A laboratory experiment was conducted during 2002-003. The purpose was
to develop an effective and rapid screening tool to assess the genetic variability
for the response of some local barley varieties to polyethylene glycol- induced
osmotic stres
s at early growth stage. Also this will help to evaluate the relevance
of pre-exposure of barley seedlings to sub-lethal (induction) levels of osmotic
stress. This might enhance the capacity of seedlings to tolerate the lethal levels
of stress.
This study was carried out at the Faculty of Agriculture, Damascus
University, and ACSAD during the year 2001 – 2002 in order to assess the
genetic variability of twenty wheat genotypes for osmotic stress tolerance by
using PEG-6000 as a water str
ess induced tool. This trial aimed to develop
a semi-natural rapid and effective screening technique in which the optimum
induction as well as lethal levels of osmotic stress are well defined .
The results revealed that the treatments –0.4 MPa and –1.5 MPa were the
optimum induction and lethal levels of osmotic stress, respectively.
Different experiments were conducted under laboratory conditions, at the
Faculty of Agriculture – Damascus University, in order to develop a suitable
and efficient screening tool, which can be applied to assess the genetic
variability among 20 sor
ghum genotypes (Izraa series) for high salt stress
tolerance.
We were able to develop a screening technique involves pre- exposing
sorghum seedlings to a sub – lethal level of salinity stress (induction stress) (150
mM NaCl) for 16 hrs which can induce the genotypes to prepare defensive
means, which may differ according to the genetic potentiality of each genotype.
These protective responses may help the genotype to endure the lethal level of
salinity stress (400 mM NaCl) for 48 hrs. At a later stage, the seedlings were
transferred to distilled water for 72 hrs and the rate of recovery growth was
taken as a criterion to select the highly salt tolerant genotypes by using Zdistribution
analysis.
Results revealed that genotypes such as: Izraa 10, Izraa 15, and Izraa 18
could be classified as salt tolerant genotypes which showed higher recovery
growth and the least growth reduction over the control. Whereas a genotype
such as Izraa 22 was grouped as salt sensitive one where the percent growth
reduction over the control was greater, indicating that this genotype has low
recovery growth ability.
Our results suggest that the proposed screening technique is rapid, effective,
and match the natural screening.
This investigation is a mimesis to what usually happens in nature, where the
plants are normally exposed to sublethal environmental stresses before their
exposure to the lethal level of stresses.
The gradual increase of environmental stress, gives
plants a suffficient time
to prepare their defensive means to withstand the lethal level of stress. In order
to develope a suitable screening technique, it was essential to determine the
induction as well as the lethal levels of stress, as important components of such
proposed tool.
This technique was applied to screen some tomato genotypes, and assess the
genetic variability among them, in order to evaluate their salinity stress
response , and selecting the highly salt tolerant types.
