Date: 25 Sep 2008

Breeding Walnuts (Juglans Regia)

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Introduction

Origin and History

Ancestral forms of walnut once spanned Europe, Asia, and the Americas as far north as Alaska. Climate changes altered the geographic distribution and further evolutionary pressures resulted in the 21 species of Juglans in existence today. All species produce nuts, but the Persian or English walnut (Juglans regia) is the only species widely cultivated for nut production and will be the focus of this chapter. Other species are grown for timber (e.g., J. nigra, eastern black walnut) or are used as rootstocks for Persian walnut (e.g., J. hindsii, northern California black walnut).

Persian walnuts are native to the mountain ranges of Central Asia extending from Xinjiang province of western China, parts of Kazakhstan, Uzbekistan, and southern Kyrgyzstan, and from the mountains of Nepal, Tibet, northern India, and Pakistan west through Afghanistan, Turkmenia, and Iran to portions of Azerbaijan, Armenia, Georgia, and eastern Turkey. Small remnant populations of J.