Persian Walnuts (Juglans regia L.) in
Central Asia
Introduction
Thomas J. Molnar , David E. Zaurov ,
John M. Capik1, Sasha W. Eisenman2,
Timothy Ford3, Lucian V. Nikolyi4, and
C. Reed Funk1, 3
1*
1
1
Department of Plant Biology & Pathology,
School of Environmental and Biological Sciences,
Rutgers University, 59 Dudley Road,
New Brunswick NJ 08901-8520 USA
2
3
Department of Landscape Architecture and Horticulture,
Temple University, 580 Meetinghouse Road,
Ambler, PA 19002 USA
Improving Perennial Plants for Food and Bio-energy, Inc.,
711 South State St., Richmond, UT 84333 USA
www.ippfbe.org
4
Republican Scientific Center for the Production of
Ornamental Plants and Forest Management,
P.O. Darkhan, 111104, Tashkent region,
Tashkent Province, Uzbekistan
*Corresponding author
Email: [email protected],
Ph: (732) 932-9711 ext 117
Abstract. Persian walnut, Juglans regia L., is grown as an
economically valuable crop in a number of semi-arid and
temperate regions worldwide. Nevertheless, the species remains underutilized when considering its wide native range
and inherent genetic diversity. The center of origin of J.
regia includes Central Asia, which covers a large and diverse expanse of land in Uzbekistan, Kyrgyzstan, Tajikistan,
Turkmenistan, and southern Kazakhstan. Much of this region has been inaccessible to the western world for centuries. However, since the dissolution of the Soviet Union,
it has become increasingly open and opportunities for reciprocal germplasm collection, exchange, and scientific collaborations are growing. To bring increased attention to the
valuable J. regia genetic resources endemic to this region
and to promote their better utilization, management, and
preservation, a brief description and history of the species
from a Central Asian perspective, along with recent and ongoing activities, including collection and evaluation efforts
at Rutgers, are discussed here.
56101st Annual Report, September 2011
T
he genus Juglans L. (Juglandaceae) includes from 7 to
45 species depending on the taxonomic study (Dode,
1906; Lee, 1935; Smolyaninova, 1936; Sczepotiev, 1957;
Manning, 1978; Komanich, 1982; Whittemore and Stone,
1997; Tsurcanu, 2004; Aradhya et al., 2007). The genus is
distributed primarily across the temperate and subtropical regions of the Northern Hemisphere (eastern and western Asia,
Eastern Europe, eastern and western North America, and
the West Indies), with several species also found in Central
America and along the Andes Mountains in western South
America (Smolyaninova, 1936; McGranahan and Leslie,
1991; Stanford et al., 2000). Two Juglans species are native
to regions of the former USSR. These include the Persian
(English) walnut of commerce, Juglans regia L. (synonyms:
Juglans duclouxiana Dode, Juglans fallax Dode, Juglans
kamaonia [C. DC.]Dode, Juglans orientis Dode, Juglans sinensis [C. DC.] Dode), which can be found in Central Asia
and the Caucasus region, and Juglans mandshurica Maxim.,
which can be found in the Russian Far East. The Central
Asian geographic area includes Uzbekistan, Tajikistan,
Turkmenistan, Kyrgyzstan, and part of Kazakhstan (Fig. 1)
(Sokolov, 1952) and represents a large and diverse region that is believed to be a center of origin and diversity
of J. regia (Vavilov, 1931 & 1951; Smolyaninova, 1936;
Sczepotiev, 1957; Zapryagaeva, 1964; Zhukovsky, 1971;
Kolov, 1984; Sczepotiev, 1985; Komanich, 1989; Leslie and
McGranahan, 1998; Mamadjanov, 2006a).
Persian walnut is a species of great importance across
Central Asia where nuts are harvested from wild stands,
backyard gardens, and commercial orchards that vary considerably in their size and degree of management. Nuts
are collected for home consumption, sale at local roadside
stands and markets, and for shipping to cities. Walnut trees
are further utilized for their high-quality timber to make a
wide array of products. The leaves, bark, and other plant
parts are used for medicinal remedies, and trees are grown
and maintained for soil conservation purposes (Mamadjanov,
2006b). A diverse mix of seedlings, local selections, and advanced cultivars are grown for nut production, many with
unknown origins, including some of which are the direct result of selection from the wild. The authors have observed
first hand the impressive diversity of nut types (shape, size,
Figure 1. Map of Central Asia, courtesy of the University of Texas Libraries. http://www.lib.utexas.edu/maps/
shell-thickness, kernel and pellicle color, flavor, etc.) sold in
local markets, as well as large bazaars, in cities like Tashkent
and Samarqand, Uzbekistan and Bishkek, Kyrgyzstan
(Fig. 2). This is unlike the uniform production practices in
the United States, which relies on only a limited number of
cultivars (Beede and Hasey, 1998). However, while a diversity of walnut germplasm exists in Central Asia, yields and
recorded harvests are quite low by world standards. For example, in 2009, China was the world’s largest producer with
979,366 MT (metric tonnes) of in-shell nuts, followed by
the United States (376,480 MT), Turkey (177,298 MT), Iran
(141,426 MT) and Ukraine (83,890 MT). These large totals
are in contrast with the 2009 reported harvest of 20,431 MT
for the whole of Central Asia, of which 13,999 MT was from
Uzbekistan alone. It should be noted that total world production has significantly increased over the past decade from
1,257,935 MT in 1999 to 2,282,264 MT in 2009 (an 81%
increase). This trend of increased world tree nut production can also be seen in pistachio (Pistacia vera L.), chestnut
(Castanea spp.), hazelnut (Corylus avellana L.), and cashew
(Anacardium occidentale L.) (FAOStat 2011).
Walnut production in the United States is primarily located in California. Walnuts became an important crop in
the state after their introduction from Spain and France in
the late 1800s and the subsequent selection and breeding
of productive, well-adapted cultivars (Beede and Hasey,
1998; Forde and McGranahan, 1996). The later introduction of more cold-tolerant germplasm from the Carpathian
Mountains of Poland to eastern North America in the 1930s
expanded the regions where this crop can be grown (Grimo,
1979). However, besides small, scattered plantings of a few
better-adapted Carpathian seedlings and clonal selections
found around the northeast and Midwestern regions of the
United States and southern Canada (largely by members of
101st Annual Report, September 2011
57
Figure 2. Example of the diversity of nut size and shape of Persian walnuts collected in Central Asia. Photo
by S. Eisenman.
the Northern Nut Growers Association), commercial production has not been established outside of the west coast of
the United States. This is mostly due to climatic limitations
of the plants (primarily late frosts in many regions), serious
diseases such as bacterial blight, Xanthomonas arboricola
pv. juglandis (Xanthomonas campestris pv. juglandis) and
walnut anthracnose (Gnomonia leptostyla [Fr.] Ces. & De
Not.), and nematode and insect pests. These pathogens and
pests reduce yields and consistency of the crop and greatly
increase the cost of production when control measures are
attempted. However, for the most part, germplasm from
Central Asia and humid parts of Eastern Europe and China
has yet to be significantly explored for its potential in North
America, and particularly outside of California. Walnut collections made in these regions may hold significant opportunities for obtaining germplasm with desirable traits such as
improved cold hardiness, pest and disease resistance, stress
tolerance, and palatability, which through breeding could
lead to the development of productive cultivars adapted to
a much wider geographic and climatic area. For example,
millions of walnut trees grow wild in the montane fruit forests of Central Asia. Some exceptionally cold hardy plants
have been identified there that produce large, thin-shelled,
high-quality nuts. Other selections have been identified that
express traits such as repeat bloom, the production of nuts on
lateral spurs, highly precocious seedlings (also called “fast58101st Annual Report, September 2011
fruiting” trees, which produce flowers one or two year from
planting the seed, as well as producing grape-like clusters of
nuts on the trees), extremely thin shells, apomictic (clonal)
seed development, and resistance to numerous pests and
diseases (Zarubin, 1949; Badalov, 1989; Thompson, 1993;
Germain et al., 1997; Popov, 1998; Mamadjanov, 2006a
& b).
To better develop our understanding of the genetic diversity and utility of Central Asian Persian walnut germplasm for breeding better-adapted, more productive plants,
a seed collection was made in Uzbekistan and Kyrgyzstan
in 2003. The resulting seedlings were established at Rutgers
University in New Jersey, with additional plants also grown
in Utah and Idaho, although not discussed in this paper. The
ongoing objective is to evaluate this new plant material for
interesting and useful traits, in addition to adaptation and
nut production in New Jersey under a relatively low-maintenance regime (no irrigation and little to no pesticide applications).
The purpose of this article is twofold. The first purpose
is to increase awareness of the unique Persian walnut genetic
resources found in Central Asia with hopes that it will spur
its better utilization, management, preservation, and study.
The second purpose is to document the introduction of a diverse Persian walnut seed collection from Central Asia to
New Jersey. To accomplish these goals, a brief description
and history of the species from a Central Asian perspective,
along with recent and ongoing activities, including collection and evaluation efforts at Rutgers, are described here.
Distribution of Persian walnut in Central Asia
Although Vavilov (1931, 1951) considered Central Asia
one of the primary centers of diversity of J. regia, the history and origin of the walnut forests in Europe and Asia
has been the subject of debate. The species has been documented growing in east and south Asia (China, Tibet, Nepal,
Pakistan, and India), Central Asia (Kyrgyzstan, Uzbekistan,
Tajikistan), Iran, the Balkans, northern Turkey, the southern Caspian region, the Caucasus, Azerbaijan, and Turkey
(McGranahan and Leslie, 1991 & 2009; Zohary and Hopf,
2004). However, the range of the species is believed to have
been substantially expanded as a result of human introduction
and cultivation (De Candolle, 1889; Carrión and SanchezGomez, 1992; Fornari et al., 1999). It is thought that prior
to the Pleistocene glaciations the species had a wide distribution, but during the glacial periods the distribution was
contracted to refugial areas located in Spain, Portugal, Italy,
the Balkans, and Kyrgyzstan (Carrión and Sanchez-Gomez,
1992; Figueiral and Terral 2002; Carrión et al., 2003). Early
pollen analysis supports a theory that the walnut forests of
Kyrgyzstan originated at the end of the Pleistocene (Grishina,
1968; Vyhodtsev, 1970). Interestingly, however, oral tradition in Kyrgyzstan has preserved a story about Alexander the
Great observing people planting walnuts on the mountain
slopes of Central Asia over 2,300 years ago.
Regardless of their origin, walnut populations in Central
Asia are remnants of previously extensive forests cut many
decades ago (Dilevsky, 1909; Masalsky, 1913; Musuraliev,
1998). Due primarily to anthropogenic effects, these forests have been substantially reduced in size. For example,
in Kyrgyzstan from 1897 to 1995, the total area of nut forest (Persian walnuts, pistachios and almonds [Prunus spp.])
declined by nearly 50%, from 1,200,000 to 630,000 ha,
including the loss of approximately 20,000 ha of walnut
trees (Ashimov, 1995 & 1998). According to Rybakov and
Ostroukhova (1972), J. regia can be found naturally occurring on about 80,000 ha in Central Asia. Of this total, about
41,000 ha are in southern Kyrgyzstan, primarily in the Tian
Shan Mountains and in the Fergana and Chatkal Mountain
Ranges of Osh and Djalal-Abad provinces. This area represents the largest naturally occurring walnut forest in the
world (Kolov et al. 2001; Mamadjanov, 2006a). Here the
trees generally can be found between 900–2,000 m above sea
level, although around 50% can be found at elevations between 1,600–1,800 m, with occasional trees as low as 600 m
and as high as 3,000 m. (Smolyaninova, 1936; Zaprygaeva,
1964; Burmistrov, 1996; Chernova, 1998).
The second largest walnut forest in Central Asia exists
in the Republic of Tajikistan (in the central part and in the
Pamir-Alai Mountains) with a total of about 30,000 ha.
More than 50% can be found in the Gissar Range, on the
slopes of the Petr Velikii and Darvaz ranges (Zapryagaeva,
1964; Rikhter and Yadrov, 1985). Here walnuts typically
grow at elevations between 1,000–2,500 m above sea level,
and as high as 3,000 m in the Western Pamir (Zaprygaeva,
1965; Sczepotiev, 1985; Kholdorov, 1990).
Additional wild populations occur in southern Kazakhstan
bordering Uzbekistan’s Tashkent province, where approximately 6,000 ha of walnut forests can be found. However,
the number of trees in this region is declining (Smolyaninova,
1936, Turganov, 1998).
Approximately 1,800 ha of naturally occurring walnut
forests remain in Uzbekistan. They are found mostly in the
western parts of the Tian Shan, Zarafshan, Nurata, and Gissar
mountains ranges, and in the Bostandik region (Kuznecov,
1956; Khanazarov, 1998). These trees generally grow at
elevations between 800–1,750 m above sea level (Ozolin,
1990). Furthermore, walnut is the second largest nut crop
(after pistachio) grown in the Republic of Uzbekistan. The
total area of commercial production is 5,200 ha, with 89%
in the province of Tashkent, 5% in Surkhandaryo, 4% in
Samarqand, and 2% in the Farghona and Andijon provinces
(Kalmikov, 1968; Khanazarov, 1998; Mirzaev et. al., 2004).
In Turkmenistan, while no notable concentrations occur, isolated walnut trees are found growing in the Western
Kopet-Dag Mountains at elevations of 800–1500 m above
sea level (Popov, 1929; Kichunov, 1931; Gursky, 1932;
Smolyaninova, 1936; Sczepotiev, 1985).
Morphology and biology of Persian walnut in
Central Asia
Walnuts are large, monoecious trees with wide, dense
crowns that can reach heights of 15–35 m. Older trees may
have trunk diameters upwards of 1.5–2.5 m (Shalit, 1951;
Gursky, 1932). Walnut trees have large, well-developed,
deep root systems that impart significant drought and stress
tolerance. At an age of 50–70 years the main roots can reach
6–7 m deep and up to 12 m laterally (Fig. 3). Young trees
have slightly furrowed, light-grey bark, while older trees
have bark that is darker-grey and strongly furrowed. The
leaves are alternate, 19–54 cm long and 15–40 cm wide, imparipinnate with 3–5 pairs of leaflets. The leaflets are typically dark-green, ovate, coriaceous and glabrous, with entire margins. The male flowers are arranged in catkins, with
each flower comprising 8–40 stamens. The female flowers
occur in groups of 1–3 on the ends of young branches. The
fruit is drupe-like and spherical, with a green, dehiscent
pericarp (husk), which releases the nut when mature. The
101st Annual Report, September 2011
59
The authors have also observed trees in Uzbekistan and
Kyrgyzstan with diameters of 2–3 meters and larger (Fig. 4).
Across Central Asia, different forms of Persian walnuts
exist with distinct morphological and biological characteristics. Based on these differences, Sczepotiev (1985) utilized
a classification largely developed by De Candolle (1864) to
divide cultivated and wild Persian walnut forms into seven
groups: 1) large-fruit cultivars (Juglans regia L. var. macrocarpa DC; 2) thin shell, dessert cultivars (Juglans regia L.
var. tenera DC; 3) almond-shaped cultivars (Juglans regia
L. var. bartheriana DC ); 4) cluster-type cultivars (Juglans
regia L. var. racemosa DC; 5) late blooming cultivars
(Juglans regia L. var. serotina DC) ; 6) hard shell cultivars
(Juglans regia L. var. dura DC; and 7) kapa-gall producing
cultivars (Juglans regia L. var. caulioma mihi Sczepotiev.)
Each group consists of dozens of cultivars.
Uses of Persian walnut in Central Asia
Figure 3. Root system of Persian walnut tree located in the
Khumsan village of Tashkent Province, Uzbekistan. Photo by
Lucian Nikolyi.
endocarp, or “shell”, is light brown and hard. The kernel is
covered with a thin, yellow to brown papery layer (pellicle).
In Central Asia, trees generally flower in April through May
and their fruits ripen in September through mid-October.
Exceptional examples of living walnut trees can be found
in Central Asia. In the village of Khavzak in the Vakhsh
mountain range in Tajikistan, there exists a tree with a crown
of over 900 m2. In this region, other trees were observed with
trunk diameters reaching 2.5 m. A tree with a trunk circumference of 11.5 m has been recorded as growing along the
Yakhsu river, in the village of Siyafark (Kholdorov, 1990).
Figure 4. Persian walnut tree with a trunk diameter greater than
2.5 meters located in Tashkent Province, Uzbekistan. Photo by D.
Zaurov.
60101st Annual Report, September 2011
The Persian walnut is one of the few plants in Central
Asia that is almost fully utilized, from the flowers to the
roots. Walnut wood is prized for its beauty and is highly
valued by woodworkers. The wood is strong, durable, resistant to pests, rarely cracks, and does not change its volume
when heated (Bemmann, 1998). It was often used to manufacture furniture in Europe in the 17th and 18th centuries.
The demand for walnut veneer remains great and is still used
for making high-quality decorative furniture, gun boxes,
and various craft projects. The trees sometimes form the
so-called Kapa-galls, or burls, which contain a very dense,
ornamental wood with curly grain and many eyes of heartwood due to the breaking of dormant buds under the bark.
These burls can weigh from 40 to 500 kg (Yaskina, 1980;
Bemmann, 1998) and are utilized by master woodworkers
to make souvenir boxes, lockets, brooches, and snuff boxes.
In traditional folk medicine, young, green fruits were
used as a health supplement. A decoction of nuts was imbibed to treat high arterial pressure, cardiac diseases, and
to rinse the mouth to treat gum disease. Juice from the fruit
husk was applied as an ointment to treat mild skin conditions, such as eczema. A tea made from the leaves has been
used to treat diabetes (Burmistrov, 1996). The leaves have
also been used as a vermifuge (a medicine used to expel intestinal worms) and to treat venereal diseases, tuberculosis,
scrofula, and rickets, and the bark from the roots has been
used to make a mild laxative (Akopov, 1981). The many
folk medicinal uses of walnut are supported by the wide
array of pharmacologically active health compounds more
recently studied from the nuts, nut husks, leaves, and bark
(Alasalvar and Shahidi, 2009).
Climatic adaptations of Persian walnut in
Central Asia
Juglans regia is widely distributed across Central Asia.
This area is far away from the influence of large bodies
of water and is classified as a sharply continental climate,
which displays distinct seasonal changes with occasional
wide daily temperature fluctuations. Walnuts from this region can be generally characterized as both cold hardy and
heat tolerant. They can be found growing on a diversity of
soils, although most can be classified as different types of
sierozem soils, black-brown, brown and light-brown carbonated soils, which generally have a low salt content and organic matter content from 1–7% (Roichenko, 1960; Pankov
1965). Zakirov (1947) divided Central Asia into four botanical-geographical zones largely based on elevation:
1)The chul zone, also called the arid plain, consists of the
flat territory of Central Asia. The chul zone spans from
sea level up to 600 meters and has a dry period of 3–6
months, typically May through October. The climate is
considered ultra-continental and is characterized by very
low precipitation (70–208 mm per year) and relative air
humidity levels that drop to as low as 1–2%. Summer
temperatures can reach 45°C (113°F), while winter temperatures often drop below –30°C (–22°F). The chul
zone occupies most of the Central Asian plain (Turan)
and displays four soil types: salty chul, sandy chul, gypsum (stony) chul, and clay chul (National Biodiversity
Strategy Project Steering Committee, 1998). In the chul
zone, isolated Persian walnut trees are only found in
backyards, not in the wild.
2)The adyr zone is a broad belt of land at an elevation of
around 600–1,500 m above sea level. This band is found
around all of the mountains ranges of Central Asia. It
occupies the land area between two contrasting ecological zones: the xerothermic chul (desert) and the mesothermic tau (mountain region). The annual precipitation
is between 250–400 mm and rarely reaches 500 mm.
The mean monthly temperature for July is 25° C (77°F),
which is 3-4° C lower than in the chul and 5-6° C higher
than in the tau zone. The dry period lasts from June to
September. The soils of the adyr zone contain less salt
and more humus than the chul soils and are classified as
sierozem (Makhmudov, 2001). Bedrock is often found
exposed on the surface. Due to its location, the adyr
zone is exposed to the influence of both the hot desert
along its lower edge and the cooling effects of the mountains on its upper edge. This causes the lower section of
the adyr zone to be closer to the environmental conditions of the chul and the upper section to be similar to the
mountainous environment of the tau zone. Because of
this gradient the adyr is divided into subzones: the lower
adyr with rolling relief and the upper adyr with broken
relief. Wild Persian walnuts can be found in abundance
across both subzones, however, at the lower boundaries
trees are typically found as isolated plants.
3)The tau (mid-mountain) zone is a broad belt of land at
an elevation of around 1,500–2,800 m above sea level. Precipitation here typically exceeds more than 500
mm per year, with a dry period that lasts from July to
September. The mean monthly temperature in July is
19° C (66° F). The dominant soil of the zone is the
brown soil type. The dominating wild and cultivated
shrub and arboreal species (Crataegus spp., Juglans regia, Malus spp., Prunus spp., etc.) of the area provide
the local population with fuel, building materials, and
food (National Biodiversity Strategy Project Steering
Committee, 1998). Wild Persian walnuts can be found
in abundance in the tau zone.
4)The yailau (high mountain) zone is the high-altitude,
subalpine to alpine zone that extends from 2,800–3,400
m above sea level. Summer is short and rather warm,
with sharp changes between day and night temperatures.
Summer daytime temperature can reach up to 25° C (77°
F) but can drop to 0° C (32° F) at night. In the winter, the
temperature may drop to –40° C (–40° F). Precipitation
varies from 400 mm to more than 600 mm per year. The
soil is mainly light brown and of the meadow-steppe type
(Kaurichev, 1989). This zone has stony taluses, glacial
valleys, glacial cirques, glacial tongues, and fields with
heavy clay soils. There are many sheer rock formations
in the southwestern Tian Shan and the western PamiroAlai. At this zone, isolated Persian walnut trees can be
found only up to 3,000 m above sea level.
Research and germplasm holdings in Central
Asia.
The most intensive and productive Persian walnut research and breeding in Central Asia was performed in the
past in Uzbekistan, Kyrgyzstan, and Tajikistan. Rikhter and
Yadrov (1985) stated that 350 Central Asian walnut cultivars
were developed, all of which were from seedling selections.
Today, walnut research is conducted at a greatly reduced
level. However, work is still conducted by several scientific organizations in the three countries. In Kyrgyzstan, the
Institute of Nut and Fruit Species of the National Academy
of Science of Kyrgyzstan, formerly known as the Forestry
Institute, currently conducts walnut breeding and holds a
very unique collection of Persian walnuts of over 300 cultivars and forms (Sczepotiev, 1985). Here, Kyrgyz scientists
have developed a number of cultivars including ‘Ak-Tersky,
‘Gavinsky’, ‘Ostrovershinnii’, ‘Desertnii’, ‘Uigursky’ and
101st Annual Report, September 2011
61
‘Oshsky’. Recently, Mamadjanov (2010) reported collecting eight new Persian walnut forms for the local populations
with excellent nut characteristics. Within this collection, two
are very late blooming (selections 2K and AB) and three are
capable of self-pollination (selections 3A, 4A, 11A). Two of
the forms (7A and 15A) are extremely precocious and are capable of blooming twice in one season (Mamadjanov, 2010).
In Uzbekistan, walnut collections are maintained at
the Schroeder Uzbek Research Institute of Fruit Growing,
Viticulture, and Wine Production and the Uzbek Scientific
Research Institute of Plant Industry, formerly named VIR
(Mirzaev et al., 2004). The Schroeder Institute also has extensive germplasm collections at its branches in the Tashkent
(Bostandik) and Samarkand provinces.
The Bostandik district (Tashkent province) is located
between 41° and 42° north latitude and has a large area of
wild growing walnut trees. The region is protected from
cold northeasterly winds by the high mountain ranges of the
western Tian Shan and is open to the west. The area has a
mild climate with a high level of precipitation (over 1,000
mm per year) and winter minimum temperatures that rarely
fall below -20° C. At the Bostandik branch of the Schroeder
Institute, the most significant walnut breeding work was
started by Dr. S.S. Kalmykov. He first worked on the selection of commercially valuable forms of walnut found in
the forests of the Bostandik region. Several hundred Persian
walnut trees with desirable characteristics, such as high
kernel quality and resistance to diseases and insects, were
selected. The walnut collection at Bostandik now contains
an exceptional diversity of cultivated and wild trees. As a
point of reference to the variation found across the collection, the nut weight and kernel content of select trees varies from 2.5–20 grams and 28–66% kernel-to-shell, respectively. There is also great diversity in shell thickness and
strength and the ability to extract the kernel from the shell.
Biologically, the different selections of walnut also vary
in terms of floral and vegetative bud phenology, nut yield,
frost and drought tolerance, and resistance to diseases and
pests. Breeders at the Institute’s Bostandik branch have developed the following cultivars: ‘Bostandiksky’, ‘Rodina’,
‘Gvardeisky, ‘Tonkoskorlupnii’, ‘Ideal’, ‘Uzbeksky krupnoplodnii’, ‘Panfilovets’, and ‘Kazahstansky’. These cultivars
have very high kernel quality, high yield, early fruit maturation, resistance to insects and diseases, and cold hardiness
(Kalmikov, 1968; Esenbaev et al., 1981; Mirzaev et al.,
1983; Abdurasulov, 1990; Mirzaev et al., 2004; Mavlyanova
et. al, 2005). Several of these cultivars are described in more
detail in Table 1.
In Tajikistan, walnut research has been conducted at the
Scientific Research Institute of Fruit Growing, Viticulture
and Vegetable Production of the Scientific-Industrial
Association “Bogparvar” and at the Tajikistan Forestry
62101st Annual Report, September 2011
Institute. Breeders in Tajikistan developed more than 20 cultivars. The most notable are: ‘Tadjikskiy #25’, ‘Gissarskiy
#7’, ‘Muminobadskiy #38’, and‘Muminobadskiy #55’
(Kholdorov, 1990).
Central Asian walnuts at Rutgers University,
New Jersey, USA
As mentioned in the introduction, the genetic resources
likely exist to develop new walnut cultivars that are consistently productive and better adapted too much of the world’s
temperate zones (McGranahan and Leslie, 1991). However,
breeding programs are limited, as are germplasm collections holding potentially valuable Central Asian accessions
expressing a diversity of useful traits. Germplasm from
Central Asia, especially in northern areas and high elevations, has not been widely evaluated in North America and
some accessions may hold great opportunities for improvement, especially in adaptation to new regions. Fortunately,
with improving political situations, access to some of this
extensive pool of genetic resources has become available to
western breeders.
In October 2003, a walnut collection trip was made by
several of the authors across a wide area of Kyrgyzstan and
Uzbekistan. Seeds from 33 different provenances totaling over 1,529 nuts, were collected in the Jalal-Abad and
Arslanbob regions of Kyrgyzstan and the Tashkent province, Bostandik, and Nurata regions of Uzbekistan (Table 2).
Collections of fresh walnuts were made from improved cultivars and selections growing in breeding orchards at a number of research institutes, as well as purchased at local markets and bazaars, where they appeared to be from backyard
gardens and/or small local farms. These collection efforts
were made in close association with the Schroeder Uzbek
Research Institute of Fruit Growing, Viticulture, and Wine
Production, the Bostandik branch of the Schroeder Institute,
the Tashkent State Agrarian University, the Tashkent Forestry
Institute in Uzbekistan, the Jalal-Abad Biosphere Institute
in Kyrgyzstan, the K.I. Skryabin Agrarian University
(Kyrgyzstan), and the Kyrgyz Agricultural Research
Institute. The seeds were cleaned and inspected by proper
authorities in Uzbekistan and Kyrgyzstan and were brought
back to the United States under proper permits. Immediately
upon arrival, they were soaked in fresh water overnight and
then placed in polyethylene bags filled with moist peat moss
to undergo stratification (moist chilling) to break dormancy.
Seeds were held for four months at 4°C. In February 2004,
they were planted in 0.61 x 0.91 x 0.15 m wooden boxes
with wire mesh on the bottom filled with a mix of 80% peat
moss and 20% perlite in a warm greenhouse. Germination
percentage was around 50% for most groups (Table 2). After
about 8 weeks, the resulting seedlings were planted into
Table 1. Examples of Persian walnut cultivars developed at the Bostandik branch of the Richard R. Schroeder
Uzbek Research Institute of Fruit Growing, Viticulture, and Wine Production
‘Ubilini’
Selected from the forest of Bostandik region. Grafted seedlings begin to bear fruit the 4th year. The fruits ripen from
September 5 to 27. The trees are slightly damaged by mites (Eriophyes tristatus), leaf rollers, moths (Sarrothripus
musculana), and walnut anthracnose. The cultivar partially self-pollinates, but the best production occurs with the
planting of pollinator trees. The best pollinators are ‘Bostandik’, ‘Tonkoskorlupnii’ and ‘Kon-Sai’. Average nut weight
is 11.72 g with 50.4 % kernel by weight. The flavor is sweet and buttery. Nuts are round in shape, 36x34x35 mm, with
a slightly prominent apex, rounded base, and broad seam. Its main advantages are high quality nuts, relatively high
yield, resistance to spring frosts, and precocious bearing.
‘Bostandik’
Selected from the forest of Bostandik region. Grafted seedlings begin to bear fruit the 4th year. The fruits ripen from
September 15 to October 1st. This cultivar is resistant to late spring frosts. It is slightly damaged by mites (Eriophyes
tristatus), leaf rollers, moths (Sarrothripus musculana), and walnut anthracnose. It is self sterile; For normal fruiting the
cultivar ‘Ubilini’ is recommended for pollinating. Nuts are oblong in shape, 39x34x53 mm, with a round base, slightly
drawn out apex, and a sharp and low seam. The average nut weight is 13.26 g. The kernel has a sweet, buttery flavor
and separates well from the shell, with 48.5 % kernel by weight. The main advantages of this cultivar are high quality
nuts, resistance to spring frosts, and precocious bearing.
‘Ideal’
Selected from cultivated plantings in the Bostandik district. The cultivar is exceedingly precocious. One-year-old
grafted trees are capable of bearing fruits and plants from seeds can produce nuts as early as two years old. The cultivar
has the ability to bloom a second time and bring a second nut crop. The first harvest is in late September and the second
can be anywhere from October through the first 10 days of November. It is slightly damaged by mites and walnut
anthracnose. ‘Ideal’ is self sterile in its first bloom. Traditional recommendations for pollinizers are seedlings of
‘Ideal’. During the second flowering male and female flowers develop simultaneously, thus ensuring self-pollination.
Nuts are flat-round, 51x50x51 mm, the apex is slightly unfolded, the base rounded, and the seam is narrow and slightly
protruding. The average nut weight is 10.25 g with 50.8% kernel; the kernel has a sweet, buttery flavor, and separates
easily from the shell. The main advantages of the variety are extremely precocious flowering, multiple flowering, fruits
produced in clusters, and high-quality kernels.
‘Rodina’
Hybrid #56, obtained from crossing the cultivars ‘Bostandik’ and ‘Orekh Serdtcovidniy’. This cultivar grows very
rapidly, has high frost resistance, and low susceptibility to walnut anthracnose. Nuts are large, 44x54x52 mm, oval
in shape, with a slightly unfolded apex, rounded base, and a narrow, slightly protruding seam. The average weight is
15.51 g, with 49.5 % kernel by weight; the kernel has a sweet, buttery flavor and separates well from the shell.
Table 2. Persian walnut (Juglans regia) collection from Uzbekistan and Kyrgyzstan established at Rutgers
University Horticultural Research Farm 1, North Brunswick, New Jersey
Number
of nuts
collected
Trees
in field
2004
Trees
in
field
2011
Trees
with
nuts
2011
Rutgers
ID #
Cultivar name (if available); Collection location, and brief description of nut
O3020
‘Kyrgyzskya’; Arslanbob Kyrgyzstan; large-size nut
82
14
11
4
O3021
Precocious form; Arslanbob Kyrgyzstan; small-med size nut, very thin shell,
not fully formed (naturally have holes in shell), very light colored kernel (nearly
white)
54
47
32
5
O3022
Wild tree; Arslanbob, Kyrgyzstan; very healthy tree, appears anthracnose
resistant, small nut with thin shell
48
35
27
6
O3023
Arslanbob mix; Arslanbob, Kyrgyzstan, healthy trees from planting, mixture of
very small to large-size nuts
131
95
57
0
O3024
‘Ak Terek’; Arslanbob, Kyrgyzstan; small nut; very thin shell, high kernel %,
anthracnose susceptible
34
25
20
3
O3025
‘Uigursky’; Arslanbob, Kyrgyzstan; med-large sized nut, well-filled with light
color kernel, good flavor, healthy tree
50
32
20
2
101st Annual Report, September 2011
63
Rutgers
ID #
Cultivar name (if available); Collection location, and brief description of nut
Number
of nuts
collected
Trees
in field
2004
Trees
in
field
2011
Trees
with
nuts
2011
O3026
‘Kyrgyzskya Bomba’; Arslanbob, Kyrgyzstan; very large nut, some well-filled;
great flavor; light-colored kernel
44
4
4
4
O3027
Thin shell form; Arslanbob, Kyrgyzstan; white colored kernel, bright yellow
shell, some shells not complete (naturally have holes in shell)
31
23
9
0
O3028
‘Ak Terek’; Jalal-Abad Biosphere Inst., Kyrgyzstan; same name but visually
different than 03024; med.-large size nut
46
17
15
0
O3029
Osh Form; Jalal-Abad Biosphere Inst., Kyrgyzstan; small-med. size nut
53
22
17
0
O3030
‘Uigursky’; Jalal-Abad Biosphere Inst., Kyrgyzstan; similar to 03025; med-lg
size nut
58
17
16
2
O3031
‘Ideal’; Bostandik Schroeder Inst. Uzbekistan; small nut from secondary
flowering
35
26
11
0
O3032
Precocious Form; Jalal-Abad Biosphere Inst., Kyrgyzstan; from secondary spike
of nuts; very small nut
39
18
5
0
O3033
‘Hybridiy’; Bostandik Schroeder Inst., Uzbekistan; medium size nut
58
45
14
3
O3034
‘Pioner’; Bostandik Schroeder Inst., Uzbekistan; med-large size nut, well-filled
47
26
12
2
O3035
‘Mirnii’; Bostandik Schroeder Inst., Uzbekistan
46
14
8
0
O3036
‘Kazahstansky’; Bostandik Schroeder Inst., Uzbekistan; very healthy tree;
2
1
0
0
O3037
‘Bostonliksky’; Bostandik Schroeder Inst., Uzbekistan; med-large size nut
52
31
19
2
O3038
‘Parkent’; Tashkent Prov., Uzbekistan; med-large size nut
41
35
15
9
O3039
Big Sam type; Samarkand Prov., Uzbekistan; very large nut
26
15
11
4
O3040
Big Sam type; Old City Market, Tashkent, Uzbekistan; similar to 03039
17
11
7
4
O3041
Pointed Nut; Old City Market, Tashkent, Uzbekistan; large size nut, well filled
39
26
13
4
O3042
PD1; Tashkent State Ag Univ., Tashkent, Uzbekistan; med. size nut
40
16
9
0
O3043
PD2; Tashkent State Ag Univ., Tashkent, Uzbekistan; med. size nut
35
12
7
0
O3044
PD3; Tashkent State Ag Univ., Tashkent, Uzbekistan; med. size nut
35
19
10
0
O3045
‘Nani’; Tashkent Prov., Bostandik; Uzbekistan, med-large size nut
34
22
10
1
O3046
PD4; Tashkent State Ag Univ., Tashkent, Uzbekistan, medium size nut
35
13
8
2
O3047
Bostandik #55; Tashkent Forestry Inst.; Uzbekistan; med-large size nut
35
17
10
1
O3048
Husk Maggot Resistant Form; Tashkent Forestry Inst. Uzbek.; small wild-type
nut
41
33
22
0
O3049
Bostandik #66; Tashkent Forestry Inst. Uzbekistan; med-large size nut
36
9
6
0
O3050
Bostandik #48; Tashkent Forestry Inst. Uzbekistan; med-large size nut
44
29
23
3
O3051
Nurata Mix; Nurata region, Uzbekistan. med to large size nuts; mixture of nuts
from a collection made by Tashkent Forestry Institute personnel
131
101
63
22
O3052
Unknown Form; Bostandik Area, Uzbekistan; medium size nut
30
21
13
2
1529
871
524
85
Totals
64101st Annual Report, September 2011
1-gallon plastic containers and in mid-summer were moved
outside under shade cloth to acclimate to outdoor conditions.
In August 2004, the 866 resulting trees were planted in
the field at the Horticultural Research Farm 1 at Rutgers
University in North Brunswick, New Jersey, USA. Trees
were organized by accession number and were planted at a
spacing of approximately 1.0 or 1.5 m in the row with 5.0
m between the rows. Trees were irrigated at planting and as
needed for the remainder of 2004 with no additional irrigation applied to the trial to date. Weed control was performed
by hand for the first two years and was then accomplished
through chemical herbicides and mowing. The trees are currently being evaluated for survival, winter-injury (cold-hardiness), growth habit (apical dominance and vigor), disease
resistance (presence of anthracnose and various stem cankers), and nut production. In the future, flowering phenology, nut quality attributes (size, shape, kernel percent, etc.),
and overall yield will be also examined.
To date, no sprays of fungicides or pesticides have been
applied to the trees to encourage natural disease and insect
infestation to look for potential sources of resistance. Over
the first eight growing seasons of the trial, very little evidence of damage to vegetative structures due to cold temperatures has been evident, suggesting cold hardiness is not
an issue for central New Jersey (USDA Cold Hardiness Zone
6B). However, most trees appear highly susceptible to walnut anthracnose, which was somewhat expected as they originate from a much less humid environment than that of New
Jersey. Furthermore, nearly all plants in the trial tend to leaf
out very early in the year if the temperatures are unusually
warm (not atypical for New Jersey), which could present a
problem if a late frost did occur (none happened to occur in
this plot since its establishment in 2004).
In fall 2010, the first round of culling was made in the
plot to reduce competition between the trees, which, when
shading one another, can reduce or inhibit the production of
nuts. Trees were selected for removal within each progeny
and were cut due to poor or weak growth habits, the presence of stem cankers due to disease, and/or for significant
numbers of dead tips in the canopy, which can be from disease or winter injury. As of 2011, approximately 60% of
the original trees remain in the field (Table 2). Of this total,
only 85 trees (approximately 16%) have begun to produce
nuts (Table 2), thus no evaluations for nut characteristics
have taken place. Most trees with nuts have less than 10
nuts per tree, with only a few trees producing more than ten
and none producing more than 25 (data not shown). Due
to the high disease and insect pressure in the field, which is
surrounded by numerous native black walnut (Juglans nigra
L.) trees, nuts most likely will not be harvested until 2012
or 2013 when a much more significant crop should be produced that can partially overcome some of the high disease,
insect, and rodent pressure. However, where possible, nuts
will be evaluated on the tree prior to being taken by squirrels
or killed by bacterial blight for approximate number of nuts,
position of bearing (terminal and/or lateral bearing), relative
size of husk (and nut), presence of bacterial blight, and nuts
per cluster (if clusters are present).
Interestingly, several trees in our planting expressed extreme precocity, bearing nuts at two and three years of age,
as well as producing a second bloom of hermaphroditic
flower spikes (Figures 5 & 6). Unfortunately, these trees
are also very dwarf and highly susceptible to anthracnose.
To date, none of the second flush of flowers has set any nuts
in our trial, perhaps due to a lack of suitable pollen at the
time. Also, many of these plants have declined in recent
years due to poor health, and as such appear poorly adapted
to our region.
In the fall of 2011, additional trees will be removed from
the planting to reduce competition in subsequent years. Trees
will be removed based on low vigor and small stem diameter (comparisons made within each progeny) with decisions
Figure 5. Precocious, three-year-old Central Asian Persian walnut
seedling in Rutgers planting showing nuts on the tree. Photo by T.
Molnar.
101st Annual Report, September 2011
65
Figure 6. Central Asian Persian walnut in Rutgers planting
showing young nut and second bloom of a hermaphroditic flower
spike. Photo by T. Molnar.
for removal also based on the presence, quality, and quantity
of nuts. Trees will also be removed based on levels of anthracnose and presence of stem cankers and other maladies
within the progenies, to make room for the superior trees
and to promote their production of nuts. It is the goal of the
authors to save several of the best trees from each of the 33
accessions for long-term evaluation, research, and possible
use in breeding. A short-term goal, which we hope to implement in 2012 or 2013, is to use SSR (microsatellite) markers
(Dangl et al., 2005) to evaluate the genetic diversity present
in the collection to increase our knowledge of Central Asian
walnuts and, more practically, to assist us in deciding what
accessions to preserve for future use.
Conclusions
Opportunities exist through targeted germplasm collection and breeding to significantly expand the geographic
and climatic range where Persian walnuts can be produced
commercially, as well as grown and enjoyed as garden and
landscape trees and as sources of high-quality timber and
66101st Annual Report, September 2011
other products. New germplasm available from the former
Soviet Union, and in particular Central Asia, may hold the
key to better utilizing this species in North America. Here,
genetically diverse germplasm holdings exist in the form of
tree orchards at research institutes containing numerous cultivars and breeding selections, locally grown plants (landraces, both clonal and seedling) found in backyard plantings,
and a number of highly diverse natural walnut forests, some
in very cold regions, which are becoming more accessible to
western researchers. However, the loss of habitat and lack
of regeneration of native trees due to development and grazing, as well as the poor financial state of institutions in this
region, is putting pressure on the walnut genetic resources
remaining in Central Asia. This article aims to highlight
these valuable resources to help promote their improved utilization, management, and preservation. Increased efforts to
study and introduce walnuts from Central Asia may facilitate
the development of new and improved cultivars with the goal
of expanding the regions where reliable walnut production is
possible. The small, yet diverse collection held at Rutgers
will be evaluated over the next five to six years with the goal
of reducing the population to around 100 select trees, each
representing superior plants of most of the individual collection accessions (progenies) in Table 2. Researchers and walnut enthusiasts interested in working with the collection are
encouraged to contact the lead author. While it was not discussed in this article, a subset of this germplasm, as well as
a number of more recent seed introductions (Ford and Funk,
2009), have also been established in Utah and Idaho for similar evaluation, to which we will compare later results. The
Intermountain west region has a climate much more similar
to that of Central Asia than New Jersey, and we expect to
find new plants from our collection efforts very well-adapted
to and productive in this region in the coming years.
Acknowledgments
The authors would like to acknowledge support from the
New Jersey Agricultural Experiment Station, the Rutgers
Center for Turfgrass Science, and Improving Perennial
Plants for Food and Bioenergy, Inc. We also thank the late
Prof. Uri M. Djavacynce (SURIFGVWP), Acad. Djamin
Akimaliev (Kyrgyz Agricultural Research Institute), Dr.
Ishembay Sodembekov (Kyrgyz Agrarian University named
after K.I. Skryabin), for their manuscript contributions and/
or for assistance in the collection of germplasm.
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