Potato Review

34 POTATO REVIEW JULY/AUGUST 2021 BLIGHT “ is is where we predominantly nd wild varieties with high levels of genetic resistance. It is the main source of genes for our breeding programmes, though we also draw from primitive and old varieties.” Sjefke and his team use DNA markers to identify genes and the biological characteristics they invoke. “We are heading for varieties that have accumulated combinations of R genes and R genes that have synergistic e ects. My view is that, over time, we will be able to introduce varieties that, in principle, can still be attacked by the late blight fungus but the economic damage is considerably lower.” Today Agrico o ers a portfolio of nine ‘Next Generation’ varieties. e company says all o er outstanding blight resistance. “Our Next Generation varieties contain di erent ‘new’ R genes. It takes longer than the usual 11 years to bring to market because we rst have to dilute the wild gene, before integrating it with the breeding programme - we call this pre-breeding or introgression breeding,” said Sjefke. ose 11 years are spent selecting and trialling the resulting varieties. “From the gene pool we select parents which, by combination, we hope will give o spring clones that meet the market demands and then we make crosses - about 500 each year.” At the glasshouse stage, the Agrico Group has more than 220,000 o spring clones in the next season. “ ese are all unique individuals that have inherited characteristics from their parents. Each one is potentially a new variety but it will take a further nine “ at is important in many parts of Europe, but not all. Within most of the U. K. for example, we tend to see more clonal lineages; a result of asexual reproduction. A very well adapted strain that has some advantageous trait, such as an ability to infect earlier for example, becomes dominant. at dominance often doesn’t last longer than 5-10 years as a clonal population has no way to rid itself of accumulating deleterious mutations. “It’s why we’re doing a lot of work on the sexual variability within populations, trying to predict which ones are going to be the winners, and which ones are going to be the losers.” One of the more recent observations is the tendency for clones to be triploid, rather than diploid. “Like hybrid vigour in vegetable seeds, with three copies of every gene these clones are arguably better able to survive some of those deleterious mutations. We don’t fully understand how that works yet but many of these clones do seem to be surviving longer.” Developing defences While David and others at the James Hutton Institute are learning more about the pathogen’s genetic evolution in near real-time, Sjefke Allefs, director of Agrico Research, and his team are delving into the genetics of potatoes. Agrico has around 220,000 potato varieties, starting 10 years of trials each year “All the cultivated potatoes originate from Peru,” explains Sjefke. “It was the Inca people that domesticated the rst potatoes over 9,000 years ago. As the potato spread across the Andes, it met with the pathogen we now know as late blight, which originates from Mexico.