RE SEARCH New breeding method leads surprisingly fast to new varieties Producing new resistant potato varieties without genetic modification. This is possible, because breeding company Solynta has introduced the new F1 hybrid breeding. The starting-point here is not potatoes but real seed. Crossing resistances in 5 years instead of 25 to 35. It is possible by breeding in diploid potatoes with the help of the newlydiscovered Sli gene as far back as the parent lines, as a result of which strong hybrid varieties can be developed. Why does Solynta not use the more common tetraploid potato? Joint owner Pim Lindhout enthusiastically explains the what and why. indhout picks up a writing pad and starts with plant breeding, lesson 1. ‘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 chromosomes. 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”.’ Subsequently, Lindhout draws three possible combinations of a diploid gene on a piece of paper: AA, Aa and aa. L ‘The reaction varies from “Pim, you’re crazy” to “If this is true, you’ll get a Nobel Prize.’ ‘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,’ Lindhout continues. 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’, Lindhout writes down on his piece of paper. ‘So much for the lesson in diploid genetics.’ ‘Our first objective is to get complete inbred lines. I hope to see the first results in 2015’, Solynta’s Pim Lindhout tells us. Hybrid breeding ‘All potato varieties, such as the Bintje, are tetraploid. When you start crossing them, it will be rather difficult to obtain the desired four times capital A genes. And because of that we’ve thought of a trick of not having fertilisation take place, but having plants grow from reproductive cells resulting in plants with half the number of genes. 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 Potato World 2012 • number 3 13 Pagina 12

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