
The performance of few selected genotypes was evaluated under stressed field conditions in two successive years (2001-2002).
The experiments were designed in RCB design, with three replications for the laboratory assessment, and two replications for the field study.
The salient research findings are as follows:
The proposed screening tool at seedling stage is considered a rapid and efficient technique, which can be used to assess the genetic variability for salinity stress tolerance among sorghum genotypes.
There was a strong positive correlation (r=0.816**) between the root length reduction at seedling stage and field grain yield, and the grain yield of positive correlated (r=0.772**) with the percent reduction in the seedling length.
These results assure the reliabilities of such a screening tool.
The sorghum genotypes such as, IZRAA-18, LOCAL-26, LOCAL-29 and GIZA-123 are classified as highly tolerant ones and they are advisable to be grown in the salt affected soils, while the genotypes, such as ICSV-115 was grouped as a high susceptible one for salinity stress conditions.
Increased salinity level in growth medium caused harmful effects on germination percentage, root, shoot, and plant length for the tested sorghum genotypes, due to significant decreases in water uptake by root, relative water content, increase in water saturation deficit, reduced leaf area / plant, leaf area ratio (LAR), relative growth rate (RGR), net assimilation rate (NAR), total chlorophyll (a+b) content, root and shoot dry matter accumulation.
All these, were accompanied with high accumulation of Na+ ions, a decrease in K+ ions, and a decrease in selectivity ratio of K+ / Na+.
Organic solutes compounds (sugar, free amino acid and proline) content were differentially increased in sorghum genotypes, through the early plant growth stage.
Plant growth was negatively affected due to increasing soluble salts in irrigation and soil solution, which induced the early flowering process.
Plant height, panicle length and grain yield (ton/ha) were significantly reduced, under salt-affected soil conditions compared with control.
Sorghum genotypes showed some differences in their responses to salinity stress, with respect to different traits such as germination percentage, root length, leaf area, and net assimilation rate (NAR), K+/Na+ selectivity rate and proline content.
Relative grain yield may be considered as a selection criterion, highly associated with salinity tolerance.
These characteristics may be considered as selection criteria for screening and evaluating the response of accessions and genotypes for salinity stress tolerance.