A living gene bank
In the fertile lands flanking the Tigris River, farmers cultivate a remarkable array of watermelons (Citrullus lanatus) that are an important repository of genetic information. Unlike the uniform seedless varieties in most global supermarkets, the watermelons of Diyarbakır are landraces—locally adapted varieties developed over centuries. These varieties include types such as 'Sürme', 'Karakış', and 'Beyazkış'. The most famous of these, the 'Sürme', is known for its immense size, with individual fruits capable of reaching weights between 50 and 60 kilograms, and in some cases, even up to 75 kg.
The traditional cultivation method is unique as the fruit itself. For the largest specimens, farmers use a technique known as "pit growing." Pits are dug into the stony alluvial soils near the river and filled with a mixture of moist sand, pigeon manure, and barn manure. This specialized fertilizer composition, combined with the local climate, contributes to the watermelons' signature size and flavor profile. The fruit's rind is thick, typically 2-3 cm, and firm, which makes it durable for transport. Inside, the flesh is fibrous and red, with a high concentration of water-soluble dry matter, reaching up to 10%. Each fruit can contain between 650 and 750 seeds, ensuring the continuation of these treasured local lines.
Genomic secrets and modern crops
The genetic diversity within Diyarbakır's watermelons interests agricultural scientists and plant breeders. Turkey is a major center for watermelon genetic diversity, and regions like Southeastern Anatolia hold landraces with traits lost to most commercial cultivars. Modern, mass-produced watermelons often have a narrow genetic base, making them more susceptible to diseases and pests.
Researchers are studying these Turkish landraces to identify valuable genes. Genomic studies using molecular markers have begun to map the diversity within these populations. Of particular importance is the identification of alleles that confer resistance to diseases like powdery mildew (Podosphaera xanthii) and pests such as the southern root-knot nematode (Meloidogyne incognita). Wild and semi-wild relatives, like Citrullus lanatus var. citroides, contain these resistance genes. By identifying and isolating these genes from the Diyarbakır landraces, breeders can reintroduce them into modern hybrid varieties. This process can produce new commercial watermelons that require fewer pesticides and are more resilient to environmental stress, a practice that benefits both farmers and consumers.