RE SEARCH Solynta: ‘At the earliest, we will present our first commercial, not yet resistant, variety in 2021’ assumption that seedlings, plants from seed, never produce sufficient yields in one growing season. This compared to seed that you plant in mid-April. Last year, we saw that potato plants from our best diploid crossings planted after late spring gave just as much yield as a good tetraploid table potato. We’re not there yet, we are well aware of that. But if you see what we started with in 2011 up to now, then we’ve made huge steps. Our crossings contain all the good characteristics for an optimal potato, but they’re not yet combined in one variety.’ ‘It is, of course, in our interests that as soon as the hybrid varieties are available, they’ll also be successful in the cultivation of consumption potatoes.’ When will this happen? ‘You just asked about the trial comparison with the Bintje that we carried out in 2016. Of the very first two hundred F1 hybrids we had available at that time, we already had one that gave the same yield as the Bintje. We’d never expected that and it was also a nice surprise for us. But that’s not enough, we need more time. For example, in the period from the first field trial in 2010 to the winter of 2014/2015, we’ve been doing nothing but improving inbreeding lines. In practice that means the same as the endless selection of crossings. That’s sheer drudgery. Important, but it takes time. Until that time we still had no idea of what good parents were. We’re only now ready to select hybrid parents on the basis of performance in the field. So the development of our hybrid programme is a stepby-step process. Take, for example, a characteristic such as seed setting. This also requires selection work. You have plants that supply a total of six seeds, but you also have those that produce 60,000 seeds. The latter are the ones we want, of course. This is also a venture that takes time. The most important thing, however, is that we’ve now reached the point where we can cross resistances from wild species into the hybrids we’ve developed. And we’ve done that within two years. The importance of this, and also the crucial difference with conventional breeding, is that the basic characteristics of a high-yielding hybrid variety don’t change if you add a resistance. For a potato grower this is a big advantage. If you’re now cultivating a new variety from conventional crosses, you have to get used to the characteristics of the new variety every time. Sometimes it’s a fertilisation strategy, sometimes it’s a different way of storing. This is not necessary for new hybrid varieties. When the variety changes, you just get a potato with the same cultivation and storage characteristics, but with a new resistance, for example. And so we now have an F1 hybrid with a good yield and an F1 hybrid with Phytophthora resistance, but not start crossing them, it will be much more difficult to obtain the desired four times capital A genes. And because of that we’ve thought up a trick whereby fertilisation doesn’t take place, but we grow plants from reproductive cells, resulting in plants with half the number of chromosomes. These are therefore not tetraploid but diploid plants. Inbreeding these over a number of generations will ultimately lead to homozygote breeding lines with AA or aa. If we cross these, we’ll get hybrid varieties, which are again heterozygote. We call this hybrid breeding. This is rather handy because it means you can easily introduce new characteristics into one of the homozygote parents. The characteristics will be passed on to the hybrid variety after crossing. This means that you can make precise crossings with characteristics you think are important. When you start breeding the above-mentioned diploid heterozygote progeny, 50 percent will be heterozygote and the other 50 percent homozygote. When you continue breeding, you halve the percentage of heterozygote with each new generation. In the 6th generation, the progeny will be over 95 percent homozygote again. When you start breeding tetraploid potatoes with four different genes on 1 allele, you need many more generations to obtain a high percentage of homozygote progeny. And this example only applies to a single gene. A potato plant has 30,000 genes. This explains why traditional breeding is a very long-term affair. And if you understand this, you’ll be able to understand the basics of what we’re doing. Incompatibility All in all, Solynta works on reversing the process of what has just been outlined. We’re only using breeding lines that are homozygote. From the Aa x Aa crossing only the progeny of AA and aa are selected. If you cross those you’ll get the 1st generation F1 hybrid. The in-breeding method is not yet being used in traditional breeding. That’s not possible with potato plants, or with diploid, because they contain a range of mechanisms that make them incapable of self-fertilisation. This is called incompatibility. Diploid potatoes are naturally self-incompatible. They do make pollen, but are blocked when the pollen ends up on their own pistils. We’re working with plants, though, that are crossed with the Sli gene, a gene that breaks through this natural self-incompatibility, thus enabling 50 percent of homozygote progeny after one generation. For tetraploid potato plants, it takes seven generations to obtain plants that are 50 percent homozygote. Moreover, we saw crossed progeny that were much better than the earlier diploid crossings. The plants had so much growing power that they were almost comparable with the tetraploid plants.’ Potato World 2018 • number 1 7 Pagina 6

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