Figure 1: Quinoa (Chenopodium quinoa)
ecotype ‘Real’, growing under traditional cultivation practices (groups
of plants spaced 1 m by 1m) near the Salar (Salt flats) de Uyuni,
Bolivia at approximately 3,656 m (11,000 ft) above sea level. Average
rainfall is 200 mm annually with night frost up to 200 days per year.
Most
people who produce quinoa are impoverished subsistence farmers living
in rural areas of the high Andes, predominantly in Bolivia and Peru.
Approximately 50% of Bolivians and 36% of Peruvians (about 14 million
people) live in this region and their principal economic activity is subsistence agriculture3, 4. For
these people, quinoa is a traditional, widely consumed, essential food
crop that is a daily part of their diet, and their principal source of
protein. Because
of extreme climatic conditions that characterize much of the high
Andean region (aridity, soil salinity, frost, and high altitude), and
small land holdings, most families produce only enough quinoa for their
own consumption with little or no surplus for the market. Current
quinoa production in this region is insufficient for most people to
meet their minimum annual nutritional requirements for protein. As a
consequence, kwashiorkor is a common nutritional disease that afflicts
many rural Andean people, particularly children.
Quinoa’s nutritional quality is exceptional. The seeds have an excellent balance of carbohydrates, lipids, and proteins for human nutrition5-7. The protein quantity and quality are especially important. The protein content of quinoa seeds varies between 14–22%, significantly higher than that of cereal grains8-10.
However, the most significant nutritional advantage for quinoa is the
amino-acid composition of the seed protein. The proportions of all
essential amino acids exceed those recommended by FAO/WHO/UNU in all
age-group categories5, 8, 11. It has the best-known composition of essential amino acids in any plant species used for human nutrition5, 12, and does not require supplementation with any other food source to provide a balanced complement of amino acids.
Most people prepare the seeds much as rice with simple boiling after
which the seeds are eaten without further preparation, or are included
as an ingredient in stews. Quinoa flour can fortify the nutritional
qualities of bread without altering the baking qualities, and it is an
important ingredient in many processed food products in the Andean
region.
Environmental conditions in the Andes are
harsh, because of high elevation (3500-3850m) and frequent drought,
soil salinity, frost, hail, wind, flooding and heat waves13.
Andean farmers have accumulated special knowledge and techniques, which
they use to farm in these conditions. Nonetheless crop production is
unpredictable and food security is tenuous. The
southern Altiplano region of Bolivia and Peru, extending into parts of
Chile and Argentina, consists largely of highly sodic and saline soils,
and is known as the Salares region (the name “Salares” a reference to
salt). Throughout much of this region, soil salinity is so high that
quinoa is the only crop that can be cultivated. Here, salt-tolerant
varieties are essential, and cultivation is often restricted by both
drought and salinity. In spite of these obstacles, the majority of
quinoa grown for export is produced in this region, providing an
essenital component to the economy. Moreover, in Peru 250,000 of the
800,000 irrigated hectares in the coastal region are affected by
salinity, often with the presence of a high water table. Here, repeated
irrigation has exacerbated the level of soil salinity. Salt-tolerant
coastal varieties of quinoa, which differ from those grown on the
Altiplano, are cultivated here.
Even without irrigation, quinoa can be an economically viable crop in
arid regions with high soil salinity. In the Salares region, quinoa is
cultivated under non-irrigated conditions with less than 200 mm annual
precipitation on highly saline soils14. It is the only field crop that can be cultivated under such conditions15, and therefore provides a unique model for genomic studies of environmental stress tolerance.
Most
crops are classified as glycophytes. Glycophytes are plants that only
tolerate low levels of soil salinity (<50 mM) without showing signs
of reduced growth and do not accumulate high concentrations of salt in
growing tissue16.
Halophytes are defined as plants that can cope with saline environment,
typically around 300 mM NaCl, without being adversely affected16.
Halophytes tolerate high salinity conditions primarily through
mechanisms that aid in water acquisition and facilitate salt avoidance.
Salt avoidance mechanisms can be further classified into mechanisms of
exclusion, secretion, shedding, and succulence16.
Exclusion mechanisms remove or prevent salt from entering tissues or
areas that would otherwise be damaged. Secretion mechanisms remove salt
from a plant by expelling it through glands. Shedding mechanisms
sequester salt into plant organs which
are then shed from the plant. Succulence mechanisms increase the water
content per unit area of the leaf, thereby diluting the salt and
minimizing its impact. During salt stress, succulent plants retain
water by reducing stomatal aperture17. The Chenopodiaceae sub-family has by far the highest proportion of halophytic genera (44%) constituting 321 species18,
and quinoa is the principal domesticated grain species in this
sub-family. Quinoa thrives from sandy to loamy soils under a wide range
of pH (4.8-8.5). It is tolerant to saline soils and can be irrigated
with water rich in salts19. Kancolla, a cultivar from the Southern salares region of Bolivia, had a germination rate of 75% at a concentration of 57 mS cm-120, 21
where 50 mS cm-1 is the electroconductivity of seawater, or 600 mM
NaCl. Several recent reports suggest that quinoa may deal with soil
salinity using unique and as yet undescribed mechanisms involving
salt-ion accumulation in specialized tissues, as well the adjustment of
leaf water potential. Wilson et al.22 stated that quinoa appears to regulate salt ions (Na+ and K+) differently than wheat. Unfortuantely, beyond these limited investigations,
little more is known about the mechanisms utilized by quinoa to
tolerate salt stress. Furthermore, it is interesting to note that
cultivated quinoa varieties can be separated into different ecotypes,
including Salares ecotypes, which are cultivated on the Southern Andean
salt flats, and Coastal and Valley ecotypes that show only modest salt
tolerance. Such phenotypic differences render quinoa amenable to
genetic dissection via microarray analysis and linkage mapping.
Because
of ever-increasing world population and global climate change, plant
adaptation to abiotic stress, including salinity, is among the most
important biological questions to be addressed in the twenty-first
century. Abiotic stress is a principal cause of crop loss, resulting in
yield reductions greater than 50% worldwide23, 24.
Although enormous economic damage is attributed to abiotic stress,
plants are often able to complete their life cycle, albeit with
decreased yields. Thus, some plants have evolved mechanisms to deal
with abiotic stress through avoidance (deep roots, rapid life cycles,
sunken stomata, etc.) and tolerance (osmoprotectants, ion antiporters,
dehydrin proteins, reactive oxygen species (ROS) genes, etc.)25-27.
In
this proposal, we request funds to develop the tools needed for the
genomic dissection of salt tolerance in quinoa. An increased
understanding of salt tolerance, including the genetic mapping of
specific genes that govern this trait, will have immediate application
to the development of improved salt-tolerant varieties of quinoa via
marker assisted selection. Moreover, this research has broader
implications on how halophytic plant species deal with salt stress.
Demand for crop productivity on marginal lands with saline soils has
been a focal point of agronomic research for centuries. Between 340 and
as much as 950 billion square kilometers, equivalent to about 20% of
the arid and semiarid soils of the world, are saline18.
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