Drought Resistance In Crops Research Articles

Effect of Exogenous Abscisic Acid on psbA Expression at Grain Filling Stage in Two Wheat Cultivars Under Drought Stress

Abscisic acid (ABA) is an important plant hormone and may be involved in drought resistance in crops. The object of this study was to understand the effects of exogenous ABA on wheat (Triticum aestivum L.) plant under drought stress. After drought stress simulated with polyethylene glycol (PEG) for 72 h at grain-filling stage, flag leaves of Yumai 949 and Shaanmai 5 showed significant increase in malondialdehyde (MDA) content and decreases in relative water content (RWC), chlorophyll content, and yield. Meanwhile, the transcription of psbA gene in photosystem II system was also depressed according to the analysis of reverse transcriptional PCR. Application of exogenous ABA had a significant effect on alleviation of these reactions from PEG stress. Compared to Yumai 949, Shaanmai 5 received smaller injury in plasma membranes and less reduces in RWC, chlorophyll content, yield, and psbA transcriptional level after PEG stress. Moreover, exogenous ABA treatment resulted in restoration of all parameters tested to the levels before stress in Shaanmai 5. This result indicated that the expression of psbA gene was closely related to drought stress resistance subject to wheat cultivar. The primary evidence of ABA regulation on psbA expression may enrich the mechanism of drought resistance and suggest the potential of exogenous ABA to enhance resistance to drought stress in wheat during grain filling period.

Agroclimatic conditions in Europe under climate change

To date, projections of European crop yields under climate change have been based almost entirely on the outputs of crop-growth models. While this strategy can provide good estimates of the effects of climatic factors, soil conditions and management on crop yield, these models usually do not capture all of the important aspects related to crop management, or the relevant environmental factors. Moreover, crop-simulation studies often have severe limitations with respect to the number of crops covered or the spatial extent. The present study, based on agroclimatic indices, provides a general picture of agroclimatic conditions in western and central Europe (study area lays between 8.5°W–27°E and 37–63.5°N), which allows for a more general assessment of climate-change impacts. The results obtained from the analysis of data from 86 different sites were clustered according to an environmental stratification of Europe. The analysis was carried for the baseline (1971–2000) and future climate conditions (time horizons of 2030, 2050 and with a global temperature increase of 5 °C) based on outputs of three global circulation models. For many environmental zones, there were clear signs of deteriorating agroclimatic condition in terms of increased drought stress and shortening of the active growing season, which in some regions become increasingly squeezed between a cold winter and a hot summer. For most zones the projections show a marked need for adaptive measures to either increase soil water availability or drought resistance of crops. This study concludes that rainfed agriculture is likely to face more climate-related risks, although the analyzed agroclimatic indicators will probably remain at a level that should permit rainfed production. However, results suggests that there is a risk of increasing number of extremely unfavorable years in many climate zones, which might result in higher interannual yield variability and constitute a challenge for proper crop management.

Yield–trait performance landscapes: from theory to application in breeding maize for drought tolerance

The effectiveness of breeding strategies to increase drought resistance in crops could be increased further if some of the complexities in gene-to-phenotype (G → P) relations associated with epistasis, pleiotropy, and genotype-by-environment interactions could be captured in realistic G → P models, and represented in a quantitative manner useful for selection. This paper outlines a promising methodology. First, the concept of landscapes was extended from the study of fitness landscapes used in evolutionary genetics to the characterization of yield-trait-performance landscapes for agricultural environments and applications in plant breeding. Second, the E(NK) model of trait genetic architecture was extended to incorporate biophysical, physiological, and statistical components. Third, a graphical representation is proposed to visualize the yield-trait performance landscape concept for use in selection decisions. The methodology was demonstrated at a particular stage of a maize breeding programme with the objective of improving the drought tolerance of maize hybrids for the US Western Corn-Belt. The application of the framework to the genetic improvement of drought tolerance in maize supported selection of Doubled Haploid (DH) lines with improved levels of drought tolerance based on physiological genetic knowledge, prediction of test-cross yield within the target population of environments, and their predicted potential to sustain further genetic progress with additional cycles of selection. The existence of rugged yield-performance landscapes with multiple peaks and intervening valleys of lower performance, as shown in this study, supports the proposition that phenotyping strategies, and the directions emphasized in genomic selection can be improved by creating knowledge of the topology of yield-trait performance landscapes.

Nonlinear Screening Indicators of Drought Resistance at Seedling Stage of Rice Based on Support Vector Machine

Screening indexes for drought resistance in crops is a puzzler characterized with a few samples, multiple indexes, and nonlinear. Rationality of linear regression model and indexes obtained by linear screening based on empirical risk minimization are controversal. On the contrary, support vector machine based on structural risk minimization has the advantages of nonlinear characteristics, fitting for a few samples, avoiding the over-fit, strong generalization ability, and high prediction precision. In this paper, setting the survival percentage under repeated drought condition as the target and support vector regression as the nonlinear screen tool, 6 integrated indexes including plant height, proline content, malondialdehyde content, leaf age, area of the first leaf under the central leaf and ascorbic acid were highlighted from 24 morphological and physiological indexes in 15 paddy rice cultivars. The results showed that support vector regression model with the 6 integrated indexes had a more distinct improvement in fitting and prediction precision than the linear reference models. Considering the simplicity of indexes measurement, the support vector regression model with only 6 morphological indexes including shoot dry weight, area of the second leaf under the central leaf, root shoot ratio, leaf age, leaf fresh weight, and area of the first leaf under the central leaf was also feasible. Furthermore, an explanatory system including the significance of regression model and the importance of single index was established based on support vector regression and F-test.

Overproduction of abscisic acid in tomato increases transpiration efficiency and root hydraulic conductivity and influences leaf expansion.

Overexpression of genes that respond to drought stress is a seemingly attractive approach for improving drought resistance in crops. However, the consequences for both water-use efficiency and productivity must be considered if agronomic utility is sought. Here, we characterize two tomato (Solanum lycopersicum) lines (sp12 and sp5) that overexpress a gene encoding 9-cis-epoxycarotenoid dioxygenase, the enzyme that catalyzes a key rate-limiting step in abscisic acid (ABA) biosynthesis. Both lines contained more ABA than the wild type, with sp5 accumulating more than sp12. Both had higher transpiration efficiency because of their lower stomatal conductance, as demonstrated by increases in delta(13)C and delta(18)O, and also by gravimetric and gas-exchange methods. They also had greater root hydraulic conductivity. Under well-watered glasshouse conditions, mature sp5 plants were found to have a shoot biomass equal to the wild type despite their lower assimilation rate per unit leaf area. These plants also had longer petioles, larger leaf area, increased specific leaf area, and reduced leaf epinasty. When exposed to root-zone water deficits, line sp12 showed an increase in xylem ABA concentration and a reduction in stomatal conductance to the same final levels as the wild type, but from a different basal level. Indeed, the main difference between the high ABA plants and the wild type was their performance under well-watered conditions: the former conserved soil water by limiting maximum stomatal conductance per unit leaf area, but also, at least in the case of sp5, developed a canopy more suited to light interception, maximizing assimilation per plant, possibly due to improved turgor or suppression of epinasty.

Up-regulation of a H + -pyrophosphatase (H + -PPase) as a strategy to engineer drought-resistant crop plants

Engineering drought -resistant crop plants is a critically important objective. Overexpression of the vacuolar H(+)-pyrophosphatase (H(+)-PPase) AVP1 in the model plant Arabidopsis thaliana results in enhanced performance under soil water deficits. Recent work demonstrates that AVP1 plays an important role in root development through the facilitation of auxin fluxes. With the objective of improving crop performance, we expressed AVP1 in a commercial cultivar of tomato. This approach resulted in (i) greater pyrophosphate-driven cation transport into root vacuolar fractions, (ii) increased root biomass, and (iii) enhanced recovery of plants from an episode of soil water deficit stress. More robust root systems allowed transgenic tomato plants to take up greater amounts of water during the imposed water deficit stress, resulting in a more favorable plant water status and less injury. This study documents a general strategy for improving drought resistance of crops.

Locating genomic regions associated with components of drought resistance in rice: comparative mapping within and across species

Direct and indirect economic loss in the agricultural sector due to drought is huge. With the advent of molecular-marker technology, research on drought resistance in crop plants has shifted from physiological descriptions of the phenomenon to genetic dissection of the mechanisms involved. Here, we report a comprehensive study of mapping the drought resistance components (osmotic adjustment and root traits) in a doubled-haploid rice (Oryza sativa L.) population of 154 lines. A genetic linkage map consisting of 315 DNA markers was constructed. A total of 41 quantitative trait loci (QTLs) were identified for osmotic adjustment and root traits, and individually explained 8–38% of the phenotypic variance. A region on chromosome 4 harbored major QTLs for several root traits. Consistent QTLs for drought responses across genetic backgrounds were detected and should be useful for marker-assisted selection towards the incorporation of a trait of interest into an elite line. Comparative mapping identified three conserved genomic regions associated with various physiological responses to drought in several grass species. These results suggest that these regions conferring drought adaptation have been conserved across grass species during genome evolution and might be directly applied across species for the improvement of drought resistance in cereal crops.

Effect of the timing of water deficit on growth, phenology and yield of pearl millet (Pennisetum glaucum(L.) R. Br.) grown in Sahelian conditions

Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit untill early grain filling, because the losses in main shoot production were fully compensated by increased tiller fertility. The present study assessed the impact of water deficits at three development stages: prior to flowering (S30), at the beginning of flowering (S45), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both biomass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage to panicle initiation and flowering of the main shoot. All treatments maintained green leaves on the main shoot during the grain filling period, and in S30 leaf growth recovered from mid-season drought. These results illustrate how pearl millet mostly escapes drought by matching its phenology to the mean rainfall distribution in the Sahel. In the case of mid-season drought, some late productive tillers and the maintenance of green leaf biomass of the main shoots limited, but did not overcome, the yield losses. This study stresses the importance of agro-ecological conditions in control treatments, particularly the water regime and crop density, when assessing crop drought resistance.

Cuticular water permeability and its physiological significance

Cuticles act as solution-diffusion membranes for water transport. Diffusion in pores does not contribute to cuticular transpiration. An extensive literature survey of cuticular permeances (P) and minimum leaf conductances (g(min)) to water is presented. The two variables cannot be distinguished with most experimental techniques. Results from different experiments are in good agreement with each other for some species, for example, Fagus sylvatica L., but not for others, such as Picea abies (L.) Karst. In a data set of 313 values of P or g(min) from 200 species, distributions of results obtained with different techniques were found to differ significantly. Likely reasons include water loss from incompletely closed or incompletely sealed stomata, and the dependence of P on moisture content of the cuticle and on storage time of isolated cuticles. Contrasting evidence for an interaction between cuticular transpiration and stomatal sensitivity to air humidity is presented. The occurrence of unusually high g(min) in trees growing at the alpine treeline and its physiological significance are discussed. It is shown that g(min) is of little value as a predictor for drought resistance of crops, with the possible exception of Sorghum bicolor L. Moench. Possible water uptake from fog or dew across cuticles is considered briefly.

Drought resistance in crops with emphasis on rice

Drought resistance in crops with emphasis on rice

Book Review: Drought Resistance in Crops. With Emphasis on Rice

Book Review: Drought Resistance in Crops. With Emphasis on Rice

Proline accumulation and varietal adaptability to drought in barley: a potential metabolic measure of drought resistance.

A reliable laboratory test for drought resistance in crops would be invaluable in breeding programmes. Experience so far has been disappointing, however, due to either a lack of differentiation between genotypes1, or poor correlation between the results of the test and field experience2–4.