**3.1. Seed vigor**

The amount of usable soil water was calculated using the agrometeorological model AVISO at 21 experimental sites for the period 1975–2007 (% AWHC) [13]. A decrease in usable soil water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the long-term trend. Statistically significant relationships were found between grain yield of spring barley and level of AWHC (% AWHC). The optimum range for the amount of usable soil water for the production of spring barley (65%–75% AWHC) was defined by long-term

calculations of soil water in combination with a series of yield trials (Fig. 7).

670 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

**Figure 7.** Relationship between the soil water supply (% AWHC) and yield of spring barley grain.

ha-1, approximately translating to an additional use of 15 mm of subsoil water [11].

Decreasing winter precipitation, increasing winter air temperatures, and increasing levels of CO2 in atmosphere were forecast as global climate changes for central Europe. The negative effects of water stress were partially compensated for by elevated CO2 concentration. Warmer winters could lead to northward expansion of the areas suitable for cropping. However, for crops with a determinate growth habit (e.g. cereals) acceleration of development under warmer conditions could reduce the time available for growth before maturity thereby tending to reduce grain yield. Combining these effects with the fertilizing effect of increasing atmos‐ pheric CO2 concentration, yield of wheat could be 30%–55% higher if there is enough water [14]. For non-determinate crops (e.g. root crops) the warmer climate would extend the growing season. However, there is the possibility that the more frequent, damagingly high summer temperature events could reduce yields of both cereal and root crops. Water can be limiting not only due to global warming but also due to higher yields caused by new varieties and by higher levels of agronomic inputs. Breeding for greater RSS could be therefore one of the strategies for avoiding the impact of water stress. For example, the grain yield of winter wheat varieties in dry years is generally positively correlated with RSS. In a dry year, the varieties that showed the greatest difference in RSS were found to exhibit a yield difference of 860 kg

Seedling establishment is critical for production especially in stressed environments. The methods for the evaluation of seed germination are designed to have high levels of reprodu‐ cibility and reliability; but worse than optimal conditions are often encountered in the field. For example, the germination percentage of barley (*Hordeum vulgare* L.) is an important character for both seed quality and malting quality. Although it is evaluated under optimal conditions for germination (laboratory temperatures and optimal moisture), it differs from germination in the soil and malting. In addition, seed lots that do not differ in germination may differ in emergence and storage potential. Seed vigor is generally described as the sum of the seed properties that determine the potential level of activity and performance of the seed during germination and seedling emergence [15]. Seed vigor is the ability of seeds to germinate and form the basis for future plant growth and development in standard and stressed conditions (drought, low temperatures, lack of nutrients). When soil conditions were unfav‐ orable, the results of field emergence for wheat were more closely correlated with the direct stress vigor tests than laboratory germination [16]. The expression of seed vigor in field conditions and the translation to higher yields depends on the environment conditions.

Seed quality is of increasing importance as a result of climate development. Thus, seed vigor with regard to tolerance to drought and low temperatures as another potentially selectable trait which can be evaluated. The significance of this trait was documented by [17], who reported that an increase in the mean germination time due to poor seed vigor resulted in a significant loss in grain yield. The largest effect was found for winter wheat in which an increase in the mean germination time from 2.1 days to 3.6 days resulted in a relative loss in grain yield of 16%. It is possible to conclude, that increasing the sowing rates of low-vigor seed lots did not secure an optimal grain yield.

High seed quality may be particularly important in low-input agriculture because poor early performance is not as readily compensated for later on by mineral fertilisers and pesticides as it is in conventional agriculture. Furthermore, quality and seed vigor are important factors for competitiveness against weeds: the seeds of low vigor resulted in a perceptible increase in weed biomass and decrease in crop yield.

Various seed germination tests, under the suboptimal conditions of temperature, oxygenation, and water potential of the medium, or undergoing accelerated ageing and controlled deteri‐ oration allows for the sensitive differentiation between seed lots. Germination and vigor also depends on multiple biochemical and molecular variables, and its characterization is expected to provide new markers of seed quality that can be used in breeding programmes.

Significant correlations between field emergence and laboratory tests of vigor have been published [18, 19, 20]. Higher precipitation shortly before the harvest decreased the seed vigor of spring barley significantly [21, 22]. Higher air temperatures during this period and during the period April–July increased vigor significantly. Seed germination and vigor were related to the parameters that are important for malting. The germination capacity of all lines was higher than their vigor and germination energy: 2.9% higher than vigor and 4.6% higher than the germination energy on average. This finding has confirmed the opinions of many authors who have reported that seed performance under optimal conditions is often higher in com‐ parison to the seed performance in vigor experiments under stress and field conditions. Moreover, it has been confirmed that samples of the same germination capacity may have different vigor and storage potential.

The influence of late-terminal drought stress during grain filling on the germination and vigor of barley seeds has been studied [23]. Stress during the grain-filling stage had no effect on the standard germination test, but it obviously decreased the vigor of the seeds. The results indicate the positive influence of high air temperature during ripening and negative influence of high precipitation on the seed vigor.

The seed vigor of soybean, as evaluated as the mean percentage accelerated ageing rate, can be improved by breeding, whereas high yields were maintained because of the predominance of the general combined effects of both the seed vigor and yield [24]. The seed vigor, as evaluated by the cold test, showed estimates of the genetic response to selection in flax [25]. The three key traits of seed vigor in *Brassica oleracea* were rapid germination, rapid initial downward growth of the seedling, and a high potential for upward shoot growth in the soil with increasing impedance. This result suggests a strategy of stress avoidance. In addition, quantitative trait loci (i.e. QTL) were identified for marker and candidate gene identification. A few genomic regions (QTL) were identified for seedling vigor in rice. For these QTLs, significant genotype and environmental temperature interactions were found [26].

Our previous results [21] indicate the possibility of successful selection for higher seed vigor as an important factor of agronomic and malting quality, even in good years (vigor 93–95%), for the traits given above. However, in the years with generally much lower vigor (61–86%), the success could be more responsive because the effect of the variety prevailed over the effect of the environment for bad years. The vigor of 12 combinations from two locations was compared with vigor of their parents. Significant correlation was found between the vigor of the mothers and their progenies (*r* = 0.832; significant on *P* ≤ 0.01), between that of the fathers and their progenies (*r* = 0.882; significant on *P* ≤ 0.01), and between the vigor of both parents and their progenies (*r* = 0.894; significant on *P* ≤ 0.01). This is further evidence for potential effective breeding for vigor.

A lower seed vigor was correlated with a high occurrence of fungi (as indicated by ergosterol assays) and to a lower percentage of field emergence [27]. Vigor was also related to bread quality [28]. Grain samples with 80–90% vigor produced the greatest bread volume. Grain with vigor below or above this range produced less voluminous loafs of bread. High-quality varieties had a higher content of total polyphenols than did varieties of lower quality and the polyphenol content was correlated to vigor.

Cultivars of wheat with enhanced early vigor are still not commercially available.

#### **3.2. Plant roots**

to the parameters that are important for malting. The germination capacity of all lines was higher than their vigor and germination energy: 2.9% higher than vigor and 4.6% higher than the germination energy on average. This finding has confirmed the opinions of many authors who have reported that seed performance under optimal conditions is often higher in com‐ parison to the seed performance in vigor experiments under stress and field conditions. Moreover, it has been confirmed that samples of the same germination capacity may have

The influence of late-terminal drought stress during grain filling on the germination and vigor of barley seeds has been studied [23]. Stress during the grain-filling stage had no effect on the standard germination test, but it obviously decreased the vigor of the seeds. The results indicate the positive influence of high air temperature during ripening and negative influence

The seed vigor of soybean, as evaluated as the mean percentage accelerated ageing rate, can be improved by breeding, whereas high yields were maintained because of the predominance of the general combined effects of both the seed vigor and yield [24]. The seed vigor, as evaluated by the cold test, showed estimates of the genetic response to selection in flax [25]. The three key traits of seed vigor in *Brassica oleracea* were rapid germination, rapid initial downward growth of the seedling, and a high potential for upward shoot growth in the soil with increasing impedance. This result suggests a strategy of stress avoidance. In addition, quantitative trait loci (i.e. QTL) were identified for marker and candidate gene identification. A few genomic regions (QTL) were identified for seedling vigor in rice. For these QTLs,

significant genotype and environmental temperature interactions were found [26].

Our previous results [21] indicate the possibility of successful selection for higher seed vigor as an important factor of agronomic and malting quality, even in good years (vigor 93–95%), for the traits given above. However, in the years with generally much lower vigor (61–86%), the success could be more responsive because the effect of the variety prevailed over the effect of the environment for bad years. The vigor of 12 combinations from two locations was compared with vigor of their parents. Significant correlation was found between the vigor of the mothers and their progenies (*r* = 0.832; significant on *P* ≤ 0.01), between that of the fathers and their progenies (*r* = 0.882; significant on *P* ≤ 0.01), and between the vigor of both parents and their progenies (*r* = 0.894; significant on *P* ≤ 0.01). This is further evidence for potential

A lower seed vigor was correlated with a high occurrence of fungi (as indicated by ergosterol assays) and to a lower percentage of field emergence [27]. Vigor was also related to bread quality [28]. Grain samples with 80–90% vigor produced the greatest bread volume. Grain with vigor below or above this range produced less voluminous loafs of bread. High-quality varieties had a higher content of total polyphenols than did varieties of lower quality and the

Cultivars of wheat with enhanced early vigor are still not commercially available.

different vigor and storage potential.

672 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

of high precipitation on the seed vigor.

effective breeding for vigor.

polyphenol content was correlated to vigor.

Contemporary knowledge confirms the possibility of selection for the root system and stress root tolerance on the basis of seedling stress tolerance, i.e. at time of the sprouting. It is possible also to evaluate characteristics of seeds and seedlings, i.e. provide selection, after plant hybridization of the plants on the basis of the seed and seedling traits, for seed quality an also classic selection in plant breeding.

Plants have developed different root system size (=RSS) during evolution and breeding. In dry and low levels of nutrients in the soil environments a greater RSS is found enabling plants to be more efficient with their use of water and nutrients from lower soil layers. Varieties of cereals with greater RSS better use soil water and nutrients in dry environments than varieties with smaller RSS. Relations between RSS and yield level, variation, and quality should be studied in a broader range of environments in central Europe for agricultural crops. However, yield is a polygenic trait and its level cannot be therefore explained by variation in only one factor (e.g. RSS). The level is limited primarily by the factor in minimum as described by Justus von Liebig. During vegetation, further limits occur either at different or similar times.

The use of natural resources of agricultural and forest ecosystems is much dependent on the functioning of plant roots. These provide several goods and services to society in the forms of, e.g., yield production, carbon sequestration, avoidance of nutrient release from the soil, alleviation of floods, and energy production. The functioning of plant roots is much less well known than that of the shoots, mostly due to methodological reasons. Only special new technology allows us to address the whole root systems quantitatively. Roots are exposed to several stresses (e.g. water stress by drought, soil frost, hypoxia, water shortage by competi‐ tion) during their lifetime which may decline their capability to provide goods and services. This is especially the case for trees whose lifespan ranges from tens to hundreds of years. Soil conditions will change with climate warming in many locations, linked to a change in precipitation in summer and winter seasons. Therefore, knowledge of the limits for stress tolerance of the roots of herbaceous and woody plants is demanded for future projections.

The "Green Revolution" created dwarf varieties capable of responding to higher fertilizer inputs without lodging, but failed to reach resource-poor farmers. Crossing early greenrevolution wheat, with an *F*2 of Norin 10 or Brevor, reduced root biomass. Later generation, semi-dwarf wheat showed genetic variation for root biomass, but some generations exhibited a further reduction in root size [29]. Beside a better use of available water resources, an improvement in the uptake efficiency of nutrients from mineral and organic fertilizers would have an important economic and ecological impact for a resource-efficient agricultural strategy. Varieties with greater roots could enable better use of available nutrients and water, as shown e.g. for phosphorus. The selected varieties with greater RSS should be better adapted to soil problems, like lowering of groundwater tables, acidification, loss of organic matter, soil compaction by heavy machines, etc. Varieties with greater RSS could be bred as catch crops or for the phytoremediation of nutrients and heavy metals. Wheat genotypes with superior root characteristics for efficient nutrient uptake, especially during the tillering and booting stages, should be developed in breeding programs to increase grain yield and minimize nitrate leaching [30].

The effect of water and nutrient application on yield has led to the overuse of these practices in the last decades. This misuse of irrigation and fertilizers is no longer sustainable, given the economic and environmental costs. Transpiration stream largely determines the availability of the mineral N in the rhizosphere. This makes our poor estimate of root densities a major obstacle to any precise assessment of nitrogen availability in fertilized crops. A larger invest‐ ment by the crop in fine roots at depth in the soil, and less proliferation of roots in surface layers, would improve yields by accessing extra resources. The economic return on investment in roots for water capture was twice the investment for nitrogen capture. An early and more extensive horizontal growth of wheat roots in the 0.2–0.7-m layer of the soil profile in glass‐ houses was found to improve substantially the uptake of N by vigorous lines [31]. There has been a long-standing interest in varietal differences in the uptake of nutrients, especially of N and P, but progress has been slow in translating this into information that can be used in breeding. Root systems limit plant breeding [32].

Breeding for RSS as a strategy for improving yield stability and crop productivity under dry conditions however is still largely ignored in the breeding process, when it is not the breeding aim as such, e.g. for root crops like sugar beet. The main reason for this shortcoming in breeding for drought tolerance is the lack of a suitable method for evaluation of RSS. An improvement in water use is relevant when soil water remains available at maturity or when deep-rooted genotypes access water in the soil profile that is normally unavailable. At moderate drought, productivity of cereals can be improved by a more effective use of available water, i.e. by increasing the plants access to a higher soil volume by a deeper root system and eventually an increased rooting density in deeper soil. Varieties with a deep root system (Fig. 8) should have more opened stomata to cool the plants by transpiration, and therefore improve their tolerance to high temperatures [33].

**Figure 8.** Vertical distribution of root length density (RLD) in spring barley varieties within the soil profile (Hrubčice, Czech Republic, 2012).

Better use of nutrients, including water, due to greater RSS, means:


The effect of water and nutrient application on yield has led to the overuse of these practices in the last decades. This misuse of irrigation and fertilizers is no longer sustainable, given the economic and environmental costs. Transpiration stream largely determines the availability of the mineral N in the rhizosphere. This makes our poor estimate of root densities a major obstacle to any precise assessment of nitrogen availability in fertilized crops. A larger invest‐ ment by the crop in fine roots at depth in the soil, and less proliferation of roots in surface layers, would improve yields by accessing extra resources. The economic return on investment in roots for water capture was twice the investment for nitrogen capture. An early and more extensive horizontal growth of wheat roots in the 0.2–0.7-m layer of the soil profile in glass‐ houses was found to improve substantially the uptake of N by vigorous lines [31]. There has been a long-standing interest in varietal differences in the uptake of nutrients, especially of N and P, but progress has been slow in translating this into information that can be used in

Breeding for RSS as a strategy for improving yield stability and crop productivity under dry conditions however is still largely ignored in the breeding process, when it is not the breeding aim as such, e.g. for root crops like sugar beet. The main reason for this shortcoming in breeding for drought tolerance is the lack of a suitable method for evaluation of RSS. An improvement in water use is relevant when soil water remains available at maturity or when deep-rooted genotypes access water in the soil profile that is normally unavailable. At moderate drought, productivity of cereals can be improved by a more effective use of available water, i.e. by increasing the plants access to a higher soil volume by a deeper root system and eventually an increased rooting density in deeper soil. Varieties with a deep root system (Fig. 8) should have more opened stomata to cool the plants by transpiration, and therefore improve their tolerance

**Figure 8.** Vertical distribution of root length density (RLD) in spring barley varieties within the soil profile (Hrubčice,

Better use of nutrients, including water, due to greater RSS, means:

breeding. Root systems limit plant breeding [32].

674 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

to high temperatures [33].

Czech Republic, 2012).

Serious environmental impacts were associated with an enrichment of surface water and groundwater by nitrogen and phosphorus. Increased intensity of livestock rearing depends in Europe in particular on large amounts of imports of nutrients – rich feedstuff from countries outside Europe. In specific areas this has led to nutrient surpluses, which have contributed to problems such as eutrophication.

There are a number of works that assess interspecies or intervariety differences in the above‐ ground biomass production of crops. Only a small number of authors deal with quantitative and qualitative assessment of underground biomass in relation to the dynamics of nitrogen in soil. An appropriate measure for the use of nitrate nitrogen from the soil in the autumn is the inclusion of cover crops into crop rotation. Field trials [34, 35] were executed to evaluate RSS in eight varieties of white mustard and five varieties of *Phacelia* on two locations, in three BBCH phases (i.e. international scale used to identify the phenological development stages of a plant) over two years. The relationship between RSS, aboveground biomass, and content of nitrogen in the soil was investigated. *Phacelia* featured on average a higher root/shoot ratio (0.45) than mustard (0.32), whereas the year impacted the ratio more than the production area type. In *Phacelia* a highly significant positive correlation was found between aboveground biomass and the amount of soil nitrate nitrogen. This phenomenon confirms that greater biomass produc‐ tion does not mean there is a lower soil nitrate nitrogen. A relationship between the RSS of mustard and the content of NO3 and NH4 + ions in the soil after harvest was observed. RSS negatively correlated with the content of nitrate nitrogen in the soil, however, the correlation was statistically not significant. Evaluation across sites revealed a positive correlation between aboveground biomass and the amount of residual NO3 - ions in the soil. On the other hand a significant negative correlation (*r*=-0.81) of RSS and NH4 + ions content was observed.

The effect of drought stress on the monitored traits of the root system and aboveground biomass of spring barley (*Hordeum vulgare* L.) was evaluated in a pot experiment by [36]. The characteristics of three varieties in a three-year observation in four different irrigation treat‐ ments were evaluated: length, surface area, weight of the root system (evaluated by the soilcore method with subsequent digital image analysis), the RSS (detected by measuring its electrical capacity), and dry matter yield of aboveground biomass and root biomass – the shoot ratio. Dry matter yield of aboveground biomass significantly correlates with the RSS (*r* = 0.700; significant on *P* ≤ 0.01). The variability of root system traits was affected by year (40%–50%), treatment (10%–11%), and variety (8%–14%).Weight ratio of aboveground biomass and root:shoot ratio were affected largely by variant (28.1% and 42.0%; significant effect). Year worked at least root: shoot (15.6%; significant effect). Variants without stress produced the most above ground and below ground biomass. However, the root:shoot ratio was the lowest in this case.

#### **3.3. Examples of effective selection for greater root system**

RSS was one of the selection criteria in the breeding for dinitrogen fixation. Breeding of varieties with greater RSS (alfalfa Zuzana), and greater RSS and higher dinitrogen fixation (alfalfa Nitro, white clover Nivel) has been successful [37].

In cereals, root densities of 1.0–1.5 cm cm-3 are needed to extract plant available water from the soil, e.g. [38, 39]. Maize plants rarely achieve this below 70 cm, but values of 3–5 cm cm-3 or more are common in the top 30 cm of soil. For better exploitation of available water, a better distribution of roots in the soil profile is preferable to partitioning more dry matter to roots [40]. A field trial with selected varieties of spring barley has been realized [36]. For five varieties RSS, its vertical distribution in the soil profile layers up to a 60-cm depth, and grain yield were evaluated. The impact of locality, year, and variety on root system attributes was quantified. Highest values of root length density (RLD) were determined in the layer between 0 cm and 10 cm (Figure 8). A tendency to increase RLD in both research localities and in most varieties in the layer between 40cm and to 60 cm was detected. A significant dependency of grain yield on RLD was only determined in the middle layers of the soil profile. In wet years a significant negative correlation was determined.

The RSS has been found to be a genetic trait, and some specific genes have been observed to control this property. In wild barley, the gene Hsdr4, involved in water-stress tolerance, was located on chromosome 3H near sdw1. This was identified as a marker of QTL for great RSS [41]. Therefore, the RSS and drought tolerance per se maybe linked.

The isolation of intact living root systems from soil in the field has not yet been published and seems impossible. This difficulty is evidenced in many observations. Biomass estimates from minirhizotrons indicate that the <0.25 mm diameter roots (Fig. 9) account for nearly 95% of the total root length [42]. Root separation using a sieve with a 0.5-mm mesh screen led to a marked underestimation of root length density and root biomass. Values up to three times higher were observed when using a 0.2-mm mesh screen in comparison to a 0.5-mm screen [43]. Ex situ methods are expensive and connected with relatively high experimental error. More progres‐ sive are in situ methods, in particular use of electric capacitance. Comparison of this method with the ex situ soil-core method found a good correlation. The electric capacitance can be therefore recommended as a quick and cheap method, which enables repeated evaluation of vegetation and retains the evaluated plants until harvest.

The capability "to see" the roots in the soil plays a key role in the evaluation of the potential of herbaceous and woody plants to produce goods and services for society and in the detection of the stress thresholds of roots. From a functional point of view, fine roots (Fig. 9) are the most important for plants. Thus, a method that gives a measure of the root surface area for absorbing water and nutrients would be valuable and it would offer wide applications for users of the natural resources of plant/forest ecosystems.

electrical capacity), and dry matter yield of aboveground biomass and root biomass – the shoot ratio. Dry matter yield of aboveground biomass significantly correlates with the RSS (*r* = 0.700; significant on *P* ≤ 0.01). The variability of root system traits was affected by year (40%–50%), treatment (10%–11%), and variety (8%–14%).Weight ratio of aboveground biomass and root:shoot ratio were affected largely by variant (28.1% and 42.0%; significant effect). Year worked at least root: shoot (15.6%; significant effect). Variants without stress produced the most above ground and below ground biomass. However, the root:shoot ratio was the lowest

RSS was one of the selection criteria in the breeding for dinitrogen fixation. Breeding of varieties with greater RSS (alfalfa Zuzana), and greater RSS and higher dinitrogen fixation

In cereals, root densities of 1.0–1.5 cm cm-3 are needed to extract plant available water from the soil, e.g. [38, 39]. Maize plants rarely achieve this below 70 cm, but values of 3–5 cm cm-3 or more are common in the top 30 cm of soil. For better exploitation of available water, a better distribution of roots in the soil profile is preferable to partitioning more dry matter to roots [40]. A field trial with selected varieties of spring barley has been realized [36]. For five varieties RSS, its vertical distribution in the soil profile layers up to a 60-cm depth, and grain yield were evaluated. The impact of locality, year, and variety on root system attributes was quantified. Highest values of root length density (RLD) were determined in the layer between 0 cm and 10 cm (Figure 8). A tendency to increase RLD in both research localities and in most varieties in the layer between 40cm and to 60 cm was detected. A significant dependency of grain yield on RLD was only determined in the middle layers of the soil profile. In wet years a significant

The RSS has been found to be a genetic trait, and some specific genes have been observed to control this property. In wild barley, the gene Hsdr4, involved in water-stress tolerance, was located on chromosome 3H near sdw1. This was identified as a marker of QTL for great RSS

The isolation of intact living root systems from soil in the field has not yet been published and seems impossible. This difficulty is evidenced in many observations. Biomass estimates from minirhizotrons indicate that the <0.25 mm diameter roots (Fig. 9) account for nearly 95% of the total root length [42]. Root separation using a sieve with a 0.5-mm mesh screen led to a marked underestimation of root length density and root biomass. Values up to three times higher were observed when using a 0.2-mm mesh screen in comparison to a 0.5-mm screen [43]. Ex situ methods are expensive and connected with relatively high experimental error. More progres‐ sive are in situ methods, in particular use of electric capacitance. Comparison of this method with the ex situ soil-core method found a good correlation. The electric capacitance can be therefore recommended as a quick and cheap method, which enables repeated evaluation of

[41]. Therefore, the RSS and drought tolerance per se maybe linked.

vegetation and retains the evaluated plants until harvest.

**3.3. Examples of effective selection for greater root system**

676 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

(alfalfa Nitro, white clover Nivel) has been successful [37].

negative correlation was determined.

in this case.

**Figure 9.** Measurement of the finest structures of a root system is possible using the method of electrical capacitance.

Wheat (*Triticum aestivum* L.) has been systematically bred for about 200 years. However, this breeding has been done using only aboveground plant parts. We evaluated previously the roots of 18 wheat populations [44]. The RSS was evaluated by its electrical capacitance directly in the field (in situ). The RSS of plants in third and fourth generations were evaluated during shooting and heading. In these evaluations plants were selected for large and small root systems. In dry environments, the progeny of plants with large and small root system had yields of 17.1 and 10.9 grams per plant in the third generation and 18.5 and 10.0 grams per plant in the fourth generation (Fig. 10). The selection process showed a greater response for larger root system size. Selection for higher wheat RSS can be easily used to breed for drought tolerance and higher efficiency of water and fertilizer use.

The study [45] introduces the evaluation of RSS for the breeding of spring barley, in particular for drought tolerance. The aim of this study was to present the method of RSS evaluation and show it in practical use, in particular in relation to drought tolerance. The varieties of spring barley were evaluated for RSS by its electrical capacity. The RSS was compared with the grain yield and grain quality of the varieties at 7–19 stations each year. Varieties with a greater RSS had a significantly higher yield in the dry part of the year. Varieties with a greater RSS had significantly higher contents of starch, saccharide extracts, and malt extracts, as well as higher

grain yield. Some varieties donated greater, some smaller roots into progeny. It was shown **Figure 10.** Regression relationship of the wheat grain yield on RSS as averaged from three locations (published in [44]).

yields of protein and starch in dry environments. It can be concluded that a small RSS is related to a low grain yield and malt quality in dry environments, even in genetically diverse varieties. that the selection for RSS was effective and responsive (more for greater than for smaller roots) in a similar way as for grain yield and can be therefore used in practical breeding.

Fig. 11 The root is the most sensitive organ of the plant. On the left: tree sample *Pinus silvestris* (Scots pine), standing on the main root, on the 4 m height, due to influence of strong soil erosion. These trees have on the basis of measurements at least twice as large a root system compared to those in a conventional environment. In the other two images are oil rape roots. The left of these images is a root located from a relatively dry, well-prepared soil. The right of these images shows a root from compacted, moist soil. Such changes have an effect on the metabolism of plants, yield, seed quality, stress resistance, i.e. not only variety, **Figure 11.** The root is the most sensitive organ of the plant. On the left: tree sample *Pinus silvestris* (Scots pine), stand‐ ing on the main root, on the 4 m height, due to influence of strong soil erosion. These trees have on the basis of meas‐ urements at least twice as large a root system compared to those in a conventional environment. In the other two images are oil rape roots. The left of these images is a root located from a relatively dry, well-prepared soil. The right of these images shows a root from compacted, moist soil. Such changes have an effect on the metabolism of plants, yield, seed quality, stress resistance, i.e. not only variety, provenance, and method of seed storage. In addition, the quality of soil preparation (at field crops) has a large influence.

provenance, and method of seed storage. In addition, the quality of soil preparation (at field crops) has a large influence. The relevance and response to selection for greater RSS of spring barley in field conditions has been studied [46]. The effect of selection in 12 barley populations developed by mutual crossing

Plant integrity looks like as a "very easy and expanded topic," but the reality is very different. "Thanks" to the rigid specialization of scientists, we are losing a holistic view of plants. It is necessary to sense a plant in its entire complexity – both roots and shoots, as well as across their life cycles. Complex research, i.e. the connection of biology, plant nutrition, ecology, and other disciplines, is hardly observable in most scientific work. Only such an integrated approach can allow us to reach the correct interpretations for experimental results **(47–54)**. For example, when interaction of three or more stressors exists, there can be a lower or higher effect of stressors (compensated through the course of metabolism, etc.). The reason is the influence of individual factors on metabolism and their possible antagonistic influences. Stressors always have pleiotropic effects on a plant, and influence on many genes. Therefore,

**4. Importance of plant integrity in crop research** 

of 4 parents in the F3 generation as a response to the selection in the preceding generation F2, for great and small RSS was evaluated. The selection was effective. The average difference in the parental segregating generation was +40 and -43%, and in progeny +4 and -2%, respectively. Grain yield responded two times more to the selection (plants with a root size greater by 3.9% had higher yield of 8.1%). Root size was found to be related to grain yield. Some varieties donated greater, some smaller roots into progeny. It was shown that the selection for RSS was effective and responsive (more for greater than for smaller roots) in a similar way as for grain yield and can be therefore used in practical breeding.
