RE SEARCH Solynta: ‘At the earliest, we will present our first commercial, not yet resistant, variety in 2021’ ‘N ew breeding method leads surprisingly quickly to new varieties’. That was the headline of the article in Aardappelwereld magazine five years ago about Solynta’s newlydeveloped and totally different method for potato breeding. At the time co-owner Pim Lindhout gave a detailed explanation in the interview. The big difference between traditional breeding and the Solynta method is that planting stock is not derived from tubers but from seed, he told us at the time. If you use seed potatoes, the multiplication factor is 10, or ten tubers per plant. If you want to provide the entire country with a new variety, you need at least five years of multiplying from mini tubers to consumption potatoes. It’s a time-consuming story, also an expensive one, plus you run the risk of losing some of the quality during those five years. This process is much quicker with seed. If you are a consumption potato grower and you say that for next year, you want that new Phytophthoraresistant hybrid variety with 5 percent more yield, it can be done. The situation now is that, after the introduction of a new variety, you have to wait at least five years before there are sufficient seed potatoes ready’, according to Lindhout five years ago. We’re now five years further. What is the hybrid breeding situation at Solynta now? ‘In the past years, we’ve been working hard to optimise the technology. At the same time, we’ve proved that all the elements needed to obtain a commercial variety from our breeding method actually work. That doesn’t happen automatically. Look, there are actually four dogmas that we have had to overcome in recent years. In 2012, we’d already reached the stage at Solynta where we had a proof-of-principle. This meant that we had a number of inbred generations available. We’d made hundreds of crossings of these, which were used to produce the first prototypes of hybrids. We didn’t have a commercial diploid variety yet, because the material we had was basically still very primitive. The reason was that there were not yet any commercial varieties of diploid potatoes available. Moreover, we should have taken the secret key we found, the Sli gene that breaks through the self-compatibility of diploid potatoes, from a wild potato variety. This comes from a source of plants that have tubers the size of rat droppings. So it took years of cross breeding before the tubers were at least as big as a Bintje. That’s the first dogma. The second is inbreeding depression. People said that we’d never manage to get through that. It wasn’t easy, it’s true. We have indeed had enormous problems with this. In the beginning a lot of plants died. A large part of what remained didn’t flower and so we only had a few plants left to continue with. Eventually, it was possible, with a great deal of patience, to obtain sufficient primitive hybrid inbreeding lines. Dogma number three is the claim that diploids are always much weaker than tetraploids. In the trial fields that we now have in some parts of the country and also at the press meeting, we’ve shown that this is not the case with our breeding method. We currently have at our disposal the first strong diploid crossings that can easily withstand tetraploid variants. The fourth dogma concerns the HYBRID BREEDING IN A NUTSHELL Five years ago, Pim Lindhout gave a detailed explanation of the working method that Solynta uses to create F1 hybrid varieties for seed breeding. Here once again are the technical details in a nutshell. ‘Everyone knows the abbreviation DNA. DNA is the carrier of hereditary information. The DNA in every organism is unique and consists of genes. Combinations of genes are called chromoso‘We’re working with plants that are crossed with the Sli gene, a gene that breaks through the natural self-incompatibility, thus enabling 50 percent of homozygote progeny after one generation,’ Pim Lindhout explains. mes. Human DNA is built up of two pairs of corresponding chromosomes and this also applies for some plants. This is called diploid. However, the potato has four sets of chromosomes. We call that tetraploid. To make things easier, in genetics, similarities or differences between genes are indicated with a capital A and lower case a. These are called “alleles”. Reproductive cells (gametes), egg-cells (ova) or pollen contain half the number of genes. This is called haploid. After fertilisation, egg-cell and pollen fuse as a result of which the progeny are also diploid again. When reproductive cells that are both capital A, or both lower case a fuse, the resulting progeny are also 100 percent capital A or lower case a. This equality also has a name: homozygote. When reproductive cells with a combination of A and a fuse, the progeny gets two different alleles. That is called heterozygote: Aa. In Aa x Aa parents, the progeny is 25 percent AA, 50 percent Aa and 25 percent aa. Trick All conventional potato varieties we know are tetraploid. When you 6 Potato World 2018 • number 1 Pagina 5

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