Richard Volz of Plant & Food Research explains the key steps in breeding a new apple cultivar. He describes ‘modified backcrossing’ – the breeding strategy that’s used to introduce a simply inherited trait like red flesh into a high-quality eating apple. He emphasises how important it is to choose the best apples to cross in each breeding step and discusses the strategies that breeders use to select breeding parents.
Transcript
Richard Volz (Plant & Food Research)
When we are looking at a trait such as red flesh, which has been discovered in the raw germplasm, what we need to do is a series of crossings to improve the quality of that red flesh. So what we do is – in the case of simply inherited traits such as red flesh – we do what we call a modified backcrossing scheme, whereby we are crossing the red-fleshed apple to high-quality white-fleshed parents.
We make the cross, select the best red-fleshed ones from the progeny, and we use those as breeding parents to cross again with the white-fleshed parent. So we’re continuously selecting our best red-fleshed seedlings in our progeny, using them as parents and continuing up the cycle. Once we've chosen our best red-fleshed seedlings out of our population, we can replicate those up into trials, grow them in Plant & Food orchards, take more information from those trees and fruit. We take the best of those, replicate them again, put them in grower trials, see how they perform on different sites throughout the fruit-growing districts of New Zealand, and after that, we are ready to take the best of those and commercialise them as a red-fleshed apple cultivar.
There are different sorts of information that we use to choose breeding parents. Some of the most important is actually the phenotype of the individual parents, and what we are trying to do is not just select the 1 parent but also think about the combination of the 2 parents to develop the new seedling that you have in mind. So you will be looking at the phenotype, the fruit quality and the productivity traits of the potential parent. And we can look at them as raw values or we can actually look at them as breeding values, which is a better measure of the ability of the parent to pass on those traits to their progeny.
We also use the genotype information such as the pedigree of the individuals. Sometimes, we want to make wide crosses, in other words, using parents with quite different pedigrees, or we might want to make close crosses whereby the parents are closely related. We also can use to a limited extent molecular marker information where we want to understand what genes are in what parents so that we can decide if those genes can go into the progeny for the future.
