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The winter and spring frosts pose a significant problem in many walnut cultivation areas as frost damage to catkins and female flowers results in low fruit set and yield. In January 2021, the temperature dropped to -17.2 °C in Yenişehir, Bursa, an important walnut production area in North-Western Turkey. The present study was carried out to determine the natural frost damage on catkins of some walnut cultivars and the effectiveness of an unmanned aerial vehicle (UAV) pollination, which has been developed and used in artificial pollination studies recently, on fruit set and fruit characteristics. For this purpose, two pollen concentrations (T1: 5% pollen two times; T2: 5% pollen in the first, 20% pollen in the second time) and the open pollination (control) were tested. Observations showed that frost damage on catkins varied from 57.31% (Ronde de Montignac) to 99.33% (Franquette). The initial fruit set was significantly higher in the T1 (87.74%) followed by T2 (83.89%). The final fruit set in T2 (75.16%) was higher than the T1 (74.11%), but the difference was found to be insignificant. The box and whisker plot shows that UAV pollination treatments (T1, T2) increased the fruit set, although this not uniform on the tree compared to open pollination. The highest nut weight, thickness, and length were obtained from control, followed by T1. The results showed that the fruit set was higher in pollination with UAV, and using less pollen (T1) was sufficient for fruit set. The research results support the use of UAV treatment on supplementary pollination for walnut. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the pomological and phenological traits, as well as yield potential and incidence of external defects of some local ('Bilecik', 'Maraş 12', 'Maraş 18', 'Şebin', 'Şen 1') and foreign ('Chandler', 'Fernette', 'Fernor', 'Howard', 'Pedro', 'Serr') walnut cultivars grown in Bursa (north-west in Turkey) conditions between 2014 and 2020. The first leafing was observed in Maraş 12, Serr, Şebin, and Maraş 18 cultivars, while Fernette and Fernor were the last leafing cultivars. The female blooming period of the cultivars was recorded to be the longest in Maraş 18 (15 days) and Şebin (16 days) and that was the shortest in Bilecik and Serr (10 days). The male blooming period was recorded as the longest in Chandler, Fernette, Bilecik, and Şebin (16-18 days) and that was the shortest in Maraş 12 and Serr (10 days). The average yield per tree of cultivars ranged between 1.87 kg (Şebin) and 14.21 kg (Pedro). Walnut blight was observed on average in 15.85%, sunburn in 10.21%, codling moth in 5.11%, anthracnose in 3.23%, and bird damage in 2.35% of the fruits. The healthy nut percentage ranged from 40.06% (Şen 1) to 76.50% (Chandler). The nut weight of cultivars was between 9.91 g (Maraş 12) and 16.27 g (Şen 1). Kernel percentage varied from 36.31% (Şen 1) to 53.56% (Maraş 12). The principal component analysis conducted to distinguish the cultivars suggests that the most important factors could be reduced to five components. The results showed that Maraş 12, Chandler, Fernor, and Howard were suitable cultivars for commercial cultivation in Bursa conditions. [ABSTRACT FROM AUTHOR]