7 CFR § 201.58a - Indistinguishable seeds.
When the identification of the kind, variety, or type of seed or determination that seed is hybrid is not possible by seed characteristics, identification may be based upon the seedling, growing plant or mature plant characteristics according to such authentic information as is available.
(a) Ryegrass. In determining the pure seed percentage of perennial ryegrass and annual ryegrass, 400 seeds shall be grown on white filter paper and the number of fluorescent seedlings determined under ultraviolet light at the end of the germination period (see § 201.58(b)(10)).
(1) Fluorescence results are to be determined as test fluorescence level (TFL) to two decimal places as follows:
(2) The percentage of perennial ryegrass is calculated as follows:
(3) Using results from the above formula, the percentage of annual ryegrass is calculated as follows:
(4) If the test fluorescence level (TFL) of a perennial ryegrass is equal to or less than the variety fluorescence level (VFL) described for the variety, all pure ryegrass is considered to be perennial ryegrass and the formula is not applied.
(5) If the test fluorescence level (TFL) of an annual ryegrass is equal to or greater than the variety fluorescence level (VFL) described for the variety, all pure ryegrass is considered to be annual ryegrass and the formula is not applied.
(6) A list of variety fluorescence level (VFL) descriptions for perennial ryegrass varieties which are more than 0 percent fluorescent and annual ryegrass varieties which are less than 100 percent fluorescent is maintained and published by the National Grass Variety Review Board of the Association of Official Seed Certifying Agencies (AOSCA). If the variety being tested is not stated or the fluorescence level has not been described, the fluorescence level shall be considered to be 0 percent for perennial ryegrass and 100 percent for annual ryegrass. Both VFL (annual) and VFL (perennial) values must always be entered in the formula. If a perennial ryegrass variety is being tested, the VFL (annual) value is 100 percent. If an annual ryegrass variety is being tested, the VFL (perennial) value is 0 percent. For blends the fluorescence level shall be interpolated according to the portion of each variety claimed to be present.
(b) Sweetclover. To determine the presence of yellow sweetclover in samples of white sweetclover, at least 400 seeds shall be subjected to the chemical test as follows:
(1) Preparation of test solution: Add 3 grams of cupric sulfate (CuSO4) to 30 ml of household ammonia (NH4 OH, approximately 4.8 percent) in a stoppered bottle to form tetraamminecopper sulfate ([Cu(NH3)4]SO4) solution used for this test. After mixing, a light blue precipitate of cupric hydroxide (Cu(OH)2) should form. If no precipitate forms, add additional CuSO4 until a precipitate appears. Since the strength of household ammonia can vary, formation of a precipitate indicates that a complete reaction has taken place between CuSO4 and NH4 OH; otherwise fumes from excess ammonium hydroxide may cause eye irritation.
(2) Preparation of seeds: To insure imbibition, scratch, prick, or otherwise scarify the seed coats of the sweetclover seeds being tested. Soak seeds in water for 2 to 5 hours in a glass container.
(3) Chemical reaction: When seeds have imbibed, remove excess water and add enough test solution to cover the seeds. Seeds coats of yellow sweetclover will begin to stain dark brown to black; seed coats of white sweetclover will be olive or yellow-green. Make the separation within 20 minutes, since the seed coats of white sweetclover will eventually turn black also.
(4) Calculation of results: Count the number of seeds which stain dark brown or black and divide by the total number of seeds tested; multiply by the pure seed percentage for Melilotus spp.; the result is the percentage of yellow sweetclover in the sample. The percentage of white sweetclover is found by subtracting the percentage of yellow sweetclover from the percentage of Melilotus spp. pure seed.
(c) Wheat. In determining varietal purity, the phenol test may be used. From the pure seed sample count four replicates of 100 seeds each. Soak the seed in distilled water for 16 hours; then flush with tap water and remove the excess water from the surface of the seeds. Place two layers of filter paper in a container and moisten with a 1 percent phenol (C6 H5 OH) solution. Place the seed, palea side down, on the two layers of filter paper and cover the container. A preliminary observation may be made at 2 hours. At 4 hours, record the number of seeds in each of the following color categories:
(1) Ivory.
(2) Fawn.
(3) Light Brown.
(4) Brown.
(5) Brown Black.
(d) Soybean. In determining the varietal purity, the peroxidase test may be used. Remove and place the dry seed coat from seeds into individual test tubes or suitable containers. Add 10 drops (0.5–1.0 ml) of 0.5 percent guaiacol (C7 H8 O2) to each test tube. After waiting 10 minutes add one drop (about 0.1 ml) of 0.1 percent hydrogen peroxide (H2 O2). One minute after adding hydrogen peroxide, record the seed coat as peroxidase positive (high peroxidase activity) indicated by a reddish-brown solution or peroxidase negative (low peroxidase activity) indicated by a colorless solution in the test tube. Various sample sizes may be used for this test. Test results shall include the sample size tested.
(e) Oat. In determining the varietal purity, the fluorescence test may be used. Place at least 400 seeds on a black background under a F15T8–BLB or comparable ultraviolet tube(s) in an area where light from other sources is excluded. Seeds are considered fluorescent if the lemma or palea fluoresce or appear light in color. “Partially fluorescent” seeds shall be considered fluorescent. Seeds are considered nonfluorescent if the lemma and palea do not fluoresce and appear dark in color under the ultraviolet light.