Radiography is a simple and nondestructive technique to detect empty, immature, and insect- and mechanically damaged seed during seed processing and testing. However, there is a lack of information on the effect of X-ray on seed quality despite recommendations by the Association of Official Seed Analysts for testing agricultural and forest tree seeds since 1979. Two experiments were carried out using lettuce seed of Seed Dynamics, Inc. (No. 52694) and Faxitron MX-20 cabinet X-ray unit set at 20 kilovoltage (kV) for 20 seconds, a standard setting to observe many species of flower seeds. In both experiments, the focus-object distance was 34 cm with no image magnification. The treatments in Experiment 1 were 0 (control), 4, 8, and 12 times of X-ray exposures and Experiment 2 were 0 (control), 15, 30, and 60 times of X-ray exposures on non- and 5-hour imbibed seed. In Experiment 1, germination was done in 288-cell seedling trays in soilless potting mix under greenhouse conditions with four replications of 50 seeds per replicate to observe germination rate, and cotyledon and young leaf discoloration and deformation. Experiment 2 was analyzed using computerized seedling imaging system on germination paper to examine seed vigor and germination rate. There were no significant differences in germination rate in both the non- and imbibed seed in the two experiments. The mean germination rates were 77.75% in Experiment 1 and 94.81% in Experiment 2. No cotyledon and young leaf discoloration and deformation were observed in Experiment 1 and no significant differences in vigor index were found in Experiment 2. The conclusion is that there was no observable effect of repeated X-ray exposures up to 60 times at 20 kV and 20 seconds on a seed lot for both non- and imbibed lettuce seed.
During the past 2 decades, automated plug production in the flower seed industry has created important requirements by growers for high-quality flower seeds. Using computerized imaging technology, a new seed vigor testing system, Seed Vigor Imaging System (SVIS), was developed at The Ohio State University. By analyzing the digital images of seedlings, it can detect and measure the length of hypocotyls and radicles separately, and then generate a value for the growth and uniformity each. This system provides a fast, labor-saving and objective approach to measuring seed quality. In this study, its capacity and correlation with field performance was studied and compared with other traditional tests, i.e. standard germination test, germinate rate, and accelerated aging test. Five species (dianthus, cleome, rudbeckia, salvia, and lettuce) were selected and their quality was tracked continuously by SVIS and other mentioned tests. It was found that stressed test (ageing test) was able to detect the quality deterioration earlier than others under ideal conditions, but SVIS could generate much more information, such as the growth, uniformity, and vigor level of the seed lot. Therefore, SVIS following 3-day ageing was developed and shown to be the most sensitive and comprehensive vigor test for those ornamental species mentioned above. Being fast and objective, this system will also benefit the global seed trade by providing a unique quality standard. In addition, it can also be of great usage to seed companies and germplasm centers worldwide for the routine quality track during shipment/storage and inventory management.