Bursa Chestnut

Bursa Chestnut, is a fruit of Castanea sativa trees native to the city of Bursa in Türkiye’s Marmara Region. This product is cultivated in villages at specific elevations on the slopes of Uludağ and is protected under geographical indication status. Its production from cultivation to storage follows specific technical and traditional methods. Distinguished by its morphological and chemical properties from other chestnut varieties, the Bursa Chestnut is characterized by the grafting techniques applied in its production and the climate and soil structure of its growing region.

^{Bursa Kestanesi, (}Bursa Büyükşehir Belediyesi Bilgi İşlem Dairesi Başkanlığı⁾

The Bursa Chestnut is cultivated in the villages of Fidyekızık Hamamlıkızık and Cumalıkızık under the district of Yıldırım; Derekızık under the district of Kestel; and İnkaya and Yiğitali (Çongara) under the district of Osmangazi, all located on the slopes of Uludağ in Bursa. This geographical boundary lies between 400 and 600 meters elevation and features volcanic-origin soils with high potassium content.

The Bursa Chestnut belongs to the family Fagaceae and grows on trees of the species Castanea sativa. The trees have a tall canopy structure and exhibit semi-erect growth. They display sympodial branching, halting the growth of the main axis and transferring development to lateral branches. Young branches are reddish-brown and contain numerous white lenticels. Leaves are alternate, long, broad and serrated. The average leaf length is 19.64 ± 6.25 cm, width 6.25 ± 0.71 cm and petiole length 2.77 ± 0.75 cm.

In terms of fruit morphology the Bursa Chestnut is large and broadly flattened with 53 to 55 fruits per kilogram. On average three fruits develop per bur. The average fruit length is 40.71 ± 2.29 mm width 31.66 ± 1.56 mm and height 23.84 ± 2.54 mm. The shell thickness of 0.368 ± 0.049 mm places it in the thin-shell category. The shell color is typical chestnut brown with a slightly striated surface. The hilum shape is wavy with a length of 26.07 ± 2.71 mm and a ratio of 13.25 ± 2.20%. There is no umbilical cavity and the kernel is light cream in color.

When evaluated on a dry matter basis the Bursa Chestnut is notable for its high starch and protein content. Chemical analyses are as follows:

• Fruit moisture content: 53.092 ± 0.264%
• Shell moisture content: 27.983 ± 1.687%
• Total carbohydrates: 64.857 ± 0.055%
• Starch content: 42.677 ± 0.087%
• Total sugars: 19.435 ± 0.038%
• Invert sugar: 2.724 ± 0.005%
• Sucrose: 15.876 ± 0.041%
• Total protein: 7.790 ± 0.28%

^{Bursa Kestanesi, (}Bursa Büyükşehir Belediyesi Bilgi İşlem Dairesi Başkanlığı⁾

The Bursa Chestnut is generally produced by grafting cultivated varieties onto wild chestnut trees found near forested areas. The establishment of new chestnut orchards and plantings for this purpose is quite limited. The product is monoecious and diclinous; therefore pollination primarily occurs through cross-pollination. Due to the wide genetic variation in seed propagation this method is used only to obtain rootstock.

In grafting wild chestnut trees with cultivated varieties cleft grafting is the preferred method. Trees selected for grafting must not be diseased or excessively old. One of the most common techniques is bark grafting which is performed during the period when sap flow begins and the bark separates easily from the wood. Grafting scions are collected from healthy branches free of chestnut blight and stored at +2 °C. For grafting the trunk is pruned to a height of approximately 90–100 cm. Thick branches of older trees are also prepared for grafting. After grafting the graft surfaces are sealed with grafting wax. Two or three scions can be placed on each branch depending on its diameter. Successful graft union typically occurs within 30 days and rootstocks with well-developed roots show rapid shoot growth.

For the production of seedlings intended for new orchards bud grafting is widely used. This method is preferred due to its practical applicability and maximum utilization of the scion. T-budding reverse T-budding and chip budding are the techniques applied in this context. The timing of grafting is critical to success. Spring grafting performed after leaf emergence in late April to early May generally yields successful results. After grafting all shoots except one or two above the graft are pruned. Dormant bud grafting can be performed in August. Scions used during this period are collected from the same year’s shoots and used immediately without storage. Grafts performed this way develop during the following growing season.

The growing region lies between 400 and 600 meters elevation on the slopes of Uludağ. Annual average rainfall in this area ranges from 600 to 700 mm. Rainfall directly influences fruit development. High daytime temperatures and low nighttime temperatures during the vegetation period are among the key factors determining the internal structure and composition of the fruit. The chestnut trees in this region are adapted to shaded environments within their natural distribution range but require increased light exposure in north-facing areas.

Since the chestnut tree has a deep taproot system the soil must be loose permeable and deep. A soil pH between 5.0 and 6.5 is considered ideal. The volcanic origin and high potassium content of soils within the geographical boundary significantly influence the structural and chemical properties of the fruit. This soil structure contributes to increased starch and protein levels.

Chestnut trees can be adversely affected by drought periods during summer. This may lead to leaf drop and reduced fruit size. Therefore irrigation is necessary especially during dry summer months.

Harvest time is determined when the spiny fruit capsules (burs) open and the chestnuts inside turn brown. Harvesting is carried out when at least half of the capsules have matured. During harvesting fruits are collected by striking branches with long poles without damaging the tree structure.

The harvested product can be stored in two different ways:

• Traditional Method: Fruits are stored in piles within their spiny burs covered with various herbs in cool shaded areas. This method provides short-term storage for two to three months. However during this natural storage the product may be exposed to diseases and pests.

• Cold Storage Method: After separation from the burs the fruits are dried in shade to a moisture content of 35–55% without direct exposure to sunlight. Dried chestnuts are packed in plastic crates jute sacks or mesh bags and stored in cold storage facilities at 0–2 °C and 85–90% relative humidity. Direct exposure to sunlight reduces shell luster and may cause discoloration.

The control process is conducted at least once annually under the coordination of the Bursa Livestock Development Union in collaboration with experts from the Bursa Metropolitan Municipality the Bursa Provincial Directorate of Agriculture and Forestry and the Osmangazi Chamber of Agriculture. The inspection includes compliance with production methods and adherence to the morphological and chemical characteristics unique to the Bursa Chestnut. Additional inspections may be carried out when necessary. The use of the geographical indication and origin designation is also evaluated within this framework.

^{Bursa Kestanesi, (}Bursa Büyükşehir Belediyesi Bilgi İşlem Dairesi Başkanlığı⁾