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Cassava is an important tropical starchy root crop that is used extensively in drought prone tropical regions. It responds to water deficit with a dehydration avoidance and growth arrest syndrome. Carbohydrate is supplied from stems via remobilization. It is very limited in its use of osmotic adjustment, compatible solute synthesis, dehydrin accumulation and other tolerance mechanisms for low water potential. Given the difficulties of conventional breeding of cassava due to its long breeding cycle, heterozygousity, and difficulties in producing seed, an important recent development is the use of molecular markers and marker assisted selection (MAS). MAS is also contributing to the introgression of traits from wild relatives [ABSTRACT FROM AUTHOR]

Defense systems are triggered when plants encounter environmental stresses such as high salinity or drought. Many studies have shown that these defense systems depend on protective mechanisms created by altering the expression levels of stress genes. The agricultural species Solanum tuberosum is an autotetraploid with a highly complicated, quantitative inheritance pattern. Thus, breeding new potato cultivars that are tolerant of saline and drought stress by conventional methods is tedious, difficult and time-consuming, and generally requires between 10 and 15 years. Genetic engineering techniques represent a faster and more reliable way to improve potato cultivars. As a first step towards developing drought- and saline-tolerant potato plants by molecular breeding methods, numerous potato stress genes, including those that code for functional and regulatory proteins, have been isolated and characterized by homologue gene screening, differential screening, microarray analysis and proteome analysis. There have been many attempts around the world to create drought- and saline-tolerant potato plants by introducing abiotic stress genes for functional proteins, such as proline synthesis protein, osmotin-like protein, GPD, trehalose synthesis protein, and regulatory proteins such as StEREBP, CBF and StRD22 [ABSTRACT FROM AUTHOR]

Plant growth and development are adversely affected by salinity - a major environmental stress that limits agricultural production. This chapter provides an overview of the physiological mechanisms by which growth and development of crop plants are affected by salinity. The initial phase of growth reduction is due to an osmotic effect, is similar to the initial response to water stress and shows little genotypic differences. The second, slower effect is the result of salt toxicity in leaves. In the second phase a salt sensitive species or genotype differs from a more salt tolerant one by its inability to prevent salt accumulation in leaves to toxic levels. Most crop plants are salt tolerant at germination but salt sensitive during emergence and vegetative development. Root and shoot growth is inhibited by salinity; however, supplemental Ca partly alleviates the growth inhibition. The Ca effect appears related to the maintenance of plasma membrane selectivity for K over Na. Reproductive development is considered less sensitive to salt stress than vegetative growth, although in wheat salt stress can hasten reproductive growth, inhibit spike development and decrease the yield potential, whereas in the more salt sensitive rice, low yield is primarily associated with reduction in tillers, and by sterile spikelets in some cultivars. Plants with improved salt tolerance must thrive under saline field conditions with numerous additional stresses. Salinity shows interactions with several stresses, among others with boron toxicity, but the mechanisms of salinity-boron interactions are still poorly known. To better understand crop tolerance under saline field conditions, future research should focus on tolerance of crops to a combination of stresses [ABSTRACT FROM AUTHOR]

Salt accumulation in soil surfaces, known as soil salinity, could lead to the impairment of plant growth and development and is manifested mostly under irrigated and dryland agriculture. Excess salts in the soil affects plants through osmotic stress; accumulation to toxic levels within the cells; and through the interference with the uptake of mineral nutrients. Rice productivity in several parts of the world is therefore severely limited by salinity on account of the prevalence of irrigation in rice farming. Tolerance to salt toxicity in plants is a genetic and physiologically complex trait. Halophytes (salt tolerant plants) are different from the salt-sensitive glycophytes in terms of peculiarities in their anatomy, ability to sequester otherwise toxic ions, and other physiologic processes. It is logical therefore to infer complexity also at the genetic level on account of the several pathways involved in these mechanisms. These complexities have confounded genetic improvement strategies for salinity tolerance in plants resulting in a paucity of saline tolerant plants, with only about 30 officially released saline tolerant crop varieties world-wide. Only one saline tolerant rice variety, Bicol, has been officially released to farmers. We review strategies being currently employed in the development of saline tolerant rice varieties. These include conventional plant breeding which is hampered by the lack of suitable genetic variation for this trait; the modest progress made through doubled haploidy; and the reliance on somaclonal variation, an unsustainably unpredictable strategy. This review also posits that while genetic transformation has led to the modification of certain physiological indices implicated in salinity tolerance in rice, in isolation, these modifications have not been translated to improved yield under salt stress. A more recently adopted strategy, induced mutagenesis, has led to some promising results. We argue that the production of induced rice mutants holds the greatest promise of these strategies for mitigating the scourge of soil salinity considering the relative ease with which other traits in this crop have been modified using this methodology. The underlying principles of induced mutagenesis; the modes of action of different mutagenic agents; and procedures for the rapid production and detection of mutants are also summarised. In order to enhance efficiency in the production, detection and incorporation of induced mutants into crop improvement programmes, we suggest the coupling of in vitro (such as doubled haploidy and cell suspension cultures) and molecular genetic techniques to this methodology. It is posited also that the efficiency of this process can be greatly enhanced by marker-aided selection while high throughput reverse genetics strategies could lead to the rapid detection of mutation events in target genes. It is concluded that with the plethora of genomics resources available for rice, the use of induced mutations for improving salinity tolerance (and other traits) would rely significantly on the concerted application of efficiency enhancing in vitro techniques and functional genomics strategies (including reverse genetics) [ABSTRACT FROM AUTHOR]

Forages play a key role in ruminant livestock production and environmental protection. Because forage grasses and forage legumes often grow in marginal areas, stress tolerance is one of the most important traits in forage cultivar development. Conventional and genetic engineering approaches have been used to improve stress tolerance of forage grasses and legumes. This review summarizes recent advances in improving drought and salt tolerances of several major forage species [ABSTRACT FROM AUTHOR]

Fiber from cotton (Gossypium hirsutum and G. barbadense) is a major product in the world economy. It is a botanically unique plant as it is a perennial allotetraploid derived from diploid Gossypium species, one of which does not produce lint, which is grown as an annual row crop. Cotton is an especially appropriate system for research into the molecular basis of plant response to water deficit and salinity, as it originates from wild perennial plants adapted to semi-arid, sub-tropical environments which experienced periodic drought and temperature extremes that are associated with soils with high salt content. The current primary molecular breeding approaches include transgenic modification and quantitative trait mapping with marker-assisted selection. The preliminary work in QTL mapping for drought response and the relationships of the QTLs with the drought-associated measurements is developing a foundation for understanding and using the molecular basis of drought tolerance. QTL mapping for salt tolerance is not moving apace. Using and/or regulating transgene effects on the plant responses to drought and salinity has shown success and will continue to increase our understanding of the complexity of plant's physiological pathways. Improvements in all areas of molecular breeding are almost certain, but the most effective improvements will come from exploiting our improved understanding of the genetic architecture [ABSTRACT FROM AUTHOR]

Drought and salinity are two important abiotic factors limiting soybean production worldwide and drought alone accounts for about 40% crop loss. Irrigation and soil reclamation are not economically viable options for soybean production under drought and salinity. Hence, genetic improvement for drought and salt tolerance are cost effective. Conventional breeding has made a significant contribution to soybean improvement in the last 50 years. Through conventional breeding, it is easy to manipulate simply inherited qualitative traits which are less sensitive to environmental variation, but quantitative traits like yield or tolerance to abiotic stress are significantly influenced by environment. Most agronomically important traits are quantitatively inherited and are difficult to improve through conventional breeding. Molecular marker technologies can dissect quantitative traits into individual components, known as quantitative trait loci enabling marker assisted selection of desired traits in much shorter time avoiding labor intensive, conventional, phenotypic selection. A molecular breeding approach can supplement the conventional breeding system. Well developed molecular genetic maps, functional genomic resources, and other molecular tools are available for soybean. Effective use of these resources will allow a greater understanding of basic mechanisms of tolerance to abiotic stress. Integration of these genomic tools coupled with well-designed breeding strategies will help to develop soybean varieties with higher tolerance to drought and salt [ABSTRACT FROM AUTHOR]

Salt tolerance in plants is a complex trait, which involves multiple genes participating in a myriad of processes that limit uptake, promote efflux, enhance vacuolar storage of Na+ and recycle Na+ from shoots to roots. In addition, the suppression of high Na+-triggered oxidative stress and cell death also increases salt tolerance. A number of salt tolerance genes have been identified and characterized using arabidopsis and rice as model plants. Mutant screens have been frequently utilized and most genes identified with this approach are overly-sensitive to salt stress, i.e.sos genes, implying that positive gene function is required for salt tolerance. To identify genes that positively contribute to salt tolerance and are more easily transferred to crops, Ceres has developed a large population of arabidopsis transgenic lines overexpressing genes from several species and used a seed pooling strategy to screen these for enhanced salt tolerance. Thus far, we have identified 10 genes that when overexpressed result in increased salt tolerance. The encoded proteins are related to calmodulin, calmodulin-binding, zinc-finger, putative cyclases, stress-related and novel proteins. These genes may be involved in the regulation of AtNHX1 and/or SOS genes, as well as the suppression of high Na+-triggered generation of reactive oxygen species and cell death. We discuss methods, such as stacking genes that provide different mechanisms for salt tolerance or using salt inducible promoters, to develop super-tolerant cultivars of crops to be grown in high salinity soils [ABSTRACT FROM AUTHOR]

Salinity and drought are among the most challenging environmental constraints to crop productivity worldwide. The cultivated tomato, Lycopersicon esculentum Mill., is moderately sensitive to both of these stresses throughout its ontogeny, including during seed germination, seedling emergence, vegetative growth and reproduction. Limited variation exists within the cultivated tomato for abiotic stress tolerance, however, the related wild species of tomato is a rich source of genetic variation which can be used for crop improvement. During the past several decades this variation has been utilized for characterization of physiological and genetic bases of tolerance to different abiotic stresses, including salinity and drought. Abiotic stress tolerance is a complex phenomenon, controlled by more than one gene and influenced by uncontrollable environmental factors. Furthermore, tomato stress tolerance is a developmentally-regulated state-specific phenomenon, such that tolerance at one stage of plant development is independent of tolerance at other stages. This has been demonstrated by analysis of response and correlated response to selection as well as identification of quantitative trait loci (QTLs) conferring tolerance at different stages. Transgenic approaches also have been employed to gain a better understanding of the genetic and physiological bases of salt and, to a lesser degree, drought tolerance in tomato, and to develop transgenic plants with improved stress tolerance. However, despite considerable traditional genetics and physiological research as well as contemporary molecular marker and transgenic studies in tomato, there is yet no report of any commercial cultivar of tomato with salt or drought tolerance. To achieve this goal, cooperation among plant geneticists, physiologists, molecular biologists and breeders engaged in tomato stress tolerance is imperative. In this chapter, I review the recent progresses in genetics and breeding of salt and drought tolerance in tomato and discuss the prospects for developing commercial cultivars with stress tolerance [ABSTRACT FROM AUTHOR]

Although enormous effort has been put into conventional breeding programmes for both drought and salt tolerance, there has been little progress in producing varieties that are adopted by farmers in their fields. This is largely due to the lack of consideration given to the specific needs of farmers in droughted and salt-affected environments, in particular in terms of non-yield post-harvest traits. We discuss with examples the advantages and disadvantages of participatory variety selection (PVS) and participatory plant breeding (PPB) in their various forms, as well as the use of the term client-oriented breeding to describe the process of involving the end-users of the breeding programme. Methods for the analysis of participatory trials, and practical considerations for their management, are presented. We also show how both participatory and molecular approaches can be combined into an integrated, client-oriented breeding programme [ABSTRACT FROM AUTHOR]

Wine grape (Vitis vinifera) is the world's most important fruit crop both in terms of crop production and economic value. For most crops, water deficit stress has negative implications for production and quality. For wine grape, however, vegetative growth is more sensitive to water-deficit stress than fruit growth. Thus, moderate water-deficit can positively influence the quality of wine produced from grapes harvested from vines grown under regulated (water) deficit irrigation (RDI) and partial root zone drying (PRD) conditions. However, the interaction between water deficit stress and berry composition is complicated by the ability to accurately measure water potential under field conditions and can be influenced by many parameters including timing of stress application within a season and across several seasons, grapevine variety and canopy, leaf to fruit ratio, and soil structure. The mechanistic basis for observed quality differences are poorly understood. However, recent studies using integrated transcriptome and metabolome data sets have revealed potential underlying changes in gene expression and determinants of fruit characteristics that explain the major effects that water deficit treatment can be expected to have on wine quality. Major responses include gene expression changes resulting in alterations in sugar content, anthocyanin accumulation, and decreased organic acid accumulation [ABSTRACT FROM AUTHOR]

Citrus is a major world horticultural commodity, and most of its world-wide production depends on irrigation, which is inevitably associated with the deterioration of water quality from run-off or ground water. Citrus, like most fruit trees, is relatively salt sensitive. The deleterious effects of salt stress lead to reduction in fruit yield and quality. In recent years, only a few relatively salt-tolerant rootstocks have been obtained through selection and conventional breeding, due to a rather limited existing genetic pool and the long period of time required for experiments. Attempts to regenerate salt-tolerant citrus plants via in vitro production of salt-tolerant callus or mutagenesis have been rather limited and as of yet not in use. Therefore, efforts should be invested to identify traits/genes that have a key role in tolerance to salt in order to speed up the process and to enlarge these genetic resources QTL analyses revealed that response to salt in citrus is a multigenic trait, as has been shown in other species, but some genes probably exist that have a major impact on salt tolerance and (or) mineral accumulation. Several robust EST databases now exist and are growing, the first microarray chips have been manufactured, and an initial genome sequencing effort is underway. These tools should allow citrus physiologists, biochemists, and geneticists to make much more rapid progress in understanding salt and water stress in the future and to design strategies to ameliorate their effects [ABSTRACT FROM AUTHOR]

Barley is the most tolerance cereal crop for drought and salinity and is an ideal model crop for genetic study of drought and salinity tolerance because of its early maturity, diploid and self-pollination. Selection for drought tolerance in convention breeding programs has achieved significant progress to improve yield and yield stability under drought through direct selection or indirect selection for early vigour, coleoptile length or "stay green". A large number of Quantitative Trait Loci (QTL) were mapped for drought and salinity tolerance related traits, including physiological biochemical traits such as osmotic adjustment capacity, proline content, stomatal conductance, water-soluble carbohydrates, relative water content, leaf turgor, ABA content, transpiration efficiency, water use efficiency and carbon isotope discrimination; and developmental/ morphological traits such as height, leaf emergence, leaf area index, tiller development, flowering time, maturity rate and root characteristics. QTLs for yield and yield components were also identified under drought. Extensive research has been devoted to the characterization of genes induced or up-regulated by drought or salinity. Numerous candidate genes were identified to associate with tolerance to drought or salinity and some of the candidate genes co-located with the QTLs for drought tolerance. Wild barley (Hordeum spontaneum) was demonstrated as a key genetic resource for drought and salinity tolerance. QTLs from the wild barley increased yield by 12-22% under drought. New germplasm and molecular tools make it possible to develop better barley variety faster for drought or salinity tolerance, but challenges still remain due to complexity of drought and salinity tolerance. Barley (Hordeum vulgare L.) is the fourth largest cereal crop in the world with annual production over 140 million tonnes. It has been used as a staple food for humans, feed for animals, and a key ingredient in beer and whiskey production. Barley has a wider ecological range than any other cereals and is widespread in temperate, subtropical and artic areas, from sea level to heights of more than 4,500 m in the Andes and Himalayas (Bothmer et al., 1995). Barley can be grown on soils unsuitable for wheat, and at altitudes unsuitable for wheat or oats. Because of its salt and drought tolerance, barley thrives in nearly every corner of the earth including extremely dry areas near deserts. Barley is a short-season, early maturing, diploid and self-pollinating crop, thus it is also an ideal model plant for genetic study of drought and salinity tolerance. Several papers have summarized research on barley abiotic stress tolerance including drought and salinity tolerance (Cattivelli et al., 2002; Stanca et al., 2003). In this chapter, we will review recently progress on molecular breeding for saline and drought tolerance in barley [ABSTRACT FROM AUTHOR]

Maize production losses due to drought and salinity prominently affect economies and the livelihoods of millions of people, given the global and regional importance of maize and its pronounced susceptibility to these stress factors. Climate change and accelerating competition for irrigation water are expected to further increase the need for adaptive strategies. There is vast evidence for genetic approaches being able to significantly improve the drought and salinity tolerance of maize. Field-based breeding approaches have resulted in average breeding gains of around 100 kg ha-1 yr-1 under drought conditions, and there are first reports on transgenic drought and salinity tolerance mechanisms increasing maize grain yields under laboratory and field conditions. Drought and salinity tolerance are based on complex genetic systems and successful genetic enhancement programs need to consider gene-by-gene, gene-by environment and gene-by-developmental stage interactions. In the case of drought, field-based and transgenic approaches have resulted in the improvement of diverse and potentially additive tolerance mechanisms. Increasing yields and yield stability of maize in the face of climate change and scarcity of irrigation water will therefore likely be the most successful if complementary investments in field-based and transgenic breeding approaches are being made [ABSTRACT FROM AUTHOR]

Substantial advances have been made in breeding wheat for dry environments that will also improve performance in saline environments. These genetic gains have been made by conventional breeding. Further gains in productivity will come from the addition of traits that increase the efficiency of water use in dry soils, and control the uptake of salts from saline soils. Conventional breeding methods will continue to be important to provide farmers with higher yielding varieties in dry or saline soils which are resistant to current diseases and which have the grain quality demanded by competitive markets. Trait-based breeding approaches, which often utilize molecular markers to improve selection efficiency, are starting to deliver new and significant gains. To target the most important traits, it is important to know how they will influence yield. Is it through more water use, more efficient use of water or a higher harvest index? For example, the trait of ‘early vigour' may be an advantage in some years but in others may lead to the exhaustion of soil water and a low yield. The challenge for breeders will be to efficiently integrate trait-based and molecular methods to increase yield in dry and saline environments [ABSTRACT FROM AUTHOR]

Many stresses trigger transient increases in minor phospholipids, such as phosphatidic acid (PA) and phosphoinositides (PIs), in plants. Such changes are early events in signaling plant stress response. Lipid mediators affect cellular functions through direct interaction with proteins and/or structural effects on cell membranes. The identified lipid targets in plants include protein phosphatases, kinases, and proteins involved in membrane trafficking and cytoskeleton. The effect of lipids on signaling, intracellular trafficking, and cytoskeletal organization plays important roles in plant coping with drought and salinity [ABSTRACT FROM AUTHOR]