Maize (Zea mays L.) landraces classified by drought stress tolerance at the seedling stage

Effect of drought and combined drought and heat stress on polyamine metabolism in proline-over-producing tobacco plants

High temperatures, drought, and salt stresses severely inhibit plant growth and production due to the effects of climate change. The Arabidopsis ARR1, ARR10, and ARR12 genes were identified as negative salt and drought stress regulators. However, in rice, the tolerance capacity of the hst1 gene, which is orthologous to the ARR1, ARR10, and ARR12 genes, to drought and multiple high temperature and drought stresses remains unknown. At the seedling and reproductive stages, we investigated the drought (DS) high temperature (HT) and multiple high temperature and drought stress (HT+DS) tolerance capacity of the YNU31−2−4 (YNU) genotype, which carries the hst1 gene, and its nearest genomic relative Sister Line (SL), which has a 99% identical genome without the hst1 gene. At the seedling stage, YNU demonstrated greater growth, photosynthesis, antioxidant enzyme activity, and decreased ROS accumulation under multiple HT+DS conditions. The YNU genotype also demonstrated improved yield potential and grain quality due to higher antioxidant enzyme activity and lower ROS generation throughout the reproductive stage under multiple HT+DS settings. Furthermore, for the first time, we discovered that the B−type response regulator hst1 gene controls ROS generation and antioxidant enzyme activities by regulating upstream and downstream genes to overcome yield reduction under multiple high temperatures and drought stress. This insight will help us to better understand the mechanisms of high temperature and drought stress tolerance in rice, as well as the evolution of tolerant crops that can survive increased salinity to provide food security during climate change.

Aegilops tauchii is a D-genome donor of hexaploid wheat and is a potential source of genes for various biotic and abiotic stresses including heat and drought. In the present study, we used multi-stage evaluation technique to understand the effects of heat and drought stresses on Ae. tauschii derived introgression lines (ILs). Preliminary evaluation (during stage-I) of 369 ILs for various agronomic traits identified 59 agronomically superior ILs. In the second stage (stage-II), selected ILs (i.e., 59 ILs) were evaluated for seedling heat (at 30°C and 35°C) and drought (at 20% poly-ethylene glycol; PEG) stress tolerance under growth chambers (stage-II). Heat and drought stress significantly reduced the seedling vigour by 59.29 and 60.37 percent, respectively. Genotype×treatment interaction analysis for seedling vigour stress tolerance index (STI) identified IL-50, IL-56, and IL-68 as high-performing ILs under heat stress and IL-42 and IL-44 as high-performing ILs under drought stress. It also revealed IL-44 and IL-50 as the stable ILs under heat and drought stresses. Furthermore, in the third stage (stage-III), selected ILs were evaluated for heat and drought stress tolerance under field condition over two cropping seasons (viz., 2020-21 and 2021-22), which significantly reduced the grain yield by 72.79 and 48.70 percent, respectively. Stability analysis was performed to identify IL-47, IL-51, and IL-259 as the most stable ILs in stage-III. Tolerant ILs with specific and wider adaptability identified in this study can serve as the potential resources to understand the genetic basis of heat and drought stress tolerance in wheat and they can also be utilized in developing high-yielding wheat cultivars with enhanced heat and drought stress tolerance.

Maize (Zea mays L.) landraces in the northern Guinea savanna and Sudan savanna in West and Central Africa appear to have some drought-adaptive traits. This study was initiated to assess the level of improvement in yield potential and other agronomic traits achieved under drought stress (DS) and in multiple locations (ML) after introgression of alleles from maize landraces into an elite maize variety (AK9443-DMRSR) via backcrossing. Six backcross (BC) populations together with recurrent parent (AK9443-DMRSR), a commercial hybrid (Oba Super-II), and an improved variety (TZLCOMP4C1) were evaluated under controlled DS and full irrigation (FI) during the dry seasons of 1999 and 2000, as well as in seven ML trials. No significant differences were observed among genotypes for grain yield and most of the traits measured under DS and FI. Significant differences were recorded among genotypes for grain yield and other agronomic traits measured in ML and across 11 environments. Drought stress reduced grain yields of the BC1F2 populations by 64% and recurrent parent by 71%. In ML trials, at least half of the populations were better than recurrent parent. The top three BC1F2 populations produced more grains than the recurrent parent (258–360 kg/ha) and Oba Super-II (555–657 kg/ha) with introgression of only 25% genome of the landraces. We concluded that backcross procedure was able to transfer a quantitative trait of grain yield of an elite recurrent parent into maize landraces. Additional backcross generations are needed for improved performance of the BC1F2 populations in drought-prone environments.

BackgroundDrought is one of the major constraints for plant productivity worldwide. Different mechanisms of drought-tolerance have been reported for several plant species including maize. However, the differences in global gene expression between drought-tolerant and susceptible genotypes and their relationship to physiological adaptations to drought are largely unknown. The study of the differences in global gene expression between tolerant and susceptible genotypes could provide important information to design more efficient breeding programs to produce maize varieties better adapted to water limiting conditions.Methodology/Principal FindingsChanges in physiological responses and gene expression patterns were studied under drought stress and recovery in three Mexican maize landraces which included two drought tolerant (Cajete criollo and Michoacán 21) and one susceptible (85-2) genotypes. Photosynthesis, stomatal conductance, soil and leaf water potentials were monitored throughout the experiment and microarray analysis was carried out on transcripts obtained at 10 and 17 days following application of stress and after recovery irrigation. The two tolerant genotypes show more drastic changes in global gene expression which correlate with different physiological mechanisms of adaptation to drought. Differences in the kinetics and number of up- and down-regulated genes were observed between the tolerant and susceptible maize genotypes, as well as differences between the two tolerant genotypes. Interestingly, the most dramatic differences between the tolerant and susceptible genotypes were observed during recovery irrigation, suggesting that the tolerant genotypes activate mechanisms that allow more efficient recovery after a severe drought.Conclusions/SignificanceA correlation between levels of photosynthesis and transcription under stress was observed and differences in the number, type and expression levels of transcription factor families were also identified under drought and recovery between the three maize landraces. Gene expression analysis suggests that the drought tolerant landraces have a greater capacity to rapidly modulate more genes under drought and recovery in comparison to the susceptible landrace. Modulation of a greater number of differentially expressed genes of different TF gene families is an important characteristic of the tolerant genotypes. Finally, important differences were also noted between the tolerant landraces that underlie different mechanisms of achieving tolerance.

Turf quality (TQ) decline due to drought is a major concern in cool‐season turfgrass management. The study was conducted to examine whether selected Texas (TBG) × Kentucky bluegrass (KBG) hybrids (HBGs) (Poa arachnifera Torr. × P. pratensis L.) exhibit improved drought stress tolerance and recuperative ability in comparison to commonly‐used KBG (P. pratensis) genotypes. Plant material included two HBG selections (HBG568 and HBG668), two commercially‐available HBGs (‘Thermal Blue’ and ‘Bandera’), and two KBG genotypes (‘Midnight’ and ‘Baron’). The experiment was conducted in field plots covered with a rainout shelter in 2006 and 2007 in North Brunswick, NJ. Treatments consisted of (i) well‐watered controls; (ii) drought stress (withholding irrigation) from June to August; and (iii) recovery (rewatering after a period of drought stress) in September and October. The HBGs Thermal Blue and Bandera generally did not show significant difference in turf growth from the two KBG genotypes in both years. HBG568 maintained significantly higher TQ, relative water content (RWC), cell membrane stability, and canopy density estimated as the reflectance ratio of infrared to red (IR/R, leaf area index) and normalized difference vegetation index (NDVI), compared with the two KBG genotypes and other HBGs following a prolonged period of drought stress (after 20 d of treatment) on most sampling dates in both years. HBG568 exhibited more rapid recovery of TQ, IR/R (IR935/R661), NDVI, and sod tensile strength than the other genotypes in both years, while HBG668 also had better recovery in 2007. The results demonstrate genetic variation in drought stress tolerance and recovery among HBGs and KBGs and the potential for the development of HBGs with improved tolerance to drought stress and performance during recovery.

Water is a precious commodity for plant growth and metabolism; however, its scarcity and saline sand conditions have a drastic effect on plant growth and development. The main objective of the current study was to understand how silicon (Si) application might help Black gram (Vigna mungo L.) against the negative impacts of salt stress and drought. The treatments of this study were: no silicon = 0 mg/kg; silicon = 40 mg/kg; control = no stress; drought stress = 50% field capacity (FC); salinity = 10 dSm-1; drought + salinity = 10 dSm-1 + 50% field capacity (FC). The findings showed that the application of silicon in the sand significantly affected growth indices such as leaf area (LA), shoot fresh weight (SFW), shoot dry weight (SDW), and shoot length (SL). Root length (RL) increased significantly up to 55.9% in response to drought stress. Applying Si to the sand increased the root length (RL) by 53.9%. In comparison to the control, the turgor potential of leaves decreased by 10.3% under salinity, while it increased by 44.7% under drought stress. However, the application of silicon to the sand significantly improved the turgor potential of leaves by 98.7%. Under both drought and salt stress, gas exchange characteristics and photosynthetic pigments dramatically decreased. Applying 40 mg/kg silicon to sand improved the gas exchange characteristics, protein contents, and photosynthetic pigments of plants under drought and salt stress, such as levels of chlorophyll (a, and b) increased by 18% and 26%, respectively. Under control conditions, the hydrogen peroxide (H2O2) concentration was lower but increased during periods of drought and salinity stress. The concentrations of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were decreased by salt and drought stress and increased by sand application of silicon at a rate of 40 mg/kg. Application of silicon at 40 mg/kg sand rate improved the growth and development under control and stress conditions. Overall, this study provides an extensive understanding of the physiological mechanisms underlying the black gram's ability to withstand under salt stress and drought stress by application of Si which will serve as a roadmap for future cellular research.

Drought stress, a major abiotic stress, severely limits sugarcane productivity through adversely altered cellular processes. Identifying key traits linked to physiological and biochemical responses during water stress and recovery is vital for screening and breeding drought stress-tolerant varieties. The present study assessed 18 sugarcane genotypes based on morpho-physiological, biochemical, and molecular changes during drought stress and at stress recovery in a complete randomized block design. Cane height, number of internodes, Soil Plant Analytical Development (SPAD) index, Leaf Area Index (LAI), Relative Water Content (RWC), Nitrate Reductase (NR), and proline were positively correlated to drought stress. Among the genotypes studied, AS-04-1687, AS-04-635, Co 86032, Co 85019, CoM 0265, AS-04-2097, and AS-04-245 were identified as potential clones with high potential for drought stress tolerance in sugarcane. Expression profiling of ten stress-induced genes, namely NAC, MYB59, peroxidase, GST (glutathione transferase), GLY I (glyoxylase I), GLY III (glyoxylase III), RAB (response to abscisic acid), CesA3 (cellulose synthase), heat shock proteins, and stress-related proteins in sugarcane stem tissues under drought-stressed conditions revealed significant differences between tolerant and susceptible genotypes. The interspecific hybrid, AS-04-1687, outperformed for all the genes under drought stress conditions and could be a potential donor in further drought tolerance breeding programmes. We have also cloned and characterised drought stress-induced transcription factor MYB59 (a negative regulator of Ca+ signalling), which could be used in genetic engineering programmes for the development of drought stress-tolerant genotypes.

Because of their local adaptation and economic factors that limit the adoption of commercial hybrids, farmer-saved maize landraces are still grown over a considerable area concentrated in southwest China. To evaluate the potential of using maize landraces, the germplasm characteristics of 96 landraces from southwest China were evaluated at phenotypic, cellular, and molecular levels. The existence of high phenotypic variation and elite germplasm tolerant to low-N, low-P, as well as drought stress was observed. Of the total landraces, 81.25, 7.29, 5.21, and 2.08% were found with 0, 1, 2, 3, and 4 B chromosomes. Using 42 microsatellite (simple sequence repeat) loci, 246 alleles were detected among the landraces. The number of alleles per SSR locus varied from 2 to 10, averaging 5.67 allele per locus, which revealed a high level of genetic diversity of maize landraces in southwest China. Cluster analysis showed that 96 landraces could distinctly be clustered into four groups, which tended to associate with their geographic origins. We propose that the genetic diversity center of maize landraces in southwest China might be in Sichuan. A sharp genetic deviation from Hardy-Weinberg equilibrium was observed from heterozygosity deficiency and a considerable genetic variation was revealed within, rather than among, the landraces. Based on their germplasm characteristics, the innovation and utilization of maize landraces in southwestern China for theoretical and applied research could be achieved by constructing heterosis groups, developing inbred lines with high combining ability, and maintaining the landraces with elite germplasm and B chromosomes using bulked pollen.

Plants have an inherent mechanism for perceiving drought stress and respond through a series of physiological, cellular and molecular changes for maintaining physiological water balance. It has been shown that nitrogen (N) and phosphate (P) can help to improve plant tolerance to water limitation by increasing the activities of the photosynthetic machinery and antioxidant enzymes. Maize is highly sensitive to drought stress, especially at the seedling stage. In this study, we used four maize genotypes (HKI-161, HKI-193-1, HQPM-1 and HQPM-7) and studied the effect of N and P application on response to drought stress and recovery at germination and seedling stage. We show that application of N and P had no effect on rate of germination but increased the seedling growth, chlorophyll content, malondialdehyde levels, proline, anthocyanin content, gas exchange parameters and antioxidant enzymes (APX, CAT and GR) during drought stress. The variation in the effect was visible across genotypes, but the observed changes indicate improved drought stress tolerance in the maize seedlings. During drought recovery, seedlings of HKI-161 and HKI-193-1 genotype that did not receive N and/or P treatment or that were pre-supplemented with only P showed rapid transition to flowering stages. Seedlings pretreated with N showed comparatively late transition to flowering. The HQPM-1 seedlings, which received N treatment moved to flowering stage while HQPM-7 seedlings showed only normal vegetative growth under all treatment conditions. Molecular analysis identified 2016 transcripts that are differentially expressed in the drought tolerant and susceptible genotypes. About 947 transcripts showed >3-fold change in expression and were expressed during stress tolerant genotype. Transcripts coding for proteins in P and N metabolism were identified within the drought regulated transcripts. The analysis showed that transcripts related to P metabolism were expressed during stress and recovery phases in the susceptible genotype while transcripts related to N metabolism were down regulated during drought stress and recovery stages in all the genotypes.

Elevated CO2 concentration affects plant responses to drought, but its effects on poststress recovery for perennial grass species with different growth habits are unclear. The objective was to determine how stoloniferous and bunch‐type grass species may exhibit differential responses to elevated CO2 concentration during drought stress and postdrought recovery upon rewatering due to different growth characteristics. Stoloniferous creeping bentgrass (Agrostis stolonifera L.) ‘Penncross’ and bunch‐type tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] ‘Sitka’ were grown at ambient CO2 (400 μl L−1) or elevated CO2 concentration (800 μl L−1) repeated in four growth chambers for 28 d, subsequently subjected to either irrigation (control) or drought stress (irrigation completely withheld) for 28 d, and then rewatered for 18 d. During drought stress, both species exposed to elevated CO2 maintained higher turf quality, leaf water content, and membrane stability than plants at ambient CO2. Elevated CO2 caused significant increases in the viability of stolon–node meristematic tissues in creeping bentgrass under drought stress and rapid regeneration of daughter plants during rewatering, as shown by increased shoot biomass and percent turfgrass cover. Elevated CO2 had no significant effects on the viability of crowns with meristematic tissues in tall fescue during drought nor shoot biomass or percent turfgrass cover during rewatering. The stoloniferous grass species was more responsive to elevated CO2 compared to bunch‐type species for poststress recovery, as creeping bentgrass rapidly regrew and recovered from drought damages. Such information is of great importance for making appropriate turfgrass selections and breeding improvements in growth habits in areas with prolonged drought and the anticipated rising CO2 levels.

Evaluation of osmoregulation and morpho-physiological responses of Borago officinalis under drought and salinity stress with equal osmotic potential

Raising crops for dry and saline lands: Challenges and the way forward.

Rhizobacteria that produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCd) that inhibits ethylene production may mitigate stress damages. The objectives of this study were to examine whether a novel strain of ACCd-producing bacteria, Paraburkholderia aspalathi "WSF23," promotes plant tolerance to drought stress and post-stress recovery and determine changes in metabolic profiles in leaves and roots associated with the positive ACCd-bacteria effects in cool-season perennial grass species. Creeping bentgrass (Agrostis Stolonifera L. cv. "Penncross") plants were inoculated with P. aspalathi "WSF23" and exposed to drought by withholding irrigation for 35 days, followed by re-watering for 15 days in growth chambers. Inoculated plants demonstrated increased turf quality, canopy density, and root growth during drought stress and more rapid re-growth upon re-watering. Metabolomic analysis demonstrated that inoculation with P. aspalathi "WSF 23" increased the content of metabolites in the metabolic pathways related to stress defense, including osmoregulation, cell wall stability, and antioxidant protection in both leaves and roots, as well as nitrogen metabolism in roots of creeping bentgrass exposed to drought stress. The promotion of post-stress recovery by P. aspalathi "WSF 23" was mainly associated with enhanced carbohydrate and pyrimidine metabolism and zeatin biosynthesis pathways in leaves and increased carbohydrates, biosynthesis of DNA and proteins, cellular metabolism, and TCA cycle activity in roots. These results provide insights into the metabolic pathways regulated by "WSF23," with the PGPR conferring improvements in drought stress tolerance and post-drought recovery in a perennial grass species.

This study aimed to assess the drought and heat stress tolerance of nine Tunisian maize populations and their potential stress tolerance mechanisms. Over two years, nine Tunisian maize populations were evaluated under five environments with varying stress levels and one optimal growth condition in Tunisia. This work formed part of a larger study that includes a total of 223 Mediterranean maize landraces. The nine Tunisian populations were specifically chosen to assess the behavior of landraces adapted to the drought and heat stress conditions prevalent in the southern Mediterranean. In all the locations, the trials followed an augmented design with five blocks and a total of five checks over the two-year study period replicated in each block.The study demonstrated that combined drought and heat stress severely reduced maize yield, with Tunisian landraces experiencing losses of 76% to 95% relative to optimal conditions. Factorial regression analyses were performed to provide a biological interpretation of the contribution of environmental and genotypic variables, as well as their interactions, to grain yield variability. The most representative genotypic covariates were plant height (PH) followed by the number of ears (NE), thousand-grain weight (1000GW), and aerial biomass, respectively, explaining 26%, 12%, 9%, and 8% of the total variability. The significant environmental covariates were cumulative hydric deficit (DHC) and the average anthesis silking interval (ASI_ENV) in each environment, representing 48% of the total environmental variation. The interaction between thousand-grain weight and cumulative hydric deficit had the highest contribution (9%) of interaction for grain yield. The factorial regression indicated that under stress conditions, maize plants appeared to adapt to maintain yield by increasing thousand-grain weight while reducing aerial biomass, number of ears, and grain number. This response likely reflects an enhanced capacity for efficient resource reallocation, supporting the plant's resilience under combined drought and heat stress conditions. The landraces BK, KAR, and MT2 consistently outperformed in most traits under stress conditions, showing significant tolerance and adaptability for across multiple stress levels with better yields and flowering synchronization. The selected best-performing populations could serve as valuable sources of drought and heat stress tolerance sources for future breeding programs.