Calibration of accelerated aging test as a vigor test to predict the seedling emergence of chickpea (Cicer arietinum L.) in field conditions

International Seed Testing Association (ISTA) defined seed vigour as "the sum of those properties of the seed which determine the level of activity and performance of the seed or seed lot during germination and seedling emergence". In any seed lot, losses of seed vigour results in the reduction of the ability of seeds to carry out all the physiological functions that allow them to perform. This process, called physiological ageing, starts before harvest and continues during harvest, processing and storage. Any given seed vigour test must be able to provide a more sensitive index of seed quality than the germination test and provide a consistent ranking of seed lots in terms of their potential performance. It must also be objective, rapid, simple and economically practical, reproducible and interpretable. Internationally, many vigour tests have been proposed such as standard germination test, cold test, electrical conductivity test, hiltner test, tetrazolium test, controlled deterioration test, accelerated aging test, etc. The accelerated aging test provides valuable information on storage and seedling field emergence po¬tentials. In the accelerated aging test, seeds are hydrated to a specific level when ex¬posed to relatively high temperature (40 to 45 oC) and humidity (around 100 % relative Humidity). Following this aging treatment, seeds are subjected to a germination test and higher vigor seed lots tolerate this aging condition better than lower vigor seed lots and produce a higher percentage of normal seedlings. In this study, chickpea seed lots were exposed to different temperatures and durations in order to calibration of accelerated aging test to predict the seedling emergence under field conditions.
This research was conducted as two laboratory and field tests at Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran, in 2012. In the laboratory test, accelerated aging treatments (temperature and duration) including 41, 43, and 45 oC and duration 0 (control), 48, 72, 96, 120, and 144 h were performed on 13 chickpea seed lots. Following this aging treatment, seeds were subjected to standard germination test and different traits (including final germination percentage, mean daily germination, daily germination speed, germination rate, germination index, seedling vigor index, and efficiency of seed storage usage) were evaluated. Theses 13 seed lots belonged to both kabloli (Hashem, Azad, ILC-482, Bivanij, Arman cultivars) and desi (Kaka and Pirooz cultivars) types. In the field tests, these 13 chickpea seed lots were planted as a randomized complete block design with four replications. In field test, different seedling traits (including final emergence percentage, mean time to emergence, mean daily emergence, daily emergence speed, emergence rate, and field emergency index) were evaluated. Finally, correlation of different traits related to seed vigor in the laboratory test was determined with percentage and rate of seedling emergence in the field.
Analysis of variance in the laboratory test showed that the effects of seed lots, accelerated aging treatments and their interaction were significant on all above mentioned traits except for efficiency of seed storage usage. Different levels of accelerated aging treatments had significant effects on germination characteristics, so that germination characteristics were decreased with increasing of temperature and duration in accelerated aging test. In the field test, chickpea seed lots were different significantly in most seedling traits. Means comparison of laboratory and field experiments showed that the new seed lots had higher germination and vigor characteristics than the old seed lots. Correlation analysis showed that, shoot dry weight in the accelerated aging test under 43 oC , 48 h and root length under 43 oC, 72 h had the highest correlation with seedling emergence percentage in the field test. Root length under 41 oC, 72 h and shoot dry weight under 43 oC, 72 h had the highest correlation with seedling emergence rate in the field test, too.
It seems that accelerated aging test is recommendable to predict the seedling emergence of chickpea in field conditions. The accelerated aging test under 41 oC, 72 h and 43 oC, 48 h had the highest correlation with both percentage and rate of seedling emergence in the field test.