Multi-year common-orchard evaluation reveals complementary yield and kernel-quality traits in local almond germplasm from southeastern Türkiye

Almonds are among the most resilient nut crops in the Mediterranean, capable of thriving in hot, dry summers and cold winters where other plants might struggle. Yet, growing them successfully is a gamble against the calendar. The trees must survive the chill of winter to produce flowers, but if they bloom too early, a sudden late frost can wipe out the entire harvest. If they bloom too late, they may miss the window for pollination or face scorching heat before the nuts are ready. Farmers and breeders spend years searching for varieties that strike the perfect balance: trees that bloom at a safe time, produce a steady crop year after year, and yield nuts that are easy to crack open to reveal a sweet, whole kernel inside. In southeastern Türkiye, a region rich in wild almond populations, scientists have long suspected that local trees hold the key to solving these puzzles, but proving which specific trees are the best requires patience and careful observation.

To find these hidden gems, researchers at the GAP International Agricultural Research and Training Center in Diyarbakır set up a long-term experiment that treated the orchard like a fair test ground. They gathered thirteen different almond trees, each a unique genetic individual selected from wild populations in the region, and grafted them onto a single, standard rootstock. This ensured that any differences in growth or fruit production came from the trees themselves, not from the soil or the roots. They planted these local trees alongside two well-known commercial varieties, Ferragnes and Ferraduel, which serve as the industry standard. The team then watched these trees for nearly a decade, recording when they flowered, how big they grew, and how much fruit they produced in the harvest years of 2021, 2023, and 2025. By keeping the conditions identical for every tree, the scientists could see clearly which local varieties were truly superior.

The results revealed a striking difference in timing. The two commercial reference trees waited until late March to reach their peak bloom, roughly ten to seventeen days later than most of the local trees. While this late flowering is often prized to avoid spring frosts, the study showed that being late is not the only path to success. The local trees, which began blooming as early as the first week of March, still managed to produce significant harvests, proving that early bloomers can be productive if they are resilient enough to handle the local weather. The data confirmed that the weather of each specific year played a massive role; some years were bountiful for all trees, while others were harsh, causing some varieties to produce almost nothing. This variability meant that a tree's total harvest over three years was not just a simple sum, but a story of how it handled different challenges.

When the researchers tallied the total weight of the nuts still in their shells, the commercial variety Ferraduel produced the most, yielding nearly 23 kilograms per tree over the three years. However, the local trees held their own. One local tree, identified as DIY 154, produced a massive 17 kilograms, while others like DIY 265 and DIY 278 also delivered impressive totals of 16 and 15.5 kilograms respectively. Yet, total weight tells only part of the story. The true value of an almond lies in the kernel inside. When the shells were cracked, the commercial tree Ferraduel again led with over 6 kilograms of kernels. Among the local trees, DIY 278 stood out, producing over 4 kilograms of kernels, the highest amount for any local variety. This tree managed to combine a heavy crop with a high percentage of edible meat, meaning less waste and more profit.

Beyond just quantity, the quality of the nuts mattered immensely. The researchers cracked open thousands of nuts to check for defects, such as double kernels (two nuts inside one shell) or bitter tastes, which can ruin a crop's market value. The commercial tree Ferragnes was excellent at producing a high percentage of kernel relative to shell weight, but the local tree DIY 278 matched this performance with a shelling percentage of over 25 percent. More importantly, DIY 278 produced sweet kernels with no double kernels, a rare and valuable combination. In contrast, another high-yielding local tree, DIY 154, produced a large volume of nuts but suffered from smaller kernels and a slightly bitter taste, making it less suitable for direct sale without further breeding work. The study also noted that some local trees were inconsistent; for instance, DIY 154 produced a huge crop in one year but almost nothing in another, whereas DIY 233 produced a steady, reliable crop every single year it was measured.

The scientists concluded that while the commercial varieties set a high bar, the local germplasm from Diyarbakır offers distinct advantages that cannot be ignored. The tree DIY 278 emerged as the most promising candidate, offering a rare balance of high yield, high-quality kernels, and sweet taste. Other local trees like DIY 265, DIY 272, and DIY 233 showed complementary strengths, such as steady production or specific physical traits that could be useful for future breeding programs. However, the researchers were careful to note that these findings are based on a single location and a limited number of harvest years. The trees have not yet been tested across different climates or over a long enough period to guarantee they will perform well everywhere. Before any of these local trees can be recommended as new commercial varieties, they must undergo further testing in multiple locations to ensure their reliability. For now, the study has successfully identified a group of local trees that are worth watching, offering a glimpse of the potential hidden within the wild almond populations of southeastern Türkiye.