Drought Susceptible Cultivars Research Articles

Evaluation of drought stress responses in two different banana genotypes from India

Farmers in outlying locations who are short on resources often rely on banana production, but this fruit crop is in danger due to drought. Given the difficulties of banana breeding, a molecular understanding of banana's drought tolerance will be invaluable in identifying markers for use in marker-assisted selection and genes for transgenic improvement of drought tolerance. The purpose of this study was to identify the genes and expression markers in banana that confer resistance to drought. Under the greenhouse, both dessert and cooking bananas were grown under ideal and water-restricted conditions and looked at how drought affected the biochemistry, structure, and function of these plants. The cooking cultivar is drought tolerant because it may reduce water loss by partially closing its stomata, as shown by morphological and physiological studies. The stomatal conductance, relative water content, plant height and number of leaves were significantly reduced in both the genotypes under water deficit stress. It was also discovered that MaADH, MaDEH19, MaNAC, MaSPS, and MaWRKY had higher expression levels in samples under water deficit stress when compared to the well watered samples. The expression of genes MaAQP, MaStpkNAK and MaRAV were found to be down regulated under water deficit stress in the drought tolerant cultivar Monthan. However, the expression of MaEXP and MaStpkNAK was non significant in the drought susceptible cultivar Amritsagar under water deficit stress. Present study finds out that MaEXP was exclusively upregulated in the drought tolerant cultivar Monthan under water deficit stress. However, its expression was non-significant in the susceptible cultivar under same condition. It is also revealed that under non stress conditions, MaAQP was upregulated in the drought tolerant cultivar as against to that of susceptible one, however, imposing water deficit stress will downregulate the gene in the tolerant cultivar. The current work proposes that cellular tolerance is founded on differences in the transcript levels of certain genes involved in processes like water transport and osmotic adjustment.

Elucidating the regulatory role of long non-coding RNAs in drought stress response during seed germination in leaf mustard.

Leaf mustard (Brassica juncea L. Czern & Coss), an important vegetable crop, experiences pronounced adversity due to seasonal drought stress, particularly at the seed germination stage. Although there is partial comprehension of drought-responsive genes, the role of long non-coding RNAs (lncRNAs) in adjusting mustard's drought stress response is largely unexplored. In this study, we showed that the drought-tolerant cultivar 'Weiliang' manifested a markedly lower base water potential (-1.073MPa vs -0.437 MPa) and higher germination percentage (41.2% vs 0%) than the drought-susceptible cultivar 'Shuidong' under drought conditions. High throughput RNA sequencing techniques revealed a significant repertoire of lncRNAs from both cultivars during germination under drought stress, resulting in the identification of 2,087 differentially expressed lncRNAs (DELs) and their correspondingly linked 12,433 target genes. It was noted that 84 genes targeted by DEL exhibited enrichment in the photosynthesis pathway. Gene network construction showed that MSTRG.150397, a regulatory lncRNA, was inferred to potentially modulate key photosynthetic genes (Psb27, PetC, PetH, and PsbW), whilst MSTRG.107159 was indicated as an inhibitory regulator of six drought-responsive PIP genes. Further, weighted gene co-expression network analysis (WGCNA) corroborated the involvement of light intensity and stress response genes targeted by the identified DELs. The precision and regulatory impact of lncRNA were verified through qPCR. This study extends our knowledge of the regulatory mechanisms governing drought stress responses in mustard, which will help strategies to augment drought tolerance in this crop.

Role of barley stem reserves in the maintenance of grain yield under terminal drought

AbstractUnder terminal drought conditions, due to the limitation of current photosynthesis, the impact of cereal stem carbohydrates reserves and their contribution to the grain yield preservation could be enhanced. The role of stem fructan remobilization on yield of barley was examined under drought conditions in the present study. The fructan accumulation and remobilization rate of the penultimate internode were studied in Morocco 9–75 and Yousef, as drought susceptible and tolerant barley (Hordeum vulgare L.) cultivars, respectively. Drought stress increased the fructan accumulation and remobilization in Yousef, supporting it from severe yield loss compared to Morocco cultivar. Under drought stress conditions, during grain filling of Yousef cultivar, the strong correlations were observed between the relative expression of the key genes involved in the fructan metabolism, that is 1‐SST and 6‐SFT (fructan biosynthesis genes) with the fructan content, as well as between the expression of 1‐FEH (fructan exohydrolase) and SUT1 (sucrose transporter) with fructan remobilization. Yousef cultivar contained considerable water‐soluble carbohydrate content of stem internodes, and a rise in osmolytes such as fructan may lead to the efficient osmotic adjustment, which in turn resulted in the maintenance of the water content and stomatal conductance. Based on the results, enhanced fructan accumulation and its induced remobilization under drought conditions can play an important role in yield stability of Yousef under stress. The barley genotypes with high potential for fructan production and remobilization under terminal drought stress could provide the appropriate materials for drought tolerance breeding and screening for these traits.

Drought-Induced Changes in The Flowering Capacity, Anthesis Quality and Seed Set in Rice (Oryza sativa L.).

Drought stress significantly reduces grain yield (GY) due to poor spikelet fertility and anthesis quality. Aim of this study was to understand the changes of flowering capacity, anthesis quality traits and seed set in the re-watered drought stressed modern high yielding drought susceptible rice cultivar, IR64 at heading (DSH) and booting (DSB) stages. The well-watered plants served as control of the experiment. Results obtained suggest that spikelet moisture content at above 80% was required to maintain optimum anthesis process in rice. Anthesis process in DSH plant was suspended when leaf relative water content (LRWC) dropped to below than 70%. Effects of drought stress on the spikelet moisture were irreversible as compared to the leaf rolling and LRWC. Hence, seed set was failed to occur at the upper rachis branches of the DSH plant. Anthesis process in the re-watered drought stress plants was resumed on the third day after re-watering with about 50% and 80% of anthers managed to dehisce in the DSH and DSB plants. Consequently, percentage of spikelet fertility and seed set in the DSH and DSB plants were increased towards the lower parts of the panicle. The GY, number of seeds, spikelet fertility, and harvest index however were significantly lower in the DSH plant (0.30 g, 13, 16.40% and 14.81) as compared to DSB plant (1.34 g, 57, 59.14% and 48.30), respectively. In addition, all interrelated traits involved in the flowering process of rice could be collectively termed as the anthesis quality traits due to their significant correlation with the grain yield and other yield components.

Dual inoculation with rhizobia and arbuscular mycorrhizal fungus improves water stress tolerance and productivity in soybean

A glasshouse experiment was conducted to understand the influence of rhizobia, Bradyrhizobium liaoningense and an arbuscular mycorrhizal fungus, Ambispora leptoticha on growth and yield performance of soybean cultivars, MAUS 2 and MAUS 212 (drought susceptible) and DSR 12 (drought tolerant) under different levels of moisture stress conditions. Three different water levels [100%, 75% and 50% FC] with three microbial inocula (B. liaoningense, A. leptoticha and B. liaoningense + A. leptoticha) served as main treatments and the water level treatments were imposed 31–45 days after sowing. Various growth, physiological and microbial parameters were recorded besides analysing the samples for nutrients. The results showed that the plant growth parameters like biovolume index, total dry biomass, root volume and seed yield were significantly higher in dual inoculated plants in all the cultivars at all the moisture levels. There was an increase in mean seed weight by 88% and dry biomass by 58% in dual inoculated plants compared to uninoculated plants. Further physiological parameters and nutrients level improved significantly with dual inoculation under stress condition. However significant difference in recorded parameters was not observed in plants grown at 100% and 75% FC suggesting dual inoculation of B. liaoningense + A. leptoticha is beneficial when stress is severe in all the 3 cultivars. The microbial and nutrient parameters followed the same trend. Further of the two drought susceptible cultivars, MAUS 2 performed better compared to MAUS 212 in all the studied parameters under stress with dual inoculation. The results therefore signify the importance of rhizobia and mycorrhizal inoculation for imparting stress tolerance in soybean.

Evaluation of water deficit tolerance in maize genotypes using biochemical, physio-morphological changes and yield traits as multivariate cluster analysis

Drought is an abiotic stress that inhibits plant growth and development and, therefore, declines crop productivity, as seen in maize plant. The aim of this investigation was to identify the candidate maize varieties that can be grown under water limited conditions using physio-morphological and yield attributes. Eight genotypes of maize including ‘Suwan4452’ (drought tolerant) as a positive check, ‘CP301’, ‘CP-DK888’, ‘DK7979’, ‘DK9901’, ‘Pac339’, ‘S7328’, and ‘Suwan5’ were selected as test plants. Physiological, biochemical and morphological characteristics at seedling (24 day after sowing; DAS) and reproductive (80 DAS) developmental stages of plants under 20-day water withholding (WD), and yield traits at harvesting period were analysed. Leaf temperature in each genotype increased with the degree of water deficit stress, leading to leaf chlorosis, and reduction in maximum quantum yield of PSII (Fv/Fm), photon yield of PSII (ΦPSII), net photosynthetic rate (Pn), overall growth and yield. Pn and stomatal conductance (gs) in drought tolerant genotype, ‘Suwan4452’, were decreased by 19.1% and 18.6%, respectively, whereas these in drought sensitive, ‘Pac339’, were significantly declined by 53.9% and 61.8%, respectively. Physio-morphological parameters, growth performance and yield-related traits of maize genotypes grown under water deficit conditions and well-watered conditions were subjected to Ward’s cluster method for identification of water deficit tolerant cultivars. Maintaining photosynthetic abilities, osmotic adjustment and CWSI in drought tolerant genotypes of maize were evidently demonstrated to keep overall growth performance and yield attributes. Based on multivariate cluster analysis and PCA (principal component analysis), ‘Suwan4452’, ‘CP-DK888’ and ‘S7328’ were categorized as drought tolerant genotypes whereas ‘Suwan5’, ‘Pac339’, ‘DK7979’, ‘CP301’ and ‘DK9901’ were identified as drought susceptible cultivars. Hybrid maize cvs. ‘CP-DK888’ and ‘S7328’ may further be suggested to be grown in the rainfed area without irrigation.

Physiological and Morphological Responses of Okra (Abelmoschus esculentus L.) to Rhizoglomus irregulare Inoculation under Ample Water and Drought Stress Conditions Are Cultivar Dependent.

Okra is an important crop species for smallholder farmers in many tropical and subtropical regions of the world. Its interaction with mycorrhiza has been rarely studied, and little is known about its mycorrhizal dependency, especially under drought stress. In a glasshouse experiment, we investigated the effect of Arbuscular Mycorrhiza Fungi (AMF) inoculation on growth, evapotranspiration, mineral nutrition and root morphology of five okra cultivars under ample water and drought stress conditions. ‘Khartoumia’, ‘HSD6719’, ‘HSD7058’, ‘Sarah’ and ‘Clemson Spineless’-cultivars commonly used by farmers in Sudan were chosen for their geographical, morphological and breeding background variations. The plants were either inoculated with R. irregulare or mock-inoculated. Seven weeks after seeding, the soil–water content was either maintained at 20% w/w or reduced to 10% w/w to impose drought stress. Drought stress resulted in plant P deficiency and decreased shoot dry biomass (DB), especially in HSD7058 and Clemson Spineless (69% and 56% decrease in shoot DB, in the respective cultivars). Plant inoculation with AMF greatly enhanced the shoot total content of P and the total DB in all treatments. The mycorrhizal dependency (MD)—the degree of total plant DB change associated with AM colonization—differed among the cultivars, irrespective of the irrigation treatment. Key determinants of MD were the root phenotype traits. Khartoumia (with the highest MD) had the lowest root DB, root-to-shoot ratio, and specific root length (SRL). Meanwhile, HSD6719 (with the lowest MD) had the highest respective root traits. Moreover, our data suggest a relationship between breeding background and MD. The improved cultivar Khartoumia showed the highest MD compared with the wild-type Sarah and the HSD7058 and HSD6719 landraces (higher MD by 46%, 17% and 32%, respectively). Interestingly, the drought-affected HSD7058 and Clemson Spineless exhibited higher MD (by 27% and 15%, respectively) under water-deficiency compared to ample water conditions. In conclusion, the mediation of drought stress in the okra plant species by AMF inoculation is cultivar dependent. The presence of AMF propagules in the field soil might be important for increasing yield production of high MD and drought susceptible cultivars, especially under drought/low P environments.

Direct Infusion Metabolomics of the Photosystem and Chlorophyll Related Metabolites within a Drought Tolerant Plant Introduction of Glycine max.

Drought is the most prolific form of abiotic stress that legumes and cereal plants alike can endure, and the planting of an improper cultivar at the beginning of a season can cause unexpected losses up to fifty percent under water deficient conditions. Herein, a plant introduction (PI) of an exotic cultivar of soybean (Glycine max), PI 567731, which demonstrates a slow wilting (SW) canopy phenotype in maturity group III, was profiled under drought conditions in field trials in Missouri against a drought susceptible check cultivar, Pana. Metabolomic profiling was carried out on samples of leaves from each of these cultivars at V5 and R2 growth stages both while irrigated and while under drought stress for three weeks. PI 567731 was observed to have differential phytochemical content, and enhanced levels of chlorophyll (Chl) a/b and pheophytin (Pheo) were profiled by direct infusion electrospray Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Indicating drought induced changes of the photosystem and photosynthetic capabilities alongside water preservation strategies are important within the SW phenotype drought response. Subsequent multivariate analysis was able to form predictive models, encompassing the variance of growth and drought stress of the cultivar. Moreover, the existence of unique Chl-related metabolites (CRM) (m/z > 900) were confirmed through tandem mass spectrometry. The resultant coordination of fatty acids to the core of the porphyrin ring was observed and played an unknown role in the proliferation of the photosynthesis. However, the relative ratio of the most abundant CRM is undisturbed by drought stress in PI 567731, in contrast to the drought susceptible cultivar. These results provide key insights into drought related metabolic mechanisms.

Transcript responses to drought in Kentucky bluegrass (Poa pratensis L.) germplasm varying in their tolerance to drought stress

For the cool-season turfgrass Kentucky bluegrass, improving germplasm for drought tolerance is an increasingly important priority. Although genetic mechanisms behind drought tolerance have been characterized for model and agronomic plant species, the critical genes, gene families, and transcript isoforms important in Kentucky bluegrass are unclear. Using an RNAseq approach across three germplasm sources that differ in their regrowth, relative water content, and turf quality under drought stress, we have identified transcript isoforms exhibiting a shared response of all three germplasm sources to drought stress and transcript isoforms exhibiting a tolerance response where the more drought-tolerant germplasm sources exhibited higher transcript differences compared to the drought-susceptible cultivar Midnight. Annotation and transcript profile groupings both identified abundant chaperone gene families with protein folding and protective functions, such as heat shock proteins, DNAj, and late embryogenesis abundant genes. Transcript isoforms within these gene families were tolerance related and known to respond to abscisic acid. Two dehydrin genes, RAB15 and HVA1, were induced in several more drought-tolerant germplasm sources and show promise as candidate genes for selection.

Identification of Main-Effect and Environmental Interaction QTL and Their Candidate Genes for Drought Tolerance in a Wheat RIL Population Between Two Elite Spring Cultivars.

Understanding the genetics of drought tolerance can expedite the development of drought-tolerant cultivars in wheat. In this study, we dissected the genetics of drought tolerance in spring wheat using a recombinant inbred line (RIL) population derived from a cross between a drought-tolerant cultivar, ‘Reeder’ (PI613586), and a high-yielding but drought-susceptible cultivar, ‘Albany.’ The RIL population was evaluated for grain yield (YLD), grain volume weight (GVW), thousand kernel weight (TKW), plant height (PH), and days to heading (DH) at nine different environments. The Infinium 90 k-based high-density genetic map was generated using 10,657 polymorphic SNP markers representing 2,057 unique loci. Quantitative trait loci (QTL) analysis detected a total of 11 consistent QTL for drought tolerance-related traits. Of these, six QTL were exclusively identified in drought-prone environments, and five were constitutive QTL (identified under both drought and normal conditions). One major QTL on chromosome 7B was identified exclusively under drought environments and explained 13.6% of the phenotypic variation (PV) for YLD. Two other major QTL were detected, one each on chromosomes 7B and 2B under drought-prone environments, and explained 14.86 and 13.94% of phenotypic variation for GVW and YLD, respectively. One novel QTL for drought tolerance was identified on chromosome 2D. In silico expression analysis of candidate genes underlaying the exclusive QTLs associated with drought stress identified the enrichment of ribosomal and chloroplast photosynthesis-associated proteins showing the most expression variability, thus possibly contributing to stress response by modulating the glycosyltransferase (TraesCS6A01G116400) and hexosyltransferase (TraesCS7B01G013300) unique genes present in QTL 21 and 24, respectively. While both parents contributed favorable alleles to these QTL, unexpectedly, the high-yielding and less drought-tolerant parent contributed desirable alleles for drought tolerance at four out of six loci. Regardless of the origin, all QTL with significant drought tolerance could assist significantly in the development of drought-tolerant wheat cultivars, using genomics-assisted breeding approaches.

Dry cultivation and cultivar affect starch synthesis and traits to define rice grain quality in various panicle parts

A pot experiment was conducted to explore the effects of high-quality (Huanghuazhan, HH), drought-resistant (IR, IRAT109) and drought-susceptible cultivars (ZS, Zhenshan97) under flooding irrigation and dry cultivation (D) on the starch accumulation and synthesis, physicochemical traits of starch granules and rice grain quality at the upper (U) and lower panicle. Under D treatment, IR and ZS had lower rice quality, especially the appearance and cooking quality. DHH-U had the highest appearance, nutritional and cooking quality among all cultivars under D treatment, which could be ascribed to the synthesis of more short-branch chain amylopectin and correspondingly higher starch granule tightness. DHH-U also maintained ordered carbohydrate structure, crystalline regions, and many hydrophilic and hydrophobic functional groups in starch granules before pasting. It could prevent the polymerization of small molecules to avoid the formation of macromolecules after pasting. Overall, these findings may facilitate the improvement of grain quality in rice dry cultivation.

Physio-morphological, biochemical, and anatomical traits of drought-tolerant and susceptible sorghum cultivars under pre- and post-anthesis drought.

Understanding the physiological mechanisms that control drought tolerance in crop plants is vital for effective breeding. In this study, we characterized drought stress responses in four sorghum cultivars exhibiting differential levels of drought tolerance at pre- and post-anthesis. Greenhouse-grown plants were subjected to two types of drought treatment, water stress (WS) and desiccant-induced water stress (DA), timed to occur at pre- and post-anthesis. Multiple physiological measurements were then made revealing varying responses among the experimental cultivars. The pre- and post-flowering drought-tolerant cultivar P898012 showed a significantly higher net photosynthetic rate, higher transpiration rate, and greater stomatal conductance compared to the drought-susceptible cultivars at both pre- and post-anthesis. A significantly greater stomatal size was also detected in P898012, while the highest stomatal density was found in the drought-susceptible cultivar P721Q. Meanwhile, the two post-flowering drought-tolerant cultivars P898082 and B35 had a higher starch content and exhibited greater osmotic potential under post-anthesis water stress. Compared to WS and well-watered control plants, a greater increase in root biomass was observed in P898012 under DA at pre-anthesis. This finding suggests that plants invested more assimilates into the roots under severe DA at pre-anthesis. Overall, our results show good conformity between drought tolerance in sorghum and key physiological mechanisms of stomatal conductance, root growth patterns, and starch accumulation, all of which act as coping mechanisms during critical drought-sensitive growth stages.

Correlation between expression and activity of ADP glucose pyrophosphorylase and starch synthase and their role in starch accumulation during grain filling under drought stress in rice

ADP glucose pyrophosphorylase (AGPase, EC 2.7.7.27) and starch synthase (SS, EC 2.4.1.21) are key regulatory enzymes involved in the starch biosynthesis. Comprehensive analysis of transcription levels of ADP-glucose pyrophosphorylase and starch synthase genes was performed in leaves, roots, and developing grains of drought susceptible (IR64) and drought-tolerant (N22) cultivars under applied water deficit stress (WDS). AGPase and SS genes are differentially regulated in leaves, roots, and grains under the drought stress. The expression pattern of SS and AGPase genes was correlated with the activity of both AGPase, SS, and starch content of developing grains under the drought. Drought stress reduced transitory starch in leaves and enhanced storage starch in developing grains. An increase in the activity of AGPase in developing grains was due to induced expression of ADP glucose pyrophosphorylase large subunit 3 (AGPL3) in N22 and both ADP glucose pyrophosphorylase small subunit 2 (AGPS2) & ADP glucose pyrophosphorylase large subunit 3 (AGPL3) in IR64 and a positive correlation was established with starch content. Similarly, an increase in the SS activity in developing grains was due to induced expression of soluble starch synthase (SSIIB, SSIVA, and SSIVB) in N22 and SSIVB in IR64.

A Synthetic Cytokinin Improves Photosynthesis in Rice under Drought Stress by Modulating the Abundance of Proteins Related to Stomatal Conductance, Chlorophyll Contents, and Rubisco Activity.

Drought susceptible rice cultivar PTT1 (Pathumthani1) was treated with drought (−72 kPa) and CPPU (N-2-(chloro-4-pyridyl)-N-phenyl urea) @ 5 mg/L at tillering and grain-filling stages. Plants were tested for the effect of synthetic cytokinin on the parameters influencing the process of photosynthesis. Exogenous spray of CPPU improved the stomatal conductance of rice leaves, which was severely reduced by drought. The abundance intensities of proteins, associated with the stomatal conductance (ZEP, NCED4, PYL9, PYL10, ABI5, SnRK4, Phot1, and Phot2), were also in agreement with the positive impact of CPPU on the stomatal conductance under drought stress. Among the photosynthetic pigments, Chl b contents were significantly reduced by drought stress, whereas CPPU treated plants retained the normal contents of Chl b under drought stress. Subsequently, we examined the abundance intensities of chlorophyll synthase and HCR proteins, implicated in the biosynthesis of chlorophyll pigments and the conversion of Chl b to Chl a, respectively. The results indicated a drought-mediated suppression of chlorophyll synthase. However, CPPU treated plants retained normal levels of chlorophyll synthase under drought stress. In addition, drought stress induced HCR proteins, which might be the cause for reduced Chl b contents in drought stressed plants. Further, CPPU treatment helped the plants sustain photosynthesis at a normal rate under drought stress, which was comparable with well-watered plants. The results were further confirmed by examining the abundance intensities of two key proteins, RAF1 and Rubisco activase, implicated in the assembly and activation of Rubisco, respectively. CPPU treatment reversed the drought mediated suppression of these proteins at both of the growth stages of rice under drought stress. Based on the results, it can be suggested that synthetic cytokinins help the plants sustain photosynthesis at a normal rate under drought stress by positively influencing the determinants of photosynthesis at a molecular level.

Effect of stress on the leaf anatomy of sugarcane cultivars with different drought tolerance (Saccharum officinarum, Poaceae)

ABSTRACT. Introduction: Drought is an important stress factor for sugarcane production in many areas of the world. Water proportion and moisture indices are applicable information for agronomic planning to forecast water excess or deficit during the crop cycle. Objective: Leaf anatomical features of two different sugarcane Saccharum ‘UT12’ (drought susceptible cultivar) and Saccharum ‘UT13’ (drought tolerant cultivar) were compared under early drought stress situation between 30 and 90 days after planting. Methods: Forty leaf anatomical features were investigated using peeling and free hand sectioning technique. Results: Some anatomical characteristics showed response to drought stress. Saccharum ‘UT12’ demonstrated higher sensitivity toward anatomical characteristics than Saccharum ‘UT13’. A total of 23 and 15 out of the 40 anatomical characteristics showed significance in Saccharum ‘UT12’ and Saccharum ‘UT13’, respectively. Some anatomical features such as cell wall and cuticle thickness, vascular bundle size, stomatal size and density can be used as important markers for drought stress assessment in sugarcane leaf. Conclusions: This is the first report describing comparative leaf anatomy of sugarcane Saccharum ‘UT12’ and Saccharum ‘UT13’ in Thailand under drought stress. Results will provide important information to improve adaptation mechanisms of tolerant sugarcane cultivars under initial drought stress situations.

Starch accumulation in rice grains subjected to drought during grain filling stage

Drought stress during the grain filling stage severely affects the quality and quantity of starch in rice grains. The enzymes such as ADP-glucose pyrophosphorylase (AGPase, EC 2.7.7.27) and starch synthase (SS, EC 2.4.1.21) are the key regulatory enzymes involved in the starch biosynthesis. In this study, the activity of the AGPase and starch synthase (SS) was correlated with the qualitative and quantitative parameters such as sucrose, starch, amylose, amylopectin, and resistant starch in leaves, roots, and grains of drought tolerant (N22) and drought susceptible (IR64) cultivars under applied water deficit stress (WDS). Drought stress enhanced the remobilization of stored starch from leaves to developing rice grains which was positively correlated with a decrease in the starch and starch synthase activity in leaves. Starch accumulation in developing grains was positively correlated with an increase in the AGPase and SS activity under drought. It was found that starch, amylopectin, and sucrose content in developing grains increased under water deficit stress (WDS), while amylose content decreased in both the varieties. However, in leaves, the SS activity decreased while AGPase activity was found to be increased under WDS in both varieties. Decreased starch content in matured grains was due to shortening of grain filling stage as drought stress caused early plant senescence. Yield reduction under drought was more in susceptible variety IR64 as compared to tolerant genotype N22.

Uni- and Multi-Variate Assessment of Drought Response Yield Indices in 10 Wheat Cultivars

Wheat (Triticum aestivum L.) is a major cereal with its productivity being highly affected by drought. In the current study, 10 wheat cultivars were evaluated for their grain yield under well-watered (Yp) and drought (Ys) conditions. Various drought response indices (mean productivity (MP), geometric productivity (GMP), tolerance index (TOL), stress susceptibility index (SSI), stress tolerance index (STI), harmonic mean of yield (HARM), yield stability index (YSI), relative drought index (RDI), two drought resistance indices (DRI1 and DRI2), yield reduction ratio (YRR) and yield index (YI)) were determined to identify high-yielding and drought tolerant cultivars. Spearman’s correlation coefficient among the estimated indices, hierarchical clustering of the concerned cultivars as well as principle component analysis (PCA) of both the indices and cultivars were employed. Wheat cultivars Sids 13 and Gemmeiza 11 were superior while Sakha 94 and Shandaweel 1 were inferior depending upon their Yp, Ys and drought response indices. Also, a non-significant positive correlation was recorded between Yp and Ys of the studied cultivars with GMP, STI and HARM being significantly correlated with both Yp and Ys. Based on PCA, Yp and Ys explained 61.6 and 38.1% of the total variation; respectively. Furthermore, cluster analysis sequestered the concerned cultivars into drought susceptible cultivars (Shandaweel 1, Giza 168 and Gemmeiza 11), drought moderate ones (Misr 2, Sakha 93 and Sakha 94) and drought tolerant ones (Misr 1, Sids 13, Gemmeiza 9 and Sids 12) based on the mean values of YSI, RDI, TOL, SSI and YRR within each group.

Chl a fluorescence and proteomics reveal protection of the photosynthetic apparatus to dehydration in tolerant but not in susceptible wheat cultivars

Seedlings of spring wheat (Triticum aestivum L.) cultivars, Ethos and Zebra, differing in drought tolerance were dehydrated to reach a water saturation deficit (WSD) in leaves ~15, 30, and 50 %. Ethos, the drought tolerant cultivar, dried slower in comparison with Zebra and regrew in 70 % upon rehydration. The effect of dehydration on photosystem II was evaluated by Chl a fluorescence (OJIP transients). The inflection point of double normalized curves (ΔWOJ) calculated for Ethos was negative for seedlings with 15 % WSD, nearly zero for those with 30 % WSD, and about +0.05 for those with 50 % WSD. In case of Zebra, the 15 % WSD already induced a positive ΔWOJ (+0.05) and 50 % WSD maximized it to +0.10, which is a sign of drought susceptibility. The proteomic studies revealed, that among identified 850 spots, 80 protein spots were differentially expressed during dehydration. The differentially expressed proteins of the drought tolerant cultivar indicated the protection of the photosynthetic apparatus and proteome rebuilding in response to drought. In the drought susceptible cultivar, protection of proteins and membranes and partial scavenging reactive oxygen species appeared.

Saturation mapping of consistent QTLs for yield and days to flowering under drought using locally adapted landrace in rice (Oryza sativa L.)

Drought stress is a major constraint for rice production in rainfed ecosystems. Landraces are reservoir of genes that can help in breeding drought tolerant cultivars. Utilizing the genetic potential of these locally adapted resilient germplasm using quantitative trait loci (QTL) mapping and marker-assisted breeding (MAB) will hasten development of high yielding drought resilient cultivars. A total of 60 genomic regions linked to phenology and plant production traits under drought predominant in rainfed target populations of environment (TPE) were mapped using rice lines derived from a locally adapted landrace, Nootripathu and drought susceptible elite cultivar, IR20 evaluated in three drought stress and one non-stress experiments in the field. QTLs important in rice adaptation to drought have been saturated and refined with additional markers. For example, consistent QTL, RM8085-RM3825 on chromosome 1 for grain yield under drought in TPE, with additive effect from the landrace has been narrowed down to 42.8 Kb (from 1.6 Mb) between RM11873-RM3825. Another QTL for yield under drought was also identified at RM11943 on chromosome 1 with additive effect from IR20 and is also linked to sd1 locus governing plant height. Similarly, the consistent QTL detected for days to 50% flowering (DFF), between RM314-RM6836 on chromosome 6 was also narrowed down to 279.8 Kb (from 4.9 Mb) between RM19715-RM19727. This QTL also harbours Hd1 locus regulating heading date. A QTL for yield under drought was also mapped on chromosome 6 near RM314. Both these QTLs for DFF and yield are located within the meta-QTL for yield under drought (MQTL6.1). These consistent QTLs for yield and DFF under drought in TPE with linkage or pleiotropy to sd1 and Hd1 loci mapped using rice lines derived from locally adapted landrace may be useful in MAB of rice cultivars suitable for water-limited environments.

English

Experiments were conducted at Sokoine University of Agriculture in Morogoro, Tanzania to assess the growth performance and grain yield of ten maize cultivars under well-watered and water stressed conditions. The ten cultivars (CML 444, CML395, CML539, WE 4107, WE 2112, WE 3102, WE 4112 and WE 4116) obtained from Water Efficiency Maize for Africa (WEMA) project and two local market cultivars (‘STAHA’ and ‘TMV1’) were grown in a Randomized Complete Block design with a 10×3 factorial treatment arrangement and three replications. The three drought stress treatments were 50, 75 or 100% of field capacity with 10 kpa (equivalent to field capacity) and 30 kpa (drought) using tensiometers. Drought stress was initiated at vegetative stage (three weeks after emergence) for thirty days and flowering stage (one week before to two weeks after flowering). Plant height, stem diameter, leaf length, leaf width and chlorophyll content were measured at weekly intervals from two weeks after planting to maturity. Days to anthesis and silking were used to calculate Anthesis-Silking Interval (ASI) and kernel dry mass were recorded at harvest. Vegetative growth responses were not affected by water stress, but plant height and leaf chlorophyll content tended to decrease, while ASI ranging from 5.2 to 11.1 days and kernel dry mass decreased with increased drought stress. Dry kernel weight was significantly greater among five of the cultivars designated drought tolerant and the lowest in the two drought susceptible cultivars. Drought tolerant genes were expressed at different levels and only a few cultivars expressed all three genes at the vegetative and flowering stages. Thus, vegetative response of maize to drought stress varied based on cultivars. However, it appears that drought stress exerted more impacts on reproductive processes compared to vegetative. Key words: Cultivars, drought, genotypes, grain yield, growth performance, hybrids. &nbsp