Drought tolerance

Inositol-(1,4,5)-trisphosphate (InsP3) is a second messenger in plants that increases in response to many stimuli. The metabolic consequences of this signalling pathway are not known. We reduced the basal level of InsP3 in tomato (Solanum lycopersicum cv. Micro-Tom) by expressing the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase) gene. Transgenic lines producing InsP 5-ptase protein had between 15% and 30% of the basal InsP3 level of control plants. This increased hydrolysis of InsP3 caused dramatic increases in drought tolerance, vegetative biomass and lycopene and hexose concentrations in the fruits. Transcript profiling of root, leaf and fruit tissues identified a small group of genes, including a cell-wall invertase inhibitor gene, that were differentially regulated in all tissues of the InsP 5-ptase expressing plants. Significant differences were found in the amounts of carbohydrates and organic phosphate in these plants. Plants with increased hydrolysis of InsP3 in the cytosol also showed increased net CO2-fixation and sucrose export into sink tissue and storage of hexoses in the source leaves. The increase in biomass was dependent on the supply of inorganic phosphate in the nutrient medium. Uptake and storage of phosphate was increased in the transgene expressing lines. This suggests that in tomato, increased flux through the inositol phosphate pathway uncoupled phosphate sensing from phosphate metabolism. Altering the second messenger, InsP3, revealed multiple coordinated changes in development and metabolism in tomato that have potential for crop improvement.

Cassava or manioc (Manihot esculenta Crantz), a perennial shrub of the New World, currently is the sixth world food crop for more than 500 million people in tropical and sub-tropical Africa, Asia and Latin America. It is cultivated mainly by resource-limited small farmers for its starchy roots, which are used as human food either fresh when low in cyanogens or in many processed forms and products, mostly starch, flour, and for animal feed. Because of its inherent tolerance to stressful environments, where other food crops would fail, it is often considered a food-security source against famine, requiring minimal care. Under optimal environmental conditions, it compares favorably in production of energy with most other major staple food crops due to its high yield potential. Recent research at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia has demonstrated the ability of cassava to assimilate carbon at very high rates under high levels of humidity, temperature and solar radiation, which correlates with productivity across all environments whether dry or humid. When grown on very poor soils under prolonged drought for more than 6 months, the crop reduce both its leaf canopy and transpiration water loss, but its attached leaves remain photosynthetically active, though at greatly reduced rates. The main physiological mechanism underlying such a remarkable tolerance to drought was rapid stomatal closure under both atmospheric and edaphic water stress, protecting the leaf against dehydration while the plant depletes available soil water slowly during long dry periods. This drought tolerance mechanism leads to high crop water use efficiency values. Although the cassava fine root system is sparse, compared to other crops, it can penetrate below 2 m soil, thus enabling the crop to exploit deep water if available. Leaves of cassava and wild Manihot possess elevated activities of the C4 enzyme PEP carboxylase but lack the leaf Kranz anatomy typical of C4 species, pointing to the need for further research on cultivated and wild Manihot to further improve its photosynthetic potential and yield, particularly under stressful environments. Moreover, a wide range in values of K m (CO2) for the C3 photosynthetic enzyme Rubisco was found among cassava cultivars indicating the possibility of selection for higher affinity to CO2, and consequently higher leaf photosynthesis. Several plant traits that may be of value in crop breeding and improvement have been identified, such as an extensive fine root system, long leaf life, strong root sink and high leaf photosynthesis. Selection of parental materials for tolerance to drought and infertile soils under representative field conditions have resulted in developing improved cultivars that have high yields in favorable environments while producing reasonable and stable yields under stress.

In this review, reasons for the slow progress in development of drought resistant cultivars for rainfed lowland rice are considered first. Recent advances in screening methods for development of drought resistant cultivars from mostly our research in Thailand in the 1990s, are then described for drought that develops early or late in the wet-season. There now appears to be a good prospect for developing drought resistant cultivars that produce higher yield than existing cultivars when drought develops late in the wet-season. Appropriate phenology to escape late-season drought and high potential yield under well-watered conditions are important characters for cultivars adapted to rainfed lowland conditions. In addition, ability to maintain higher leaf water potential when drought develops late in the season is another desirable character. Maintenance of leaf water potential just prior to flowering is associated with higher panicle water potential, reduced delay in flowering time, and reduced spikelet sterility, and hence contributes to higher yield. Genotypes that are adapted to areas of late-season drought should also have high harvest index, intermediate height and rather small total dry matter compared to existing traditional cultivars, under well-watered conditions. This combination of characters would ensure high potential yield under favourable conditions and also contribute to resistance against late-season drought. Screening against early-season drought that develops during the vegetative stage is more difficult, as the genotype’s ability to recover from the stress appears more important than drought tolerance during the stress period.Other than appropriate phenology, high potential yield and ability to maintain high leaf water potential, no specific physiological and morphological characters appear to contribute directly to higher yield under drought conditions in rainfed lowland rice in Thailand, where drought develops rather rapidly due to the prevailing coarse textured soils. It is thus appropriate to develop a breeding program that is primarily based on selection for grain yield. There are large genotype by environment interactions for yield in rainfed lowland rice and hence it is important that genotypes are selected for yield under appropriate target environments. Addition of a drought screening program that is conducted in the field in the wet-season to the overall breeding program would enhance the opportunity to select for drought resistance within the breeding materials and increase the chance of developing high yielding cultivars adapted to the drought-prone rainfed lowland environments.

The effects of water deficit on photochemical parameters and activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as, cellular damages were investigated in two clones of Coffea canephora differing in drought tolerance. After 6 days without irrigation, predawn leaf water potential fell to −3.0 MPa that was accompanied by the suppression of net photosynthesis in both clones. The variable to maximum chlorophyll fluorescence ratio remained unchanged regardless of the imposed treatments. Both clones showed a similar decline (about 25%) in the photochemical quenching coefficient, but only the drought-sensitive clone exhibited an enhancement (31%) of thermal deactivation under water deficit conditions. The quantum yield of electron transport decreased similarly in both genotypes. Under drought conditions, activities of SOD, CAT and APX increased to a greater extent in the drought-tolerant clone than in the drought-sensitive one. This seemed to be matched with higher protection against oxidative stress, as judged from the lower levels of lipid peroxidation and electrolyte leakage in the drought-tolerant clone. Thus, the ability to increase the antioxidant system activity in order to limit cellular damages might be an important attribute linked to the drought tolerance in C. canephora.

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

The purpose of this Communication is to compare the efficacy of different seed priming osmotica on the germination and emergence of maize caryopses. First, a laboratory experiment was carried out to determine the effects of different seed priming osmotica on germination. The osmotica used are 0.1% copper sulphate, 0.1% zinc sulphate and 0.1% sodium sulphate. A control of unprimed caryopses was used for comparative analysis. In general, seed priming significantly increased the final caryopses germination. Caryopses primed in copper sulphate, however, gave the highest final germination. Then, field trials to determine the final seedling emergence of caryopsis in the field were carried out in a semi-arid area in southern Zimbabwe. Results testify that priming in copper sulphate and zinc sulphate significantly increased seed emergence by 43% and 29%, respectively, while priming in sodium sulphate did not significantly increase emergence. The study thus recommends copper sulphate as the most suitable seed priming osmotica.

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

Two durum wheat (Triticum durum Desf.) cultivars were tested for salt and drought tolerance at germination, seedling emergence and early seedling growth in NaCl and PEG-8000 solutions of different osmotic potentials (–0.2, –0.4, –0.6 and –0.8 MPa). Daily and final germination and emergence percentage, as well as germination and seedling emergence rate, seedling growth, fresh and dry weight were recorded under controlled conditions. Results showed that germination and emergence rates were delayed by both solutions in both cultivars, but Omrabia showed higher germination and emergence rates than BD290273 in NaCl while BD290273 was less affected by NaCl and PEG solutions at the emergence stage. Sodium chloride had a lesser effect on both cultivars in terms of germination rate, emergence rate, final germination and emergence percentage than did PEG-8000. This conclusively proves that the adverse effect of PEG-8000 on germination, emergence and early seedling growth was due to the osmoti...

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

Water stress, one of the devastating abiotic stresses in rain fed rice ecosystems
causes huge loss to rice yields. Enhancement of production as well as productivity
in rain fed areas requires development of improved varieties for such regions. Slow
progress in drought breeding is an impediment in this way. Maker assisted
approach is an alternative for fast track improvements of crops for drought.
Validation of markers associated with drought related traits across the populations
would add value to their application. In the present study, four SSR markers viz.,
RM 263, RM 3825, RM 212 and RM 22 associated with drought tolerance QTLs,
qDTY2.3, MQTL1.1, MQTL1.2 and qDTY 3.2 respectively, were evaluated for
their use in marker assisted selection (MAS) in BC1F1 individual plants, derived
from the cross (HUR 3022 × Nagina 22) × HUR 3022, (HUR 3022 × Birsa Gora) ×
HUR 3022, (Sarjoo 52 × Nagina 22) × Sarjoo 52 and (Sarjoo 52× Birsa Gora) ×
Sarjoo 52. Marker RM 263 (qDTY2.3) and RM 3825 (MQTL1.1) were
consistently associated with yield per plant in all the cultivars and their derived
backcross populations. Therefore, these two SSR markers RM 263 and RM 3825
were found suitable for selection of drought tolerant rice lines in marker assisted
backcross breeding (MAB) programs. Besides, SSR marker RM 212 (MQTL1.2)
was reported to validate in BC1F1 population of (Sarjoo 52 × Nagina 22) × Sarjoo
52 and (Sarjoo 52 × Birsa Gora) × Sarjoo 52 whereas, SSR marker RM 22
(qDTY3.2) was validated in (HUR 3022 × Nagina 22) × HUR 3022 and (Sarjoo 52
× Nagina 22) × Sarjoo 52. Thus, these SSR markers would also be useful for
improvement of drought tolerance in rice through MAS.

According to Food and Agriculture Organization (FAO), droughts have significant economic, environmental, and social impacts, both direct and indirect. All field crops are affected by drought. Global warming and climate change are expected to exacerbate this phenomenon. Barley (Hordeum vulgare L.) ranks fourth among cereals after wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.). Drought is a significant issue in barley breeding programs. The purpose of this chapter is to review pertinent literature on general drought-tolerance mechanisms in important field crops and provide the latest state-of-the-art information on drought-coping mechanisms in barley, including molecular basis of crop response in moisture-limited environments. We highlight research insights, existing gaps, and future research directions regarding drought tolerance in barley. Known quantitative trait loci (QTL) and genes, such as Dhn and DREB, and their use in marker-assisted selection for drought tolerance are summarized. Traits associated with improved performance (early vigor, plant height, spike waxiness, and thousand-grain weight) under low-moisture stress environments have been identified as useful criteria in breeding for drought-tolerant barley. Low stomatal density cultivars of barley should be developed to combat drought and climate change. Latest innovations in genome-editing technology, such as clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), clustered regularly interspaced short palindromic repeats from Prevotella and Francisella 1 (CRISPR-Cpf1), and multiplexed accurate genome editing with short, trackable, integrated cellular barcodes (MAGESTIC), should be useful for plant breeders in modifying the barley genome, as needed, to develop drought-tolerant cultivars.

"A catastrophic draught event was reported across much of the north of South America during August - December 2005. This resulted in extensive and irreversible damage in parts of the
Amazon river network. The 2005 Amazon draught followed very unusual changes in the Atlantic Ocean’s circulatory system that altered typical wind and rain patterns. Many climatic models predict the future desiccation of the Amazon region. This paper discusses dangers of sudden swings in the Amazon’s climate and how these risks can be reduced and securing the future of the river system.

The Amazon river systems’ inability to adapt to the new seasonal climate patterns in 2005, which led to a complete destruction of some river ecosystems, suggested us to look at water engineering solutions to prevent the risks of more tributaries of such dying. We made a case study to oxygenate the Amazon river to raise its draught-stress threshold during the likely future draughts that may be even worse than today if the Atlantic weather system generates more storms as the world’s temperature rises.

We studied a 100 kilometre wide section near the Amazon’s mouth. We assumed temperature +30C (when 100% oxygenated water contains 7,6 mg O2 / litre). The addition of 2,5 mg O2 / l represents 1/3 of the total, i.e. raising from 70% to 100%. This large water body oxygenation project requires 4 million kg O2 / day. 2,000 MIXOX units consume 80 MW / 100 km of river. 1,000 km demand is at 800 MW (1 power station), costing ~500 million euros p.a." http://www.vesieko.fi/yhteystiedot

Scarcity of water is a severe environmental constraint to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Here, we have reviewed the effects of drought stress on the growth, phenology, water and nutrient relations, photosynthesis, assimilate partitioning, and respiration in plants. This article also describes the mechanism of drought resistance in plants on a morphological, physiological and molecular basis. Various management strategies have been proposed to cope with drought stress. Drought stress reduces leaf size, stem extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. Plants display a variety of physiological and biochemical responses at cellular and whole-organism levels towards prevailing drought stress, thus making it a complex phenomenon. CO2 assimilation by leaves is reduced mainly by stomatal closure, membrane damage and disturbed activity of various enzymes, especially those of CO2 fixation and adenosine triphosphate synthesis. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on the tissues as both processes generate reactive oxygen species. Injury caused by reactive oxygen species to biological macromolecules under drought stress is among the major deterrents to growth. Plants display a range of mechanisms to withstand drought stress. The major mechanisms include curtailed water loss by increased diffusive resistance, enhanced water uptake with prolific and deep root systems and its efficient use, and smaller and succulent leaves to reduce the transpirational loss. Among the nutrients, potassium ions help in osmotic adjustment; silicon increases root endodermal silicification and improves the cell water balance. Low-molecular-weight osmolytes, including glycinebetaine, proline and other amino acids, organic acids, and polyols, are crucial to sustain cellular functions under drought. Plant growth substances such as salicylic acid, auxins, gibberrellins, cytokinin and abscisic acid modulate the plant responses towards drought. Polyamines, citrulline and several enzymes act as antioxidants and reduce the adverse effects of water deficit. At molecular levels several drought-responsive genes and transcription factors have been identified, such as the dehydration-responsive element-binding gene, aquaporin, late embryogenesis abundant proteins and dehydrins. Plant drought tolerance can be managed by adopting strategies such as mass screening and breeding, marker-assisted selection and exogenous application of hormones and osmoprotectants to seed or growing plants, as well as engineering for drought resistance.

Gmelina arborea Roxb. (gmelina) is a rapidly growing tree, which due to its drought tolerance and excellent wood properties, is emerging as an important plantation species. Perhaps the greatest threat to plantations of this tree is damage due to pests and diseases. Numerous insect pests and pathogens have been recorded in stands of gmelina in areas where the trees are native. Some fungal pathogens have been introduced into areas where the trees have been established as exotics. Among these, leaf spot caused by Pseudocercospora ranjita is most widespread although it has not caused any substantial damage. A serious vascular wilt disease caused by Ceratocystis fimbriata in Brazil has caused the most significant failure of G. arborea in plantations. In plantations within the natural range of the tree, insects have caused substantial damage. Among these, the defoliator Calopepla leayana (Chrysomelidae) appears to be most important. No serious insect pest problems have been recorded where G. arborea is grown as an exotic. All indications are that pathogens and insect pests will become much more serious impediments to the propagation of gmelina in the future. However, excellent opportunities exist to resolve such problems through biological control of insects and integrated disease and pest management. In addition, gmelina can be vegetatively propagated and thus, breeding and selection for insect and pathogen tolerance will facilitate the propagation of healthy trees. Palabras clave: Control biológico, Cuarentena, Especies exóticas, Implementación operacional de clones Resumen. La Gmelina arborea Roxb. (gmelina) es un árbol de rápido crecimiento, el cual debido a su tolerancia a las sequías y a sus excelentes propiedades de la madera se está convirtiendo en una especie de importancia para las plantaciones forestales. Tal vez, la amenaza más grande para las plantaciones de estos árboles es el daño causado por las plagas y las enfermedades. En las áreas en donde la especie es nativa, se han reportado gran cantidad de plagas de insectos y de patógenos. Algunos hongos patógenos se han introducido dentro de las áreas en donde los árboles han sido establecidos como especies exóticas. Entre estos, las manchas de las hojas ocasionadas por el hongo Pseudocercospora ranjita, es el más extendido aunque no ha causado ningún daño sustancial. Una seria enfermedad de marchitamiento vascular causada por el Ceratocystis fimbriata en el Brasil, ha causado la pérdida más seria en las plantaciones de G. arborea. En las plantaciones dentro del rango natural del árbol, los insectos han causado un daño considerable. Entre estos insectos, el defoliador más importante parece ser el Calopepla leayana (Chrysomelidae). En las áreas en donde la gmelina crece como una especie exótica no se han reportado problemas con las plagas de insectos. Todo parece indicar que en un futuro, los agentes patógenos y las plagas de insectos se convertirán en un impedimento más serio para la progagación de la gmelina. Sin embargo, a través del control biológico de insectos y del manejo integrado de las enfermedades y plagas, existen excelentes oportunidades para resolver este tipo de problemas. Además, la gmelina puede ser propagada vegetativamente y por lo tanto su mejoramiento y selección facilitará la propagación de árboles saludables por su resistenciacia contra los insectos y los patógenos.