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Seed Selection

Posted by Cropking on 2/16/2008

Authored by: Jim Brown

As the seed catalogs arrive, the thoughts of starting plants for outdoor or greenhouse growing get an invigorating mind set established in any gardener looking out the window at leafless trees and possibly snow-covered ground. The anticipation of renewed plant growth is irresistible and compelling. Seed companies know when to time the arrival of their catalogs to get the highest level attention from gardeners. The sheer number of plant and seed choices, however, is often overwhelming. We shall not tackle the entire complex issue here, but we will look at some basic differences in the way some of the different cultivars were developed and what some of their features are. This way, you will be able to more readily determine what best matches your desires and expectations of the resulting plants.

Some Questions to be Considered in the Decision-Making Process

Before making your selections from the myriad variety in the seed catalogs, there are some questions to consider to help you make the right buying decisions, so that the plants you grow meet your needs and expectations. By answering some questions and making some basic choices up front, you can better navigate your way through the overwhelming array of choices you face in the catalogs you peruse. Choosing among the available plant seed is necessary because most people don’t have the space to grow everything in the catalog, or even all the choices within one category of plant. It may just be my perspective, but it seems that the catalog descriptions summarize just about every plant as “This is the greatest yet! Grow this one!” This does not help the grower make the necessary, realistic decisions. The questions to be kept in mind as you read on include the following: Why am I growing these plants? Am I trying to take a look at the newest cultivar available? Do I want the characteristics and qualities I know are present in an old favorite? Am I interested in maximum production? Am I looking to produce the area’s first red tomato in the spring? How important is the extent of disease resistance in the cultivars I grow?

Two Mutually Exclusive Categories of Plant Cultivar Seeds

Seeds for plant production can be divided into one of two categories based on how the parent plants were produced and bred. There are general characteristics, advantages and disadvantages of each group. A basic understanding of the breeding program used in the development and production of the cultivar is helpful in understanding the potential and limitations of each system. F1 Hybrids of medium to large fruit sized plants are fairly common among annual flowering plants grown for their fruit, vegetable parts or flowers. Open pollinated cultivars or Heirloom Cultivars of this type of plant are also popular among gardeners. Often, small seeded plants with small, complete flowers are not hybridized because of the tedious hand work that would be required.

F1 Hybrids

Advantages of F1 Hybrids include hybrid vigor, uniformity of plant, flower or fruit size and type from plant to plant, and uniformity of plant characteristics from year to year. This is important for commercial growers who want a predictable and fairly uniform product at a fairly predictable harvest time. These characteristics may also be important to hobbyists and home gardeners who have specific desires and expectations about the appearance or productivity of their plants.

Without getting into a great deal of detail, we will look at the outline of one F1 Hybrid breeding program. For each F1 Hybrid, there are two inbred parent lines developed. Actually, several lines are developed at the same time and a combination of trial crosses are made by the plant breeder. Only the resulting F1 Hybrids with enough desirable characteristics are kept and introduced to the market. We will just trace the two lines of the one hybrid to keep the details simple and easier to follow.

Different breeding lines are developed with different characteristics in each. Since it is often difficult to get multiple desirable characteristics into one breeding line, some of the desirable characteristics are bred into the one parent line and others are bred into the second breeding line. This can be done with conventional breeding techniques. No gene manipulation such as that done in genetically modified organisms (GMO) is used in conventional hybridization. The source for many of the characteristics sought for the hybrids is found in old heirloom selections or wild-type plants that have been collected and maintained by or for plant breeders. In any breeding program, choices need to be made. Some plant characteristics are eliminated in order to keep other characteristics. When a desirable trait is missing, such as resistance to a particular disease, the plant breeder often has to go back to a wild-plant source to regain that trait. Over years of cultivation, there are many other characteristics present in the wild plant that have been left behind as undesirable or of less importance than other characteristics. Plant characteristics exist in groups on a plant chromosome. Individual genes on chromosomes control each plant characteristic. During the reproductive sorting of the genetic material, whole chromosomes rather than individual genes are sorted and grouped in the process. Every time a characteristic is chosen in a breeding program, a number of other characteristics come along with it on the same chromosome and another group of characteristics is eliminated from the program and the resulting cultivar.

Once plant breeding lines are developed, each having different and desirable bundles of genetic material determining desirable plant characteristics, they are self-pollinated and the resulting plants selected on the basis of how closely they match the original desired plant type and characteristics. Because there are two genes for each characteristic, variation will occur as the plants are self-pollinated. It takes several generations of self-pollination and selection to get the plants to the point where they have two genes of the same character at the same location on the chromosome pair. At this stage, the plants are called homozygous, and will deliver the desirable traits consistently. They will pass the same bundle of genetic information along to the next generation no matter how it is divided at gamete production. The breeding lines are now ready for hybridization. At hybridization, one line becomes the male parent and the other line becomes the female parent for the hybrid. The cross is made by pollinating the flower on the female parent with the pollen from the male parent. The pollen-producing structures (anthers) are removed from the flowers on the female parent so that all the seeds produced will be a cross between the two breeding lines. This is the first filial generation of the cross between the two breeding lines and thus is called an F1 Hybrid.

The breeding lines are maintained through self pollinating them and selecting for plant type. They are probably never completely homozygous so a few off-type plants show up once in a while and are eliminated from the seed production program. Each growing season, the crosses are made and a new batch of F1 Hybrid seed is harvested, processed and packaged for the market. F1 Hybrid seed is available from only the producer of the seed unless it is sold by them to secondary seed suppliers. The F1 Hybrid seed is what would be sold for resale. The breeding lines themselves are virtually never sold by the developer unless the plant breeder works for one of the universities. The breeding process is sometimes conducted in a greenhouse, but can also be conducted outside for some plants. In corn (Zea maize) where the male flowers are up on the tassel of the plant and the female flowers are down on the stem in what becomes the cob, crosses can be made in the field by alternately planting five or six rows of each breeding line and then removing the tassels of the female parent line. All seed that is produced on the female parent plant will be the F1 Hybrid and all seed produced on the male parent will be the inbred male parent line.

Open Pollinated or Heirloom Cultivars

Open-pollinated cultivars are developed in much the same way as the breeding lines for the F1 Hybrids. With these cultivars, crosses are made in the breeding process and plants exhibiting promising characteristics are selected. Those selections can be crossed with other selections, the parent plant or even some wild-type plants as a way to introduce desired characters. The crossing and selection process can go on for several generations. Once the final selection is made, that selection is then self-pollinated for several generations to assure that it will breed true to type. The seeds of open-pollinated cultivar plants can be used to produce the next generation of plant as long as the pollen came from the same cultivar. In tomato and pepper plants, this will happen naturally unless measures are intentionally taken to introduce other pollen from another source. The tomato and pepper flowers are designed for self pollination because the plants contain a single type of flower in which the stigma is surrounded by and enclosed by the stamens of the flower. On plants such as cucumbers and other members of the gourd family, on the other hand, there are separate male and female flowers. Not only is cross-pollination possible in these plants, but it is very likely if more than one cultivar of the plant is being grown in the same area. When insects are involved in pollinating, they will transfer pollen from one cultivar to another if the plants are in the same area. The term “Heirloom” is usually applied to an old open-pollinated cultivar that has been around for a number of years. It may apply to a cultivar that has been developed by conventional breeding and has been maintained by people long after most or all seed catalogs dropped the cultivar from the listings. A few of the Heirlooms could have been selections made by people who liked something about a plant they had growing in their garden. They saved the seed and propagated it and kept selecting the “best” plant as the parent for the next generation of plants.

Seed Availability and Cost

F1 Hybrid seed will often have a more limited availability than many open-pollinated or Heirloom cultivars. F1 Hybrid seed for a given type is produced by only one seed producer. It may be sold to a few or many other seed suppliers for final distribution to the grower. The cost of F1 Hybrid seed will often be more expensive than the seeds of open-pollinated or heirloom cultivars. Open-pollinated cultivars may be marketed by many seed suppliers. Sometimes, the same open pollinated cultivar can be a little different from one seed supplier to another. Whether a cultivar is an F1 Hybrid or an open-pollinated cultivar gives you some indication of what you can expect from the plants you will grow. You can save seeds from your open pollinated plants if you do it properly. You do not want to save seeds from F1 Hybrid plants or tomatoes and peppers you get at the grocery store, because the plants produced by their seeds will not be true to type of the F1 Hybrid plant they came from. Chances are that tomatoes and peppers you buy at the grocery store will be F1 Hybrids unless you buy them as the fruit of heirloom plants. Seeds can be saved from heirlooms with the expectation that very similar plants will be produced.

Making Your Seed Selections

Now that you have read through the definitions and characteristics of F1 Hybrid, Open-Pollinated and Heirloom cultivars, you understand the differences and can make better choices for your greenhouse or garden. Make a list of what plant and fruit traits are most important to you – e.g. growing and harvest periods, characteristics of the fruits themselves, or hardiness and disease tolerance. Armed with this information, you will be better able to make your way through the seed catalogs and enjoy making your plant choices.

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