The Art & Science of Plant Breeding

QQA: Is modern plant breeding an art or a science?

Nabil Ahmad: The objective of any plant breeding program is to develop varieties which are superior in some way, whether in yield, fruit characteristics, hardiness or nutritional value. The plant breeder must be equipped with the skills to make use of the natural variability found in all species, and also to create new genetic variability and so create better crops.

So I would say the plant breeder needs to be an artist first and foremost but have the expertise to use the tools of science to create his or her art.


QQA: Can you take us a little deeper into how you go about this?

Nabil Ahmad: Well, traditional techniques include selective breeding as well as interbreeding or crossing of related plants to produce hybrids which have desirable traits.

We go further, greatly speeding up the process. We don’t use genetic engineering or transformation, though. The actual breeding techniques are conventional but we use tools like marker assisted selection where we identify DNA markers associated with desirable plant characteristics, to select plants to work with further.


QQA: Okay but how do you actually create new variability in a species?

Nabil Ahmad: We rely largely on a natural process known as chromosomal crossover where chromosomes exchange genetic material during sexual reproduction.

We may also use a number of in vitro techniques to produce plants that would not often occur in nature. For example, variability can occur in a process called somaclonal variation, which occurs in plants produced from tissue culture, particularly plants derived from callus (a mass of undifferentiated cells).

In other cases, variability may occur by changing the number of chromosomes, by adding or removing chromosomes or inducing polyploidy (where the cells contain more than two paired sets of chromosomes).

Sometimes we cross breed varieties which are able to produce embyos sexually but where some genetic incompatibility causes those embryos to fail and abort before maturation. In this case we can rescue the embryos and grow them in tissue culture to produce a new plant variety.


QQA: So you create variability by cross breeding two plants which are normally very difficult to successfully breed together?

Nabil Ahmad: Yes and we can go further still. Sometimes an incompatibility will stop the two parent plants from sexually producing any embryos at all. In this case hybrids may be produced by a technique called somatic cell hybridisation or protoplast fusion. We do this by stripping away the cell walls from each of the parent cells and forcing the resulting protoplasts to fuse together.


QQA: But sometimes the new variations won’t be useful, I imagine. Sometimes they’ll be detrimental.

Nabil Ahmad: That’s right so we select the plants with desirable characteristics to work with further. And we can control and speed up the process using haploid culture techniques. That’s where we take a gametic cell (a reproductive cell with only one set of chromosomes), culture haploid plantlet out of it and then diploidise it – duplicate its chromosomes. It now has two identical sets of chromosomes so it’s called homozygous diploid. If we breed it with another homozygous plant, we avoid all the usual shuffling of genes to create consistent outcomes with the vigour of hybrids.


QQA: All of that sounds a lot more like science than art.

Nabil Ahmad: Science provides the tools, like the keys, hammers, strings and pedals of a piano. The plant breeder is like the pianist who uses the tools of science to create something wonderful.


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