Breeders leverage DNA variation
Humans have performed plant breeding for thousands of years to find, and add traits to our crop plants that are beneficial to us. These traits can be the number of kernels in a wheat spikes, the size of tomato fruits, and the height of a rice plant. It has been relatively recent that we found out that there is a simple basis at the heart of these traits: variation in DNA. Nowadays, conventional breeding utilizes modern laboratory techniques to leverage the potential of these variations in DNA to great effect.
Let us zoom in on the height of rice for instance. Rice plants used to be tall, causing them to tip over under strong winds. Nowadays, rice farmers use dwarf varieties: short stocky plants that can resist the winds. Scientists later found out that a simple, single base change in the DNA of the rice plant was responsible for this trait. And it is not only this trait: traits of any plant, no matter if we talk about plants in nature or plants in our agricultural settings, the basis of these traits is a small change on the DNA.
Now that we know the importance of DNA variation we want to answer two questions below: where can we find this DNA variation; and how do breeders utilize this variation in conventional breeding techniques?
DNA variation can be found in our crops, in wild relatives, or even created
Whenever a plant grows, it is exposed to many threats, but one in particular is incredibly dangerous: sunlight, or more specifically UV-light. For us humans, extreme exposure to UV-light can cause redness and irritation of the skin, and in the long term even skin-cancer. This is because UV-light damages our DNA, leading to mutations. It is the same for a plant. Leave it in the sun and its DNA will be damaged, leading to mutations. Or in other words: DNA variations. While this might sound bad, we have to thank mutations for creating this wonderful amount of plant life on earth. An avocado is different from a tomato because it has accumulated thousands or millions of years of mutations throughout its evolution.
So now we know that exposure to sunlight can cause DNA variation, and this caused the variation of plant life that we see today. This has three implications: 1) DNA variations will occur in our crops plants simply by virtue of them growing on the fields, 2) that wild relatives of our crop plants have significant variation in their DNA, and 3) that we can increase the rate of DNA mutations by overexposing plants to UV-light. This in turn means that new, valuable plant traits can pop up spontaneously in our crops, that we can find valuable traits in nature, and that we can induce DNA variation to create new traits. Modern plant breeders are experts in using these techniques to add valuable traits into our crop plants to make them more nutritious, more stress-resistant, and increase their yield.