Olives are part of any good Greek salad – or Bulgarian shopska salad, or any other variation of the tomato-cucumber-olive salad that heralds summer. From fat, plump Kalamata, to the sort of sad, de-stoned kinds straggling at the back of your fridge, all types wriggle their way in.
Somewhat surprisingly, as researchers noted this week in PLOS One, a huge diversity exists not only on supermarket shelves, but also in Iranian olives. What’s more, this variation is separate from the large variation in olives that grow in the Mediterranean. To find out whether olive types in the two areas are related, the researchers looked at SSR markers, regions in the olive’s DNA in which short combinations of bases encoding information are repeated many times. Looking at the length of SSR markers in different varieties, the researchers work out which olive types are related and which aren’t. They find that olives in the Mediterranean and Iran probably separated early on in the olive’s history. Olives are cultivated only in a few regions of Iran, but the research shows that Iranian olive types vary greatly. Most of the diversityin Iran’s olive trees is actually found in patches of trees and small groves, abandoned from cultivation or remnants of a former cultivation as “holy trees”.
Why should we care? Iranian olive trees are not fickle: some survive at low temperatures nearly unheard of in the Mediterranean, others withstand over 40°C, while some grow at high altitudes and poor soil condition. In face of dwindling diversity, an unexpected source of genetic variation is rare and welcome news. A large pool of diversity seems like a good hedge of bets for an uncertain climatic future, but low numbers and threats to their environment endanger also this olive source. Thankfully, some Iranian olive trees bear large fruits, which bodes well for the summer salads of our future. For which a good recipe, as always, comes from smitten kitchen: smittenkitchen.com/blog/2013/05/greek-salad-with-lemon-and-oregano/
Original paper in PLOS One: www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0093146