In seed lots with high viability, the ability to produce usable seedlings under less than optimal germination conditions is related to seed vigor. Thus, seed vigor testing is an essential tool used to evaluate commercial seed lots. The most common vigor tests are based on germination behavior (Hampton and TeKrony, 1995). These include normal germination percentage after a stress imposition, germination speed (time to radicle protrusion), and early seedling growth following germination. Tests that measure germination speed or seedling growth appear to have the widest adaptability across the large number of commercially grown small-seeded flower species.
Germination speed has been used as an indicator of seed vigor, especially in seed priming experiments (Geneve, 2005), and it is an important measurement used to model seed germination (Bradford, 1990). However, the actual time of radicle protrusion can be difficult to determine accurately because time intervals between evaluations is limited by the technician's time and can be as long as 24 h.
Seedling growth is measured as length, area, or dry weight at periodic times after imbibition. Vigor tests for seedling growth usually require growing seedlings on a slant-board to generate straight seedlings that are hand measured by an analyst (Smith et al., 1973). It has been used successfully to test vigor in a number of small-seeded vegetable crops (Finch-Savage, 1986; McCormac et al., 1990; Perry, 1981; Smith et al., 1973). These studies have established a strong correlation between radicle growth and seed vigor (Bingham et al., 1994). Woodstock (1969) concluded that seedling growth rate is a sensitive measure of seed vigor but is difficult to incorporate in routine vigor testing because it is too labor intensive to evaluate seedling growth over time.
Germination speed and early seedling growth are key parameters for describing seed lot quality beyond standard germination. However, the fundamental relationship between those seeds that germinate rapidly and their subsequent early seedling growth has not been studied in detail due to the limitations of accurately and repeatedly evaluating these parameters. Use of computer-aided digital imaging of seed germination has overcome some of these limitations for evaluating seed germination (McDonald et al., 2001). A process for nondestructive, repeated measurements of individual seeds (seedlings) would enhance the ability to study these two measures of germination. Therefore, the objective of this research was to develop a sequential imaging system to evaluate seed germination and seedling growth on an individual seed basis. Sequential imaging was used to evaluate the relationship between germination speed and seedling growth rate on a population and an individual seed basis in seed lots of different vigor.
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