N. E. Cheatham
For wildflower seed growers, it is important to be able to provide top-quality seed. Seed testing is a good way for growers and buyers alike to obtain information regarding seed quality.
Wildflower seeds can be tested for a variety of qualities and characteristics. The Pure Live Seed (PLS) measurement is often the most important indicator of seed quality, because it is based upon the combined measurements of seed germination and seed purity (Johnson, 2001). Purity percentages and germination percentages are multiplied together then divided by 100 to give the PLS percentage. For example, if the germination percentage of a sample is 75% and its purity percentage is 80%, then ([75x80]/100) = 60% would be the PLS. This gives the percent of germinable seed by weight. Multiplying by the number of pure seed/unit weight gives you the number of PLS which is important in calculating planting rates.
Seed germination tests calculate the chance that a seed will produce a plant under optimum growing conditions. Germination percentage is measured by the combination of the percentage of seeds that germinate in a batch and how quickly they germinate (Seed Testing - USDA Forest Service). Higher germination percentages generally indicate higher quality seed (Johnson, 2001). For quality control purposes, seeds should have a minimum live seed or germination percentage of at least 75%, but could vary depending on the wildflower specie (Parris, Shock, Feibert, & Shaw, 2010).
Seed viability estimations can be made using a tetrazolium test or by using x-rays. These tests determine the amount of live seeds in any given sample. The tetrazolium solution stains the living tissues of seeds a red color, allowing producers to differentiate between dead tissues. X radiography is a nonintrusive method to view the internal structures of seeds, allowing growers, wholesale sellers, and buyers to differentiate between empty, full, or physically damaged seed. Seed viability estimations can also help storage facilities determine if seeds are still able to germinate after prolonged storage (“Seed Testing - USDA Forest Service”).
Seed purity is a measurement based on the ratio of pure, whole seeds of the desired wildflower versus noxious weed seeds, broken seeds, trash, stems, and other debris by weight. A minimum number of seeds, varying by specie, is required to conduct purity testing (“Seed Testing - USDA Forest Service”; Johnson, 2001).
Other qualities and characteristics of seeds can also be tested, including moisture content, the number of seeds per pound, and the presence of weed seeds. Moisture content is the calculated percentage of moisture held by a seed based on their dry weight. Determining the moisture content of seeds helps storage facilities maintain optimal conditions for seed curing and preservation.
Currently, wildflower seed producers have the option of sending seeds to accredited public or private seed laboratories in their state or to the National Seed Laboratory for proper testing. Seed testing protocols and accreditation are handled by the Association of Official Seed Analysts. Growers of certified seed in Oregon must produce seed in accordance with Oregon State Seed Certification Service rules and regulations (Cornforth & Ogle, 2002).