Which is the most common method of obtaining improved variety of crops?

How can I effectively grow a San Pedro cactus indoors? What products all come from some type of material raised on a ranch or farm? At what temperature does it become too cold for pepper plants to thrive? Is wood ash safe for around olive trees? What kind of roots does a bamboo tree have? Why are my azalea's leaves turning brown? How can I successfully grow pistachios from seed? What is the structure of a sunflower? Are possums and African bush baby is the same animal family? How to make oobleck with only flower and water? Why are my tomato plant's leaves turning yellow with brown spots? Can you help me identify a tree with berries? What are compost piles? What are the characteristics of bamboo? How can algae be effectively utilized as a fertilizer for enhancing plant growth and soil health? What stops the cactus blowing away in the wind? How much space does a carrot need to grow? How can I prevent the propagating wandering jew in soil from spreading and taking over my garden? What noise do zebras make? What kind of tree or bush supplies blackberry?