HOW TO BREED PLANTS Which technique is best for you?

As you know, breeding involves bringing pollen to the seed plant. One can look at pollen transfer in two ways, cross-pollination and self-pollination. Both have their importance in the science of plant breeding. With cross-pollination the pollen is transferred from one plant to another plant. In self-pollination the pollen is transferred within the same flower or to another flower of the same plant. If you can self pollinate plants you will have a much better chance of getting a pure breeding seed population in a few generations. However, self pollination does not allow you to combine two different traits. And, even if you have a superior plant, with some species you may have problems with self-pollination, i.e. not getting seeds. Some plants must be cross pollinated to produce seeds.
With cross-pollination you try to combine two excellent traits from two parents. Both parents can have the same trait say big flowers, or you can try to combine two different traits into one plant like if you cross a short plant with one that produces huge flowers to try and get a short plant with big beautiful flowers. The problem with crossing two plants is that in most cases you get a lot more variety in the next generation (a lot of tall plants with small flowers and other unwanted things that were not even in your parent plants). This gives you more options to select your prize winner from, but more plants will need to be grown. So, with all breeding you must start with the best plants you have. In breeding you do not build up, you only peel away to expose what is already there.
The keystone of breeding is Heritability – You can look at how traits are inherited in two basic ways: 1) Quantitative traits that occur along a scale or gradient, like yield and plant height 2)Discrete traits which occur with no scale, flower color for example where the flowers are red OR yellow. Discrete means there is a definite beginning and end, no in-between. With quantitative traits there is not just 1 or 2 but you will have 1.1 and 1.2 and 1.75 etc. Quantitative traits can often be attributed to the interactions between two or more genes and their environment. They are involved in important agricultural traits such as crop yield, flower diameter, number of flower parts, and in animals, weight gain, and fat content of meat are quantitative traits, as well as human traits like IQ, learning ability and blood pressure.

Some traits are easily inherited, others not so much. Easily inherited means you can breed plants with a trait and the offspring will have the same trait you want. Some traits are not easily inherited because they only occur under certain environmental conditions. Be mindful, as an indoor grower or gardener, you provide the environment. The environment you provide is important! You may never get flowers to bloom big w/o certain fertilizers (phosphorus). However, most of the time you will deal with a mixture of genetics and environment. This means that some fertilizers may make one plant flower and grow superbly, and the same fertilizer may only make another plant average at best. This is why I always advise experimenting with new products, and why it is important to keep notes over time, to compare and find what is best for your plants in your space.
As a breeder, you need to be observant, take notes and have a goal. It does not involve a lot more work than just growing plants, you just need consistent observations. Write down dates and traits when they occur, be precise. Other than that, each individual grower decides what they want to breed for, big flowers, a mild yet flavorful pepper, tomato’s that fit perfectly on a slice of bread. Be mindful of why you grow, and then breed your plants to be what you want. I will present three basic breeding strategies; pick the one that best suits you.

1. Backcross breeding -- This is used to introduce or improve one trait. This is NOT effective with quantitative traits. A cross is made between the donor and the recipient parents. In general the donor will have a trait that you want to introduce into the recipient parent. The recipient should be an awesome plant and the donor should have a trait that you want to introduce or incorporate in the recipient plant. You then cross the F1 generation (back to) with the recipient parent. The genetic contribution of the donor will be halved each generation. For example -- The F1 will have only 50% recipient plant genetics, but the first backcross BC1 will have 87.5% of the recipients genes the BC2 will have 93.75% and the BC3 will have 96.87%. So you will be close to the original recipient with a new trait introduced with three backcrosses. BENEFITS are that you can repeat the results easily, and few records are needed. The problem is this works well only with discrete traits.

Example of back cross breeding. You grow a variety of sweet bell pepper, and you want to make it resistant to fungal attack. You can cross your sweet pepper with a pepper that does not get the rot to try to introduce the resistance. You then need to grow the F1 generation and cross it with the original sweet pepper (or genetically identical seeds to that sweet pepper). You cross the F1 plants that are resistant with the original sweet pepper and then cross the BC1, BC2 etc. with the sweet pepper until you get the original pepper that is also resistant to rot.

2. Mass/recurrent selection -- This is the most effective breeding strategy for quantitative traits like yield and plant size. This is the most effective in cross pollinators as well. If you think about it, this is common sense breeding, you pick the plants that have the best traits as parents for the next generation. For example, if you want shorter plants, you pick the shortest plants as the parents. As with all breeding techniques, the success of this depends on the heritability of the trait. This type of breeding is often used to rogue out poor types of plants to improve your plant population: remove the weak and inferior plants. BENEFIT- easy to do. COST takes a long time (many generations) to this I say, “If you start off with plants you enjoy it will be a fun journey improving what you have.”

Example of recurrent selection --As an indoor grower, you have special needs and restrictions on your plants, most notably space. A common indoor trait would be to select for plants that are short. To breed a population of plants that are short, you would select a male and female parent that is short. From their seeds you grow many plants and pick the shortest plants as the next parents. You continue this until all plants are as short as you want. Recurrent breeding begins with “best” plants --> 1. Evaluate progeny and pick best for breeding, --> 2. Propagate next population --> 3. Evaluate progeny and pick best for breeding -->4. Propagate next population --> go back to 1.

3. If you are working with traits that seem to have low heritability, and you just can’t get the trait to breed consistently into the next generation you can use something called SINGLE SEED DESCENT (SSD) which involves growing (descending) one seed per plant each generation. By doing SSD over multiple generations it is possible to create a population of genetically identical seeds. After at least five generations (F5) and if each generation has the trait you want then in the F6 you can bulk up, meaning produce a lot of seeds all of which will be genetically identical. Only now can you say that you have your own seeds. This is what you are buying when you buy a packet of seeds, time and energy. You can see that plant breeding takes time. If you enjoy it, it is not a burden, but a hobby. The BENEFIT of using SSC is you will end up with a large consistent population of seeds that have the trait you desire. The cost is that it will take several generations and you risk loosing all your work if something happens to that one seed/plant during the process before you can bulk up. You can store seed from the original parent or each generation (See seed storage) and if you loose the traits, or the plant dies, you can start over. But you are always choosing one seed to start the next generation with.
Example of SSD. You have a hot chilli pepper that you love and want to grow many more of them. You let it self pollinate. Choose one seed as the offspring, and if it has the same trait as the parent, let it self and grow its offspring. If you get plants you like each generation (there is no loss of the desired trait) after 5 generations you have a PURE BREEDING* plant. You can bulk up (Make a lot of seeds) and say with confidence that the seeds and plants that come from them will all be the same.
The art of breeding is creating a plant that best fits to your environment. If you start your own breeding program, you will be the one to choose what you like. I hope you find success with the above information, and of course you can modify these as you see fit. As always, feel free to post a comment or E-mail me a question.
Good Growing,
Dr. E. R. Myers


hillbilly said...

ok Dr. Myers - i will confess that i have made an attempt at breeding some plants in my indoor garden AND that i am sure I've been mired in mediocrity. the mediocrity comes from my lack of experience breeding plants. i crossed 2 "breeds" of plants by collecting pollen/ applying it to female plant parts. i am pleased with the results (however mired in mediocrity they may be) - but maybe just because it actually worked. anyway, what i'd like to ask is this: what's up with only SOME "clones" of the mother plant grow partial leaf sets until 4 or 5 nodes of new growth? after 4 or 5 nodes of new growth, the partial leaf sets stop and typical leaf sets grow. these partial leaf sets occur on 2 out of 10 clones. is this partial leaf set growth a result of my poor breeding attempt?

. said...

If your plants were flowering when you took the clones, it might have affected leaf formation. Also, the cloning process can be stressful, so that could be a reason for the leaf formation. Breeding traits you select for, color, taste, growth habit, should not change when you take the clones.