Early Drought Research Articles

Identification of Drought Tolerant Mutant Lines of TEF [ERAGROSTIS TEF (ZUCC.) TROTTER


 
 
 Introduction: Tef [Eragrostis tef (Zucc.) Trotter] is the major food crop in Ethiopia where it is annually cultivated on about 30% of the total area allocated to cereals. The productivity of tef is, however, significantly reduced by drought which can occur at either the early or the late developmental stage of the crop.
 Methodology: A total of 10,000 EMS (ethyl methane sulfonate) mutagenized M2 tef populations were screened first for early and second for terminal drought tolerance. The performance of candidate lines was investigated using diverse agronomical and physiological parameters.
 Results and discussion: Several promising lines were obtained for both early and terminal drought tolerance. Among these, genotypes with outstanding performance were found for two drought tolerant tef lines targeting early drought tolerance (dtt2 and dtt13) and three terminal drought tolerant lines targeting terminal drought tolerance (tdt9, tdt15 and tdt19).
 Conclusions: Candidate lines for both early and terminal drought tolerance will play vital roles in deve- loping drought tolerance in tef improvement.
 KEY WORDS: DROUGHT TOLERANCE, ERAGROSTIS TEF, ORPHAN CROP, MOISTURE SCARCITY, TEF
 
 

Algerian durum wheat assessment for early drought tolerance shows landraces superiority

VIGOROUS seedling growth is important for good crop establishment, particularly under drought conditions. Our study was set out to identify useful traits and genotypes to enhance early drought tolerance of durum wheat. Two experiments were carried out. In the first one, thirty-five genotypes (Landrace and improved) were tested in a phytotron at germination and early seedling stages, subjected to three osmotic stress levels induced by polyethylene glycol PEG 6000 (0, -3, -6 bar). The second experiment was conducted in the field, with 27 out of the 35 genotypes. Root and shoot traits were measured at seedling stage in both experiments. High PEG 6000 treatment decreased final germination percentage (FGP) by 2.7% and delayed the time to reach 50% germination (t50) by 2.9h. Shoot length was the trait most affected by drought (40% reduction) as compared with other root traits, which even increased under drought, like root to shoot length ratio, root to shoot weight ratio, root dry weight and root number. Coleoptile length (CL) showed a contrasting relationship with other traits, it was negatively correlated in general under no stress, but with positive correlations under stress. Based on drought susceptibility index (DSI), Algerian wheat landraces were the most tolerant compared to modern genotypes. Correlations between traits measured in field and controlled conditions were low. CL could be a potential trait for screening drought tolerant genotypes. Algerian wheat landraces presented a clearly distinct ability for early drought tolerance, and could be a good resource for breeding programs.

Using Small Unmanned Aircraft Systems for Early Detection of Drought Stress in Turfgrass

ABSTRACTRecent advances in small unmanned aircraft systems (sUAS) and sensors may improve accuracy and efficiency in turfgrass research and management compared with conventional methods. We evaluated the ability of sUAS combined with ultra‐high spatial resolution remote sensing to detect early drought stress. Results were compared with ground‐based techniques in creeping bentgrass (Agrostis stolonifera L.) irrigated at different levels from well‐watered to severe deficit (100 to 15% evapotranspiration [ET] replacement). Small UAS‐based measurements with a modified digital camera included three reflectance bands (near infrared [NIR, 680–780 nm] and overlapping green [G] and blue [B] bands [400–580 nm]) and eight derived vegetation indices (VIs). Ground‐based measurements included soil volumetric water content (VWC), turfgrass quality (TQ), green cover (GC), soil temperature (Tsoil), and reflectance with handheld optical sensors. Declines in VWC in deficit‐irrigation treatments were detected with NIR and six of eight VIs from sUAS, and the normalized difference vegetation index (NDVI) and red band reflectance from a handheld sensor, before symptoms appeared in TQ and GC. The most consistently sensitive parameters of sUAS throughout the 3‐yr study were NIR and GreenBlue VI [(G − B)/(G + B)], which detected drought stress >5 d before decreases in TQ. Results indicate that ultra‐high spatial resolution remote sensing with sUAS detected drought stress before it was visible to a human observer and could be valuable for improving irrigation management in turfgrass.

Screening for drought resistance during germination of modern and old Iberian wheat cultivars

Abstract Climate change is expected to reduce water availability in several wheat (Triticum aestivum L.) growing areas. Drought, during and immediately after sowing can compromise germination, seedling development, and ultimately crop yield. Our study’s objective was to investigate early drought stress resistance and evaluate genetic diversity of four bread wheat cultivars – three modern elite germplasm lines (‘Antequera’, ‘Jordão’ and ‘Roxo’) and an ancient Portuguese cultivar (‘Mestiço’) – at five water potentials, ranging from 0 to –1.5 MPa. Germination was annotated daily during eight days. Dry and fresh weights as well as root and shoot growth were measured. Genetic variability among cultivars was evaluated using start codon targeted (SCoT) markers. Overall, when water potential was lowered, germination rate and seedling growth were delayed. Final germination percentages were only affected by the higher stress intensity. This study reinforces the importance of research into ancient wheat cultivars, such as ‘Mestiço’. This cultivar showed the highest genetic difference when compared with the remaining cultivars. ‘Mestiço’ presented the highest coleoptile size, high vigor index values, and the lowest variation in water content due to stress conditions. Therefore, it may be able to germinate in extremly dry soil and be the least affected by drought stress. Still, due to the comparatively reduced yield of older wheat cultivars, stress tolerance should be researched within elite cultivars. Among these, Jordão revealed particularly good germination and early biomass development characteristics across water potentials, presenting a likely choice for future studies under drought stress conditions.

Norway Spruce (Picea abies L.) Provenances Use Different Physiological Strategies to Cope with Water Deficit

Research Highlights: In this study, we found different regulatory mechanisms in two contrasting provenances of Norway spruce responding to progressive drought stress. Background and Objectives: In the context of climate and environmental changes, the following question of high importance in scientific studies is: How will Norway spruce, which forms a dominant component in European mountain and boreal forests, be able to cope with the increasing frequencies and intensities of drought periods? The aim of the study was to investigate the physiological responses of eight-month-old seedlings, as a most vulnerable phase of forest tree life, for different spruce provenances, to find out variable strategies in relation to controlled drought stress. Materials and Methods: We performed an experiment under controlled conditions with spruce seedlings from a climatologically warmer stand of 410 m above sea level (a.s.l.), and a moderately cool stand of 931 m a.s.l. The soil water content, leaf predawn water potential, the osmotic potential of needles, the relative water content of needles, and the photosynthetic performance and the contents of primary metabolites (proline and abscisic acid) were investigated as indicators of the spruce seedlings’ responses to water stress. The status of the indicators was analyzed at different temporal intervals, using repeated measures analysis of variance (ANOVA), reflecting the seedlings’ water conditions (early drought, drought, or recovery). On a daily basis, the differences among the indicators were tested with one-way ANOVA. A principal component analysis (PCA) was used to identify the provenance-specific responses of tree drought indicators in a multi-dimensional data set. Results: The responses to drought stress differed between the provenances. Whereas seedlings of ‘warm’ provenance from a low altitude performed a conservation strategy, with high amounts of accumulated abscisic acid and closing the stomata faster, the reactions of ‘cool’ provenance seedlings from a higher altitude were not so sensitive and the plants’ water supply and photosynthetic performance remained significantly higher. These findings indicate that a higher drought resistance in ‘cool’ provenance could be related to greater amounts of proline amino-acids, which are accumulated from the beginning of the drought simulation. Furthermore, proline accumulation resulting in increased stress tolerance is controlled through another mechanism than osmotic adjustment. Conclusions: The observed variations in the regulatory mechanisms used to develop adaptive strategies in different provenances are an important factor for seedling survival under a changing climate.

Observing Severe Drought Influences on Ozone Air Pollution in California.

Drought conditions affect ozone air quality, potentially altering multiple terms in the O3 mass balance equation. Here, we present a multiyear observational analysis using data collected before, during, and after the record-breaking California drought (2011-2015) at the O3-polluted locations of Fresno and Bakersfield near the Sierra Nevada foothills. We separately assess drought influences on O3 chemical production ( PO3) from O3 concentration. We show that isoprene concentrations, which are a source of O3-forming organic reactivity, were relatively insensitive to early drought conditions but decreased by more than 50% during the most severe drought years (2014-2015), with recovery a function of location. We find drought-isoprene effects are temperature-dependent, even after accounting for changes in leaf area, consistent with laboratory studies but not previously observed at landscape scales with atmospheric observations. Drought-driven decreases in organic reactivity are contemporaneous with a change in dominant oxidation mechanism, with PO3 becoming more NO x-suppressed, leading to a decrease in PO3 of ∼20%. We infer reductions in atmospheric O3 loss of ∼15% during the most severe drought period, consistent with past observations of decreases in O3 uptake by plants. We consider drought-related trends in O3 variability on synoptic time scales by analyzing statistics of multiday high-O3 events. We discuss implications for regulating O3 air pollution in California and other locations under more prevalent drought conditions.

English

The low national   tef productivity is mainly attributed by lack of improved agronomic practices.  The row planting and transplanting is one of the promising planting techniques proved to boost the yield of tef. The objective was to determine the optimum seed rate, row, broadcasting and plant population in intra and inter row spacing of transplanted tef. A field experiment was carried out at Laelay maychew and Naeder adet for two years. The experiment was laid out in RCBD with three replications having 3×3 (9 m2)  and seven treatments.  The analysis of variance showed that there were a significance difference at (P≤0.001) for days to maturity, plant height and panicle length, whereas grain yield was significantly difference at (P≤0.01). The treatment with transplanting 20 cm intra row spacing distance resulted in the highest grain yield of 2586 kgha-1 followed by broadcasting at 5 kgha-1 (2547.2 kgha-1). Even though there was a significant difference among the treatments, combined mean performance of grain yield showed that there was no statically significant difference mainly among treatments of transplanting with 20×20 and 20×15 cm inters and intra row spacing and broadcasting at 5 kg ha-1 which was recorded as the higher grain yield. The present study recommended that the use of the broadcasting with seed rate of 5 kgha-1 and even though the transplanting is a labor consumer, it might be important for early drought faced tef growing areas with intra row spacing of 20×15 cm depending on the rain fail condition. Further tef planter machine development for lower seed rate is needed. Key words: Tef transplanting, seeding rate, row spacing. &nbsp

Identification of Drought Tolerant Mutant Lines of Tef [Eragrostis Tef (Zucc.) Trotter

Introduction: Tef [Eragrostis tef (Zucc.) Trotter] is the major food crop in Ethiopia where it is annually cultivated on about 30% of the total area allocated to cereals. The productivity of tef is, however, significantly reduced by drought which can occur at either the early or the late developmental stage of the crop. Methodology: A total of 10,000 EMS (ethyl methane sulfonate) mutagenized M2 tef populations were screened first for early and second for terminal drought tolerance. The performance of candidate lines was investigated using diverse agronomical and physiological parameters. Results and discussion: Several promising lines were obtained for both early and terminal drought tolerance. Among these, genotypes with outstanding performance were found for two drought tolerant tef lines targeting early drought tolerance (dtt2 and dtt13) and three terminal drought tolerant lines targeting terminal drought tolerance (tdt9, tdt15 and tdt19). Conclusions: Candidate lines for both early and terminal drought tolerance will play vital roles in developing drought tolerance in tef improvement.

Drought stress induces a biphasic NO accumulation in Arabidopsis thaliana

ABSTRACTWe have recently reported the proteomic signature of the early (≤30 min) drought stress responses in Arabidopsis thaliana suspension cells challenged with PEG. We found an over-representation in the gene ontology categories “Ribosome” and “Oxidative stress along with an increased abundance of late embryogenesis abundant (LEA) and early response to dehydration (ERD) proteins. Since nitric oxide (NO) plays a pivotal role in plant responses to drought stress and induces LEA and DREB proteins, here we monitored the levels of NO in Arabidopsis cell suspensions and leaf disks challenged with PEG, and performed comparative analyses of the proteomics and transcriptomics data in public domain to search for a common set of early drought and NO responsive proteins.We show that under drought-stress, NO shows a biphasic time course, much like in response to ozone stress and that among the early drought and NO responsive proteins, the categories “DNA binding”, “Nucleotide binding” and “Transcription regulator activity” are enriched. Taken together, present study suggests that in Arabidopsis the changing NO levels may play a critical role in early drought responsive processes and notably in the transcriptional and translational reprograming observed under drought stress.

Comparative analysis of two sister Erythrophleum species (Leguminosae) reveal contrasting transcriptome-wide responses to early drought stress

With the ongoing climate change, African rainforests are expected to experience severe drought events in the future. In Africa, the tropical genus Erythrophleum (Fabaceae) includes two forest sister timber tree species displaying contrasting geographical distributions. Erythrophleum ivorense is adapted to wet evergreen Guineo-Congolian forests, whereas E. suaveolens occurs in a wider range of climates, being found in moist dense forests but also in gallery forests under a relatively drier climate. This geographical distribution pattern suggests that the two species might cope differently to drought at the genomic level. Yet, the genetic basis of tolerance response to drought stress in both species is still uncharacterized. To bridge this gap, we performed an RNA-seq approach on seedlings from each species to monitor their transcriptional responses at different levels of drought stress (0, 2 and 6 weeks after stopping watering seedlings).Monitoring of wilting symptoms revealed that E. suaveolens displayed an earlier phenotypic response to drought stress than E. ivorense. At the transcriptomic level, results revealed 2020 (1204 down-regulated/816 up-regulated) and 1495 differentially expressed genes (DEGs) in response to drought stress from a total of 67,432 and 66,605 contigs assembled in E. ivorense and E. suaveolens, respectively. After identifying 30,374 orthologs between species, we found that only 7 of them were DEGs shared between species, while 587 and 458 were differentially expressed only in E. ivorense or E. suaveolens, respectively. GO and KEGG enrichment analysis revealed that the two species differ in terms of significantly regulated pathways as well as the number and expression profile of DEGs (Up/Down) associated with each pathway in the two stress stages. Our results suggested that the two studied species react differently to drought. E. suaveolens seems displaying a prompt response to drought at its early stage strengthened by the down-regulation of many DEGs encoding for signaling and metabolism-related pathways. A considerable up-regulation of these pathways was also found in E. ivorense at the late stage of drought, suggesting this species may be a late responder. Overall, our data may serve as basis for further understanding the genetic control of drought tolerance in tropical trees and favor the selection of crucial genes for genetically enhancing drought resistance.

Distinctive phytohormonal and metabolic profiles of Arabidopsis thaliana and Eutrema salsugineum under similar soil drying.

Arabidopsis and Eutrema show similar stomatal sensitivity to drying soil. In Arabidopsis, larger metabolic adjustments than in Eutrema occurred, with considerable differences in the phytohormonal responses of the two species. Although plants respond to soil drying via a series of concurrent physiological and molecular events, drought tolerance differs greatly within the plant kingdom. While Eutrema salsugineum (formerly Thellungiella salsuginea) is regarded as more stress tolerant than its close relative Arabidopsis thaliana, their responses to soil water deficit have not previously been directly compared. To ensure a similar rate of soil drying for the two species, daily soil water depletion was controlled to 5-10% of the soil water content. While partial stomatal closure occurred earlier in Arabidopsis (Day 4) than Eutrema (from Day 6 onwards), thereafter both species showed similar stomatal sensitivity to drying soil. However, both targeted and untargeted metabolite analysis revealed greater response to drought in Arabidopsis than Eutrema. Early peaks in foliar phytohormone concentrations and different sugar profiles between species were accompanied by opposing patterns in the bioactive cytokinin profiles. Untargeted analysis showed greater metabolic adjustment in Arabidopsis with more statistically significant changes in both early and severe drought stress. The distinct metabolic responses of each species during early drought, which occurred prior to leaf water status declining, seemed independent of later stomatal closure in response to drought. The two species also showed distinct water usage, with earlier reduction in water consumption in Eutrema (Day 3) than Arabidopsis (Day 6), likely reflecting temporal differences in growth responses. We propose Arabidopsis as a promising model to evaluate the mechanisms responsible for stress-induced growth inhibition under the mild/moderate soil drying that crop plants are typically exposed to.

Yield, N Uptake and N Utilization of Early Maturing, Drought and Striga-Tolerant Maize Varieties under Low N Conditions

ABSTRACT Performance under sub-optimal nitrogen (N) conditions, of early maturing maize cultivars bred for tolerance to drought and Striga parasitism in the Nigerian savanna is not known. This study evaluated the tolerance of selected early maturing drought and Striga-tolerant maize cultivars to low N conditions in Northern Nigeria. The cultivars were evaluated at 30 and 100 kg N ha−1. The varieties were compared with an improved maize cultivar that is not tolerant to drought and Striga. Maize grain yield was 26% higher at 100 kg N ha−1 than at 30 kg N ha−1 in 2010 and 161% higher100 kg Nha−1 than at 30 kg Nha−1 in 2011. The drought and Striga-tolerant varieties produced consistently higher yields than the non-drought-tolerant variety particularly at 30 kg Nha−1. These cultivars also accumulated higher amount of N, had higher N-uptake efficiency or N-utilization efficiency than the non-drought-tolerant variety ACR 95 TZE-COMP4 C3. Grains yield at low nitrogen rate was associated with high ears m−2, high dry matter accumulation, high grains m−2, suggesting that these traits are linked to low-N tolerance. The good performance of the drought-tolerant maize varieties under low N suggests that varieties developed for drought tolerance may be tolerant to low-N conditions.

Drought escape can provide high grain yields under early drought in lentils

In the current context of climate change, evaluation of intraspecific genetic and phenotypic variability of lentil (Lens culinaris Medik) in response to early droughts is fundamental to gain novel insight on the adaptive potential of lentil to water deficit. Here we studied in the field the variability of functional traits, leaf biochemical composition and yield components of three Spanish lentil cultivars submitted to an atypically dry spring. The genetic variability was also studied using amplified fragment length polymorphisms based on 156 polymorphic bands. The vulnerability of the cultivars to future drier scenarios was assessed and we identified potential traits related with lentil’s tolerance to early water deficit. Inter-cultivar variability was found in the response pattern of stomatal conductance to water availability but also in other functional traits and yield components. The small-seeded commercial cultivar PAR had the highest harvest index, grain yield, maximum stomatal conductance, stomatal density and specific leaf area while the lowest root-to-shoot ratio. PAR also had early flowering and the shortest life cycle as well as high leaf polyphenol and carotenoid contents. Therefore, the drought escape strategy exhibited by PAR could be beneficial under dry springs in Mediterranean environments. In contrast, despite the big-seeded non-commercial traditional cultivar MAN displayed drought tolerant traits and high genetic and phenotypic variability, it had the lowest grain yield, suggesting that MAN is less valuable than PAR as a source of early drought resistance for the genetic improvement of lentils.

To what extent is drought‐induced tree mortality a natural phenomenon?

AbstractAimCatastrophic forest mortality due to more extreme rainfall deficits and higher temperatures under future climate scenarios has been predicted. The aim of this study is to explore the magnitude of historical drought‐induced tree mortality under pre‐warming conditions.LocationNorth‐eastern Australia.Time period1845–2017.Major taxa studiedTrees.MethodsField survey, historical analysis and climate analysis.ResultsWe present evidence of 18%–30% tree mortality from recent droughts across three regions of north‐eastern Australia with rainfall deficits less severe than earlier historical droughts. The corrected temperature record represents modest warming at the stations with long records in the vicinity of the study areas. In terms of rainfall deficit the most severe drought on record occurred in the early 20th century, and historical evidence confirms that this drought and earlier droughts before the advent of pastoralism coincided with substantial tree mortality.Main conclusionsDramatic declines in woody biomass in response to drought historically occurred more than once a century and are a natural phenomenon in semi‐arid Australia. The magnitude of drought‐induced tree mortality under natural climate fluctuations requires further investigation in other continents. Widespread drought‐induced tree mortality is not just a recent global change phenomenon and has been underestimated as a natural ecological process. However, even more severe forest die‐off events from more extreme hotter droughts are predicted if Earth’s warming proceeds as currently projected.

Fore-warning of early season agricultural drought condition over Indian region – a fractional wetness approach

Fore-warning plays an essential role for effective drought mitigation planning. A new approach, i.e. fractional wetness (fw), has been proposed towards fore-warning of early season agricultural drought over Indian region. The optimum soil moisture triggers the subsequent crop sowing activities that has been conceptualized in this approach. Shortwave Angle Slope Index (SASI) images derived from time-series (2001–2012) MODIS data was used for fractional-wetness (fw) computation. fw is the surrogate indicator for the percentage moisture available for a given time, based on its long-term range. The zone-wise fwthresholds was developed to estimate the area-favourable-for-crop-sowing (AFCS), which was validated with subsequent months’ crop-planted-area derived from fractional vegetation cover (fc). The mean absolute error (MAE) was found to be ∼5.73% of the agricultural area. The present methodology is capable of fore-warning the agricultural-drought one month prior to the traditional method. Moreover, the comparison of predicted AFCS with all India food-grains area corroborates the feasibility of proposed approach in quantifying the agricultural-drought, in terms of its intensity, extent and progression.

ІНДЕКСАЦІЯ МЕТЕОРОЛОГІЧНОЇ ПОСУХИ

Drought is a serious extreme climatic event that negatively affects the physical environment and water systems causing disruptions in the hydrological cycle of the region. This is a stochastic natural hazard caused by persistent rainfall scarcity. The life cycle of the drought begins with a meteorological phenomenon, and further influence is realized throughout the hydrological cycle. Adequate measures are needed to respond and mitigate the various effects of drought. Developing and implementing drought mitigation and response strategies requires understanding the various indicators used to study drought. Drought characteristics are an important condition that allows both retrospective analysis and forward planning – risk assessment. Thus, it is necessary to objectively identify the events of drought by time, duration, scale and severity of manifestation. This can be implemented with integrated indicators that involve the main characteristics of the drought. More than 150 drought indices have now been proposed, some of which are perceived as operational information used to characterize drought through maps at regional and national levels. By quantifying the level of severity and announcing the onset and end of drought, drought indices are now assisting in a variety of operations, including early warning, drought monitoring and contingency planning. Despite their diversity and continuous development, it is important to provide a comprehensive overview of the available weather indicators, which highlights their differences and studies their trends and which can be used in a special given manner regional climate.

Thermal Imaging Detects Early Drought Stress in Turfgrass Utilizing Small Unmanned Aircraft Systems

Thermal Imaging Detects Early Drought Stress in Turfgrass Utilizing Small Unmanned Aircraft Systems

Reaction of some rapeseed (Brassica napus L.) genotypes to different drought stress levels during germination and seedling growth stages

Drought is a major abiotic stress that affects seed germination and plant growth in arid and semi-arid regions. Rapeseed is an oilseed crop adapted to Mediterranean area; however, it is reported that it is sensitive to water stress occurring during seed germination. In this study, we investigated how seed germination and early seedling growth of six rapeseed genotypes were influenced by different water stress levels. In addition to the control (absence of drought stress), three drought levels were simulated using three osmotic potentials of polyethylene glycol (PEG-6000), −9, −10 and −11 bars. A completely randomized design with three replications was used for this experiment. Germination percentage (GP), shoot length (SL), root length (RL), shoot elongation rate (SER) and root elongation rate (RER) were determined to evaluate the genotypes response to PEG-induced drought stress. Results showed drought stress, genotype and interaction stress × genotype had a significant effect on the studied parameters. GP decreased with the increase in stress level. The genotype ‛Nap9’ was the most interesting, having the highest GP values, namely 63.33, 62.67 and 28% under the stress levels −9, −10 and −11 bars, respectively. The genotype ‛H2M-5’, which ranked second with respect to this parameter, was statistically comparable to ‛Nap9’. Also, SL, RL, SER and RER decreased with the increase in drought stress level. However, the studied genotypes reacted differently to various water stress levels. Once again, the genotype ‛H2M-5’ exhibited the highest average RL and RER under all drought levels. Particularly, for severe drought conditions (−11 bars), ‛H2M-5’ had an average RL of 1.54 cm and RER of 0.36 cm/d. Field evaluation under controlled conditions is needed to confirm findings of the present experiment. The mutant ‛H2M-5’ could be a valuable and promising germplasm for developing a performant and adapted variety to be designed for harsh environments particularly characterized by early drought coinciding with germination and seedling growth stages.

Thermal Imaging Detects Early Drought Stress in Turfgrass Utilizing Small Unmanned Aircraft Systems

Core Ideas Canopy temperature via measurements in turfgrass via drones have not been assessed. Rises in canopy temperature were detected before visible drought symptoms. This early detection was similar to top spectral parameters on companion flights. Canopy temperature was closely correlated with spectral data. Recent advances in aerial platforms and thermal imaging provide opportunities to improve water management in turfgrass, but research on this topic is limited. Our objectives were to: (i) evaluate the ability of canopy temperature (Tc) imaging from small unmanned aircraft systems (sUAS) to detect drought stress early in turfgrass; (ii) compare early drought‐stress detection ability of Tc measurements with that of sUAS‐mounted and handheld optical sensors; and (iii) evaluate thermal data's relationship to spectral reflectance from sUAS‐mounted and handheld sensors, soil volumetric water content (VWC), soil temperature, turfgrass visual quality (VQ), and percentage green cover (PGC). The study was conducted during summer 2017 on creeping bentgrass (Agrostis stolonifera L.) irrigated with 15 to 100% evapotranspiration (ET) replacements to impose a gradient of drought stress. Airborne spectral reflectance measurements included three bands (near infrared [NIR, 680–780 nm], green and blue bands [overlapped, 400–580 nm]) and eight derived vegetation indices. Results indicated Tc measurements via the sUAS detected rises of Tc in 15 and 30% compared with 100% ET plots, corresponding with declines in VWC, before drought stress became visible. This was comparable to the best spectral parameters on companion flights, and Tc was closely correlated with spectral data from sUAS‐mounted (|r| = 0.52–0.69) and handheld sensors (|r| = 0.75–0.82). Thermal data were more strongly correlated with turfgrass VQ (r = −0.60 to −0.77) and PGC (r = −0.58 to −0.78) than with VWC (r = −0.43 to −0.63) and soil temperature (|r| = 0.27–0.41).

Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy. Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses-in particular, regulation of ABA accumulation-remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5' untranslated region (5' UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3 Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress. These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations. These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.