Phenological evaluation.

‘Ourania’ is a high-yield cultivar when it comes to full production at 9 years of age, with an estimated yield of 29.00 kg/tree. This cultivar presents 80% lateral bearing habit, whereas that of its maternal ‘Hartley’ has been found to be 5% to 10%, and its paternal ‘Gustine’, 85% to 90%. ‘Ourania’ trees present intermediate vigor, a semierect growth habit, and dense branching, similar to ‘Chandler’ and ‘Hartley’ (Table 1). Budbreak occurs on 6 Apr. ± 8.22 d, depending on climatic conditions, at the same date as ‘Chandler’ and 1 d earlier than ‘Hartley’. Its first female flowers bloom on 24 Apr. ± 6.15 d, 3 d and 1 d earlier than ‘Chandler’ and ‘Hartley’, respectively. The last female flowers bloom on 6 May ± 4.76 d, 3 d earlier than ‘Chandler’ and on the same date as ‘Hartley’. The first male-flower bloom date is the same as ‘Chandler’ (18 Apr. ± 7.82 d) and 1 d later than ‘Hartley’. The last male-flower bloom date occurs on 28 Apr. ± 5.66 d, the same date as ‘Hartley’ and 1 d earlier than ‘Chandler’. Harvest of nuts occurs ≈29 Sept., similar to ‘Hartley’, and 4 d earlier than ‘Chandler’ (Table 1). Flowering of ‘Ourania’ is protandrous, with the first catkins appearing at 4 years and the first female flowers appearing at 1 year. It presents easy hull dehiscence (similar to ‘Chandler’ and ‘Hartley’) low sunburn susceptibility of the hull, intermediate susceptibility to the codling moth (Cydia pomonella L.), and a very low susceptibility to walnut blight (Χanthomonas campestris) (Table 1).

Pomological traits.

Fruit characteristics are presented in Table 2 and were collected over 10 consecutive years. Measurements concerning nut dimensions and weights are presented as mean ± sd. The ‘Ourania’ nut has a medium size and a triangular shape, similar to ‘Hartley’. The shell texture is rough and light in color, with intermediate shell integrity. The nut shape in a longitudinal section through the suture and in a longitudinal section perpendicular to suture is triangular. The shape in cross-section is oblate; the shape of the base perpendicular to the suture is truncate. The shape of the apex perpendicular to the suture is pointed; the prominence of the apical tip is medium. The position of the pad on the suture is found on the upper two-thirds of the nut, the prominence of the pad on the suture is strong, the width of the pad is broad, and the depth of the groove along the pad on the suture is medium. The structure of the surface of the ‘Ourania’ nutshell is slightly grooved. Nuts present medium adherence of the two halves of shell, and a thin thickness of primary and secondary membranes. All these nut characteristics are the same as those for ‘Hartley’ nuts, except for the prominence of the apical tip and the depth of the groove along the pad on the suture, which differ. Most of these characteristics differ from those of ‘Chandler’, as shown in Table 2. The mean weight of the ‘Ourania’ nut in the shell is 14.38 ± 0.77 g, the mean kernel weight is 6.43 ± 0.36 g, and the mean kernel percentage is 44.74% ± 2.14%. Although ‘Ourania’ in-shell nuts are heavier than the reference cultivars, the percentage of the kernel is less than that of ‘Chandler’. ‘Ourania’ nuts have a light kernel color, with well kernel fill and easy removal of the kernel halves, similar to ‘Hartley’ nuts (Table 2; Supplemental Fig. 1).

In conclusion, the new cross-bred walnut cultivar Ourania combines the high yield and good nut traits of ‘Hartley’ with the high lateral bearing habit of ‘Gustine’. Its phenological characteristics reveal that it is suitable for the climatic conditions of Greece, in mountainous areas, and even more in lowland areas of North Greece. Its nut traits are comparable to that of one of the top walnut cultivars (Chandler), making it a promising cultivar not only for Greece, but also for other regions with similar climatic conditions.