Vegetable Seed Production

Vegetable seed technology

Introduction

Although some vegetables like potatoes are vegetatively propagated, most are established from seeds. Using quality seeds is a prerequisite for successful vegetable production. Although many of the F-1 hybrid seeds used today are more expensive than the open-pollinated seeds used in the past, vegetable seeds are still a rather small investment compared to other production costs.

It is generally unwise to cut costs by saving a few dollars on seeds of a substandard cultivar or by purchasing lower quality seeds. Cutting corners on seed costs will generally end up costing even more because of lost revenues from lower yields. Like so many other areas of agriculture, seed handling practices have changed dramatically over the years. For generations, farmers saved their own vegetable seeds and maintained their own cultivars. More recently, seeds were often obtained from local agricultural retailers. Today, vegetable growers are faced with a wide array of seed treatments and cultivars that may be purchased from sources around the world.

Seed Companies

There are many companies that sell vegetable seeds. However, the number of companies that actually grow their own seeds and develop new cultivars has been steadily decreasing over the past 50 years. Like other industries, the seed industry is rapidly becoming highly specialized.

For example, some companies specialize in retail sales. Of these companies, there are those that specialize in the home garden trade and others who deal with commercial growers. Some seed companies specialize in seed production and cultivar development and do not retail the seeds they produce, while other companies are involved in all aspects of the seed trade. Several companies do not sell seeds but specialize in coating seeds produced by other companies. Some companies specialize in specific crops such as the Hollar Seed Company which only produces cucurbit seeds and wholesales them to companies specializing in retail sales.

Many of the large vegetable seed companies are multinational. Very few of these companies are privately owned. Many are owned by other large multinational corporations. For example, Petoseed, Royal Sluis, Asgrow vegetable seeds and several other seed companies are now all owned by the Mexican Company, Seminis.

Seed Laws

The Federal Seed Act specifies minimum standards for vegetable seed quality and labeling. Each state also has a seed law that is similar to the federal seed law. All vegetable seeds sold commercially must meet standards for minimum germination percentage, be true-to-type, and not exceed tolerances for inert matter. State seed laws may have additional restrictions on noxious weed seed content and package labeling requirements. The germination tests used to verify viability are conducted under optimal conditions for each species as specified by the Association of Official Seed Analysts. >>

However, these tests provide little information about the vigor of seeds. A simple definition of vigor would be the ability of the seeds to germinate under stressful conditions. Unfortunately, there are no minimum standards for seed vigor in either the state or federal seeds laws.

State Seed Labs

Each state has a lab that will test for viability, purity, and freedom from noxious weed seeds. The Virginia State Seed lab is in Richmond. These labs will also test seed samples from the public for a small fee. In most cases, state and federal agencies monitor vegetable seed sales to ensure that they conform to state and federal standards. Most prepackaged seeds far exceed the minimum requirements established by the state and federal seeds laws. For example, by the Virginia State Seed Law, tomato seeds must have at least 75% germination to be sold in the state. Most tomato seeds purchased commercially will have germination percentages of at least 95%.

Certified Seeds

Many states have seed certification programs. Certified seeds are carefully monitored during production and are certified to be true-to-type, of high germinability, and to contain low percentages of weed seeds and inert matter. Generally, only agronomic crops are entered into seed certification programs, however, vegetables may also be included in the program. For example, California at one time certified the production of 'Charleston Gray' watermelon seeds.

Seed Treatments

Untreated seeds are rarely used by commercial growers. Many growers use F-1 hybrid seeds >> that are more expensive than the open-pollinated seeds used in the past.

Many growers are willing to pay more for treated seeds to insure the best possible stand establishment.

Pesticide applications are one of the more common seed treatments used today. A light coating of fungicide is usually applied to the seed surface. A brightly colored dye is sometimes added as a reminder that a fungicide has been applied. Systemic insecticides have also been used as a seed treatment for certain crops.
Inoculation of legume seeds with rhizobium to improve nitrogen fixation after germination is another common treatment.
Coating and pelleting >> are two widely used seed treatments, particularly with small-seeded species. Coated seeds have a thin layer of material such as clay or diatomaceous earth added to make the seeds larger but not to change the overall shape. Seeds are coated to make them easier to handle, to deliver chemicals, to improve soil contact, or to inoculate seeds with microbes The exact composition of coating material is a carefully guarded secret by the companies who develop them. Pelleted seeds have been coated until they are round. This makes seeds easier to handle and plant, particularly when planters that utilize belts with prepunched holes of a specific size are used. To make identification easier, coated seeds are often color coded, so cultivars or types are not mixed at planting. One successful pelleting treatment splits upon hydration and does not pose a barrier to radicle growth or limit oxygen availability to the seeds.
Film coating is another recent innovation. Many coating materials are very dusty. However, film coatings are made of the same materials used by the pharmaceutical industry to coat pills. These coatings are water soluble but dust free.
Pregerminated seeds, particularly celery, have been marketed by some companies in Europe. One company marketed pregerminated celery seeds in the United States briefly during the mid-1980's, but they are no longer sold in this country to my knowledge because the are very perishable.
Fertilizer treatments should not be applied to seeds, such as legumes, that are sensitive to high salts. However, some seeds are relatively tolerant of salts and additions of very small quantities of fertilizer with low salt index can boost early seedling growth. Research suggests that some matric priming materials, such as diatomaceous earth, boost early seedling growth because mineral nutrients are absorbed by the seed.
Synthetic seeds >> derived from tissue culture and coated in gelatinous material have been developed but are expensive, difficult to ship, have a short shelf-life, and are excessively variable for commercial use. Current research has focused on developing synthetic seeds that are desiccation tolerant and can be handled like other seeds. Although progress has been made in developing desiccation tolerant synthetic seeds, it is unlikely that they will be commercially available for many years.
Primed seeds have been subjected to a controlled hydration process followed by redrying. Generally, priming reduces the time to germination and may improve the seed's ability to germinate under temperature or moisture stress. Priming does not usually improve the viability of poor quality seeds. Peppers, tomatoes, and lettuce show a greater response to priming than some other types of seeds. Since the seed law does not require that primed seeds be labeled, they seldom are. Some seed companies advertise seeds as "vigorized" instead of calling them primed.
Precision sized seeds >> are often available and have been carefully sorted so all seeds are the same size. Sized seeds often have greater uniformity of germination. In many cases, large seeds are sold at a premium, because they are often more vigorous and may produce more uniform emergence. Some growers prefer sized seeds in order to get more uniform placement when belt seeders are used. It is possible to buy seeds spaced at a specific interval on tape. The tape is buried in the ground and dissolves when wetted.
"Seed tapes" are used mainly by home gardeners. Seeds are imbedded in water soluble tape for ease of planting.

Seed Production and Storage

Seeds for propagation are generally grown in special production fields by farmers who specialize in seed production. >>
The longevity of seed storage is determined by seed moisture content and temperature. >>
As a general rule, seed storage life decreases by half for every 5 degree C rise in temperature from 0 to 50 degree C, or for every 1% increase in moisture content from 5 to 14%.
Another helpful rule is that the % relative humidity + the temperature in degrees F should be kept below 100 during seed storage.
Seeds are hygroscopic and can gain or lose moisture from the air. If seeds are stored at moisture contents greater than 18%, damage can occur from heat buildup due to high respiration. Between 10 and 18%, fungi and mold can grow on seeds. Between 9 and 14% moisture content, insects may be active.
For open storage, starchy seeds should be stored at less than 12% moisture content, while oily seeds such as watermelon should be maintained at moisture contents less than 9%. Sealed storage requires moisture contents from 6 to 8%. In some seeds, storage at less than 4% moisture content can be damaging due to auto oxidation of lipids. Beans are more susceptible to mechanical damage when dried to less than 10% moisture content. As a general rule, the best moisture content for seed storage is about 5%. For storage at home, temperatures should be low but not below freezing. In some germplasm repositories, some seeds are now stored in liquid nitrogen, but seed moisture must be low and carefully controlled to protect the seeds from damage. Seeds stored properly in liquid nitrogen should last indefinitely.
To protect genetic resources, the USDA maintains collections of diverse cultivars for mainy of the important crops grown in the United States at the National Center for Genetic Resources Preservation (NCGRP) - Pictures >> in Fort Collins, Colorado, formerly called the National Seed Storage Laboratory.

Seed Containers

Seeds are packaged in many types of containers.
The best containers can be resealed to keep the moisture content low.
Containers made of paper or cloth should be avoided, because they do not prevent moisture uptake by the seeds, and they are more easily broken than other materials.
Small quantities of seed are often sold in packets.
Foil or plastic, hermetically sealed packets are preferred because they keep seed moisture content low.
Self-sealing packets are easy to use and protect the seeds from changes in moisture content.
Larger quantities of seeds are often sold in metal cans. >> These provide effective protection from rodents and moisture until opened. Cans should be supplied with a resealable cap to protect the unused seeds.
Large-seeded crops, such as beans or peas, are often shipped in bags. Plastic bags are good, because they protect against changes in water content. When seeds are packaged in cloth bags, they should be placed in a cool dry place until use so they do not absorb moisture from the air.

Selecting Cultivars

New cultivars are released by seed companies each year.
Don't be unduly influenced by glossy pictures and extravagant claims in a catalog!
New cultivars should be trialed on a limited basis before an established cultivar is replaced.
Many states publish lists of recommended cultivars (the commercial vegetable production guide for Virginia contains cultivar recommendations). These are cultivars that have performed well in Virginia over a number of years.
The All-American Trials test newly released cultivars from seed companies at a number of locations around the country. If a cultivar is an All-American winner, it simply means that it has performed well at a number of locations in the US. There is no assurance that a new cultivar will be superior to existing cultivars until its performance has been tested in your area.

Planting Seeds in the Field

The planting of seeds or transplants in the field is frequently called "stand establishment" >>.
Non-dormant, viable vegetable seeds germinate most rapidly when they are fully hydrated (no moisture stress) at the optimum temperature for germination.
Always plant seeds deep enough so that they have access to moisture. If moisture is limiting, plant seeds a little deeper so they will have sufficient moisture to germinate. A rule of thumb is to plant seeds to a depth 3 times the length of the seed, so large seeds are planted deeper than small seeds. As the saying goes, "Plant to moisture" (but of course don't plant seeds so deep that they cannot emerge).
Ensure that there is good seed to soil contact to facilitate water uptake by the seed. This may be accomplished by using coated or pelleted seeds and by proper seed bed preparation.
Soils with high clay content can "crust" and inhibit field emergence. Crusting can be eliminated by keeping the soil moist until emergence. Sprinkler irrigation may be used to prevent crusting. It also helps cool the soil which is important when planting a cool-season-crop into warm soil. When the soil temperature exceeds the optimum for germination, night planting may be an option, particularly for rapid germinating seeds like broccoli or lettuce.
Many crops are established from transplants >> to reduce the time in the field, increase uniformity, and insure a good stand.

Standards of Seed Purity and Germination

Seeds entering into interstate commerce must meet the requirements of the Federal Seed Act. Most state seed laws conform to the federal standards. The kinds of primary noxious weeds, sometimes subject to tolerances, and the secondary noxious weeds listed by the laws of the individual states differ to a considerable extent. The weed seed regulations and the tolerances allowed, if any, may be ascertained by contacting the State Seed Laboratory of any state.

Each container of vegetable seeds must contain or have attached to it a label that gives the following information:

Name of kind, variety, or hybrid of the seed. The representation of kind and variety shall be confined to the recognized name of the kind and variety. It shall not have affixed thereto words or terms that create a misleading impression about the history or characteristics of the kind of variety.
Full name and address of the person who transports the seed in interstate commerce or the person to whom the seed is shipped.
Germination information:
1. Percentage of germination, exclusive of hard seed.
2. Percentage of hard seed, if present.
3. Date of test.
4. Statement as to any seed treatment including the name of substance or process.

Small packets of seed for home garden use are not required to meet these labeling requirements in some states.

The Reproductive Characteristics of Some Common Vegetables

Please refer to this handy reference table summarizing the reproductive characteristics of many of the important vegetables we will discuss in detail later in the class. Don't attempt to memorize this information now, will discuss the detailed life cycle of each crop separately. At this time please note the various strategies different vegetables use to reproduce.

< Previous: Genetic Engineering >