Hi

We have to measure and report stress effects in different stage of plant growth. Sometimes one stage is more sensitive and other stage is tolerant. In general seeds are more tolerant in germination stage than emergency in the soil or other substrates. For example black cumin seed germinated in 20dS/m but in 10dS/m dried. Thus we have to treat from first day if we want to measure germination ability.

Hello Yousef, If I understood your question well, it depends if you are looking for a general genotype adaptability (seed germination tolerance in salt, PEG, etc.) or if you are looking on Genotype x Environment adaptability (plants have to be older and cultivate in more "natural" conditions). According to my research, there is some correlation between germination rate or rapeseed in stress conditions to the response of plants in the field, but very low...Generally you can say, that higher germination rate (not only total germination!!!) is connected to better adaptability (I think "tolerance" is not the right word) of plant in later stages of development or in field conditions...So, what you are looking for?

Dear Milan Oldřich Urban,

Hi and thanks for your answer.

As you know, Some of researchers use of PEG in the first day of planting with water, but some of researchers use of that after 3 or 4 day of planting in petri dish and in laboratory.

Now i mean is, which of ways is true? we must use of stress condition in the firs day of planting or some days after planting in germination level?

Dear Dr Yousef Alaei,

I would like to thank you for your question. Their are different kinds of drought tolerance mechanism. 

you could determine the germination stage (germination percent with different % of PEG), or at seedling stage. You can germinate the seeds till have good seedling and then start do the treatment (stress) after one-two weeks and after that determine the seedling traits at control and different stress conditions

with best regards

Khaled

Mechanism of drought tolerance

Drought tolerance in wild plant species is often defined as survival, but in crop species it is defined in terms of productivity (Passioura, 1983). Rosielle and Hamblin (1981) defined drought tolerance as the difference in yield between stress and non-stress environments, while productivity is the average yield in stress and non-stress. A different definition regards drought tolerance as minimization of reduction in yield caused by stress compared to yield under non-stress environments (Fischer and Maurer, 1978; Langer et al., 1979; Blum, 1983a; Blum, 1988). Also, it is defined as the relative yield of a genotype compared to other genotypes subjected to the same drought stress (Hall, 1993). Drought tolerance comprises drought escape, dehydration avoidance and dehydration tolerance mechanisms (Blum, 1988).

Now I hope understand better to you question. DEFINITIVELY {if we are still talking about seed germination}  I will use the stress till the VERY BEGINNING, because you are probably looking for a genotype based response to stress. Imagine how it work in the field! There is no lack in stress, if the salt is present in the soil, the seed has to overcome the osmotic potential till the very first moments. I know that for example rapeseed is germinating in 18-19% PEG 4000, but not in 20%! Also temperature is very important, because viscozity changes the osmotic potential of solution. Also seed has to be in very good contact with the filter paper /but be sure about the paper quality, because in some papers there is to many of calcium which can promote germination!!!/ and seed sterilization is the MOST important thing of all! The seed has not to be long in the sterile water during sterilization and definitively not long in chlorox (sodium nitrate) solution. The better is to use vapours from concentrate chloric acid (but I am not sure, how to do this, sorry), because vapours contain almost no humidity!

So, definitively, start your stress condition at the very beginning of your experiment and you will be sure about you results, if you are looking for genotype differences. But of course in higher osmotica concentration, seed will germinate, but then suddenly die or are necrotic or malformed. The seedling are very sensitive to every changes, and you still have to know, that there is a strong maternal effect on every physiological response in very small seedlings and correlation to the field conditions can be really confusing...

Prior to planting seed, a usual practice for germinating seed is imbibe in water.  So, the effect of drought on seeds germination should be monitored commencing from just after transplantation into various drought level growth media.  

Dear Dr. Adiputra, your response  with imbibition in water can be tricky for these genotypes which need lesser amount of water to shift from anaerobic to aerobic phase of germination (there are big differences in rapidity of germination even within one specie or cultivar). In PEG solution, there is still a lot of water for imbibition so you can miss the pure water imbibition. Otherwise, your results are based on pure water imbibition instead of "drought-related" adaptation. However prior imbibition in pure water first can be really useful for beans and other big seeds, which need to absorb more than 200% of water their original weight just to start germinate...Also, I recommend use not only total germination rate, but more rapidity of germination (based on sum of daily germination). To complete this test, some heavy agar solution (more than 10% of agar in solid media) can be used to verify the root penetration ability which can be taken as a general genotype-based response to lack of water-media.

Dear Researchers,

For Example: We want to study the drought stress with use of PEG in germination indices in wheat plant.

So We have 2 condition's; Normal (Water) and drought stress (PEG).

As you know all of seeds will germinate maximum in 10-14 days, if we want to add the PEG to petri dishes, of course the seeds can not be start to germination completely.

Also, i want to know, this way is correct way and method? Or not, we must use of PEG after 4 days and give the permission to start the germination then add the PEG?

Thanks Again for your answers

Dear Youssef;

there were several talks about that. You can do both - one will measure the ability of your seed to germinate in a  high stressing environment. The other the capacity of growing in  a water deficient environment.

 If you use a osmotic agent as PEG your seeds, depending on the concentration, will not germinate or they will delay that.

My single suggestion is to germinate in water, an at he first signs of germination to transfer to the treatments, if possible in a place where the water content do not vary by evaporation.