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For more information visit www.intechopen.com Chapter 25 Sunflower Breeding for Resistance to Abiotic and Biotic Stresses Dragan Škorić Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62159 Abstract Due to a specific structure of its main organs (root, stem, leaves, and head), sunflower can be successfully grown on marginal soils and in semiarid conditions, and it is more resist‐ ant to abiotic stresses, than other field crops. Unfortunately, it is very sensitive to biotic stresses. In sunflower breeding for resistance to abiotic stresses, the greatest progress has been made in selection for drought resistance. Breeders use over 30 different parameters in sunflower screening for drought resistance, with physiological ones being the predomi‐ nant type. The best breeding results have been achieved using the phenomenon of stay- green, with the added bonus that this method incorporates into the cultivated sunflower not only drought resistance but resistance to Macrophomina and Phomopsis as well. The di‐ versity of the wild Helianthus species offers great possibilities for increasing the genetic resistance of the cultivated sunflower toward abiotic stresses. In using wild sunflower species in sunflower breeding for drought resistance and resistance to salinity, best re‐ sults have so far been achieved with H. argophyllus and H. paradoxus, respectively. In ad‐ dition to the use of wild Helianthus species, sunflower breeding for abiotic stress resistance should also make more use of molecular breeding techniques. More progress has been made in sunflower breeding for heat resistance than in that for cold resistance. Specific breeding programs dealing with sunflower resistance to mineral deficiency and mineral toxicity have yet to be established. Concerning biotic stresses, the main problem in sunflower cultivation is caused by fungal diseases. Genetic variability of cultivated sunflower is very low and deficient in disease- resistance genes. Due to wild sunflower species of the Helianthus genus, genes that con‐ fer resistance to certain diseases were discovered and incorporated into the genotypes of the cultivated sunflower. Based on the wild species, genes were found that confer resist‐ ance to Plasmopara halstedii, Puccinia helianthi, Verticillium dahliae, V. albo-atrum, and Erysi‐ phe cichoracearum. Furthermore, wild sunflower species provide a high level of tolerance (field resistance) to Phomopsis/Diaporthe helianthi, Macrophomina phaseolina, Albugo erago‐ pognis, and Alternaria ssp. Sources of resistance to other harmful diseases are sought after within wild sunflower species. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 586 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives With the use of one wild species of H. annuus from Kansas (USA.), genes conferring re‐ sistance to a group of imidazolinone (IMI) or sulfonylurea herbicides were discovered. Moreover, similar genes were found through induced mutations. These sources of resist‐ ance provide successful control over a broad spectrum of weeds, which infest sunflower crops, including broomrape. The growth of the parasitic weed sunflower broomrape (Orobanche cumana Wallr) is a ma‐ jor issue in sunflower production, especially in Central and Eastern Europe, as well as in Spain. Six races of broomrape have been detected (A, B, C, D, E, and F) and dominant resistance genes (Or, Or, Or, Or, Or, and Or) were found in wild sunflower species. 1 2 3 4 4 6 During the last 4–10 years, new virulent races of broomrape emerged in several European countries. Geneticists and breeders work on finding the sources of resistance to the new broomrape races in wild sunflower species. Numerous insect species cause economic damages during sunflower production, espe‐ cially in North America (the homeland of sunflower). Homoeosoma species are the most widespread insects that infest sunflower. Homoeosoma nebulella infests sunflower in Eu‐ rope and Asia, while infestation with H. electellum poses a major problem in USA, Cana‐ da, and Mexico. Based on the use of wild sunflower species H. tuberosus, genes conferring resistance to Homoeosoma species were incorporated. Sunflower has an armored layer in the hull, which provides resistance to this insect. Sources of resistance to other economi‐ cally harmful insects are sought after. New methods in biotechnology, particularly marker genes, have been frequently used in breeding for abiotic and biotic stresses. Keywords: Abiotic and biotic stresses, breeding, interspecies hybridization, resistance, sunflower, wild species 1. Introduction 1.1. Sunflower breeding for resistance to abiotic stresses Abiotic stresses not only determine the geographical and regional distribution of crops but also dictate if a potentially arable piece of land can actually be used for cultivation. According to an estimate, 24.2% of the world's geographic area is potentially arable. However, only 10.6% of the geographic area is under actual cultivation, while the rest is not available for cultivation due to one or more abiotic stresses [1]. According to the same author, drought is the main abiotic factor, as it affects 26% of the arable area. Mineral toxicities/deficiencies are second in importance, while frost stands third. Drought is the most limiting of all abiotic stresses, and it affects well over one-third of the soils worldwide. Plants that manage to survive the effects of drought stress show a decrease in fertility, yield, and product quality [2]. Characterization of drought tolerance is very complex and interrelated to many factors. Drought is a multidimensional stress affecting plants at various levels of their organization. Sunflower is grown in a number of countries on so-called marginal soils, often in semiarid conditions where almost every year an abiotic stress of one kind or another is present acting Sunflower Breeding for Resistance to Abiotic and Biotic Stresses 587 http://dx.doi.org/10.5772/62159 as a limiting factor on crop production. However, of all field crops, sunflower is best able to withstand drought conditions, primarily on account of the structure of its organs [3]. Drought is the main cause not only of differences between mean yield and potential yield but also of yield variations from year to year and therefore of yield instability [2]. Using the results of our own studies and those of other authors, the present chapter discusses the progress that has so far been made in sunflower breeding for resistance to abiotic stresses and indicates possible future directions in this area of sunflower research. 1.2. Sunflower breeding for resistance to drought Previous experiences in sunflower cultivation have shown that drought can be a limiting factor in realizing the potential of a variety or a hybrid. In sunflower breeding for resistance to drought, just like in the other crops, a number of physical and morphological parameters are at play. The accumulation of genes for these parameters in a single genotype makes it possible to increase resistance to drought [4]. Škorić [5] states that sunflowers must be resistant to both soil and air drought, that is, to high temperatures during flowering (pollination) and the oil synthesis stage. The ways to achieve this desired goal are as follows: a more efficient root system, a certain systemic composition of the main organs, and resistance to certain diseases (Macrophomina phaseoli). In addition to efficient water use, the root system must have the ability for efficient nutrient use under stress conditions. On the one hand, resistance depends on the selection of genotypes whose flowering and maturity end before the occurrence of stress (early maturity). On the other hand, mechanism of drought resistance incorporates the modification of certain physiological and morphological parameters, which enables a more efficient use of water reserves during the period of stress. The mechanism manifests itself through a more aggressive root system or water use reduction via a more efficient stomatal apparatus plus the interaction of these factors. The inheritance of tolerance of drought based on high osmotic pressure was found to be controlled by partial dominance and overdominance. The inheritance of drought tolerance measured by temperature shock was found to be based on nonallelic interaction of genes contained in the system of partial dominance [6]. Soil drought limits water uptake and consumption by plants. Transpiration intensity decreases strongly, which, in combination with high air temperature, leads to overheating of plants. The protective reaction of plants against water shortage is the increased ability of cells to retain water. Respiration intensity typically increases under the influence of drought. Prolonged drought forces the plants to reduce the energy efficiency of respiration [22]. Fulda et al. [8] used their own results and those of other authors to conclude as follows. Obviously, water stress acclimation is a multigene acclimation, in which many different physiological processes and many drought stress-inducible genes are involved. Functionally, 588 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives these gene products can be distinguished into osmolyte synthesis, protection factors for macromolecules (chaperons, LEA/dehyndrtype genes), proteases, membrane proteins (aquaporins, transporters, detoxification enzymes (glutathione-S-transferase (GST) and superoxide dismutase (SOD)), and genes of regulatory proteins such as transcription factors (TFs), protein kinases, and protein phosphatases. Although the alterations in all of these processes related to drought stress have been widely investigated in many model species and a few crop species, reports on sunflower are limited. Studying the influence of water deficit and canopy senescence pattern on sunflower root functionality during the grain-filling phase, Lisanti et al. [9] have concluded that both water deficit and intrinsic canopy senescence dynamics can profoundly affect root functionality during grain-filling. The effects of these factors and their interactions, especially under drought, on yield merit focused attention in future research According to Singh [1], drought seems rather difficult to define and more difficult to quantify. For example, the common criteria used in the various definitions are precipitation, air temperature, relative humidity, evaporation from free water surface, transpiration, wind, air flow, soil moisture, and plant conditions. A working definition of drought may be "the inadequacy of water availability, including precipitation and soil moisture storage capacity, in quantity and distribution during the life cycle of a crop to restrict the expression of its full genetic yield potential". Therefore, under conditions of drought, water stress develops in the plants as the demand exceeds water supply; this may occur due to atmospheric or soil conditions and is reflected in a gradient of water potentials developed in the soil/soil–root interface and the leaf, the transpiring organ. Thus, moisture stress may be defined as the inability of plants to meet the evapotranspirational demand. Moisture stress is likely to develop to a different rate in different plant organs along this gradient [10]. Drought resistance may be defined as mechanism(s) causing minimal loss of yield in a drought environment relative to the maximum yield in a constraint-free, that is, optimal environment for the crop. However, it does not exist as a unique heritable plant attribute. The various mechanisms by which a crop can minimize yield loss due to drought are grouped into the following three categories: 1. drought escape 2. dehydration avoidance, and 3. dehydration tolerance [1] Drought escape describes the situation where an otherwise drought-susceptible variety performs well in a drought environment simply by avoiding the period of drought. Early maturity is an important vehicle for drought escape, suitable for environments subjected to late-season drought stress [1]. Early sunflower hybrids generally have lower leaf area index (LAI), lower total evapotrans‐ piration, and lower yield potential than the later ones. According to Škorić [11], early sunflower Sunflower Breeding for Resistance to Abiotic and Biotic Stresses 589 http://dx.doi.org/10.5772/62159 hybrids are most often susceptible to Macrophomina, and thus in cases where there is an early occurrence of drought such hybrids may become affected, thus nullifying any positive effect early maturity may bring. Dehydration avoidance is the ability of a plant "to retain a relatively higher level of hydration under conditions of soil or atmospheric water stress." Therefore, the various physiological, biochemical, and metabolic processes involved in plant growth and yield production are not internally exposed to stress, but they are protected from water stress [10]. The common measure of dehydration avoidance is the tissue water status as expressed by water or turgor potential under conditions of water stress. This can be achieved by either reducing transpira‐ tion (such plants are often called water savers) or increasing water uptake (such plants are often termed as water spenders). Wild species are readily classifiable as water savers and water spenders, but crop plants ordinarily exhibit a combination of both features, probably as a result of selection by man. Drought not only reduces the rate of photosynthesis but also directs the photosynthetic metabolism toward increased formation of low-molecular weight compounds such as alanine, hexoses, and malic acid [12]. When the drought ends, sunflower plants are capable of again having a high rate of photosynthesis, thus compensating for the negative effects of water deficiency. As sunflower plants respond to drought, the free proline content of their leaves increases, because proline, due to its structure, increases the water retention capacity of the cell [13]. When breeding for dehydration avoidance, it is highly important that a considerable attention is paid to parameters such as reduced transpiration, osmotic adjustment, abscisic acid (ABA), cuticular wax, and leaf characteristics (leaf pubescence, altering the leaf angle, and leaf rolling). It is also especially important to find ways to increase water uptake by creating a more powerful, deeper, and well-branched root system [14]. 1.2.1. Sources of drought resistance Several types of germplasms are used in sunflower breeding for drought resistance: 1. landraces; 2. cultivated hybrids and varieties; 3. wild species of the genus Helianthus; [15]; and 4. genetically engineered germplasm. Use of landraces and cultivated hybrids and varieties has produced some positive results, but not to the extent that would secure stable sunflower production under drought conditions. The best results in increasing the drought resistance of cultivated sunflower have been achieved using wild species of the genus Helianthus. Over the last 10–14 years, highly drought-tolerant germplasms based on H. argophyllus, which have a commercial value, have been created in various breeding centers. 590 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives Research and characterization of physiological mechanisms in wild sunflower are just beginning. Škorić [16] suggests that in breeding for drought tolerance, there should be a greater effort to expand the use of other wild species such as H. deserticola, H. hirsutus, H. maximiliani, H. Tuberosus, and others. 1.2.2. Using different traits in sunflower breeding for drought resistance Škorić [7] reported that over 30 different parameters were used in the study of drought resistance and breeding for drought resistance in sunflower. Among these, the most frequently used were physiological parameters. Chimenti et al. [17] reported that high osmotic families extracted more water from the profile during the stress period and had greater grain yield and leaf area duration than families with a low degree of osmotic adjustment. The same authors concluded that osmotic adjustment can contribute to post-anthesis drought tolerance in sunflower through increased water uptake, reduced impact on grain number, grain size, and greater leaf area duration. Andrei [18] concluded that high self-fertility (24–49%) in some hybrids ensured a greater stability in sunflower yield under stress conditions. Studying the influence of drought stress on growth, protein expression, and osmolyte accumulation in sunflower, Fulda et al. [8] reported that osmolyte analysis revealed an accumulation of glucose (24–30-fold), inositol (20–30-fold), proline (10–20-fold), fructose (3–6- fold), and sucrose (4–4-fold) in extracts from leaves of drought-stressed plants. Changes in protein expression of drought-stressed versus control plants were detected in colloidal Coomasie-stained 2D-polyacrylamide gel electrophoresis (PAGE). Sato et al. [19] studied the correlation between the responses of leaf expansion and hypocotyl elongation to water deficit in sunflower genotypes. Based on the results obtained, they reported that the response of hypocotyl growth to water deficit ranged between 31 and 48%, while that of leaf growth ranged between 40 and 63%. There was a significant positive correlation (p < 0.01 R2 = 0.61) between both responses. The correlation was also significant using Pearson’s correlation test (p < 0.04, r = 0.78). Petcu et al. [20] studied physiological traits for the quantification of drought tolerance in sunflower and determined as follows. The reduction in leaf area, shoot size, and biomass accumulation of sunflower seedlings under water stress conditions determined the increase in root/shoot ratio. This suggests that for young plants the main sink was survival. In a late stage of vegetation, the root/shoot ratio decreased under drought stress in some hybrids but increased in others, suggesting that for mature plants the main sink was the yield. The physiology work has focused on morpho-physiological traits induced by drought and associated with drought tolerance of plants and the elaboration of screening methods for rapidly measuring drought tolerance using plants in an early stage of vegetation. Based on the results of Škorić [7, 11], practical results in sunflower breeding for drought resistance have been achieved by using the stay-green phenomenon. Here, we should warn Sunflower Breeding for Resistance to Abiotic and Biotic Stresses 591 http://dx.doi.org/10.5772/62159 that in the selection of lines on the basis of stay-green criteria, only lines with a high degree of self-fertility should be looked for, otherwise a wrong choice of genotypes will be made. The use of the stay-green criterion involves the selection of not only genotypes resistant to drought but also those resistant to Macrophomina, which tends to be a problem under stress conditions. Also, genotypes resistant to Phomopsis may be simultanously selected, as confirmed by the inbred lines Ha-48, Ha-22, CMS-1-40, PH-BC-2-91, PR-ST-3, RHA-SES, RHA-483, etc. as well as the hybrids made from these lines, which combine several resistance systems. Vrânceanu [21] confirmed the validity of using the stay-green criterion in the selection for drought resistance [22]. Petrović et al. [23] concluded that nitrate reductase activity and free-proline accumulation rate, which underwent large modifications in plants under water stress, may serve as parameters for the evaluation of sunflower genotypes for drought tolerance. Working on the determination of water stress index in sunflower, Orta et al. [24] found statistically significant correlations between CWSI (crop water stress index) calculated from single leaf temperatures on the one hand and stomatal resistance, leaf area index, and available water in the root on the other. Early sunflower hybrids generally have lower leaf area index, total evapotranspiration, and yield potential than the later hybrids. However, according to Škorić [11], early hybrids are typically sensitive to Macrophomina, so in the case of an early manifestation of drought they become infected and thus the advantage of earliness is nullified. Some breeders believe that drought avoidance can be achieved by developing very early sunflower hybrids or by moving the sowing date (early or late sowing) in order to avoid the dry period. Dehydration avoidance can be achieved in several ways, for example, by selecting genotypes with reduced transpiration (water savers) or by increasing the uptake of available water from the soil by a powerful root system (water spenders). Characteristics that appear to be correlated with drought tolerance include deeper rooting depth and more efficient root uptake of water, tolerance to high osmotic pressure, low transpiration rates, and plant ability to recover after wilting under heat stress. The genetics of sunflower resistance to drought has not been studied sufficiently, despite numerous attempts and use of different plant characteristics. It appears safe to say that the drought resistance (tolerance) is controlled by a set of genes. 1.3. Sunflower breeding for resistance to salinity Abiotic stress can be generated by mineral salts, which affect a considerable portion of the global arable land. Salinity ranks second after moisture stress. This stress may occur in the form of a specific mineral deficiency or toxicity, or as accumulation of an excess amount of soluble salts in the root zone [1]. Sunflowers are grown on low-to-medium-saline soils in many countries. These countries face soil salinity as a serious limiting factor in sunflower production. However, it should be 592 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives remembered that there are several wild Helianthus species that naturally grow on saline soils. These species are important sources of genes for resistance to salinity. Breeders should apply effective screening methods in order to identify the wild species that possess genes useful in breeding for salinity resistance and equally effective breeding methods to transfer these genes into cultivated sunflower genotypes [22]. Seiler [25] stated that several wild species of Helianthus are native to salt-impacted habitats and may possess genes for salt tolerance. The same author reports that Chandler and Jan [26] evaluated three wild Helianthus species for salt tolerance, namely H. paradoxus, H. Debilis, and H. annuus population native to salty desert areas, and obtained the following results. Helianthus debilis tolerated a salt concentration about the same as cultivated sunflower, wilting at an NaCl concentration of 240–400 mM. The wild ecotype of H. annuus had a higher tolerance, with some plants surviving the NaCl concentration of 800 mM. Helianthus paradoxus was highly salt tolerant, with some plants surviving at 1300 mM of NaCl. Salt tolerance was a dominant trait in hybrids between H. paradoxus and cultivated H. annuus, which did as well as the wild parent. The emergence percentage, emergence index, shoot length, and shoot fresh weight can be used as selection criteria for salt tolerance in sunflower at the seedling stage [27]. Tolerance of sunflower genotypes to salinity has been investigated by a number of researchers. Prakash et al. [28] found that turgor is not correlated with salt tolerance. The accumulation of proline shows a higher impact on tolerance to salinity. Since callus development, seed germination, and vigor are associated, the former could be a more reliable index of salt tolerance. The involvement of turgor and proline in salt tolerance seems to be doubtful [29]. Prakash et al. [28] stated that turgor cannot be related to salt tolerance. However, proline accumulation seems to be more due to the effect of salinity. Evidently, using H. paradoxus and possibly some other wild Helianthus species, sunflower breeders can successfully achieve high resistance to salinity. It is important to determine the selection criteria that can be applied in the breeding program, and these can be cell survival, seed germination, dry matter accumulation, leaf death or senescence, leaf ion content, leaf necrosis, root growth, osmoregulation, etc. [1]. 1.4. Sunflower breeding for resistance to mineral deficiency and mineral toxicity Sunflowers require only 10 macroelements (C, O, H, N, P, K, S, Ca, Fe, and Mg) and 6 micro‐ elements (B, Mn, Cu, Zn, Mo, and Co) for their growth and development. Air and water are the sources of carbon, oxygen, and hydrogen. The rest of the elements are taken up from the soil or fertilizers and are divided into primary elements, secondary elements, and microele‐ ments [14]. Sunflower nutrition has been the subject of many books and scientific papers, which have established optimum levels of each individual macro- and microelement needed for the normal growth and development of sunflower on different types of soil. There is also volu‐ minous literature on the deficiencies or excess levels (toxicity) of individual elements and how they affect sunflower growth and development. Sunflower Breeding for Resistance to Abiotic and Biotic Stresses 593 http://dx.doi.org/10.5772/62159 Studying the diversity of elements in sunflower inbred lines, Sarić et al. [30] came to the conclusion that the genetic specificity for mineral nutrition is manifested not only through different contents of mineral elements but also through their distribution into individual plant organs. As there are unfortunately no major breeding programs anywhere in the world that deal specifically with sunflower resistance to mineral deficiency and mineral toxicity, sunflower breeders should consider a possibility of establishing one or more such programs. They would have to choose appropriate breeding methods and targets, define selection criteria, and select potential resistance sources (most likely wild Helianthus species) [16]. 1.5. Sunflower breeding for heat resistance Singh [1] made a very good definition of the heat and cold resistance, which reads: "Each plant species, more particularly genotype, has an optimum range of temperatures for its normal growth and development: the specific temperatures would depend not only on the genotype but also on the stage of growth and development of a given genotype. When temperature moves beyond this optimal range, it generates temperature stress, i.e., temperature interferes with the performance. Temperature stress may be grouped into the following three categories: (1) heat stress, (2) chilling stress and (3) freezing stress." Sunflower is characterized by high adaptability to high temperatures. At high temperatures, sunflower intensifies the process of transpiration so that its leaves remain relatively cool. Transpiration rate can be increased only if sufficient water is supplied and this calls for a deep and well-developed root system. Therefore, the choice of genotypes with a deep and powerful root system is an important criterion in the selection for sunflower tolerance to high temper‐ atures [22]. Another important criterion is the tolerance to intensive transpiration. For the environments in which high air temperatures frequently occur at the flowering stage, breeders should select genotypes capable of producing large quantities of pollen and maintain pollen viability under such conditions. It is also important for the pistil and its stigma, or for the disk flowers on the whole, to be tolerant to high temperatures, which ensures pollination and seed formation [22]. Yet another criterion for the selection of genotypes adapted to climates with high temperatures and air and soil drought is the capacity for high seed (formation) filling rate and rapid synthesis of oil in response to stress conditions. In order for sunflower breeders to be able to determine the right breeding methods, targets, and selection criteria and to choose their breeding materials for selection for heat resistance, they must have a detailed knowledge of how sunflower organs respond to high temperatures. Sunflower is exposed to high temperatures in arid and semiarid conditions, which have been prevalent in much of Europe in 2007. High temperatures may be accompanied by high, but also low humidity levels.