Assessing the ability of osmotic stress test to predict emergence and establishment of chickpea (Cicer arietinum L.) seedlings in the field

Introduction
Chickpea (Cicer arietinum L.) is the most important pulse crop of rainfed systems, traditionally grown in rotation with wheat and barley in the west of Iran. Since the seed is the most important inputs in agriculture, it has the largest effect on increase or decreases the crop yield, so using of high quality seeds is very important. The vigorous seeds can germinate better and have higher germination and emergence percentage in exposure to environmental stresses and eventually produce more powerful seedlings (Salehian, 1996). The rate and percentage of seedling emergence are important factors that affect on plant density, plant growth rate, and finally crop yield in farm (Hussain et al., 2006; Begnamy and Cortelazz, 1996). Different laboratory tests has been proposed to determine the seed vigor such as accelerated aging test (Hampton et al., 2004), the electrical conductivity test (Khavari et al., 2009), cold test (Noli et al., 2008), osmotic stress test (Hampton and TeKrony, 1995), and etc. In osmotic stress test, seed is germinated in exposure to osmotic potentials prepared using poly-ethylene-glycol (PEG) or mannitol (Hampton and TeKrony, 1995). PEG is a neutral polymer available in a range of molecular weights, highly soluble in water and with low toxicity (Slama et al., 2007). Because of these properties, it has been used by several investigators to impose water stress in plants by decreasing the water potential. In this experiment, ability of osmotic stress test using PEG, as a laboratory seed vigor test, was studied to predict emergence and establishment of chickpea seedling in field.
Materials and Methods
The experiment was done at Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran, during 2012. The experiment was conducted under two conditions including laboratory and field. In laboratory experiment, 13 chickpea seed lots were germinated under osmotic potential -6 bar using PEG-6000. Different germination characteristics such as final germination percentage, germination rate, germination index, root and shoot length, root and shoot dry weight, and seedling vigor index were measured. In field experiment, these 13 chickpea seed lots were planted and seedling characteristics such as final seedling emergence percentage mean daily emergence, seedling emergence rate, and seedling emergence index were measured. The correlation coefficients of germination characteristics in laboratory test with the percentage and rate of seedling emergence in field experiment were evaluated.
Results and discussion
The results showed that, under both laboratory and field conditions, seed lots were different in seed germination and seedling emergence characteristics. Orthogonal analysis showed that the new seed lots had higher germination and emergence characteristics than the old seed lots under both laboratory and field conditions. The seed lots belonged to Desi type had higher germination and emergence characteristics than the Kabuli type, too. The correlation analysis showed that there was positive and significant correlations among seedling emergence percentage in field with shoot length and shoot dry weight in laboratory test. There was, also, positive and significant correlations among seedling emergence rate in field with shoot and root length, shoot weight and seedling vigor index in laboratory experiment.    
Conclusions
Correlation between some traits in laboratory test and field experiment shows that the osmotic stress test has ability to predict percentage and rate of seedling emergence in the field up to 30%.