Viola is a popular bedding plant. The relatively high initial cost of flower seeds has led growers to use precision seeding and transplant production systems to maximize seedling stands (McDonald and Kwong, 2005). Maximum efficiency in plug production to obtain optimum seedling emergence and uniformity requires high-quality seeds. Germination tests are used to evaluate the production of normal seedlings under optimal germination conditions (Atwater, 1978; Geneve, 2008). However, these do not always reflect the emergence potential of a seed lot under greenhouse or field conditions. Conditions in the transplant production environment are also not always ideal. Such environmental conditions may also vary depending on the season of sowing in flower seeds, e.g., summer sowing for fall planting or winter sowing for spring planting. Vigor tests help determine failures in emergence and stand establishment and identify the level of physiological aging of a seed lot and its potential for the development of normal seedlings under a wide range of sowing conditions (McDonald, 1975). Tests are widely used in a number of agronomic and vegetable crops (Hampton and TeKrony, 1995), but information in flower seeds is scarce.
Accelerated aging is a well-established vigor test used for large-seeded agronomic crops (Association of Official Seed Analysts, 2009; TeKrony, 1995). In this test, seeds are subjected to high temperature (41 to 43 °C) and relative humidity (100%) over a few days (72 h) to induce aging, and subsequently evaluation is done by a standard germination test. The AA test is correlated with field emergence and storage longevity of various crop seeds (Association of Official Seed Analysts, 2009; TeKrony, 1995). However, AA conditions cause a rapid increase in seed moisture in small-seeded crops because of high relative humidity (RH) in the chamber. High RH stimulates fungal infection. High seed moisture content and storage fungi can influence aging level and variation among seed lots. To eliminate these undesired aspects of AA, Jianhua and McDonald (1996) proposed a SSAA test in which the RH of air that seeds are aged under is controlled by saturated salt solutions. They concluded that an aging environment of 41 °C for 48 h with KCl and NaCl, which provide 87% and 76% relative humidity, respectively, best predicted seed vigor for impatiens seed lots. McDonald (1997) suggested 41 °C for 72-h SSAA conditions for pansy seeds. He also showed that the SSAA test was repeatable among seed testing laboratories. SSAA conditions also prevented fungal disease development during the aging period (Hyatt and Tekrony, 2008). Time to radicle protrusion and seedling size were also successfully used to rank petunia and impatiens seed lots (Dutt and Geneve, 2007). However, although such studies used the vigor tests to rank the seed lots, they did not correlate vigor test results with emergence or storage potential in flower seeds. Transplant production in viola is particularly sensitive to environmental stress conditions in the greenhouse (Carpenter and Boucher, 1991; Yoon et al., 1997). Viola seeds were described as microbiotic and may lose viability within a year (Corbineau and Côme, 1991). Therefore, vigor information regarding seedling emergence in plugs and storage potential of any viola seed lots is valuable. This was designed to evaluate the use of AA, SSAA, mean germination time vigor tests for estimating seedling emergence, and storage potential of viola seed lots.
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