Targeted Breeding Innovations in Nut Tree Cultivars

Photo: Prof. Kourosh Vahdati.

Prof. Kourosh Vahdati

Professor of Horticulture, Department of Horticulture, College of Agricultural Technology (College of Aburaihan), University of Tehran, Iran. Prof. Kourosh Vahdati specializes in innovative solutions for challenging nut tree cultivation. He has consulted and managed commercial tissue culture labs and orchards, and introduced successful propagation protocols, demonstrating his commitment to sustainability.

In a chapter titled “Cultivars and Genetic Improvement” in the recent book Temperate Nuts, Prof. Vahdati and colleagues outline the main breeding objectives for temperate tree nuts and the various conventional and molecular strategies used to achieve these objectives. This article addresses recent cultivar development, emphasizing regional preferences and performance, particularly for walnut, hazelnut, pistachio, pecan and almond trees.

The demand for nut production has significantly increased due to the high economic value of nuts and their ease of storage and handling. This surge in demand, along with the necessity of developing nut trees for diverse climate conditions and to mitigate the negative impacts of climate change, has led to the implementation of multiple nut tree breeding programs worldwide. These programs aim to develop cultivars and rootstocks resilient to environmental stressors such as drought, heat and pests while maintaining high yields and superior nut quality.

Walnut

Walnut breeding programs globally have introduced a variety of new cultivars to meet the evolving needs of walnut growers. Notable additions include UC Wolfskill and Durham in the United States. UC Wolfskill shares similarities with Chandler in terms of yield, quality and color. Its high yield, early harvest, light kernel color, thin shell and adaptability to various climates have made it a market favorite. Durham, with a harvest date 10 days earlier than Chandler, produces jumbo-sized walnuts with light-colored kernels. This variety is known for its mid-season harvest, good yield, large nuts and light kernel color, positioning it alongside established cultivars like Howard, Tulare and Chandler. In France, new walnut cultivars such as Feradam, Ferbel, Fertignac and Ferouette stand out for their high yield, lateral bearing, thin shell, extra light kernel color and other desirable traits. New cultivars from China such as Xin2, Xin185 and Xiangling offer features such as moderate to high yield, lateral bearing, thin shell, early leafing, light kernel color and early harvest. However, their thin shell and lack of shell seal make them unsuitable for mechanical harvesting. In Iran, newly released Persia and Caspian showcase high yield, lateral bearing, late leafing, extra light kernel color and medium to early harvest.

Hazelnut

In Oregon, cultivars such as McDonald, Yamhill, Sacajawea, Jefferson, Dorris, Wepster, PollyO, Theta and Thompson have gained popularity for their resistance to diseases like Eastern filbert blight (EFB), bud mites and aphids. However, a new aggressive strain of EFB is infecting resistant hazelnut varieties in the Oregon and Pacific Northwest hazelnut industry, leading to increased surveillance and management efforts. The new Oregon-released varieties are currently undergoing field trials in Europe and Chile, where EFB is less of a concern. McDonald is favored for its EFB resistance, high yield and quality, while Yamhill has seen success in Chile and the US for its high yield, excellent kernel quality and EFB resistance, among other qualities. Varieties like Jefferson, Dorris, Wepster, PollyO and Theta offer reliable yields, good nut sizes and pest resistance. Thompson, tailored for high-density orchards, exhibits high resistance to EFB. However, older cultivars such as Barcelona, Daviana, Tonda di Giffoni and Tonda Pacifica face challenges due to disease susceptibility. Barcelona is now considered obsolete in Oregon due to its vulnerability to EFB. Daviana is outdated, Tonda di Giffoni struggles with moldy kernels and Tonda Pacifica is not favored due to its susceptibility to EFB. While Tonda Pacifica suits Europe’s blanched and roasted kernel market, its nuts are too small for the in-shell market. Tonda Francescana is gaining demand for its large nuts, high yield and excellent flavor in Europe, though it is still undergoing field trials in the US and Chile.

Pistachio

Advancements in breeding have led to the development of pistachio cultivars with higher yield, earlier harvest and better green kernel color. Rootstock development has focused on tolerance to soil-borne diseases, salinity and water stress. These developments have been instrumental in expanding pistachio cultivation to regions with challenging growing conditions. The new male and female pistachio cultivars are synchronized in their bloom periods, ensuring optimal pollination and fruit set. The Randy male variety is characterized by early flowering with a long bloom period, while Famoso produces a large quantity of pollen and has a bloom synchronized with Kerman. Lost Hills and Golden Hills, the newest California pistachio cultivars, have higher yields and earlier harvest and disease resistance. Lost Hills has large nuts and improved resistance to Botryosphaeria. Golden Hills has higher yields and early splitting, medium-sized nuts. In Iran, most growers cultivate the local cultivars Akbari, Ahmad Aghaei, Ohadi and Kaleh Ghoochi. In Türkiye, Kirmizi, Uzun, Halebi and Siirt are the major pistachio cultivars. The new Turkish cultivars Tekin and Akinci have higher yield and splitting rate than Siirt. Pistachio production has traditionally been under unirrigated conditions in Türkiye. However, in the past two decades, orchards have been irrigated, necessitating the need for new, suitable varieties.

Pecan

Several new pecan cultivars have recently been released in the US, each with unique characteristics and target markets. Pueblo is early-producing and well-suited for higher-density planting. Seneca is prized for its cream-colored kernels and adaptability to northern climates. Zuni is known for its disease resistance and large, well-filled kernels. Avalon and Kalos are both known for their scab resistance and high productivity, with Kalos offering larger, higher-quality nuts and a higher kernel yield. Zinner and Avalon are relatively new cultivars showing promise, with Zinner offering excellent nut quality, consistent production and good scab resistance, while Avalon boasts good precocity, stability in production and resistance to scab. Both cultivars provide potential solutions for growers looking to reduce input costs and maintain quality in pecan production in the Southeast. Among the older cultivars, Wichita is one of the most widely planted cultivars, known for its medium-sized nuts with a high percent kernel and good fill, but it is extremely susceptible to scab and water-stage split. Pawnee stands out for its large nut size and very early nut maturity. Choctaw produces thin-shelled nuts with a high oil content and rich flavor, ripening in late fall. Mahan is recognized for its large nut size and thin shell. Western requires a dry climate to lower the risk of scab disease and is considered low-maintenance in the right conditions. Desirable is a high-quality cultivar known for its large nuts and consistent crops, but it requires intensive fungicide protection due to its susceptibility to scab. Lakota requires significant management, such as thinning the nuts and addressing vivipary issues, making it a more challenging choice for growers due to its tendency for alternate bearing.

Almond

In the US, leading old cultivars include Nonpareil, Monterey, Independence, Butte and Carmel. Sweetheart was released later with mid-blooming and resistance to postharvest damage. Liberty offers high productivity and late harvest. Pyrenees is praised for its flavor and production. Yorizane, is self-compatible and comparable to Nonpareil. In France, Ferragnes is a popular self-incompatible variety known for its quality nuts. The newer self-compatible variety Lauranne offers versatility with its hard shell and big kernels. In Spain, Tardona and Mardia, with ultra-late flowering and self-compatibility, are valuable additions for orchards needing late blooming traits. Penta is another late-flowering variety (blooming a bit earlier than Tardona) that is very productive. Other self-compatible Spanish cultivars like Macao, Vairo, Marta, Marinada and Soleta provide growers with options suited to different conditions. Marinada is a highly productive, late flowering and very precocious variety. The Spanish cultivars of Florida and Alaska are self-compatible, soft-shelled and highly productive. Both cultivars have attractive kernels, with Florida ripening early and Alaska ripening later than Nonpareil. Most recently, two late-flowering cultivars named Saba and Aydin have been released in Iran.

Acknowledgment

Appreciation is extended to those involved in the research and development of these cultivars, whose work underpins the ongoing success and innovation within the nut industry. I also would like to express my gratitude to Asaad Habibi for his valuable assistance. Additionally, I extend my appreciation to Shawn Mehlenbacher, Pedro Martinez Gomez, Xinwang Wang, Lu Zhang, Charles Leslie, Louise Ferguson and Salih Kafkas for their help in pre-reviewing the characteristics of the nut cultivars.

Sources

Vahdati, K., Arab, M. M., & Sarikhani, S. (2020). Advances in biotechnology and propagation of nut trees in Iran. In BIO Web of Conferences (Vol. 25, p. 01003). EDP Sciences.

Vahdati, K., Sarikhani, S., Arab, M. M., Leslie, C. A., Dandekar, A. M., Aletà, N., … & Mehlenbacher, S. A. (2021). Advances in rootstock breeding of nut trees: objectives and strategies. Plants, 10(11), 2234.

Vahdati, K., Sheikhi, A., Arab, M. M., Sarikhani, S., Habibi, A., & Ataee, H. (2023). Cultivars and Genetic Improvement. In Temperate Nuts (pp. 79-111). Singapore: Springer Nature Singapore.