Origin

In Iran, the walnut breeding program started in 1984 through the selection of native germplasm. This project led to the selection of some superior genotypes, of which two new cultivars, Jamal and Damavand, were released in 2010 (Hassani et al., 2012a, 2012b). The second phase of this program, with the aim of selecting for late leafing and lateral-bearing cultivars, was carried out during early 2000. A total of 39 promising walnut genotypes were selected from more than 41,000 ha of walnut plantations in the Alborz, Qazvin, Zanjan, West Azarbaijan, Kerman, Khorasan Razavi, Semnan, and Yazd Provinces. In 2006, the genotypes were grafted onto seedling rootstocks and were planted at a 7 × 7-m planting distance (square system) in a 6 × 7 lattice experimental design, with two replications and three trees per plot. The experimental orchard was established in Karaj (lat. 35.760560°N, long. 50.96843°E; elevation, 1268 m above sea level) and at the Rabor Walnut Research Station in Kerman Province (lat. 29.26264°N, long. 57.04825°E; elevation, 2300 m above sea level). Three commercial cultivars, including ‘Chandler’, ‘Jamal’ and ‘Ronde de Montignac’, were included in this trial as reference cultivars. Phenological and pomological characteristics of promising genotypes were studied until 2018. Four new cultivars were released in 2019 (Hassani et al., 2019).

Methods

Phenological and pomological traits of the selected cultivars were evaluated using International Plant Genetic Resources Institute (1994) and International Union for the Protection of New Varieties of Plants (1999) walnut descriptors. Moreover, the relative susceptibility of the new cultivars to anthracnose was tested as described by Dastjerdi and Hassani (2009). Blight and bark canker diseases were also evaluated as described by Silsepur et al. (2011) and Soleymani et al. (2019).

Description

‘Persia’.

‘Persia’ is characterized by late leafing behavior (around ‘Chandler’ leafing date), which helps to avoid late-spring frosts (Supplemental Table 1, Supplemental Fig. 1). The protogynous flowering habits of this cultivar allows it to cross-pollinate with ‘Chandler’ (Supplemental Fig 1). It has a lateral bearing habit (Fig. 1), and most of the buds are productive (60% to 80%). Vigor is intermediate. Yield in this cultivar is as high as ‘Chandler’ (Supplemental Table 1). Nut size is medium and nut weight is 10.5 g, and the nut has a thin shell (0.93 mm) and a greater percentage of kernel (63%) in comparison with ‘Chandler’ and other cultivars (Supplemental Table 2). The kernel is removed easily from the shell and has a light and extralight color. Kernel plumpness is good. The ripening time is early-medium, about 25 d earlier than ‘Chandler’ (Supplemental Table 1, Supplemental Fig. 1). This cultivar is moderately resistant to anthracnose, bark canker, and blight.

‘Caspian’.

‘Caspian’ is characterized by a relatively late leafing property, which helps it to avoid late-spring frosts. This variety leafs out at the same time as ‘Chandler’ (Supplemental Table 1, Supplemental Fig. 1). The protogynous flowering habit of ‘Caspian’ allows it to cross-pollinate with ‘Chandler’ (Supplemental Fig. 1). It has a lateral bearing habit (Fig. 1), and lateral buds are 60% to 80% fruitful. ‘Caspian’ yield is high and very similar to ‘Chandler’ (Supplemental Table 1). Nut weight is medium (average, 9.2 g). It has a thin shell (0.99 mm) and a kernel that consists of ≈56% of the nut weight (Supplemental Table 2). Plumpness, light and extralight color, along with good removal are the most important traits of the ‘Caspian’ kernel. Its ripening time is early-medium, 23 d earlier than ‘Chandler’ (Supplemental Table 1, Supplemental Fig. 1). This cultivar has intermediate vigor and is moderately resistant to anthracnose and blight.

‘Chaldoran’.

‘Chaldoran’ has a tree with intermediate vigor, and precocious and high fruit-bearing potential (Supplemental Table 1, Fig. 1; Rezaee et al., 2008). The lateral buds are 90% to 100% fruitful. The nuts are large (average weight, 13 g) (Supplemental Tables 1 and 2). The leafing date is early to medium, and products may get damaged by late-spring frost, but because this cultivar has a long flowering period, it can produce enough crop after spring frosts when pollen is available. ‘Chaldoran’ is early ripening (Supplemental Fig. 1). Kernels are large and include 56% of the nut weight. The kernel is an amber color and is removed easily from the shell (Supplemental Table 2). This cultivar is moderately tolerant to blight as well as anthracnose.

‘Alvand’.

Tree growth vigor is very low in ‘Alvand’ (Fig. 1). This feature makes the cultivar suitable to be planted densely, at distances of 4 to 5 m. ‘Alvand’ is precocious, has a good bearing potential on lateral buds (Fig. 1), and 90% to 100% of the buds are fruitful (Supplemental Table 1). The leafing date is early to medium, and products may be damaged by late-spring frost, but because it has a long flowering period, similar to ‘Chaldoran’, it could produce enough crops after spring frosts if pollen is available. ‘Alvand’ is an early-ripening cultivar (Supplemental Fig. 1). Kernels are a medium size (nut weight average, 11.3 g), and the kernel weight is 50% of the nut weight. Kernels are removed easily from the shell (Supplemental Table 2). This cultivar is relatively sensitive to anthracnose, bark canker, and blight.

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Availability

Because of the late leafing and early-to-medium ripening habits of ‘Persia’ and ‘Caspian’, they can be recommended for walnut-growing areas with late-spring and early-autumn frosts; however, ‘Chaldoran’ and ‘Alvand’ are more suitable for regions with less late-spring frost risk.

‘Persia’, ‘Caspian’, ‘Chaldoran’, and ‘Alvand’ were released officially in Mar. 2019 by the Horticultural Sciences Research Institute of Iran (Hassani et al., 2019), and are in the stage of propagation.