Evaluation of osmotic stress test to predict the emergence of lentil (Lens culinaris Medic.) seedlings in the field

Lentil (Lens culinaris Medic.) is one of the most important pulse crops in the world. High protein content in lentil seed (about 20-28%) makes it as a good food source for developing countries and low-income people. In the west of Iran, such as Kermanshah Province, lentil is an important pulse crop of rain-fed systems, traditionally grown in rotation with wheat and barley. Many seed tests have been proposed to evaluation of seed vigor, such as standard germination test, cold test, electrical conductivity test, hiltner test, tetrazolium test, controlled deterioration test, accelerated aging test, osmotic stress test, etc. To osmotic stress test, the seeds germinate at a specific osmotic potential. Osmotic potential is prepared by various chemicals such as sodium chloride, glycerol, sucrose, polyethylene glycol (PEG) or mannitol. Some of these chemicals enter the seed during germination. But PEG has the ability to reduce the osmotic potential of the solution without entering the seed. Therefore, it is often used for osmotic stress test to prepare the solution. Regarding the fact that smotic stress test to predict seedling emergence in the field for common lentil cultivars has not been carried out under dry land conditions of Iran. Therefore, in the present study, the relationship between osmotic stress test and emergence and establishment of lentil seedlings in the field was investigated.

This research was carried out in two experiments in the laboratory and the field at Razi University during 2015. In laboratory, osmotic stress test was done as a factorial based on CRD with three replications. Treatments included eight lentil seed lots and four osmotic stress levels (0, -3, -6 and -9 bar). Eight lentil seed lots belonging to the four cultivars Kimia, Bilesavar, Qazvin and Local which were different in seed age were considered for testing. PEG-6000 solution was used to prepare osmotic potential. The seeds germinated at 20 ± 1 °C. During germination, various traits related to seed vigor were investigated. In the field, eight above mentioned lentil seed lots were planted as rainfed in RCBD with three replications. Each plot consisted of four rows at intervals of 25 cm, seed spacing 2.5 cm and sowing depth 4-5 cm. The seeding date was March 2014. The first rainfall after planting was considered as seeding date. By observing the first emergence of seedlings in the field, the seedlings were counted daily in each plot, and counting continued until the number of seedlings was fixed. In the field, indices related to the seedling vigor were studied.

Analysis of variance for osmotic stress test showed that the effects of seed lot, osmotic potential and their interaction were significant on most traits. Mean comparisons showed that with decreasing of osmotic potential from 0 to -6 bar, the final germination percentage, germination rate and other characteristics related to seed vigor decreased. Analysis of variance and mean comparisons in field experiment showed that the lentil seed lots were different in terms of the traits final emergence percentage, mean daily emergence, mean time to emergence and seedling emergence rate. In orthogonal comparisons of laboratory and field tests, new seed lots had higher germination and emergence characteristics than stored seed lots. Correlation analysis showed that in the osmotic potential 0 bar traits of the use of seed storage, root and stem dry weight; at -3 bar traits of the mean daily germination and the use of seed storage; at -6 bar traits of the mean daily germination, germination rate, normal seedling percentage and the use of seed storage had positive and significant correlations with the seedling emergence percentage in the field. In the osmotic potential 0 bar, traits of the germination rate, seed vigor index, stem length, root and stem dry weight; at -3 bar traits of the final germination percentage, mean daily germination, germination rate and normal seedling percentage; at -6 bar traits of the final germination percentage, mean daily germination, germination rate, normal seedling percentage and seedling vigor index showed higher correlations with the seedling emergence rate in the field.

The highest positive and significant correlations were observed between seedling emergence percentage in the field with the osmotic stress test associated with mean daily germination and normal seedling percentage in -6 bar. Also, the highest positive and significant correlations were observed between seedling emergence rate in the field with the osmotic stress test associated with mean daily germination, germination rate and normal seedling percentage in -6 bar. Therefore, it seems that osmotic stress test at -6 bar can predict the emergence of lentil seedlings in the field under rainfed conditions.