Tests for Germination In the Laboratory

VERA L. COLBRY, THOMAS F. SWOFFORD, AND ROBERT P. MOORE.

WHATSOEVER a man soweth, that shall he also reap applies to the seeds you plant for crops, gardens, lawns, and forests. Sowing seeds that will not grow or are low in viability is a loss of money and time.

To save both, we have the laboratory germination test.

It is designed to indicate as closely as possible the proportion of the seeds that can be expected to sprout and develop into strong plants in the field, garden, and forest.

Experience has taught us that the mere fact a seed will absorb water, swell, and send out a tiny root does not guarantee that it will continue to grow and develop into a plant. It may have only enough vigor to form a root, or it may start to form a shoot and then die. It may even grow into a seedling, but one so weak that it cannot establish itself in the soil and continue to develop into a strong plant. So many hazards are encountered in establishing plants in nurseries, fields, gardens, and lawns that it is only commonsense to plant seeds that will have a good chance of survival.

AGRICULTURAL, vegetable, flower, and herb seeds grown for seeding in the United States are regularly tested for germination by private, commercial, State, and Federal laboratories.

The term "agricultural seeds" denotes the kinds that are planted as field crops or lawns and are not ordinarily considered as vegetables. Herb seeds are those of plants, such as sage and dill, that are grown mostly for food seasonings.

To comply with State laws and interstate and import provisions of the Federal Seed Act, agricultural and vegetable seeds ordinarily are tested before being placed on the market. They also may be tested later by seed law enforcement laboratories. Standardized procedures are necessary to assure that results of the different laboratories are uniform.

Flower and herb seeds usually need not be labeled to meet minimum germination standards. Many kinds of them are tested nevertheless.

The adoption of uniform rules for testing these seeds has been slow, partly because economically they are less necessary than agricultural and vegetable seeds. Testing them has been done mostly in laboratories that serve producers and distributors.

Flower and herb seeds and several new kinds of agricultural and vegetable seeds were added in 1959 to the rules for testing seeds of the Association of Official Seed Analysts. We have standardized germination procedures for 172 kinds of agricultural seeds, 6o kinds of vegetable seeds, 145 kinds of flower seeds, and 18 kinds of herbs.

Uniform germination results cannot be expected unless the analysts follow precise laboratory procedures, among them such operations as subdividing the sample to be used, unbiased selection of the seeds tested, the use of a standard number of seeds for the test (400 is the usual number), adequate spacing of the seeds on the germination medium, and correct regulation of moisture of the substratum, which is the material or medium on which the seeds are placed.

THE EQUIPMENT and substrata must provide and maintain throughout the test period the conditions of moisture, temperatures, aeration, and light to induce the various kinds of seeds to sprout.

An adequate space under controlled conditions also must be provided for conducting sand or soil tests. The amount depends on the kinds of seeds tested in the laboratory and any problems the samples present in evaluation of seedlings that make it necessary to test them in soil or sand.

The usual type of germinator in the United States is the insulated cabinet or sometimes a room equipped with movable shelves or trays, on which the tests are placed. The temperature is controlled by a regulated balance between refrigerated water and heating coils, both controlled by thermostats. Light comes through glass walls or doors and from electric lights.

Most of the testing is done on nontoxic substrata such as blotters, towels, or filter paper, which are used alone or enclosed in glass petri dishes or other containers. This type of test saves germinator space and is easy to do.

Sand or soil must be sterilized before use as germination media to destroy fungi, bacteria, and weed seeds. Expanded mica and granulated peat moss, alone or mixed with sand or soil, are used in some laboratories, especially for tests that require long pre-chilling or test periods.

ADEQUATE MOISTURE must be supplied to seeds throughout the test period.

Except for a few kinds adapted to growth in water, the moisture in the substrata should never be so much that a visible film of water surrounds the seeds. Excessive moisture can cause restriction of respiration (the intake of oxygen and the giving off of carbon dioxide by the seed) and stop germination of the seed. It also can cause certain types of abnormal development, such as lack of root hairs and transparent or "glassy" seedlings.

The temperature must be controlled accurately. Some kinds of seeds germinate over a fairly wide range of temperature, but others sprout promptly only in certain narrow ranges. Seeds germinate generally at temperatures to which they have been acclimated in the place they were produced. For instance, seeds of crops grown in the Southern States germinate well under warm, alternating temperatures; seeds of crops grown in Northern States germinate well in cool temperatures.

Most nondormant seeds are tested at temperatures of 59 to 86 F. A few southern crops require temperatures as high as 95 . The particular temperature under which seeds are placed depends on the kind. Some are placed at constant temperatures, usually 59 or 68 . Others are subjected to temperature alternations during the course of the test period. That is, they are placed at a low temperature during the night (16 hours) and at a higher temperature during the day (8 hours). The most common alternation is 68 at night and 86 during the day.

Light is supplied for a few hours daily to most of the grasses and to some of the vegetable, flower, and herb seeds, whether they are dormant or not. This is because light has a stimulating effect on the germination of many seeds of these kinds, especially when they are freshly harvested, and seedlings exposed to light during part of their test period are easier to evaluate because they are not too pale.

BREAKING the dormancy is a big problem in inducing seeds to sprout. Seed analysts consider dormant seeds as those that are potentially viable but do not sprout promptly when placed under favorable temperature conditions unless they have been subjected to some special treatment. Seeds that have been domesticated for long periods generally germinate readily. They comprise such crops as beans, corn, wheat, rye, peas, and onions. Range grasses are hard to germinate.

Laboratory methods for overcoming dormancy have been restricted as far as possible to techniques that are practical, rapid, and easily performed, will not require excessive equipment, and will approximate the field performance of the seeds.

Sometimes several treatments are necessary. The analyst draws on his experience as to the requirements of the seeds usually grown or received for test in a certain area and as to the age of the seed. If information is lacking about the previous history of samples, he often has to conduct a double test one under usual conditions and one under conditions specified for dormant seeds.

Commonly used treatments for overcoming dormancy are prechilling, the use of low-high alternating temperatures during the test period, moistening the substratum with a dilute solution of potassium nitrate, and predrying.