Lettuce (Lactuca sativa L.) seed quality evaluation using seed physical attributes, saturated salt accelerated aging and the seed vigour imaging system

Patricia Peñaloza*
Departamento de Hortalizas y Flores
Facultad de Agronomía
Pontificia Universidad Católica de Valparaíso
Quillota, Chile
Tel: 56 32 274512
Fax: 56 32 274570
E-mail: ppenaloz@ucv.cl

Gerardo Ramirez-Rosales
Department of Horticulture and Crop Science
The Ohio State University
Columbus, OH 43210-1086 USA
E-mail: gramirez@sakata.com

Miller B. McDonald
Department of Horticulture and Crop Science
The Ohio State University
Columbus, OH 43210-1086 USA
Tel: 61422929003
E-mail: mcdonald.2@osu.edu

Mark A. Bennett
Department of Horticulture and Crop Science
The Ohio State University
Columbus, OH 43210-1086 USA
E-mail: bennett.18@osu.edu

*Corresponding author

High seed quality is essential for optimum stand establishment in lettuce. Seed quality assessed by physical and physiological vigour tests (McDonald, 1999), provides information on the growth potential of the crop. The standard germination test is still the most commonly used evaluation of seed quality. An ideal seed quality test should efficiently separate the good seed lots from the poor seed lots (Trawatha et al. 1990). The problem that arises is how to predict the future performance of the seed under field conditions, as these tests normally use fresh seed, but commercial seed often undergoes a storage period prior to its sale. The exposure of the seed to high relative humidity (99%) and high temperature (41ºC), occurs in a test known as the Saturated Salt Accelerated Aging (SSAA) (Jianhua and McDonald, 1996; McDonald, 1999), which makes possible a prediction of seed quality after storage. However, these tests are time-consuming and are subject to human error, thus automated systems are being developed to use computer tools like the Seed Vigour Imaging System (SVIS) (Sako et al. 2001; Hoffmaster et al. 2003). The SVIS is used to assess a quality component known as vigour the capacity of the seed to perform well under non-ideal conditions. As of yet, there have been no publications on comparisons of SVIS against other vigour tests or with actual greenhouse performance in lettuce. Physical characteristics, such as seed coatcolour, have also been associated with seed quality (Karivarhadaraaju et al. 2001). Additionally, seed size is another physical aspect associated with seed germination performance, root and hypocotyl development (Liu et al. 1993; Soltani et al. 2002).

This study compares the physical attributes of lettuce seeds with seed quality tests: percentage germination, SSAA, SVIS, and seedling emergence under greenhouse conditions. Using SVIS we were able to determine the speed of growth and uniformity of hypocotyl and radicle length. Seedling emergence was quantified in the greenhouse. All of these variables were correlated using statistical software, comparing 6 lettuce varieties and a total of 24 seed lots.

We found that large-seeded lettuce varieties have higher percentage germination, higher SSAA values, higher SVIS index and more rapid and uniform greenhouse emergence (Table 1). No correlation was found between seed shape and quality.

As seen in Figure 1, among the six varieties evaluated, there were differences in seedling length and uniformity. Growth responses of seedlings in the greenhouse could not be predicted from the germination percentages measured in the laboratory, but were correctly identified by the SSAA test (Table 5 and Table 6). These results emphasize the necessity of using stress-imposing treatments on predicting seed vigour (Hacisalihoglu et al. 1999). The agronomic significance of the SVIS index was more closely related to the number of emerged seedlings and seedling growth (Table 3), as described by Trawatha et al. 1990 for seed performance under field conditions.

References

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