Variability For Drought Tolerance Research Articles

Reciprocal Grafting Reveals Differential Metabolic Responses Between Robusta Clones with Contrasting Tolerances to Drought

Faced with global warming, the surface area of coffee cultivation regions is expected to diminish significantly in the near future. As a result, new varieties or agronomical practices improving drought tolerance need to be found. The aim of this work is to characterize drought tolerance of Coffea canephora genotypes and their reciprocal grafted plants with physiological tools and biochemical analyses. Under greenhouse conditions, control plants (sensitive or tolerant) and reciprocal grafted plants submitted to 14 days of water deprivation show variations of the monitored parameters, such as soil and leaf water potential, stomatal conductance, and osmoprotectant compounds (sugars, polyols, amino acids). The variations observed confirm the differences between the phenotypes defined as drought-tolerant and drought-sensitive. Reciprocal grafting shows enhanced and contrasting situations. A sensitive clone grafted onto tolerant rootstock presents higher tolerance to drought and physiological or biochemical parameters similar to a drought-tolerant clone. The opposite is observed for tolerant clones grafted onto a sensitive one. More contrasted results are obtained with glucose, fructose, proline, and mannitol content which could be used as indicators for drought tolerance. Our finding shows strong variability for drought tolerance in our Robusta clones and demonstrates the impact of grafting on physiological and biochemical parameters linked to drought tolerance. The use of drought-tolerant rootstock leads to better regulation of water management and biochemical composition of the scion in drought-sensitive clones. This could be an approach to improving drought tolerance of Coffea canephora genotypes and to limiting the impact of global warming on coffee farming.

Classification of Potato Varieties Drought Stress Tolerance Using Supervised Learning

The presented study was aimed at investigating the variability for drought tolerance among potato cultivars. To achieve this, the stability of drought tolerance of potato cultivars under different water regime conditions was inspected during 11 years of consecutive experiments. The data on 50 potato cultivars’ responses to drought stress, based on the morphological features of plants, i.e., leaf and stem mass and size of the assimilation area, have been collected. The tuber yield, as well as calculated plant tolerance indexes and Climatic Water Balance for each growing season, were analyzed. The studied cultivars were later assigned into one of three tolerance groups for soil drought. The highest linear relationship was found between the mass of leaves and stems and the tuber yield but was found too weak to raise any conclusions. Thus, the ensemble learning models have been evaluated and returned better performance results, and the final classifier is the implementation of extreme gradient boosting. The final classifier of the 96.7% accuracy, which used several measured potato parameters (Relative yield decrease, Stem mass, Maturity, Assimilation area, Leaves mass, Yield per plant, calculated Climatic water balance, and indices: MSTI and DSI) that could distinguish the different tolerance groups were evaluated in the study.

BIOMASS AND CHEMICAL RESPONSES OF Desmanthus spp. ACCESSIONS SUBMITTED TO WATER DEPRIVATION1

ABSTRACT Due to the predictions of climate change, there is a need to identify forage plants that can keep their productivity and nutritive value under hydric stress. The objective of this study was to evaluate the biomass and chemical responses of three Desmanthus spp. accessions under two water deprivation regimens (7 and 21-day). The experimental design used was randomized blocks in a 3 × 2 factorial arrangement (access and water deprivation) with four replications. There were reductions in the biomasses of leaf and stem fractions of 64% and 51%, respectively. The 43F accession showed greater leaf (1.86 g.plant-1) and stem (1.97 g.plant-1) biomasses under a total water restriction of 21 days, compared to the 89F and AusT accessions. In accessions 43F and 89F, there were carbohydrate accumulations in the leaves of 28% and 51%, respectively, under the 21-day water restriction, while AusT decreased 38% within a 7-day interval. Water deprivation affected the chemical characteristics of the accessions. Free proline was similar among accessions and accumulated 463% more in the leaves of plants submitted to 21-day water deprivation (90.22 mg.kg-1) compared to those subjected to water deprivation for 7 days (16.03 mg.kg-1). Proline and total soluble carbohydrate accumulation in 43F and 89F were insufficient to regulate crude protein, C content, and C:N ratios. These results demonstrate the variability in drought tolerance among accessions. Accessions 43F and 89F were more susceptible to 21-day water deprivation, while AusT showed greater drought tolerance.

Root system of Medicago sativa and Medicago truncatula: drought effects on carbon metabolism

Here, we assess the differential impact of drought on root carbon metabolism in the widely cultivated alfalfa (Medicago sativa, Ms) and the model legume Medicago truncatula (Mt). Understanding how carbon allocation is regulated under drought stress conditions is a central issue to improving alfalfa productivity under future climate change scenarios. Alfalfa and Medicago truncatula were compared under water deficit conditions. Root carbon metabolism of the taproot and fibrous roots was analysed. M. truncatula drought tolerance variability was compared to that of alfalfa using six accessions of the Medicago Hapmap project. The prominent taproot is much less developed in M. truncatula than in alfalfa with the former exhibiting an extensive fibrous root system. In both examined Medicago species the taproot contained the major pools of soluble protein, sucrose and pinitol, whereas the major pools of hexoses and carbon metabolism enzymes appeared to be in the fibrous roots. Under water-deficit conditions, the response of M. sativa strongly differed from that of M. truncatula at the root level. Water deficit conditions differentially modulate the root carbon metabolism of M. sativa and M. truncatula. Mt maintained a more active carbon metabolism in the fibRs, as sucrose, myo-inositol and pinitol accumulated to cope with the water deficit (WD). Conversely, the root system of Ms did not accumulate cyclitols and carbon metabolism was more severely affected under water deficit conditions. This differentially exerted control may determine the drought response of these two close relatives.

Drought tolerance and regrowth capacity revealed in the Festuca-Lolium complex

The climate change appears to have accelerated in recent years, and more changes are envisaged in the near future. With this in mind, breeders should consider the choices of materials to be used in breeding for the future to potentially mitigate the impacts of changes. In forage grasses, a special attention has to be paid to drought and heat tolerance. Here, in a screening trial of numerous accessions, we investigated drought tolerance and after-drought recovery rates among the species of the Festuca-Lolium complex, including cultivars and breeding materials as well as various ecotypes of wild species. Experimental trials were done using rainout shelters during three successive years 2017 - 2019. The most drought tolerant genotypes belonged to the species F. glaucescens and F. mairei, followed by F. atlantigena, F. arundinacea, and some genotypes of F. pratensis. These genotypes should be considered as suitable candidates for intergeneric hybridization with L. multiflorum and L. perenne. Our test shows that Festulolium krasanii (L. multiflorum × F. arundinacea) is a good candidate to replace pure tall fescue (F. arundinacea) stands. It has the same or similar drought tolerance and drought recovery as tall fescue and at least some cultivars are known for their high feeding value, unlike tall fescue itself. A large variability for drought tolerance and recovery rates in Fl. braunii (the L. multiflorum × F. pratensis hybrid) and Fl. loliaceum (the L. perenne × F. pratensis hybrid) permit selection of genotypes that can outperform the original L. multiflorum and L. perenne.

Evaluation of drought tolerance indices for barley landraces under irrigated and dry conditions

Barley cultivation for drought areas requires reliable assessment of drought tolerance variability among the breeding germplasms. Hence, 121 barley landraces, advanced breeding lines and varieties were evaluated under both moisture non-stress and stress field conditions using a lattice square (11×11) design with two replications for each set of trials. Twelve drought tolerance indices (SSI, TOL, MP, GMP, STI, YI, YSI, HM, SDI, DI, RDI and SSPI) were used based on grain yield under normal (Yp) and drought (Ys) conditions. Analysis of variance showed a significant genetic variation among genotypes for all indices with the exception of TOL and SSPI indices. Yp had a very strong association with Ys (r=0.92**) that indicates high yield potential under non-stress can predict better yield under stress conditions. Yp and Ys were positively and significantly correlated with MP, GMP, STI, YI, HM and DI indices, whereas they were negatively correlated with SSI and SDI. In principal component analysis (PCA), the first PC explained 64% of total variation with Yp, Ys, MP, GMP, STI, YI, HM and DI. The second PC explained 35.6% of the total variation and had positive correlation with SSI, TOL, SDI and SSPI. It can be concluded that MP, GMP, STI, YI, HM and DI indices with the most positive and significant correlation with yield at both non-stress and stress environments would be better indices to screen barley genotypes, although none of the indices could undoubtedly identify high yield genotypes under both conditions.

Screening of Worldwide Barley Collection for Drought Tolerance: The Assessment of Various Physiological Measures as the Selection Criteria.

Drought is a devastating environmental constraint affecting the agronomic production of barley. To facilitate the breeding process, abundant germplasm resources and reliable evaluation systems to identify the true drought-tolerant barley genotypes are needed. In this study, 237 cultivated and 190 wild barley genotypes, originating from 28 countries, were screened for drought tolerance under the conditions of both water deficit and polyethylene glycol (PEG)-simulated drought at seedling stage. Drought stress significantly reduced the plant growth of all barley genotypes, but no significant difference in drought-induced reduction in the performance of barley seedlings was observed under these two drought conditions. Both cultivated and wild barley subspecies displayed considerable genotypic variability in drought tolerance, which underpinned the identification of 18 genotypes contrasting in drought tolerance. A comparative analysis of drought effects on biomass, water relation, photosynthesis, and osmotic adjustment was undertaken using these contrasting barley genotypes, in order to verify the reliability of the screening and to obtain the credible traits as screening criteria of drought tolerance in barley. As expected, the selected drought-tolerant genotypes showed much less reduction in shoot biomass than drought-sensitive ones under water deficit, which was significantly positively correlated with the results of large-scale screening, confirming the reliability of the screening for drought tolerance under two drought conditions in this study. Likewise, the traits of water relation, photosynthetic activity, and osmotic adjustment differed greatly between the contrasting genotypes under water deficit stress, and they were highly correlated to the growth of barley seedlings, suggesting the potential of them to be the selection criteria for drought tolerance. The analysis of the variable importance of these traits in drought tolerance indicated that sap osmolality and relative water content in the youngest fully-expanded leaf are the suitable selection criteria of screening for drought tolerance in barley at seedling stage.

GENETIC PARAMETERS OF Eucalyptus spp. CLONES IN NORTHEASTERN BRAZIL

Brazil is the largest charcoal producers in the world, with the main centers of charcoal consumption located in the states of Minas Gerais, Mato Grosso do Sul, Espírito Santo, Maranhão, and Pará. Planting of Eucalyptus in the northern and northeastern states of Brazil is relatively new and is limited the lack of genetic materials adapted to the region’s high temperatures and severe, prolonged periods of drought. The objective of this study was to assess the genetic parameters and variability and determine the genotype x environment interaction for drought tolerance in Eucalyptus clonal tests established in two environments in the municipality of Grajaú, Maranhão State, Brazil. The tests were planted in January 2011 in clayey and sandy soils in a randomized complete block design with 130 clones, one plant per plot, and 20 replicates. The studied clones showed high genetic variability for drought tolerance, with coefficients of relative variance () consistently greater than 0.8 for DBH and volume. This indicates high levels of genetic control and less influence of environmental factors on the phenotype, which allows for selection and obtaining gains through breeding. Heritability estimates were high for growth traits, with average clone heritabilities () greater than 0.85, as well as acuracies () above 0.9 for DBH and volume in clone selection. There was a simple interaction between genotype x environment for the clones under the two different soil conditions.

Long-term impact of deficit irrigation on the physiology and growth of grapevine cv. ‘Prima’ grafted on various rootstocks

Testing the globally popular grapevine rootstocks for affinity with new grape cultivars or tolerance potential to stress factors like drought is essential for districts where supplemental irrigation is more frequently needed due to the pressures of a global climate change. In this study, a seasonal evaluation of leaf gas exchange, leaf temperature, leaf greenness (chlorophyll content prediction) and vegetative development of Vitis vinifera L. cv. ‘Prima’ grafted to different rootstock genotypes having great variability in drought tolerance, were investigated. The experiment was conducted in a controlled experimental glasshouse on two-year-old soilless grown ‘Prima’ vines grafted on nine rootstocks [44-53 M, 5 BB, 140 Ru, Ramsey (Syn. Salt Creek), 99 R, Saint George (Syn. Rupestris du Lot), 41 B, 1613 C and 420 A]. A long-term deficit irrigation (DI) was imposed before bud break by reducing water supply to 40% of field capacity derived from concurrent measurements of water content of growth medium and maintained until the end of vegetation period. The rootstocks significantly modulated the physiology and vegetative growth of the scion cultivar in varying degrees according to their genetic features. Among them, 140 Ru rootstock found to be more prominent in terms of mitigating the adverse effect of water deficit on physiology and growth of the scion genotype ‘Prima’ as there were no significant difference between deficit and full irrigation treatments for most of parameters investigated. In general, the ‘Prima’ scion performed better when the rootstocks coming from V. berlandieri × V. rupestris pedigree rather than the others including V. berlendieri × V. riparia.

An assessment of genetic variability for drought tolerance in rice

The genetic variability for yield and yield contributing traits were studied in forty genotypes of rice under moisture-stress (rainfed) and moisture non-stress (irrigated) conditions. The results revealed highly significant differences among the genotypes for all the characters studied. This indicated the ample scope for selection of promising genotypes from the present set of genotypes for yield improvement. The high estimates of GCV and PCV coupled with high heritability and expected genetic advance for yield and important yield contributing traits showed their importance in selection for improving rice yield. The correlation study revealed that grain yield per plant had strong positive associations with effective panicle bearing tillers, days to 50% flowering, days to maturity, panicle weight, filled grains per panicle, total grains per panicle and length of main panicle. This indicated that grain yield of rice can be improved under both the environments having higher per se performances for the above traits. The genotypes such as HUR 105, NDR 359, Swarna were found to be best for yield and yield contributing traits. However, based on the different drought parameters, the varieties such as HUR105, HUR 4–3 and IET-20556 has been identified as drought tolerant which might be utilised in future breeding programmes.

Genetic analysis of drought-adaptive traits at seedling stage in early-maturing maize inbred lines and field performance under stress conditions

Maize hybrids that are tolerant to drought at the seedling stage are needed to boost productivity in the rainforest agro-ecology of West Africa. Genetics of tolerance of maize seedling to drought stress is not well understood and is poorly documented. The objectives of this study were to screen early-maturing maize lines for seedling drought tolerance, determine the inheritance and the combining ability of selected inbred lines, and evaluate the performance of seedling drought-tolerant hybrids under field conditions. Forty-nine early maize lines were screened for drought tolerance at the seedling stage. Ten drought-tolerant and two susceptible inbred lines were selected and used in diallel crosses to generate 66 hybrids. The twelve inbred lines and their hybrids were evaluated under induced drought at seedling stage in the screen house and under marginal growing conditions on the field for two seasons. Data collected were subjected to analysis of variance using the DIALLEL-SAS program. Mean squares for both GCA and SCA were significant for most traits in all research environments, indicating that additive and non-additive gene actions are controlling seedling traits under stress conditions. However, for most traits, SCA was preponderant over GCA in all environments, indicating overdominating effect of non-additive gene action. Which in turn implied that the best improvement method for the traits is hybridization. Inbred TZEI 7 had the best GCA effect for seedling traits under screenhouse conditions and for grain yield and other agronomic traits under drought conditions in the field. Hybrids TZEI 357 × TZEI 411 and TZEI 380 × TZEI 410 showed superior SCA effects under screen house conditions. In conclusion, the study established wide genetic variability for drought tolerance at seedling stage among tropical early-maturing maize germplasm however, the non-additive gene action was more important for most seedling traits.

Identification of drought tolerant populations at multi-stage growth phases in temperate maize germplasm

Drought is one of the main abiotic stresses in agriculture worldwide. Drought could increase under the predicted scenario of climate change, particularly in the Mediterranean area. Breeding for drought tolerance requires screening of germplasm in order to identify sources of tolerance; therefore, were evaluated 51 diverse open-pollinated maize populations from various temperate regions under increasing levels of drought at germination, seedling establishment and early growth. There was genetic variability for drought tolerance among populations at all growth phases. Several populations from diverse origins and germplasm groups exhibited high germination across stress treatments. Some of those populations had high ability to sustain root development and showed differential performance depending on the stage of development and the phenotypic aspect considered. In general, BS17 showed high germination rate, fast seedling growth and early vigor under drought. Longlellow and Grano de trigo showed high germination and growth establishment rates, whereas AS3(HT)C3 showed high germination rate and early vigor under drought. The photosynthetic rate, stomatal conductance and transpiration of Enano Levantino/Hembrilla (ELH) and BS17 populations were not affected by drought. Water use efficiency of BS17, ELH, Northwestern Dent (NWD) and Viana was not affected by drought. Some of these populations are promising sources of drought tolerance which can provide different mechanisms of drought tolerance at different stages of plant development. Therefore, these results open new possibilities of breeding for drought tolerance by combining those mechanisms through crosses among potential donors. Furthermore, these findings indicate that it is worthwhile to study the genetic and biological basis of such mechanisms.

Morphological and molecular characterization of maize inbred lines showing variability for drought tolerance

A set of hundred maize inbred lines were analyzed for resilience to moisture stress for twenty-four traits related to maturity, morphological, physiological, yield, quality and root traits. Evaluation confirmed a wide range of variability revealing significant response of main effects (lines, irrigations and years and their respective digenic and trigenic interactions). Fifteen elite identified lines performed well under moisture stress conditions showing inbuilt tolerance towards moisture stress. A set of 32 SSR markers, having genome-wide coverage, was chosen for genotyping the selected 15 inbred lines. These markers generated a total of 239 polymorphic alleles with an average of 7.47 alleles per locus. The minimum and maximum PIC value was 0.886 and 0.608 with a mean of 0.782. The coefficient of genetic dissimilarity ranged from 0.215 to 0.148. DARwin derived cluster analysis grouped 15 elite maize lines in three major clusters with five lines each in cluster-III and II and four lines in cluster-I with KDM-361A as root (at origin point. Molecular marker data however, confirmed diverse genetic nature of six lines (KDM-372, KDM-343A, KDM-331, KDM-961, KDM-1051 and KDM-1156) with favorable drought resilient traits with no yield penalty under moisture stress. Exploitation of these identified elite lines in involving all possible combinations helped to develop single cross hybrids under moisture stress conditions.

Variation in Ecophysiological Traits and Drought Tolerance of Beech (Fagus sylvatica L.) Seedlings from Different Populations.

Frequency and intensity of heat waves and drought events are expected to increase in Europe due to climate change. European beech (Fagus sylvatica L.) is one of the most important native tree species in Europe. Beech populations originating throughout its native range were selected for common-garden experiments with the aim to determine whether there are functional variations in drought stress responses among different populations. One-year old seedlings from four to seven beech populations were grown and drought-treated in a greenhouse, replicating the experiment at two contrasting sites, in Italy (Mediterranean mountains) and Germany (Central Europe). Experimental findings indicated that: (1) drought (water stress) mainly affected gas exchange describing a critical threshold of drought response between 30 and 26% SWA for photosynthetic rate and Ci/Ca, respectively; (2) the Ci to Ca ratio increased substantially with severe water stress suggesting a stable instantaneous water use efficiency and an efficient regulation capacity of water balance achieved by a tight stomatal control; (3) there was a different response to water stress among the considered beech populations, differently combining traits, although there was not a well-defined variability in drought tolerance. A combined analysis of functional and structural traits for detecting stress signals in beech seedlings is suggested to assess plant performance under limiting moisture conditions and, consequently, to estimate evolutionary potential of beech under a changing environmental scenario.

Interactive effects on CO2, drought, and ultraviolet-B radiation on maize growth and development

Crop growth and development are highly responsive to global climate change components such as elevated carbon dioxide (CO2), drought, and ultraviolet-B (UV-B) radiation. Plant tolerance to these environmental stresses comprises its genetic potential, physiological changes, metabolism, and signaling pathways. An inclusive understanding of morphological, physiological, and biochemical responses to these abiotic stresses is imperative for the development of stress tolerant varieties for future environments. The objectives of this study were to characterize the changes in vegetative and physiological traits in maize hybrids in their response to multiple environmental factors of (CO2) [400 and 750μmolmol−1 (+(CO2)], irrigation treatments based evapotranspiration (ET) [100 and 50% (−ET)], and UV-B radiation [0 and 10kJm−2d−1 (+UV-B)] and to identify the multiple stress tolerant hybrids aid in mitigating projected climate change for shaping future agriculture. Six maize hybrids (P1498, DKC 65–81, N75H-GTA, P1319, DKC 66–97, and N77P-3111) with known drought tolerance variability were grown in eight sunlit, controlled environment chambers in which control treatment consisted of 400μmolmol−1 [CO2], 100% ET-based irrigation, and 0kJ UV-B. Plants grown at +UV-B alone or combination with 50% ET produced shorter plants and smaller leaf area while elevated CO2 treatments ameliorated the damaging effects of drought and higher UV-B levels on maize hybrids. Plant height, leaf area, total dry matter chlorophyll, carotenoids, and net photosynthesis measured were increased in response to CO2 enrichment. Total stress response index (TSRI) for each hybrid, developed from the cumulative sum of response indices of vegetative and physiological parameters, varied among the maize hybrids. The hybrids were classified as tolerant (P1498), intermediate (DKC 65–81, N75H-GTA, N77P-3111) and sensitive (P1319 and DKC 66–97) to multiple environmental stresses. The positive correlation between TSRI and vegetative and physiological index developed in this study demonstrates that a combination of vegetative and physiological traits is an effective screening tool to identify germplasm best suited to cope with future changing climates. Furthermore, the tolerant hybrids identified in this study indicate that the possibility of cultivar selection for enhanced agronomic performance and stability in a water limited environment with higher UV-B, anticipated to occur in future climates.

Genetic variability and selection criteria of drought tolerant rice (Oryza sativaL.)

Rice improvement for drought tolerance requires reliable assessment of drought tolerance variability among segregation populations. The present study was undertaken to assess the genetic variability among different drought tolerant genotypes. Seven rice genotypes and three check varieties were evaluated in this study in the drought-prone environments of the farmers’ fields. Drought stress was applied, through proper draining of water from the field, starting four weeks after transplanting up to maturity. In the field under drought stress conditions, the highest grain yield was found in IR82635-B-B-145-1 (4.1 t/ha) followed by IR82635-B-B-75-2 (3.8 t/ha), while the yield of check varieties ranged from 2.9–3.6 t/ha. Plant height, growth duration and grain yield were considered for selecting the drought tolerant variety through participatory variety selection (PVS) by farmers, GOs, NGOs (BRAC, ASHA and RDRS), extension personnel and researchers. According to drought tolerance indices analysis, the line IR82635-B-B-145-1 was selected as a genotype with the most yield potential under drought environments in the Rangpur region of Bangladesh.

MORPHO-PHYSIOLOGICAL AND BIOCHEMICAL TRAIT BASED SELECTION OF WHEAT GENOTYPES FOR DROUGHT TOLERANCE

Drought stress is now become the most important abiotic stress for wheat in Bangladesh. Rabi season often compromised wheat production by imposing drought stress. Therefore, it has been a priority to develop drought tolerant wheat variety for Bangladesh. However, the lack of genetic variability for drought tolerance in wheat has been a major bottleneck for developing drought tolerance wheat variety. The present investigation was carried out in an aim to evaluate several exotic and locally cultivated wheat genotypes for drought tolerance based on morpho-physiological and biochemical traits. Experiment was carried out at the net house of Field Laboratory of Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh with seven replications in a RCBD design. Ten locally cultivated and exotic wheat genotypes were grown under control (100% field capacity) and drought (30% field capacity) conditions. Genotypes used in the study were identified with different types of drought tolerance mechanisms, viz., Berkut for earliness, Shatabdi for grain weight, BARI Gom 26 for spike and grain number, along with Vorobey, Berkut for enhanced biosynthesis of proline, Sokoll for undamaged leaf Chlorophyll content and relative water content, Sakha8, Gaurav, Sonalika and Shatabdi for membrane thermostability; Sakha8 and Sourav for improved stress tolerance index. The genotypes screened out with different traits related to drought tolerance can be utilized as gene source for future breeding programs.

In vitro selection of sorghum (Sorghum bicolor (L) Moench) for polyethylene glycol (PEG) induced drought stress

Drought is one of the main environmental factors affecting growth and yield of sorghum in arid and semi-arid areas of the world. In vitro selection of Sorghum bicolor for drought tolerance was undertaken by the use of somaclonal variation. The experiment was carried out with a collection of sixteen sorghum genotypes and tested in a completely randomized design. Data were recorded at five different PEG 6000 (polyethylene glycol) levels (0, 0.5, 1.0, 1.5, 2.0% (w/v) treatments)) on coleoptile length (CL), root length (RL), shoot dry weight (SDW), root dry weight (RDW), root number (RN) and statistically analyzed for significant differences. Significant differences were observed among the genotypes, treatments and their interactions for the evaluated plant traits suggesting a great amount of variability for drought tolerance in sorghum. In general, embryogenic callus induction and plantlet regeneration was found to be indirectly proportional to increased PEG concentrations. By taking into consideration all the measured traits, Mann Whitney rank sum test revealed that 76T1#23 and Teshale followed by Gambella-1107 and Melkam showed better drought stress tolerance while Chelenko appeared to be drought sensitive.

Assessing the drought tolerance variability in Mediterranean alfalfa (Medicago sativa L.) genotypes under arid conditions

This work investigated the variability in drought tolerance under arid conditions of Mediterranean alfalfa genotypes with the overall aim to assess the main criteria that are associated with the relative tolerance and to discover the most tolerant ecotypes. For this, 16 alfalfa genotypes originating from seven countries of the Mediterranean basin were tested in an experimental station in south of Tunisia. The trial was conducted under two irrigation treatments. The first was normally irrigated by providing an amount of water corresponding to the potential evapotranspiration of the crop, and in the second with water deficit which was applied by stopping the irrigation during 8 weeks in summer. A significant decrease was observed under water deficit for biomass production, leaf stem ratio and water use efficiency. The sensitive index, in stress treatment, varies between 13.8% and 46.2% for dry yield. Results showed that some genotypes exhibited high-forage yield potential even in the presence of stress, mainly Amerist, Sardi10 and Siriver. Proline accumulation in leaves was greater in water-stressed plants, while the K+ osmo-regulatory role was not definite. High biomass production, accumulation of proline and constancy of K+ in leaves are the most important criteria for tolerant alfalfa.

Genetic variation for agronomic characters and drought tolerance among the recombinant inbred lines of wheat from the Norstar × Zagross cross

Interest in developing drought tolerant varieties is growing due to global warming. Identification of genetic variability for drought tolerance is a prerequisite to achieve this objective. In this study a sample of 28 recombinant inbred lines (RILs) of wheat developed from the cross of Norstar and Zagross varieties, together with their parents, were evaluated for two years (2010-2012) under normal and water stress conditions using split plot design with three replications. Main plots included two irrigation treatments of 70 and 140 mm evaporation from Class A pan and sub-plots consisted of 30 genotypes. The effect of genotypes and interaction of genotypes with years and water regimes were significant for all characters. Significant genotypic effect implies the existence of genetic variation among the lines under study. Heritability estimates were high for 1000 grain weight (0.87), flag leaf area (0.84), and days to heading (0.82). Biomass, grain yield, and straw yield showed the lowest heritability values (0.42, 0.50, and 0.51, respectively). Moderate genetic advance for most of the traits suggested the feasibility of selection among the RILs under investigation. Some RILs were higher yielding than either parent at both environments. Transgressive segregation was also observed for geometric mean productivity (GMP) and stress tolerance index (STI), indicating the possibility of selecting lines that are more drought tolerant than Norstar and Zagross varieties. Cluster analysis based on yield in the normal and water stress conditions, STI, and GMP identified six promising lines that can be evaluated further for drought tolerance in more environments.