Prospects of Breeding Quinoa for Tolerance to Abiotic Stress

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Prospects of Breeding Quinoa for Tolerance to AbioticStressBodo R. Trognitz aa Dept. of Crop Improvement and Genetic Resources , International Potato Center , Lima,PeruPublished online: 18 Aug 2006.

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Prospects of Breeding Quinoa for Tolerance to Abiotic Stress

Bodo R. Trognitz*

Dept. of Crop Improvement and Genetic Resources, International Potato Center,

Lima, Peru

ABSTRACT

Aspects related to the breeding of quinoa for increased tolerance against frost, drought,

and salinity are presented with special emphasis on the conditions existing in the

Peruvian Andes. Evidence from the literature indicates that plants’ responses to these

stresses are essentially similar, and the physiological processes involved are

interrelated. The evidence suggests that tolerance to abiotic stress is polygenically

inherited, justifying the application of appropriate plant breeding methods. A

compilation of meteorological studies is presented that can be used to define the

specific climatic phenomena of night frosts occurring in the quinoa-growing region of

the Andes and to specify the conditions for selection of tolerant varieties. A composite-

bulk breeding scheme is proposed that could be useful for highly efficient breeding of

quinoa varieties. Possible future application of molecular-marker-assisted selection is

discussed.

Key Words: Quinoa; Abiotic stress; Breeding for stress tolerance.

IMPORTANCE OF ABIOTIC STRESS TOLERANCE FOR THE QUINOA CROP

The extreme climatic conditions in the Peruvian Andes, where quinoa is grown, such

as in the Mantaro valley (central Peru), in Cusco (central-south), and in the Altiplano

129

DOI: 10.1081/FRI-120018879 8755-9129 (Print); 1525-6103 (Online)

Copyright q 2003 by Marcel Dekker, Inc. www.dekker.com

*Correspondence: Bodo R. Trognitz, ARC Seibersdorf Research G.m.b.H., Biotechnology Dept.,

A-2444 Seibersdorf, Austria; Fax: 0043 (0)50550 3444; E-mail: [email protected].

FOOD REVIEWS INTERNATIONALVol. 19, Nos. 1 & 2, pp. 129–137, 2003

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016

©2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

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surrounding the town of Puno at the shores of Lake Titicaca (southern Peru), require

specific adaptation of the crop. The climate of the tropical highland has two seasons: the

humid and the dry periods. Night frosts (“heladas”) and drought periods occur frequently,

there are large day–night temperature differences, and heavy rainstorms with precipitation

of more than 30 mm per hour and hail are not unusual.

The quinoa crop has evolved under these extreme climatic conditions, and therefore,

its diverse gene pool includes varieties that possess high levels of tolerance to frost,

drought, and soil salinity, as well as to other adverse conditions (Canahua, 1992; Ramos

and Arze, 1977). This phenotypic variability among the existing landraces and varieties

also indicates that there is great potential to achieve progress via conventional breeding, as

part of the variation in the trait expression observed is genetic and heritable.

This article reviews the literature on the physiological nature of stress tolerance in

plants, and it presents examples of efficient ways of breeding for stress tolerance that can

be of use for further varietal development of the quinoa crop.

INTRINSIC RELATIONSHIPS BETWEEN PROTEINS AND ABSCISICACID IN RESPONSE TO STRESS

Recent advances in plant physiology indicate that the growth regulator abscisic acid

(ABA) plays a central role in the cell’s regulatory metabolism. ABA signaling can cause

an elevated level of tolerance to various types of stress, such as cold and frost, drought and

osmotic stress, and soil and water salinity.

Adaptation to Cold Stress

The presence of ABA can increase the tolerance of plants to low temperatures,

resulting in cold-hardiness (Guy, 1990). Likewise, exposure of plants to high

concentrations of salt has been shown to increase their frost resistance (Ryu et al.,

1995; Schmidt et al., 1986). In contrast, elevated soil salinity or addition of sodium

chloride in controlled experiments reduced the vernalization effect (i.e., adaptation to the

climatic conditions of the winter season in the Northern hemisphere) of wheat and rye

(Fowler and Hamm, 1980; Gusta et al., 1982).

Adaptation to Salinity

In model plants, such as Solanum commersonii, barley, indica rice, and grapes, salt

stress induced the de novo production of up to nine proteins (Moons et al., 1995;

Ramagopal, 1987; Ryu et al., 1995). Likewise, the ABA concentration within the cell is

increased under saline conditions (Downton and Loveys, 1981. Low concentrations of

Naþ ions and elevated Kþ concentrations produce toxic effects in the cell and, therefore,

the regulation of influx of these ions into the plant is crucial to avoid damage. For this

regulation of ion channels, the plant employs Ca2þ, and it is conceivable that in this way, it

increases its tolerance to salinity (Epstein, 1998; Rubio et al., 1995).

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Tolerance to Frost

Chen et al. (1975) found that the frost tolerance of plants was increased after they had

been exposed to drought stress. These authors observed an unknown transcription factor

that adheres to specific drought-response proteins. This factor also induced the expression

of cold-response genes. In a different study, a transcription factor that binds to drought-

response genes was also found to induce the expression of cold-response factors (Jaglo-

Ottosen et al., 1998).

The Role of Abscisic Acid for Adaptation to Abiotic Stress

External application of ABA reduces the stomatal aperture. This physical response, in

turn, can reduce water consumption by up to 30%, whereas the accompanying yield

reduction is only marginal (Rademacher, 1989). Pruvot et al. (1996) identified two

proteins that are formed in the stoma under water stress.

ABA plays a central role in the processes that lead to stomatal closure, which

represents a complex of orchestrated activity of various ion channels (Ca2þ, Kþ, others)

that are localized in the plasmalemma and the tonoplast of the stomatal guard cells (Grill

and Ziegler, 1998). Pei et al. (1998), analyzing a mutant of the ERA-1 gene of Arabidopsis,

concluded that this mutant encodes a factor that causes the inhibition of the farnesylation

of an unknown protein. As a result of omitting this farnesylation step, the Kþ-ion

channeling directed outward of the cell causes closure of the stoma.

The complex of physiological stress response of plants may be sketched as shown in

Fig. 1.

Interference of the Photoinhibition Mechanism with Cold Tolerance

An important phenomenon in the physiology of photosynthesis is the process of

photoinhibition. Under conditions of high light intensity at low temperature,

photosynthesis can be inhibited, because the quantity of light available to the plant

exceeds the quantity required for photosynthesis to function (Karpinski et al., 1999;

Powles, 1984). Some plants, such as Arabidopsis, become insensitive to photoinhibition

when they are adapted to the cold prior to light application (Karpinski et al., 1999).

However, many other plants, such as the wild potato S. commersonii, maintain their

sensitivity to photoinhibition even when they have been grown in the cold for a long period

(Griffith et al., 1994). The sensitivity of quinoa to photoinhibition has been little

investigated.

In conclusion, this brief review of factors contributing to abiotic stress tolerance

indicates that a complex of interrelated, quantitative characters are involved. Several

genetic components of this complex have already been analyzed to some extent, whereas

others require further research. Previous investigations on the response to abiotic stress

have been carried out on several different model plant species, such as Arabidopsis and S.

commersonii, as well as on crop plants such as spinach, cereals, cucumber, and citrus spp.

Tolerance to Abiotic Stress 131



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ASPECTS FOR CONSIDERATION IN THE BREEDING OF QUINOA FOR

TOLERANCE TO ABIOTIC STRESS

As is the case with many other crops, the breeding of quinoa varieties, to some extent,

represents a holistic approach. Breeders have to consider a complex of environmental

conditions that occur at varying intensities and include different components. The

objective is to develop a crop that is adapted to the specific, and sometimes unique,

conditions in the field of a particular geographic area. Of course, breeders will take into

account the results of research on the crop’s physiology to design the most efficient

breeding methodologies.

For the breeding of quinoa in the high Andes of South America, stresses due to night

frosts, drought, and soil and water salinity require major attention. Most of these stresses

recur annually, and knowledge of these periods and the specific nature of the phenomena

causing the stress allows for the correct identification of the requirements needed to select

for in order to breed a crop of increased sustainability.

There exists great genetic diversity within the quinoa germplasm available, and

ideotypes possessing elevated tolerance to adverse conditions can be readily detected. The

production of varieties with increased levels of stress tolerance will contribute to an

increase in the crop’s yield stability and, thus, to an increase in yield.

Breeding for Frost Tolerance

Frost tolerance under Andean conditions is characterized by the sudden exposure of a

crop that has not been previously adapted to the cold to temperatures around and below

08C for several hours. The degree of frost resistance required for a new variety may vary,

depending on the specific area where the variety will be grown, as will be illustrated in the

following section.

Figure 1. Abiotic stress factors and their interaction with physiological processes within a plant.

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Of the three types of night frost in meteorological terms, the frosts caused by

radiational cooling are most frequent in the Andes. For example, in a study by Villegas

(1991) carried out in the Mantaro valley in central Peru, 62% of all events were radiation

frosts, only 4% resulted entirely from advection, and 34% had mixed causes (radiation and

advection), although radiation was the prevailing causal component. Only 22% of all night

frosts observed during this study (spanning several years) had a temperature below 08C.

Typically, night frosts of around 228C had a duration of only 0.7 hours, whereas

temperature drops to around 08C lasted for 7 hours, on average.

In an analysis of 3 years of meteorological data for the potato-growing area in the

Altiplano–Puno region of Peru, Hijmans (1999) found that the probability for occurrence

of a night frost with a minimum temperature of 228C at the soil surface was not greater

than 66%. Frosts with a minimum temperature of 248C occurred only once in 3 years,

with a probability of 25%. In general, the temperature during a night frost did not drop

below 248C, and seldom it was as low as 278C at the soil surface.

The frost-free period of the year depends on altitude and exact geographic position

within the high Andean valleys. Meteorological observations over several decades

indicate that the annual frost-free period within the Mantaro valley of central Peru is 220

days, in the northern Altiplano (near Cusco) it is 140 days, whereas the southern Altiplano

near Puno and the border to Bolivia has a 110-day frost-free period.

Overall, it seems possible to define several parameters of importance for successful

screening of quinoa’s frost tolerance under the specific requirements of a site. The breeder

can make use of standardized, controlled conditions for the screening that include

experiments in the growth cabinet using pot plants. It seems appropriate to apply

intermediate, not extreme, stress and low selection intensity, to keep the largest possible

number of plants that show increased tolerance. These plants will then be used for the

screening of self and cross progenies in the field. An advantage of using controlled

conditions for the first steps of selection is the availability of exact methods to measure the

damage caused by frost, such as the measurement of increased electrolyte leakage. This

type of experiment also produces highly reproducible results that permit an exact estimate

of the genotypic value of the material used.

Other, indirect, characters that can contribute to frost tolerance include morphology

aspects of the individual plant and features of the crop stand in the field. However, far most

attention should be paid to the individual enzymatic properties, which to a large part,

reflect the contribution of the genotype to the buildup of stress tolerance. One enzyme that

is involved in the defense against pathogens and possibly involved in cold adaptation is

osmotin. However, recent work by Zhu et al. (1996) shows that this enzyme is not a

principal determinant of frost tolerance.

Breeding for Drought Tolerance

Precipitation below the normal level during a period of weeks or even months may

cause the soil water content to drop below the level of free water accessible to the plant.

This stress condition is not unusual in the Andes.

It is difficult to reproduce these conditions in the greenhouse or laboratory, and

therefore, selection for tolerance to drought must be performed in the field in an area where




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the appropriate drought conditions occur regularly. The elevated variance of selection in

the field requires, however, that several repetitions within a single year’s experiment be

included and the evaluation be repeated in several years of appropriate drought. The need

for many repetitions is also indicated by the type of selection criteria that can be evaluated.

Only indirect criteria for assessment of tolerance to drought are available, such as

reduction of yield, wilting, and early senescence symptoms of plants, as well as their

ability to quickly recover after a period of drought stress.

Breeding for Tolerance to Salinity

Salt stress can result when plants are exposed to excess salt builtup in the soil or the

water used for irrigation. Because the composition and concentration of salt depend on the

specific local characteristics and represent a more permanent condition, screening in

the field is an appropriate methodology. Controlled conditions using containers for the

growth substrate of defined levels of salinity can also be used but require greater

investment. Again, criteria for selection are indirect characteristics, such as wilting

behavior, chlorosis of the foliage, and yield. It is useful to compare treatments including

saline and nonsaline conditions. However, the possible occurrence of plant–treatment

interaction in response to salinity is well documented; a high yielding variety under

salinity may not adapt to nonsaline conditions. In other words, it is necessary to develop

varieties that are specifically adapted to salinity in a specific area. These locally adapted

varieties may not be suited for areas of normal levels of salt content in the water.

A COMPOSITE BULK SCHEME FOR QUINOA BREEDING

Quinoa is well suited for the production of stress-tolerant varieties using the standard

methods of conventional breeding. The crop is autogamous, highly fertile, and the existing

landraces and breeding lines are greatly diverse. These characteristics suggest the

application of a composite bulk breeding scheme (Schmalz, 1980; Fig. 2). This scheme

includes two selection steps and several generations of selfing in the field. Genetically

variable material is initially generated through a cross between two lines or landraces.

Seed obtained from individual plants of this cross generate separate lines, which are self-

pollinated to generate the F2 generation. In the F2 generation, all those lines are eliminated

that produce uniform plants, as they are likely to have resulted from accidental, undesired

selfing of one parent of the original cross. The difference of this breeding scheme to a

simple bulk scheme is the inclusion of an interim selection step in the F3 generation. Only

lines expressing the highest average of the desired characteristics are maintained. In this

way, the sources with the highest enrichment of advantageous genes are retained in

separate sub-bulks, while the total volume of material and the labor required for its

elaboration is kept to a minimum. In the subsequent selfing generations (F4–F6) of sub-

bulks, no selection is made, and the level of homozygosity is increased as a result of the

recurrent self-pollination. Poor-performing individuals are eliminated naturally, as the

superior individuals outcompete them in the crop stand. Lines that combine the best

characteristics are enriched in number. This procedure facilitates the selection of

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individual plants from elite lines in the F7 generation. The seeds harvested from the F7

generation represent the variety candidates that are tested in the F8 generation. This final

selection will be carried out during experiments that are ideally repeated throughout

several years.

PROSPECTS FOR MOLECULAR MARKER ASSISTED SELECTION FOR

ABIOTIC STRESS TOLERANCE

Monforte et al. (1996) investigated the possibilities for using molecular markers in the

selection for tolerance to salinity of hybrid tomato (L. esculentum £ L. pimpinellifolium).

Genotypes possessing the largest numbers of markers for quantitative trait loci (QTL)

related to increased salt tolerance were selected from the third hybrid generation

(corresponding to an F4). The selection index calculated for the resulting F5 generation

was compared to the selection indices obtained on the F3 and F4 generations that were

selected conventionally by the phenotype. The step using molecular markers had the

largest selection index, indicating that, for quantitative traits, this technique can be of

advantage over conventional selection methods.

Preconditions for a possible future application of this technique in quinoa breeding are

the development of a genetic map and of molecular markers for genes and QTLs of high

Figure 2. Composite bulk breeding scheme for autogamous crops; a first round of selection is

carried out in the F3 generation, and variety candidates are selected from sub-bulks at the F7

(Adapted from Schmalz (1980) with permission by Deutscher Landwirtschaftsverlag Berlin, DLV).




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importance for the expression of stress tolerance. Information available at present does not

provide evidence that quinoa breeding will become more cost efficient when molecular

markers are developed and used. Alternatively, enhancement of the crop through

conventional breeding methodology and the application of molecular techniques for

specific characters that have low heritability, as expressed during the breeding process,

may be an appropriate strategy.

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Prospects of Breeding Quinoa for Tolerance to Abiotic Stress