One method is to cross strains you like and see what results. This method takes little discipline and can produce unusual and novel plants with many combinations of characteristics. Desirable plants from several generations of crosses may provide you with plants with the exact characteristics that you are looking for. The problem is that the results are impossible to duplicate easily, so a desirable plant can only be reliably reproduced using cuttings (cloning), not by seed.
An advantage of crossing two hybrids is that the offspring have “hybrid vigor,” and each plant will have its own unique set of combinations of characteristics. Once the best plants are chosen, they are reproduced using cloning.
Another approach to breeding results in stable varieties. You start with a mental picture of an ideal plant, and work towards it.
First, two hybrid lines that have desirable characteristics are stabilized by inbreeding them for five or six generations. Then they are crossed with one another, creating an F1 hybrid. This F1 plant is easily reproducible by crossing the two stabilized varieties at any time.
If you are starting with clones, you probably have only females. This is a problem since there is no male from the line to cross with. All is not lost. You can pollinate the female with a male plant from a variety that has some characteristics similar to its chosen mate. However, a male from a dissimilar plant can be used.
The F1 plants that result receive half of their DNA from the mother. Backcrossing one of the males back with its mother produces F2 plants to which the mother contributes 75% of the DNA. Backcrossing a male from the F2 generation to the same mother creates the F3’s that receive 87.50% of their DNA from the mother plant. Backcrossed F4’s have 93.75% and the F5’s have 96.87% of their DNA contributed by the hybrid mother.
Each backcross provides an opportunity to affect the genetic development of the stabilized hybrid. Instead of choosing the best female, the best male is chosen. The plant is selected for potency and quality of high, ripening time, odor, shape, vigor and other characteristics that are important to you.
By the fourth or fifth generation of backcrosses to the original hybrid, the plants should be similar to the plant they were backcrossed to, only better, because of your selective breeding. Now select both females and males from the last generation for breeding. Two or three more generations should be enough to stabilize the variety. By this I mean that plants grown from seed will look, grow and produce similarly. The stabilized hybrid is now ready to be used to produce the new hybrid.
Plants grown from seed don’t need to be backcrossed. They should just be inbred for three or four generations to stabilize the variety. Then they will be ready to use for breeding the new hybrid.
As plant lines are bred to themselves, the plants can lose some of their vitality or vigor. This results from the genetic makeup becoming more homogeneous as siblings are bred to each other or progeny are backcrossed to parents. When two such lines are crossed, they produce a hybrid that will exhibit “hybrid vigor.” Once a desirable hybrid is created, it is possible to take cuttings from it and its clone progeny repeatedly without loss of vigor.
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