Tekirdağ Onion, belonging to the Allium cepa L. species, is a culinary onion cultivated exclusively within Tekirdağ province and its districts. It possesses unique morphological and biochemical characteristics. It is registered as a designation of origin under the Industrial Property Law No. 6769 and is protected by a geographical indication.

Geographical Boundaries and Climatic Features

The production area covers the districts of Süleymanpaşa, Çorlu, Hayrabolu, Malkara, Muratlı, Marmaraereğlisi, Saray, and Şarköy within the provincial borders of Tekirdağ. The region is located within the Marmara and Meriç basins and has a semi-humid climate. The soil is rich in organic matter with a light clay-loam texture. These conditions directly affect the distinctive structure and durability of Tekirdağ Onion.

Botanical Classification and Species Characteristics

Tekirdağ Onion belongs to the family Alliaceae, the genus Allium, and the species Allium cepa L. It is classified within the A. cepa L. var. cepa variety. In shape, it appears slightly inversely conical when viewed from the side and round when viewed from above. It has a thin neck, with bright orange-copper colored outer skins. The flesh color ranges between pink and light purple, with fleshy leaves that are compact in texture and of medium thickness.

Morphological Features and Distinguishing Qualities

Tekirdağ Onion is notable for its low number of outer skins (2–4 layers), its slightly bitter taste, and pungent aroma. It exhibits 3–6 tillers and forms a white stem (“leg”), which allows it to be used as a mother plant for green onion production. The average bulb diameter is 69.45 mm, with bulb weight and bulb height meeting the species standard. The flesh tissue is dense and durable.

Production Method

Tekirdağ Onion follows a three-year production cycle:

• First year: Selected seed onions from the previous season are planted in well-prepared fields. After flowering, the resulting “black seeds” are harvested, dried, and stored.
• Second year: Black seeds are used to produce seedling bulbs (arpacık). Sowing is performed by broadcasting or seed drills, and the seedling bulbs are harvested in summer.
• Third year: The seedling bulbs are planted in the field. During the growth period, hoeing, irrigation, disease, and weed control are carried out. Harvesting takes place in June–July.

Chemical and Nutritional Composition

Tekirdağ Onion has a high water-soluble dry matter content (17.50%). Its moisture content is 83.72%, and total dry matter is 16.28%. Additionally, per 100 g of product, it contains approximately 1.88 g of protein, 18.72 mg of vitamin C, and 5.52 g of invert sugar. These components contribute to its storability and structural resilience.

Storage and Preservation Conditions

After drying, the onions can be stored at 0–2 °C and 64% relative humidity for 6–8 months. It is crucial that the bulbs are fully dried and free from disease or mechanical damage prior to storage; otherwise, sprouting risk increases. The relative humidity in storage areas must not exceed 70%.

Geographical Indication and Legal Status

Tekirdağ Onion is protected as a designation of origin. It was officially registered on 21 September 2022, under Registration No. 1228, Application No. C2021/040. The registering body is the Tekirdağ Chamber of Commerce and Industry. The geographical indication label and the designation of origin emblem must appear on the product or its packaging. If not on the packaging, they must be visibly displayed at the sales location.

Usage and Marketing

The product is generally sold after drying, packed in 50-kg sacks or crates. The geographical indication logo and the designation of origin emblem must be clearly displayed on the packaging or at the point of sale. This practice helps prevent imitation and misleading use of Tekirdağ Onion.

Inspection and Quality Control Mechanism

Production, storage, and labeling processes are inspected at least twice a year under the coordination of the Tekirdağ Chamber of Commerce and Industry by a four-member control authority. This authority includes representatives from the Provincial Directorate of Agriculture and Forestry, Süleymanpaşa Chamber of Agriculture, and Süleymanpaşa Municipality. Additional inspections may be conducted if necessary, and services may be obtained from public or private institutions.