Conserving Wheat Genetic Resources

Abstract

Wheat genetic resources (WGR) are represented by wheat crop wild relatives (WCWR) and cultivated wheat varieties (landraces, old and modern cultivars). The conservation and accessibility of WGR are fundamental due to their: (1) importance for wheat breeding, (2) cultural value associated with traditional food products, (3) significance for biodiversity conservation, since some WCWR are endangered in their natural habitats. Two strategies are employed to conserve WGR: namely in situ and ex situ conservation. In situ conservation, i.e. the conservation of the diversity at the location where it is found, consists in genetic reserves for WCWR and on farm programs for landraces and old cultivars. Ex situ conservation of WGR consists in the storage of dry seeds at cold temperatures in germplasm banks. It is currently the most employed conservation strategy for WGR because it allows the long-term storage of many samples in relatively small spaces. Due to the great number of seed samples of WGR and associated passport data stored in genebanks, it is increasingly important for the management of ex situ collections to: (1) employ efficient database systems, (2) understand seed longevity of the seed accessions, (3) setup safety backups of the collections at external sites.

Full text

299© The Author(s) 2022
M. P. Reynolds, H.-J. Braun (eds.), Wheat Improvement,
https://doi.org/10.1007/978-3-030-90673-3_17
Chapter 17
Conserving Wheat Genetic Resources
FilippoGuzzon, MaraevaGianella, PeterGiovannini, andThomasS.Payne
Abstract Wheat genetic resources (WGR) are represented by wheat crop wild
relatives (WCWR) and cultivated wheat varieties (landraces, old and modern culti-
vars). The conservation and accessibility of WGR are fundamental due to their: (1)
importance for wheat breeding, (2) cultural value associated with traditional food
products, (3) signicance for biodiversity conservation, since some WCWR are
endangered in their natural habitats. Two strategies are employed to conserve WGR:
namely in situ and ex situ conservation. In situ conservation, i.e. the conservation of
the diversity at the location where it is found, consists in genetic reserves for WCWR
and on farm programs for landraces and old cultivars. Ex situ conservation of WGR
consists in the storage of dry seeds at cold temperatures in germplasm banks. It is
currently the most employed conservation strategy for WGR because it allows the
long-term storage of many samples in relatively small spaces. Due to the great num-
ber of seed samples of WGR and associated passport data stored in genebanks, it is
increasingly important for the management of ex situ collections to: (1) employ
efcient database systems, (2) understand seed longevity of the seed accessions, (3)
setup safety backups of the collections at external sites.
Keywords Germplasm banks · Genetic reserves · On farm conservation · Seed
conservation · Seed viability · Wheat wild relatives
F. Guzzon (*) · T. S. Payne
International Maize and Wheat Improvement Center (CIMMYT), Texcoco, Mexico
e-mail: f.guzzon@cgiar.org; t.payne@cgiar.org
M. Gianella
Department of Biology and Biotechnology “L.Spallanzani”, University of Pavia, Pavia, Italy
e-mail: maraeva.gianella01@universitadipavia.it
P. Giovannini
Global Crop Diversity Trust, Bonn, Germany
e-mail: peter.giovannini@croptrust.org

300
17.1 Learning Objectives
• To know the principal categories of wheat genetic resources,
• To know the principles of in situ conservation of wheat genetic resources,
• To know the principles of ex situ seed conservation of wheat genetic resources in
germplasm banks.
17.2 Introduction– Plant Genetic Resources (PGR)
andtheir Conservation
Wheat domestication occurred 9000 to 12,000BCE, resulting in cereal crops within
the genus Triticum, two of which are among the most widely grown crops world-
wide, namely bread wheat (T. aestivum subsp. aestivum) and durum wheat (T. turgi-
dum subsp. durum). Wheat genetic resources are represented by several domesticated
and wild taxa.
Overall, plant genetic resources for food and agriculture (PGRFA) are dened as
“any genetic material of plant origin of actual or potential value for food and agri-
culture” [1]. Genetic diversity is the foundation for crop improvement and is an
insurance against unforeseen threats to agricultural production such as plant patho-
gens and climate changes [2].
Wheat genetic resources can be grouped in the following biological/agronomic
categories:
– Cultivated wheats: wheat species were gathered by ancient societies, gradually
resulting in the domestication of several wheat crop taxa. Cultivated materials
consist of:
• Landraces (or primitive cultivars): “dynamic populations of a cultivated plant
that have historical origin, distinct identity and lacks formal crop improve-
ment, as well as often being genetically diverse, locally adapted and associ-
ated with traditional farming systems” [3];
• Old cultivars: sometimes known as obsolete cultivars, the term refers to culti-
vated varieties which have fallen into disuse;
• Modern cultivated varieties (modern cultivars): agronomic varieties in current
use and newly developed varieties;
• Special stocks: such as advanced breeding lines (i.e. pre-released varieties
developed by plant breeders), mapping populations, CRISPR-edited lines and
cytogenetic stocks.
– Crop wild relatives (CWR): wild plant species that are genetically related to
cultivated crops. CWR are not only the wild ancestors of the domesticated plant
but also other more distantly related species.
F. Guzzon et al.

301
Another category of PGR of signicance are the neglected crops, also referred as
underutilized or orphan crops: “crop species that have been ignored by science and
development but are still being used in those areas where they are well adapted and
competitive” [4]. An example is the einkorn (Triticum monococcum subsp. mono-
coccum) currently cultivated by small-holder farmers in limited areas in Europe,
Middle East and North Africa. In recent years, there is a renewed interest for ein-
korn, mainly due to its nutraceutical properties and adaptations to organic agricul-
ture [5].
The aim of plant genetic resources conservation is to ensure that the maximum
possible allelic genetic diversity, and therefore potential useful traits for breeding of
a crop, is maintained and is available and accessible for utilization. Crop domestica-
tion and selection have favored preferred haplotypes and have reduced genetic
diversity. The conservation of landraces and CWR is particularly important consid-
ering that in those plants is concentrated the bulk of genetic diversity and of poten-
tial useful traits within a crop genepool. The conservation of modern cultivar is also
of great importance since breeders often wish to access “improved” or rened
sources of PGR diversity. Conserving PGR is important not only in order to provide
useful traits for crop improvement but also for cultural reasons, since many landra-
ces and neglected crops are connected to local identities, especially through local
foods and ceremonial products.
Two main strategies are employed for the conservation of PGR, namely in situ
and ex situ conservation. In situ conservation, i.e. the conservation of the diversity
in its natural habitat, means the designation, management and monitoring of a popu-
lation at the location where it is currently found. On the other hand, the ex situ
conservation, i.e. the conservation of a genetic resources outside its natural habitat,
is intended as the sampling, transfer and storage of a sample of a population of a
certain species away from the original location where it was collected. Several ex
situ conservation strategies are employed for different crops e.g. in vitro storage,
seed banking, eld genebanks, DNA banks. Seed banking allows the storage of
many seed accessions in relatively small spaces; seed collections are economically
viable and can provide a good sample of the genetic diversity within the crop gene-
pool, usually remaining viable for the long-term [6].
17.3 Wheat Genetic Resources (WGR)
17.3.1 Domesticated Wheats
Two species of wheat are widely cultivated, namely: the hexaploid Triticum aesti-
vum (ABD genome) and the tetraploid T. turgidum (AB genome, Table17.1). Both
species include several subspecies (Table17.1). As previously mentioned, einkorn
(Triticum monococcum L. subsp. monococcum, A genome) is a locally cultivated,
diploid wheat.
17 Conserving Wheat Genetic Resources

302
Two additional species of wheat were cultivated in western Georgia but are prob-
ably currently extinct under cultivation and conserved only in germplasm banks:
T. timophevii subsp. timopheevii (Chelta Zanduri or Timopheevi wheat, tetraploid,
AG) and T. zhukovskyi (Zhukovsky’s wheat, hexaploid, AGG, Table17.1). The
Zhukovsky’s wheat was described in the 1960s growing in a restricted area of west-
ern Georgia. This hexaploid wheat is an allopolyploid, spontaneous hybrid between
Timopheevi wheat (T. timopheevii) and einkorn (T. monococcum). Zhukovsky’s
wheat and the two parental species used to be cultivated together in a complex of
domesticated wheats named zanduri.
Table 17.1 Domesticated wheats. The more common domesticated subspecies of T. aestivum and
T. turgidum are also presented
Taxonomic name
Common English
Name Genome(s)
Accessions
conserved ex situa
Triticum monococcum L. subsp.
monococcum
Einkorn A 6971
Triticum monococcum L. subsp. sinskajae
(Filat. & Kurkiev) Valdés & H.Scholz
Naked einkorn A 23
Triticum turgidum L. Rivet wheat AB 179,701
Triticum turgidum L. subsp. dicoccon
Schrank (Thell.)
Emmer AB 8793
Triticum turgidum L. subsp. durum (Desf.)
van Slageren
Durum wheat AB 149,485
Triticum turgidum L. subsp. carthlicum
(Nevski) Á. Löve & D.Löve
Persian wheat AB 1382
Triticum turgidum L. subsp. polonicum (L.)
Thell.
Polish wheat AB 766
Triticum turgidum L. subsp. turanicum
(Jakubz.) Á. Löve & D.Löve
Khorasan wheat AB 461
Triticum turgidum L. subsp. turgidum Poulard wheat AB 7171
Triticum timopheevii (Zhuk.) Zhuk. subsp.
timopheevii
Chelta Zanduri AG 189
Triticum aestivum L. ABD 511,130
Triticum aestivum L. subsp. aestivum Bread wheat ABD 243,634
Triticum aestivum subsp. compactum
(Host) Mac Key
Club wheat ABD 1921
Triticum aestivum subsp. macha (Dekapr.
& Menabde) Mac Key
Macha wheat ABD 374
Triticum aestivum L. subsp. spelta (L.)
Thell.
Spelt ABD 7070
Triticum aestivum subsp. sphaerococcum
(Percival) Mac Key
Indian wheat ABD 684
Triticum zhukovskyi Menabde & Eritzjan Zhukovsky’s
wheat
AAG 71
aAccessions conserved ex situ estimated using data from [7], FAO-WIEWS, USDA GRIN and data
provided directly by CIMMYT.The number of accessions of T. aestivum and T. turgidum includes
also the accessions of the different subspecies
F. Guzzon et al.

303
Wheat landrace cultivation was endemic throughout the Mediterranean Basin,
Europe, Near East, Ethiopia, Caucasus, China and Southern Asia, since time imme-
morial. Wheat landraces were subsequently diffused to Australia, South Africa and
the Americas. For example, the Creole wheats descendant of Spanish wheats
imported from the sixteenth century were cultivated in Mexico for four centuries by
small-scale farmers. In many areas of the world those landraces were replaced since
the twentieth century by modern, improved varieties.
Formal wheat breeding started in the eighteenth century, eventually resulting in
a plethora of old and modern cultivars. Noteworthy examples of old cultivars of
bread wheat are: ‘Sherriff’s Squarehead’, selected in the end of the nineteenth cen-
tury in Great Britain, ‘Ardito’ and ‘Mentana’ selected in Italy in the rst decades of
twentieth century, ‘Marquis’ selected in Canada at the beginning of twentieth cen-
tury, the semi-dwarf cultivar ‘Norin 10’ selected in Japan in 1935 and the cultivar
‘Bezostaya 1’ selected in Russia in the1950s. Several old cultivars of durum wheat
also exist, e.g. the renowned ‘Senatore Cappelli’ released in Italy in 1915. Today,
many old cultivars gure in the pedigree of modern wheat varieties and are there-
fore of great priority for conservation (see Chap. 2 for a history of wheat breeding).
17.3.2 Wheat Crop Wild Relatives (WCWR)
A crop “genepool concept” was dened by Harlan and De Wet [8] based on formal
taxonomy and genetic relatedness, determined by the crossing ability between
related species. Three main categories are considered: Primary Gene Pool (GP-1)
comprising the domesticated crop and its closed wild forms with which the crop can
cross producing fertile hybrids; Secondary Gene Pool (GP-2) which includes less
closely related species, from which gene ow, even if difcult, is still possible using
conventional breeding techniques; Tertiary Gene Pool (GP-3) which includes spe-
cies from which gene transfer to the crop is impossible without the use of “rather
extreme or radical measures”. The gene pool levels here presented are based on:
“The Harlan and de Wet Crop Wild Relative Inventory” (see: https://www.cwrdiver-
sity.org/checklist/). An additional gene pool level classication system is histori-
cally used in wheat based on chromosome pairing and recombination (see Sect. 16.4).
The primary gene pool (GP-1, Fig.17.1) of wheat comprises, beside the afore-
mentioned domesticated wheats (Table17.1), also the four wild species of the genus
Triticum (sensu van Slageren 1994 [9]) included in Table17.2.
GP-2 includes 22 species of the genus Aegilops and Amblyopyrum muticum
(Table 17.3, Figs. 17.1 and 17.2). The geographic center of diversity, the areas
where the most Aegilops grows in sympatry, is the Fertile Crescent, Turkey, the
southern Caucasus, as well as the shores of the Aegean Sea. Spontaneous crosses
between Aegilops species and cultivated wheats have been observed in several areas
of the natural distribution of Aegilops. Those hybrids are classied in the genus x
Aegilotriticum and are mostly sterile.
17 Conserving Wheat Genetic Resources

304
Nevertheless, hybridization events between Aegilops and Triticum species were
indeed involved in the process of evolution and domestication of tetraploid and
Fig. 17.1 Schematic representation of the genepool of wheat, only some species are shown
Table 17.2 Wild wheats of the genus Triticum
Taxonomic name
GP-1 ancestor
of Native to Genome(s)
Accessions
conserved ex
situa
Triticum monococcum L.
subsp. aegilopoides (Link)
Thell.
Einkorn Near East,
Western Asia,
southern Balkans
A 5816
T. timopheevii (Zhuk.)
Zhuk. subsp. armeniacum
(Jakubz.) van Slageren
Timopheevi Near East,
southern
Caucasus
AG 1849
T. turgidum L. subsp.
dicoccoides (Körn. ex Asch.
& Graebn.) Thell.
Emmer &
tetraploid
wheats
Near East AB 11,535
T. urartu Tumanjan ex
Gandilyan
Tetraploid
wheats
Near East,
southern
Caucasus
A 2274
aAccessions conserved ex situ estimated using data from Genesys PGR, FAO-WIEWS, USDA
GRIN and data provided directly by CIMMYT
F. Guzzon et al.

305
Table 17.3 The species of Aegilops, organized in the different sections in which is divided the
genus, and Amblyopyrum. Data on the genome, ploidy and natural distribution are also provided
Section Species name Genome(s) Ploidy Distribution
Accessions
conserved ex
situa
Aegilops Ae. umbellulata
Zhuk.
U Diploid Turkey, Fertile
Crescent, Caucasus,
Iran
794
Ae. biuncialis
Vis.
UM Tetraploid Mediterranean
Basin, Fertile
crescent, Caucasus,
Russia, Ukraine
2505
Ae. columnaris
Zhuk.
UM Tetraploid Turkey, Crete,
Fertile Crescent,
Iran
509
Ae. geniculata
Roth
MU Tetraploid Mediterranean
Basin, Caucasus,
Turkey, Crimea
3218
Ae. kotschyi
Boiss.
SU Tetraploid Middle East, North
Africa, Arabia,
Central Asia
613
Ae. neglecta Req.
ex Bertol.
UM/UMN Tetra/
Hexaploid
Mediterranean
Basin, Crimea,
Middle East,
Turkmenistan
1818
Ae. peregrina
(Hack.) Maire &
Weiller
SU Tetraploid Middle East,
Greece, North
Africa, Arabia
1642
Ae. triuncialis L. UC Tetraploid Mediterraean Basin,
Crimea, Caucasus,
Central Asia
6647
Comopyrum Ae. comosa Sm. M Diploid Southern Balkans,
Cyprus, Turkey
423
Ae. uniaristata
Vis.
N Diploid Croatia, Greece,
Albania, Italy,
Turkey
79
Cylindropyron Ae. caudata L. C Diploid Aegean, Turkey,
Fertile Crescent
701
Ae. cylindrica
Host
DC Tetraploid Eastern Europe,
Middle East,
Caucasus, Central
Asia
3893
(continued)
17 Conserving Wheat Genetic Resources

306
hexaploid wheats. The wild tetraploid wheats (i.e. T. turgidum subsp. dicoccoides
and T. timopheevi subsp. armeniacum) resulted from hybridization events that
occurred a few hundred thousand years ago between T. urartu and an unknown spe-
cies of the genus Aegilops, probably similar to the only existing outcrossing species
of this genus, Ae. speltoides. Hexaploid wheats belonging to T. aestivum do not have
a single wild progenitor. This crop arose from hybridization events that occurred
probably 8000BCE in the coastal areas of the Caspian Sea, between the domesti-
cated T. turgidum susbsp. dicoccon and the wild species Ae. tauschii (Fig.17.3).
Wild species of Triticum and Aegilops have signicantly contributed to wheat
improvement, especially in terms of biotic resistances, as well as for grain yield and
Table 17.3 (continued)
Section Species name Genome(s) Ploidy Distribution
Accessions
conserved ex
situa
Sitopsis Ae. bicornis
(Forssk.) Jaub. &
Spach
SbDiploid Cyprus, North
Africa, Middle East
505
Ae. longissima
Schweinf. &
Muschl.
SlDiploid Egypt, Israel/
Palestine, Jordan
1779
Ae. sharonensis
Eig
Ssh Diploid Israel/Palestine,
Lebanon
2546
Ae. searsii
Feldman &
Kislev ex
K.Hammer
SsDiploid Israel/Palestine,
Syria, Jordan, and
Lebanon
519
Ae. speltoides
Tausch
S Diploid Fertile crescent,
Turkey,
Southeastern
Europe
3369
Vertebrata Ae. tauschii
Coss.
D Diploid Caspian seashores,
Caucasus, Central
Asia, China
7186
Ae. crassa Boiss. DM/DDM Tetra/
Hexaploid
Middle East,
Central Asia
608
Ae. vavilovii
(Zhuk.) Chennav.
DMS Hexaploid Middle East 345
Ae. ventricosa
Tausch
DN Tetraploid Mediterranean
Basin, North Africa
486
Ae. juvenalis
(Thell.) Eig
DMU Hexaploid Central Asia,
Azerbaijan, Fertile
Crescent
132
Genus
Amblyopyrum
Amblyopyrum
muticum (Boiss.)
Eig
T Diploid Turkey, Armenia 181
aAccessions conserved ex situ estimated using data from Genesys PGR, FAO-WIEWS, USDA
GRIN and data provided directly by CIMMYT
F. Guzzon et al.

307
abiotic stress tolerance [11]. The genetic diversity of species belonging to the GP-1
and GP-2 can be exploited to generate Synthetic Wheat Hexaploid (SWH) and chro-
mosomal translocation introgressions. The most common SWH are produced by
hybridizing durum wheat with Ae. tauschii, as the latter is a huge source of diversity,
being adapted to a variety of environments in different subspecies and morphologi-
cal varieties (see Chap. 18).
The GP-3 of wheat includes grass species of the genera Agropyron, Elymus,
Leymus and Thinopyrum (Fig.17.1). Those species have been hybridized with cul-
tivated wheat as genetic sources for disease resistance, salinity tolerance, and other
traits. Given the sexual barrier between cultivated wheat species and their tertiary
gene pool, to transfer traits from GP-3 species both physical and genetic methods
(causing random chromosome breaks and promoting recombination) have been
used, namely: spontaneous translocations, in vitro cultures, irradiation, and induced
homologous recombination [12] (see Chap. 18).
Fig. 17.2 Examples of
Wheat Crop Wild Relatives
(WCWR): (a) T. turgidum
subsp. dicoccoides at
CIMMYT screenhouse
(Texcoco, Mexico); (b) Ae.
biuncialis, wild population
at Santeramo in Colle
(Italy); (c) Ae. geniculata
(left) and Ae. ventricosa
(right) growing together in
Garda (Italy); (d) Ae.
tauschii at CIMMYT
screenhouse (Texcoco,
Mexico); (e) x-ray scan of
a spikelet of Ae. biuncialis,
a dimorphic pair of seeds
can be noticed in the basal
fertile spikelet; (f) x-ray
scan of a spike of Ae.
cylindrica, in some of the
spikelets composing the
spike a pair of dimorphic
seeds can be noticed
17 Conserving Wheat Genetic Resources

308
17.4 Wheat Genetic Resources Conservation
17.4.1 In situ Conservation
Some wheat wild relatives are considered endangered by the International Union for
Conservation of Nature (IUCN) at global level and therefore their conservation is
considered priority: i.e. Amblyopyrum muticum (EN-endangered), Aegilops sharo-
nensis (VU-vulnerable), Agropyron dasyanthum (EN) and Agropyron cimmericum
(EN). Other species, even if labeled as of “least concern” are showing populations
declines in their natural habitats (e.g. Aegilops longissima). At continental level
some species are recognized as endangered, e.g. in Europe Ae. tauschii is consid-
ered EN and Ae. bicornis is VU [13]. Considering the importance of wheat wild
relatives for wheat breeding, it is also important to guarantee the conservation of
species and populations that are not threatened but that have a great impact on wheat
improvement as carriers of useful traits.
Fig. 17.3 Schematic representation of wheat evolution and domestication. Solid line represents
spontaneous events of speciation and hybridization. Dashed line indicates human selection events.
(Redrawn with permission from [10] by Marco Canella, Padua, Italy)
F. Guzzon et al.

309
In this context, the implementation of in situ conservation strategies for wheat
wild relatives is necessary. Indeed, even if ex situ conservation of genetic resources
is easy and cost effective, in situ conservation has the advantage of allowing species
to evolve in their original place and to retain a higher genetic diversity compared to
seed bank accessions.
Maxted etal. [14] and Phillips etal. [15] identied regional diversity hot spots of
Aegilops in which conservation reserves should be established: Syria and north
Lebanon, central Israel, north-west Turkey, the Hatay region of Turkey, Turkmenistan
and south France.
In Table17.4 are listed the existing in situ reserves that conserve wild wheats.
In situ conservatories for crop wild relatives are also called genetic reserves and
are generally located where protected areas have been established to conserve also
other aspects of biodiversity, and so the additional resource requirements to con-
serve wild wheats may be minimal. Nevertheless, some specic actions are sug-
gested to enhance the conservation of those species, for example: (I) reduce
over-grazing, (II) decrease re frequency and intensity, (III) reduce use of herbi-
cides and pesticide (e.g. on eld margins and roadsides), (IV) perform systematic
monitoring of threatened populations, (V) carry out population reinforcement mea-
sures of the threatened populations, using seeds of the same populations conserved
in genebanks [16]. National parks, military reserves, mountainous and controlled
pastoral areas are often ideal locations for in situ reserves. Climate change will
probably decrease, in the next few decades, the range of many wild wheats in core
areas of WCWR diversity such as: North Africa, Middle East and southern Europe
[17]. This underlines the importance of protecting populations of WCWR and of
complementing in situ reserves with ex situ conservation to prevent the loss of many
of these populations.
The in situ conservation of landraces and old cultivars is known as on-farm con-
servation, dened as: “the management of genetic diversity of locally developed
crop varieties by farmers within their own agricultural systems” [18]. While in the
abovementioned genetic reserves wild populations of WCWR are conserved in their
natural habitats, on-farm conservation consists in the cultivation by farmers of
Table 17.4 In situ reserves for wheat and other cereals genetic resources conservation
Reserve name Country Taxa
Erebuni Armenia Wild wheats (T. urartu, Triticum monococcum subsp. aegilopoides
and T. timopheevii subsp. armeniacum), goatgrasses (Aegilops spp.);
also conserving: Vavilov’s rye (Secale vavilovii), wild barley
(Hordeum spp.)
Ammiad
Project
Israel Triticum spp. (also conserving Hordeum spp.)
Ham Lebanon Triticum spp. (also conserving Hordeum spp.)
Wadi Sweid Lebanon Ae. biuncialis, Ae. geniculata, Ae. triuncialis, T. urartu
Sale-Rsheida Syria T. dicoccoides (also conserving Hordeum spp.)
Ceylanpinar
State Farm
Turkey Triticum spp., Aegilops spp., (also conserving Avena spp. and
Hordeum spp.)
17 Conserving Wheat Genetic Resources

310
locally developed, domesticated wheat varieties (landraces and/or old cultivars) to
prevent their genetic erosion and eventual extinction. Strengthen value chains and
therefore market opportunities for these varieties is likely the best incentive to pro-
mote their on-farm conservation by farmers.
On-farm conservation of wheat landraces and old cultivars is being put in place
to enhance conservation as well as revival of those entities in several areas of the
world. In particular, in some regions (e.g. East Shewa, Ethiopia; Emilia-Romagna,
Italy; New England, USA; Czechia) wheat landraces are being rediscovered and
re-introduced in cultivation often starting from ex situ collections.
17.4.2 Ex situ Conservation
Seed banking is currently considered as the most suitable ex situ conservation strat-
egy for plants, like wheat, with orthodox seeds, i.e. seeds that can tolerate drying to
low moisture content and subsequent freezing. The Commission on Genetic
Resources for Food and Agriculture of the FAO proposed a series of standards for
ex situ conservation of PGRFA that are currently followed by many international
genebanks [19].
Ex situ seed conservation in genebanks can be divided into seven main activities:
acquisition, seed drying, seed storage, viability monitoring, regeneration, character-
ization and distribution.
17.4.2.1 Acquisition
Materials can be acquired either from genebanks or from research or breeding pro-
grams. Wild relatives or landraces can be collected in the wild or obtained from
farmers, respectively. When collecting populations of wild relatives in their natural
habitat, it is important not to exceed the 20% of total seeds available in the sampled
population not to affect the natural recruitment of natural populations.
Materials must be acquired legally, in accordance with local, national and inter-
national regulations. Materials must be described with Multi-crop Passport
Descriptor data [20] and characterization data. A seed sample and its related pass-
port data is dened as a seed accession.
17.4.2.2 Drying
Seed drying is one of the most crucial steps in seed conservation. High seed mois-
ture content detrimentally affects seed storage viability. Seeds are dried to equilib-
rium in controlled environments (‘drying rooms’) with a temperature of 5–20°C
and 10–25% of relative humidity. Seed moisture content is regularly monitored until
the seeds reach equilibrium, i.e. the moisture content of the seeds is in equilibrium
F. Guzzon et al.

311
with the relative humidity of the surrounding air. Wheat seeds are conserved in
genebanks when they reach a moisture content between 5% and 8%. It is fundamen-
tal that, after the drying phase, seeds are stored in airtight containers to maintain the
low moisture content. In some national and regional seed banks, equilibrium drying
in drying rooms is not possible due to lack of infrastructure or capacity. In those
cases, desiccants such as silica gel or zeolite beads can be used for seed drying [21].
17.4.2.3 Seed Storage
High temperatures also detrimentally affect seed longevity in storage. For long-term
conservation, it is recommended to store dried seed accessions at a temperature of
−18±3°C.In addition to the long-term (‘base’ collection), some banks have dupli-
cate samples in an active short-medium term collection stored at a temperature
range between −5 and 10°C.Seed conserved in this ‘active’ collection are gener-
ally employed for regeneration, distribution and characterization, not to decrease
the stocks conserved in the base collection.
It is important that seed accessions conserved in a germplasm bank are safety
duplicated, e.g. the same accession is stored at other locations to provide an insur-
ance against loss of material. Many genebanks duplicate their accessions at the
Svalbard Global Seed Vault, located in the Artic Island of Spitsbergen, a seedbank
that currently holds more than one million (with a capacity of 4.5 millions) of store
duplicates (backups) of seed samples from the world’s crop collections [22].
17.4.2.4 Viability Monitoring
Initial and regular seed viability testing is required to evaluate the quality of a seed
lot. Seed germination is generally tested using standard protocols [23] with light
and temperature-controlled incubators, using agar or lter paper as the germination
medium. International standards recommend that initial germination percentage
should exceed 85% for crop seed accessions stored for conservation purposes. As
some specic wild relatives’ accessions do not reach this threshold a lower viability
can be accepted. The International Seed Testing Association (ISTA) suggests that
the most suitable temperature to test wheat seed germination is 20°C [23], while
some Aegilops species were demonstrated to reach a higher germination when incu-
bated at alternating temperature (e.g. 20/10° C) [24]. The germination of some
wheat wild relatives can also be elicited by after-ripening, a period of dry storage
during which seeds lose dormancy (i.e. the inability of viable seeds to germinate
under optimal environmental conditions).
Many wheat wild relatives species show seed heteromorphism, dened as the
production, within a spike, of two or more seed types that differ in morphological
and/or eco-physiological traits. Indeed, within the genera Aegilops and Triticum, a
dimorphic pair of seeds is often present in each of the spikelets composing the
spike, with one seed being larger and brighter-colored than the other (Fig.17.2). In
17 Conserving Wheat Genetic Resources

312
the eld, larger seeds germinate few weeks after dispersal, while the smaller ones
remain dormant for several months due to the presence of a germination inhibitor in
the glume. Due to this complex germination strategy, seeds of wild wheats need to
be extracted from the spikelets and manually dehulled prior to the germination test-
ing. Seed heteromorphism has implications also in longevity and conservation: it
has been observed that smaller seeds of several Aegilops and wild Triticum species
are longer-lived than their larger paired seeds when subjected to articial ageing,
having a greater endowment of antioxidant compounds, these being possibly
involved in protection against ageing-related oxidative stress. Preliminary results
revealed that smaller seeds of wild wheats are longer-lived also in ex situ conserva-
tion within genebanks [25].
Seed germination of stored accessions must be tested at regular intervals(e.g.
every 10-15 years) to understand the loss of viability in storage and to plan re-
collection or schedule regeneration activities. Walters etal. [26] found that the p50
(i.e. the time for seed viability to fall by 50%) for wheat seed accessions conserved
in genebank conditions was 54 years. When the viability of an accessions falls
below the 85% of the initial, regeneration or recollection activities need to be car-
ried out in order to maintain available an accession with a high viability.
17.4.2.5 Regeneration
Seed multiplication is required when seed germination drops below 85% of the
initial value, or when the quantity of seeds has been depleted due to frequent use of
the accession. A sufcient number of seeds needs to be used for regeneration activi-
ties in order to maintain the genetic variability within the accessions. Commonly
used approach is to employ between 7 and 10g of seeds (approximately 140 to 250
seeds) for regeneration of wheat varieties. 100–130 plants should be regenerated for
each accessions of wheat wild relatives. As wild wheats are considered as possible
noxious weeds outside their native range, accessions belonging to those taxa are
regenerated in controlled environments (i.e. screenhouses).
17.4.2.6 Characterization
A detailed description of different important traits is fundamental to ensure the
maximum usability of the accessions by plant breeders. The characterization stage
is often carried out during regeneration when several morphological, phenological
and agronomical descriptors are assessed, also in order to conrm accessions’ true-
ness to type. Regarding wheat genetic resources, these descriptors can be grouped
as follows:
1. Seed traits, comprising morphological traits (e.g. germination, color, size,
weight, vitreousness, number of shriveled seeds) but also grain quality (e.g. pro-
tein content and suitability for food processing) and agronomical traits (e.g. pre-
harvest sprouting).
F. Guzzon et al.

313
2. Spike morphology, with a characterization of the awns, glumes and spikelets.
3. Plant morphology, considering traits such as: plant height, young plant habit
(e.g. upright or prostrate), straw color, leaf pubescence and tillering capacity.
4. Phenological traits, such as growth classes, i.e. classifying if an accession is a
spring, winter or intermediate wheat. Inorescence traits are also considered,
e.g. days to owering and daylength sensitivity (i.e. extent to which long days
hasten owering).
5. Stress susceptibility, considering the effects on plant growth of abiotic stresses
(e.g. cold/high temperatures, drought, salinity) as well as biotic ones in terms of
fungi (e.g. rust, powdery mildew, glume blotch, eye spot), pests (e.g. nematodes,
hessian y) and viruses (e.g. barley yellow dwarf virus).
Beside the morphological and agronomical traits, physiological and molecular
descriptors are often employed to achieve the most reliable and complete character-
ization of wheat germplasm collections: this allows to evaluate trueness-to-type, to
understand and organize the diversity of large germplasm collections and to mine
collections for useful traits for breeding.
Some of the most used molecular techniques in wheat genotyping are:
• Studies based on restriction fragment length polymorphisms (RFLP), randomly
amplied polymorphic DNA (RAPD), amplied fragment length polymor-
phisms (AFLP).
• Use of wheat microsatellites (WMS), simple sequence repeats (SSR), commonly
known as microsatellites, have been shown to be very useful markers for trueness-
to- type evaluation in wheat germplasm, being highly polymorphic both in culti-
vated and wild species. SSR can be genomic or ‘expressed sequence tag’
(EST-SSR), the latter having the advantage of possessing good generality
between species.
• DArTseq genotyping, in-depth and robust technique to estimate genetic diver-
sity among germplasm accessions. Single nucleotide polymorphisms (SNPs)
detected through DArTseq can be investigated by assessing their allelic effects
(i.e., genome wide association study, GWAS) and subsequently exploited for
breeding.
17.4.2.7 Distribution
Germplasm distribution consists in the shipment of a sample of a seed accession
conserved in a genebank in response to a request from a germplasm user. The acces-
sibility of PGR accessions is strictly linked with the existence and updating of infor-
mation databases, where the users can search the different conserved accession and
linked passport data and order seed samples of the accessions they are interested in.
The major database of PGR accessions conserved worldwide is Genesys PGR
(https://www.genesys- pgr.org/). It brings together four million accessions located in
over 450 genebank around the globe and allows the users to quickly search for and
request germplasm accessions. Distribution is a fundamental activity for genebanks,
17 Conserving Wheat Genetic Resources

314
involving a great number of accessions, for example the genebank of the International
Maize and Wheat Improvement Center (CIMMYT, Mexico) sends worldwide, on
average, more than nine thousand seed samples of WGR in more than 100 ship-
ments annually, those seed samples are employed by the users mainly for research
activities, breeding and direct cultivation.
Acquisition and distribution of germplasm across borders must follow interna-
tional rules on phytosanitary certication and adhere to international treaties and
conventions. Two main international treaties regulate the access and share of PGR:
the Convention on Biological Diversity (CBD) and the International Treaty on Plant
Genetic Resources for Food and Agriculture (ITPGRFA). The CBD of 1992 has
three main aims: (1) the conservation of biological diversity; (2) the sustainable use
of the components of biological diversity; (3) the fair and equitable sharing of the
benets arising out of the utilization of genetic resources. The Nagoya Protocol on
Access to Genetic Resources and the Fair and Equitable Sharing of Benets Arising
from their Utilization to the Convention on Biological Diversity, also known as the
Nagoya Protocol on Access and Benet Sharing is a 2010 supplementary agreement
to the CBD, it is an international agreement which aims at sharing the benets aris-
ing from the utilization of genetic resources in a fair and equitable way. The
ITPGRFA, adopted in 2001, aims at promoting the conservation of plant genetic
resources and protecting farmers’ rights to access and have fair and equitable shar-
ing of benets arising from the use of PGR. ITPGFRA established a multilateral
system to exchange plant germplasm of a pool of 64 species of crops (Annex I spe-
cies), through a Standard Material Transfer Agreement (SMTA). The SMTA is a
private contract with standard terms and conditions that ensures that the relevant
provisions of the ITPGRFA are followed by providers and recipients of material of
plant genetic resources.
17.4.3 Wheat Genetic Resources Collections Worldwide
Since the end of nineteenth century, researchers highlighted the importance for
breeding of the conservation and availability of landraces and crop wild relatives,
especially witnessing the risk of genetic erosion of landraces due to their substitu-
tion with high-yielding improved varieties. The present concept of a genebank, as a
facility for the long-term conservation of PGR, was rst concretized, at the begin-
ning of twentieth century, at the N.I. Vavilov Institute of Plant Industry in Saint
Petersburg by its director R.Regel and especially its successor N.I.Vavilov, who
personally focused a signicant part of his research activity in collecting, conserv-
ing and studying wheat genetic resources. After the World War II, many genebanks
were established in several country of the world to conserve and keep available
wheat genetic resources and prevent the loss of landraces [27].
Currently, according to FAO (2010), there are more than eight hundred and fty
thousand accessions of wheat and wheat wild relative stored worldwide in gene-
banks. Accordingly, in our dataset there are 784,753 accessions of the genera
F. Guzzon et al.

315
Triticum and Aegilops recorded in the databases: Genesys PGR, FAO-WIEWS and
USDA-GRIN (when the same accession is recorded in more than one of these data-
bases, it is counted only once). Considering individual genebanks, CIMMYT holds
the greatest number of accessions worldwide (with more than 140 thousand acces-
sions) followed by the National Small Grains Germplasm Research Facility, USDA-
ARS (USA) and the Australian Grain Genebank (Table17.5).
However, it is difcult to estimate the number of unique accessions conserved ex
situ as in many cases information about duplication is not recorded in passport data,
although it is possible to do it. A study genotyping a sample of accessions of Ae.
tauschii from 3 genebanks found that over 50% of the accessions in the sample were
redundant [29].
To assess the representativeness of the diversity of the germplasm conserved ex
situ, as opposed to the one existing (or that existed) in cultivation or in the wild, dif-
ferent approaches have been used, considering: the total size of collections, taxo-
nomic coverage (number of genera and species), and ecogeographic coverage. A
recent gap analysis conducted by the CGIAR Genebank Platform divided the diver-
sity within the wheat genepool in hierarchical clusters (https://www.genesys- pgr.
org/c/wheat) based on literature and experts’ opinion, and estimated the number of
accessions conserved ex situ for each group. This methodology was originally sug-
gested by Van Treuren etal. 2009 to assess the composition of a germplasm collec-
tion. The results of this analysis suggested that in ex situ there are gaps of Durum
wheat landraces from arid areas of Mali, Chad, Niger, Sudan, Libya, and Mauritania
as well as T. aestivum subsp. tibeticum and T. aestivum subsp. yunnanense from
China. Several gaps were also found in the coverage of the geographical distribution
of wild and domesticated emmer.
When dealing with very large seed collections, in order to increase the accessi-
bility of the conserved material, it is useful to cluster the accessions in core collec-
tions, grouping accessions with similar characteristics in terms of e.g. taxonomy,
distribution, breeding history, characterization data.
Table 17.5 The ten largest wheat genebanks (by number of accessions) worldwide
Institution
code Institution name Country
Number of
accessions
AUS 165 AGG Australia 48,065
CHN001 ICGR-CAAS China 43,039
IND001 NBPGR India 32,154
ITA436 IBBR-CNR Italy 32,751
LBN002 ICARDA Lebanon 47,152
JPN183 NARO Japan 37,907
MAR088 CRRA Morocco 42,191
MEX002 CIMMYT Mexico 141,759
RUS001 N.I.Vavilov Research Institute of Plant
Industry
Russia 41,679
USA029 NSGC: USDA-ARS USA 62,119
Data extracted from Genesys PGR [7], WIEWS and USDA databases and FAO [28]
17 Conserving Wheat Genetic Resources

316
Given the importance of wheat for agriculture worldwide, the seed conservation
of wheat genetic resources is important not only for international and national gene-
banks but also for much smaller institutions, like community seed banks (CSB): i.e.
small-scale local organizations that conserve seeds of landraces and wild useful
plants on a medium-term basis and serve the needs of local communities [30]. For
example, wheat accessions are conserved in CSB in Guatemala, Palestine and India.
17.5 Key Concepts
• Genetic resources of wheat are represented by: (1) WCWR, (2) landraces, (3) old
cultivars, (4) modern cultivars and (5) special stocks.
• In situ conservation is the conservation of the diversity at the location where it is
found, it consists in genetic reserves for WCWR and on farm programs for land-
races and old cultivars. This conservation strategy allows genetic resources to
evolve in their original area of distribution under selection by farmers and envi-
ronmental factors and to retain a higher genetic diversity compared to seed bank
accessions.
• Ex situ conservation of WGR consists in the storage of dry seeds at cold tempera-
tures in germplasm banks. It is currently the most employed conservation strat-
egy for WGR because it allows the long-term storage of many samples in
relatively small spaces.
17.6 Conclusions
• To enhance the conservation of WGR it will be increasingly important to com-
plement ex situ long-term conservation of seed accessions within genebanks with
in situ conservation strategies both as genetic reserves for wheat wild relatives
and on farm programs for landraces.
• To increase the usability of WGR collections, genebanks need to provide users
with the most complete possible passport data, integrating information about col-
lecting sites and phenotypic characterization with novel molecular data.
• Due to this increasing amount of passport information, genebanks need to invest
in database systems that can efciently store and keep available these data.
• Due to the increasing age of historical genebanks and therefore the storage time
of many wheat seed accessions, the number of accessions that needs regenera-
tion is going to increase. For this reason, is fundamental to characterize seed
longevity of wheat genetic resources to prioritize accessions for viability moni-
toring and regeneration and avoid losses of germplasm.
• Safety duplication of seed accessions of WGR in external sites is a top-priority
for genebanks in order to reduce the risk of losing the collections.
F. Guzzon et al.

317
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