Different Levels Of Drought Tolerance Research Articles

Nutrient uptake and nutrient use efficiency of Valencia peanut genotypes with different levels of drought tolerance under terminal drought

Selection of suitable peanut genotypes with resistance to drought is an important strategy to combat problems of drought. This study aimed to investigate nutrient uptake and nutrient use efficiencies of Valencia peanut genotypes in response to terminal drought. A pot experiment was conducted in a factorial randomized complete block design with 4 replications. Factor A consisted of two soil water regimes (field capacity and 1/3 available water), and ten Valencia peanut genotypes were assigned as factor B. Macronutrient uptakes and nutrient use efficiencies (NUE) were examined; drought reduced nutrient uptakes, NUE for biomass and NUE for pod yield. Unique behaviors of some tested Valencia peanut genotypes on given traits were found. Genotype PI536121 had the highest K, Ca and Mg uptakes, while two genotypes ICG10890 and ICG10092 showed the highest NUE for biomass and pod yield. Genotype ICG14127 performed well regarding K, Ca and Mg uptakes and NUE for pod yield. Total nutrient uptakes of N, P, K, Ca and Mg were significantly positively correlated with biomass and pod yield (r = 0.48**–0.76**), whereas the number of seeds per pod and 100-seed weight were positively correlated with total nutrient uptakes of N, K, Ca and Mg (r = 0.23*–0.47**). Three tested genotypes ICG10092, ICG10890 and ICG14127 are promising genetic sources for further improvements of Valencia peanuts for drought tolerance.

Biological nitrogen fixation in soybean with different levels of drought tolerance

Biological nitrogen fixation in soybean with different levels of drought tolerance

Comparative Transcriptome Analysis of Deep-Rooting and Shallow-Rooting Potato (Solanum tuberosum L.) Genotypes under Drought Stress.

The selection and breeding of deep rooting and drought-tolerant varieties has become a promising approach for improving the yield and adaptability of potato (Solanum tuberosum L.) in arid and semiarid areas. Therefore, the discovery of root-development-related genes and drought tolerance signaling pathways in potato is important. In this study, we used deep-rooting (C119) and shallow-rooting (C16) potato genotypes, with different levels of drought tolerance, to achieve this objective. Both genotypes were treated with 150 mM mannitol for 0 h (T0), 2 h (T2), 6 h (T6), 12 h (T12), and 24 h (T24), and their root tissues were subjected to comparative transcriptome analysis. A total of 531, 1571, 1247, and 3540 differentially expressed genes (DEGs) in C16 and 1531, 1108, 674, and 4850 DEGs in C119 were identified in T2 vs. T0, T6 vs. T2, T12 vs. T6, and T24 vs. T12 comparisons, respectively. Gene expression analysis indicated that a delay in the onset of drought-induced transcriptional changes in C16 compared with C119. Functional enrichment analysis revealed genotype-specific biological processes involved in drought stress tolerance. The metabolic pathways of plant hormone transduction and MAPK signaling were heavily involved in the resistance of C16 and C119 to drought, while abscisic acid (ABA), ethylene, and salicylic acid signal transduction pathways likely played more important roles in C119 stress responses. Furthermore, genes involved in root cell elongation and division showed differential expression between the two genotypes under drought stress. Overall, this study provides important information for the marker-assisted selection and breeding of drought-tolerant potato genotypes.

Unraveling the Genetic Architecture of Two Complex, Stomata-Related Drought-Responsive Traits by High-Throughput Physiological Phenotyping and GWAS in Cowpea (Vigna. Unguiculata L. Walp).

Drought is one of the most devasting and frequent abiotic stresses in agriculture. While many morphological, biochemical and physiological indicators are being used to quantify plant drought responses, stomatal control, and hence the transpiration and photosynthesis regulation through it, is of particular importance in marking the plant capacity of balancing stress response and yield. Due to the difficulties in simultaneous, large-scale measurement of stomatal traits such as sensitivity and speed of stomatal closure under progressive soil drought, forward genetic mapping of these important behaviors has long been unavailable. The recent emerging phenomic technologies offer solutions to identify the water relations of whole plant and assay the stomatal regulation in a dynamic process at the population level. Here, we report high-throughput physiological phenotyping of water relations of 106 cowpea accessions under progressive drought stress, which, in combination of genome-wide association study (GWAS), enables genetic mapping of the complex, stomata-related drought responsive traits “critical soil water content” (θcri) and “slope of transpiration rate declining” (KTr). The 106 accessions showed large variations in θcri and KTr, indicating that they had broad spectrum of stomatal control in response to soil water deficit, which may confer them different levels of drought tolerance. Univariate GWAS identified six and fourteen significant SNPs associated with θcri and KTr, respectively. The detected SNPs distributed in nine chromosomes and accounted for 8.7–21% of the phenotypic variation, suggesting that both stomatal sensitivity to soil drought and the speed of stomatal closure to completion were controlled by multiple genes with moderate effects. Multivariate GWAS detected ten more significant SNPs in addition to confirming eight of the twenty SNPs as detected by univariate GWAS. Integrated, a final set of 30 significant SNPs associated with stomatal closure were reported. Taken together, our work, by combining phenomics and genetics, enables forward genetic mapping of the genetic architecture of stomatal traits related to drought tolerance, which not only provides a basis for molecular breeding of drought resistant cultivars of cowpea, but offers a new methodology to explore the genetic determinants of water budgeting in crops under stressful conditions in the phenomics era.

BIOCHEMICAL CHARACTERISTIC OF SOLUBLE LECTINS IN CORN UNDER THE IMPACT OF WATER DEFICIT AND HYPERTHERMIA

Introduction. Drought and high temperature are two of the key factors of the environment limiting crop capacity of grains. Response of the plants to drought and high temperature is very complex and includes interaction between various molecular, physiological and biochemical processes. Synthesis of a number of proteins present under normal conditions, including lectins, increases along with synthesis of stress proteins under adverse conditions.Aim. The goal of our study is to identify the changes in the activity and biochemical characteristics of soluble lectins in maize seedlings with different drought tolerance under water and heat stress in order to create new biochemical methods for assessing drought tolerance.Methods. Three-day young sprouts of corn lines (Zea mays L.) with different levels of drought tolerance were used in the research: drought-tolerant lines Od 329, IK107 zM, non-drought tolerant lines GK 26, IK107VS3 / 66. Lectin activity was defined on the basis of their ability to agglutinate trypsinized erythrocytes of white rats. Electrophoresis was performed in 10 % PAGE following the Laemmli method.Results. The study enabled us to identify increase in soluble lectin activity (244-281 % of the reference value) under the given stress factors in drought-tolerant lines, and decrease in soluble lectin activity (39 - 79 % of reference value) under the given stress factors in non-drought-tolerant lines. Soluble lectins were isolated and purifid using salting out with ammonium sulfate, dialysis and affiity chromatography. The molecular weight of the isolated soluble lectins is in the range of 50-60 kDa. The isolated lectins had a high affiity for N-acetylglucosamine and D-fructose-6-phosphate.Conclusion. Therefore, it has been established that corn lines with positively different levels of drought tolerance are characterized by varying activity of soluble lectins.

Effect of Terminal Drought on Arginine Content in Peanut Genotypes with Difference in Levels of Drought Resistance

Drought is a problem for peanut production as drought at any growth stage generally reduces pod yield and alters protein and amino acid compositions in kernels. The aim of work was to examine effects of terminal drought on arginine content in kernels of peanut genotypes with different levels of drought tolerance. Five peanut genotypes were planted under two water treatments, field capacity (FC) and 1/3 available water (1/3 AW). Arginine content, physiological traits and pod yield were recorded at harvest. The results showed that drought increased arginine content in sensitive and resistant genotypes, and the increase in arginine content was highest in sensitive genotype (Tainan 9). The variation in arginine content in peanut depended on peanut genotype rather than the level of drought resistance. No correlation between arginine content and drought-resistance physiological traits and pod yield were not found. These findings indicated that arginine content and resistance to terminal drought in a peanut may be improved simultaneously through selection in a breeding program.

Association of photosynthetic traits with water use efficiency and SPAD chlorophyll meter reading of Jerusalem artichoke under drought conditions

The impact of water stress on plant growth, tuber yield and inulin content has been widely studied but there is limited information on the effect of drought on photosynthetic characteristics. Therefore, this study was to investigate the effect of water stress on photosynthetic characteristics in Jerusalem artichoke genotypes with different levels of drought tolerance. Two experiments were conducted in rhizobox under greenhouse conditions during August to October in 2015 and 2016. A factorial experiment in randomized complete block design with three replications was used. Factor A were two water regimes (irrigated=field capacity; (FC) and water stress) and factor B were three Jerusalem artichoke genotypes. Data were recorded for relative water content, SPAD chlorophyll meter reading (SCMR), photosynthetic characteristics and water use efficiency (WUE) at 7 and 30days after imposing drought. Leaf area and dry matter was recorded at 30days after imposing drought. Our results revealed that drought caused a greater reduction in stomatal conductance (gs), net photosynthetic rate (Pn), leaf area and biomass production than in other traits measured. In contrast, WUE and SCMR were increased under drought conditions. However, gs and Pn decreases were less in resistant Jerusalem artichoke genotypes than in susceptible genotypes. Also, resistant genotypes had higher WUE increases than susceptible genotypes. Improved Pn combined with high WUE could contribute to higher biomass production. Interestingly, SCMR was associated with Pn and this trait could be used as surrogate trait for improved Pn under drought conditions.

Predicting habitat affinities of herbaceous dicots to soil wetness based on physiological traits of drought tolerance.

Soil water availability is an important mechanism filtering plant species but the functional basis of this filtering in herbaceous dicots is poorly studied. The authors address three questions: Which physiological traits best predict different levels of drought tolerance or avoidance in herbaceous dicots? To what degree can species' habitat preferences along the gradient of soil moisture availability be predicted by their physiological responses to drought? What are the direct and indirect relationships between the physiological traits and how do they interact to determine the species' habitat preferences? Twenty-five species of herbaceous dicots whose field distributions span a gradient of soil moisture from continually moist to dry were chosen. Under controlled conditions, watering was stopped in a treatment group, the plants were monitored until death of the above-ground tissues and compared with a control group watered at field capacity. Fourteen traits related to plant water economy were measured, including stomatal conductance, net photosynthesis and the visual wilting of leaves. Traits were then analysed using a cumulative link model and path analysis. Five physiological traits (stomatal conductance and net photosynthesis measured at soil field capacity, water use efficiency, stomatal conductance and soil water potential measured when leaves begin to wilt) related to the ability to acquire resources (when water is not limiting) or conserve water (when it is limiting) best predicted different levels of drought tolerance or avoidance in herbaceous dicots. Species' habitat preferences can be fairly predicted by their physiological responses to drought ( R 2 = 0·48). Strong direct and indirect relationships between the five identified traits (plus net photosynthesis at wilting and the time until death) led to synergistic and antagonistic relationship in a path analysis model. To allow better prediction of species distributions along a wetness gradient, the next step would be to link these physiological traits to more accessible functional traits.

Identification and Validation of Selected Universal Stress Protein Domain Containing Drought-Responsive Genes in Pigeonpea (Cajanus cajan L.).

Pigeonpea is a resilient crop, which is relatively more drought tolerant than many other legume crops. To understand the molecular mechanisms of this unique feature of pigeonpea, 51 genes were selected using the Hidden Markov Models (HMM) those codes for proteins having close similarity to universal stress protein domain. Validation of these genes was conducted on three pigeonpea genotypes (ICPL 151, ICPL 8755, and ICPL 227) having different levels of drought tolerance. Gene expression analysis using qRT-PCR revealed 6, 8, and 18 genes to be ≥2-fold differentially expressed in ICPL 151, ICPL 8755, and ICPL 227, respectively. A total of 10 differentially expressed genes showed ≥2-fold up-regulation in the more drought tolerant genotype, which encoded four different classes of proteins. These include plant U-box protein (four genes), universal stress protein A-like protein (four genes), cation/H(+) antiporter protein (one gene) and an uncharacterized protein (one gene). Genes C.cajan_29830 and C.cajan_33874 belonging to uspA, were found significantly expressed in all the three genotypes with ≥2-fold expression variations. Expression profiling of these two genes on the four other legume crops revealed their specific role in pigeonpea. Therefore, these genes seem to be promising candidates for conferring drought tolerance specifically to pigeonpea.

Effects of water regimes on inulin content and inulin yield of Jerusalem artichoke genotypes with different levels of drought tolerance

Drought is a recurring problem of Jerusalem artichoke (Helianthus tuberosus L.) production under rainfed conditions. A better understanding of the responses of Jerusalem artichoke genotypes to drought can lead to the improvement of inulin content and inulin yield in Jerusalem artichoke and its production planning. The objective of this study was to compare the responses of five Jerusalem artichoke genotypes (JA60, JA125, JA5, JA89, and HEL65) to three water regimes (100% available water (AW; field capacity), 50% AW, and 25% AW) for inulin content and inulin yield. The experimental results showed that water regimes and Jerusalem artichoke genotypes were significantly different for inulin content and inulin yield. The interactions between Jerusalem artichoke genotypes and water regimes were also significant for inulin content and inulin yield. Under field capacity level, the results from the experimental years (2012 and 2013) showed that JA125, JA5, JA60, and HEL65 had the highest inulin content. Under 50% and 25% AW, JA5 and HEL65 had high inulin content, while JA5 had the highest inulin yield. The results indicated that if irrigation is available, JA5 should be planted because of its high inulin content under well-irrigated conditions. However, JA5, JA125, and JA60 are highly recommended under rainfed conditions because of their high inulin content under drought conditions. The results were limited to a pot experiment, and further field experiments are still required.

Transcriptional profiling of the leaves of near-isogenic rice lines with contrasting drought tolerance at the reproductive stage in response to water deficit.

BackgroundDrought tolerance is a complex quantitative trait that involves the coordination of a vast array of genes belonging to different pathways. To identify genes related to the drought-tolerance pathway in rice, we carried out gene-expression profiling of the leaves of near-isogenic lines (NILs) with similar genetic backgrounds and different set of QTLs but contrasting drought tolerance levels in response to long-term drought-stress treatments. This work will help differentiate mechanisms of tolerance in contrasting NILs and accelerate molecular breeding programs to improve drought tolerance in this crop.ResultsThe two pairs of rice NILs, developed at the International Rice Research Institute, along with the drought-susceptible parent, IR64, showed distinct gene-expression profiles in leaves under different water-deficit (WD) treatments. Drought tolerance in the highly drought-tolerant NIL (DTN), IR77298-14-1-2-B-10, could be attributed to the up-regulation of genes with calcium ion binding, transferase, hydrolase and transcription factor activities, whereas in the moderate DTN, IR77298-5-6-B-18, genes with transporter, catalytic and structural molecule activities were up-regulated under WD. In IR77298-14-1-2-B-10, the induced genes were characterized by the presence of regulatory motifs in their promoters, including TGGTTAGTACC and ([CT]AAC[GT]G){2}, which are specific to the TFIIIA and Myb transcription factors, respectively. In IR77298-5-6-B-18, promoters containing a GCAC[AG][ACGT][AT]TCCC[AG]A[ACGT]G[CT] motif, common to MADS(AP1), HD-ZIP, AP2 and YABBY, were induced, suggesting that these factors may play key roles in the regulation of drought tolerance in these two DTNs under severe WD.ConclusionsWe report here that the two pairs of NILs with different levels of drought tolerance may elucidate potential mechanisms and pathways through transcriptome data from leaf tissue. The present study serves as a resource for marker discovery and provides detailed insight into the gene-expression profiles of rice leaves, including the main functional categories of drought-responsive genes and the genes that are involved in drought-tolerance mechanisms, to help breeders identify candidate genes (both up- and down-regulated) associated with drought tolerance and suitable targets for manipulating the drought-tolerance trait in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2335-1) contains supplementary material, which is available to authorized users.

Agronomic performances of three vetch species growing under different drought levels

The current challenge of agriculture is to get the best yields while overcoming frequent water deficit conditions. The objective of this study was to compare performances of three vetch species (Vicia narbonensis L., V. sativa L., and V. villosa Roth) subjected to water stress. Plants were sown in pots under rainout shelter and submitted to four water regimes: control (100% field capacity [FC]), 80%, 60%, and 40% FC through 3 yr experiment. Results showed that V. narbonensis had the smallest declines in all the studied variables in response to water restriction but the highest water use efficiency (WUE) and stress tolerance index (STI) in both control and water-treated plants. This indicates the greater tolerance of this species to water constraint and its better water use. Vicia villosa was characterized by drastic declines in leaf area and DM yield (75% and 64%, respectively). It had also the smallest WUE and STI suggesting its low adaptation to water stress. Vicia sativa showed severe reductions in seed yield and yield components; accordingly, it was the most sensitive species in terms of seed yield. The three species implied avoidance strategies to cope with water stress. The different levels of drought tolerance explain the species ecological distribution in Tunisia.

Relations Between Barley Root Traits and Osmotic Adjustment Under Terminal Drought Stress

The root responses to water deficit and osmotic adjustment are two main mechanisms that plants use to cope with drought stress. In order to evaluate relations between these mechanisms a greenhouse study was carried out in factorial based on CRD with three replications. In present work, three barley cultivars with different levels of drought tolerance have been subjected to terminal drought stress. Water stress was imposed by withholding water at the anthesis stage. The samplings were done when the available water content (AWC) in soil reached to 30% AWC (moderate stress) and 10% AWC (severe stress). Biological yield (BY) and grain yield (GY) were calculated at the end of the growth period. The results indicated that by increasing water stress severity, water potential (WP), osmotic potential (OP) and root volume (RV) decreased. In contrast, osmotic adjustment (OA) was higher in drought tolerant cultivar, Yousof, in severe drought stress condition (10% AWC). It seems that osmotic adjustment significantly caused to increase root to shoot ratio in this cultivar. Finally, the lowest grain yield reduction obtained from Yousof. The significant correlations were obtained between OA and root traits (p<0.05) in 10% AWC condition. The highest significant correlations were observed between OA and RWC (r=+0.92), BY (r=+0.83), GY (r=+0.96) in 10% AWC condition (p<0.01). The results underline the efficient relations between different drought resistance mechanisms especially in drought tolerant cultivar.

Nutrient uptake of peanut genotypes with different levels of drought tolerance under midseason drought

The objective of this study was to investigate the responses of peanut genotypes to midseason drought, regarding in particular nutrient uptakes and their correlations with biomass production and pod yield. The experiment was conducted during the dry seasons of 2011/12 and 2012/13. Five peanut genotypes with different levels of drought tolerance and 2 water regimes (well-watered and midseason drought) were laid out in a split-plot design with 4 replications. Midseason drought was imitated by stopping irrigation at 30 days after planting (DAP) and then rewatering at 60 DAP. The data were recorded for contents of N, P, K, Ca, and Mg in plant tissues, biomass production, yield components, and pod yield at harvest. The results showed that midseason drought significantly reduced the uptake of all nutrient elements. Peanut genotypes with higher levels of drought tolerance took up more nutrients than those with lower levels. The uptake of all nutrient elements contributed to biomass production, pod yield, and the number of pods per plant. ICGV 98305 was the best genotype with the highest uptakes of all observed nutrient elements.

Genome-Wide Analysis of ZmDREB Genes and Their Association with Natural Variation in Drought Tolerance at Seedling Stage of Zea mays L

The worldwide production of maize (Zea mays L.) is frequently impacted by water scarcity and as a result, increased drought tolerance is a priority target in maize breeding programs. While DREB transcription factors have been demonstrated to play a central role in desiccation tolerance, whether or not natural sequence variations in these genes are associated with the phenotypic variability of this trait is largely unknown. In the present study, eighteen ZmDREB genes present in the maize B73 genome were cloned and systematically analyzed to determine their phylogenetic relationship, synteny with rice, maize and sorghum genomes; pattern of drought-responsive gene expression, and protein transactivation activity. Importantly, the association between the nucleic acid variation of each ZmDREB gene with drought tolerance was evaluated using a diverse population of maize consisting of 368 varieties from tropical and temperate regions. A significant association between the genetic variation of ZmDREB2.7 and drought tolerance at seedling stage was identified. Further analysis found that the DNA polymorphisms in the promoter region of ZmDREB2.7, but not the protein coding region itself, was associated with different levels of drought tolerance among maize varieties, likely due to distinct patterns of gene expression in response to drought stress. In vitro, protein-DNA binding assay demonstrated that ZmDREB2.7 protein could specifically interact with the target DNA sequences. The transgenic Arabidopsis overexpressing ZmDREB2.7 displayed enhanced tolerance to drought stress. Moreover, a favorable allele of ZmDREB2.7, identified in the drought-tolerant maize varieties, was effective in imparting plant tolerance to drought stress. Based upon these findings, we conclude that natural variation in the promoter of ZmDREB2.7 contributes to maize drought tolerance, and that the gene and its favorable allele may be an important genetic resource for the genetic improvement of drought tolerance in maize.

Salicylic Acid and Abiotic Stress Responses in Rice

AbstractAmong plant species rice (Oryza sativa L.) leaves can be characterised with a very high level of salicylic acid content; however, its exact role is still poorly understood. In the present work, rice genotypes with different levels of drought tolerance have been subjected to PEG‐induced drought or cold stress at 10 °C in order to find relationship between the salicylic acid metabolism and the level of stress tolerance; and between the salicylic acid level and other protective mechanisms. Although the drought‐sensitive genotypes usually contained slightly higher amount of salicylic acid than the tolerant ones, there was no strong correlation between the salicylic acid contents and the degree of drought tolerance. Because the expression pattern of the chorismate synthase and isochorismate synthase genes did not correlate with the level of salicylic acid, but there was a correlation between the levels of salicylic acid and ortho‐hydroxy‐cinnamic, it is assumed that the salicylic acid synthesis via ortho‐hydroxy‐cinnamic acid may play a more decisive role than the chorismate–isochorismate–salicylic acid pathway in rice. While the activity of the glutathione reductase enzyme did not show correlation with drought tolerance, the glutathione S‐transferase activities were usually higher in the leaves of the drought‐tolerant varieties than in the sensitive ones. The salicylic acid contents in the leaves were not substantially affected by the applied stress conditions; however, other stress‐related compounds polyamines showed marked, stress‐specific responses. Correlation data suggest that there is no direct link between the abiotic stress‐induced polyamine changes and the salicylic acid metabolism in rice.

Avaliação de cultivares de soja quanto à tolerância ao estresse hídrico em substrato contendo polietileno glicol

The objective of this work was to evaluate the tolerance of soybean genotypes to water stress in substract soaked with polyethylene glycol (PEG 6000). The study used seeds stored for one year in laboratory uncontrolled conditions, of the following cultivars: CD 201, CD 202, CD 204, CD 205, CD 206, CD 208, CD 215, CD 216, Embrapa 48, BRS 132, BRS 184 and BRS 212. The soybean seeds were evaluated through germination tests, seedling vigor classification tests, seedling length and dry biomass, under water stress conditions using two levels of osmotic potential (0.0 and -0.1 MPa). Cultivars were them grouped in different levels of drought tolerance, by the percentage reduction in the appraised characteristics {% Reduction = [1-(Germination or Vigor in PEG 6000 / Germination or Vigor in water)] x 100}, for the technique of grouping analysis, according to the nearest neighbor hierarchical method. The soybean genotypes presented differentiated behavior regarding drought tolerance. The Embrapa 48 cultivar presented the greatest tolerance to water stress. Comparing the results obtained by multivariate analysis and by the Scott-Knott grouping method, good concordance was observed between the two methods in the constitution of the groups. The method used and the statistical procedure adopted allowed to differentiate the soybean cultivars in a short period of time

Preharvest Aflatoxin Contamination in Drought-Tolerant and Drought-Intolerant Peanut Genotypes1

Abstract Peanuts become contaminated with aflatoxins when subjected to prolonged periods of heat and drought stress. The effect of drought tolerance on aflatoxin contamination is not known. The objectives of this research were to evaluate preharvest aflatoxin contamination in peanut genotypes known to have drought tolerance and to determine the correlation of drought tolerance characteristics with aflatoxin contamination. Twenty genotypes with different levels of drought tolerance were grown in Yuma, AZ (a desert environment) and under rain-protected shelters in Tifton, GA. Two drought-tolerant genotypes (PI 145681 and Tifton 8) and an intolerant genotype (PI 196754) were selected for further examination in a second experiment with two planting dates in 1997 at Tifton. Drought and heat stress conditions were imposed for the 40 d preceding harvest. The drought-intolerant genotype had greater preharvest aflatoxin contamination than Florunner (the check cultivar) in the tests conducted in 1997. Both drought-tolerant genotypes had less preharvest aflatoxin contamination than Florunner in these tests. Significant positive correlations were observed between aflatoxin contamination and leaf temperature and between aflatoxin contamination and visual stress ratings. Leaf temperature and visual stress ratings are less variable and less expensive to measure than aflatoxin contamination. Leaf temperature and visual stress ratings maybe useful in indirectly selecting for reduced aflatoxin contamination in breeding populations.

Drought tolerance of photosynthetic electron transport under CO2‐enriched and normal air in cereal species

The quantum yield of photosynthetic electron transport (ΦPSII), evaluated by means of chlorophyll (Chl) fluorescence analysis, has proven to be a useful screening test for drought tolerance in durum wheat (Triticum durum Desf.). To explore the potential of this parameter further in detecting drought‐tolerant genotypes, three cereal species were studied; ΦPSII measurements were carried out under two different gas mixtures, at three points of the induction curve (to obtain the maximal ΦPSII and both the transient and steady‐state actual ΦPSII), and at three different water stress levels (moderate, severe and drastic). The species investigated were durum and bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.); two cultivars per species, characterized by different levels of drought tolerance, were tested. The two gas mixtures used were normal air (21% O2, 0.035% CO2 in N2) to monitor the whole photosynthetic process under physiological conditions, and CO2 enriched‐low O2 air (1% O2, 5% CO2 in N2) to monitor ΦPSII reduction under stress mainly related to Calvin cycle activity. When ΦPSII related to both assimilatory and non‐assimilatory metabolism was evaluated, the cultivar differences observed under normal Air were more representative of the agronomic performance upon drought stress than under high CO2‐low O2 air. Maximal ΦPSII showed no difference among either cultivars, gas mixtures or stress levels, the efficiency of excitation capture being highly resistant to drought. The ΦPSII evaluated during the transient yielded predictable values in respect of drought tolerance for durum wheat and barley cultivars, highlighting the key role of regulatory processes such as the Mehler peroxidase reaction and possibly also cyclic electron transport, in preventing overreduction under stress. The results clearly show that when Chl fluorescence analysis is used as a parameter in plant breeding, different experimental conditions should be used depending on the physiological mechanism that is bred or selected for.

Effects of water stress on plant growth and root proteins in three cultivars of rice (Oryza sativa) with different levels of drought tolerance

Effects of water stress on plant growth and root proteins in three cultivars of rice (Oryza sativa) with different levels of drought tolerance