Moderate Drought Stress Conditions Research Articles

Improvement of the yield and essential oil of fennel (Foeniculum vulgare Mill.) using external proline, uniconazole and methyl jasmonate under drought stress conditions

Drought stress is a significant environmental constraint that seriously limits crop productivity. A two-year field study was carried out as a split plot based on a randomized complete block design (RCBD) with three replicates in the experimental station of the agricultural faculty of Azarbaijan Shahid Madani University, Tabriz, Iran. This study evaluated the impacts of various irrigation regimes and plant growth regulators/proline on yield, its components, and essential oil content. Water shortage led to considerable decreases in umbels per plant, umbellets per umbel, fruits per umbellet, 1000-fruit weight, biological yield, and finally, fruit yield, despite increases in fruit essential oil content under moderate drought stress conditions. External methyl jasmonate, uniconazole, and proline significantly increased these parameters measured in fennel plants compared with the control. Improved effects of external plant growth regulators/proline tended to be greater in drought-stress plants, as it enhanced yield, its components, and fruit essential oil content compared with control. Foliar spraying, particularly methyl jasmonate, and uniconazole, enhanced e- anethole content under drought stress. Fenchone and methyl chavicol contents increased in plant growth regulators/proline-treated plants when they were kept under moderate drought stress conditions; however, their contents decreased by the severity of drought stress apart from the application of methyl jasmonate. Hence, applying these PGRs or proline could be critical in cultivating fennel plants under water shortage conditions to achieve higher essential oils yield and its constituents, particularly anethole, compared with control.

Wheat breeding for early heading: Does it improve grain yield under drought stress and well-watered conditions?

Terminal drought stress strongly affects wheat grain yield under Mediterranean conditions. Therefore, developing early-heading bread wheat cultivars in these conditions is an important breeding strategy. In the present research, earliness was transferred from the Australian cultivar, Excalibur, to three Iranian cultivars, Roshan, Kalheydari and Mahdavi, in separate backcross (BC) breeding programs from 2012 to 2018. The earliest and latest heading genotypes of each BC 3 population, were selected as near-isogenic lines (NILs). NILs and their parents were assessed under diverse field conditions including rain-fed, moderate drought stress and well-watered conditions in three locations, Kerman, Sepidan and Semirom, during two growing seasons, 2018–2019 and 2019–2020. Breeding for early heading significantly improved earliness in all genetic backgrounds and increased grain yield by 36.4% and 9.6%, in the rain-fed and moderate drought stress conditions, respectively. Whereas, grain yield was not significantly affected by early heading under well-watered conditions. Results showed that breeding for early heading, a highly heritable trait, is an appropriate method to increase grain yield and reduce water consumption under drought stress and well-watered conditions, respectively. Based on these findings, we recommend transferring early heading to high yield late heading commercial cultivars using backcrossing. • For the first time, near isogenic lines of early heading were developed. • Breeding for early heading increased grain yield by 36.4% in rain-fed conditions. • Early heading increased grain yield by 9.6% in moderate drought stress conditions. • Early heading did not affect grain yield under well-watered conditions in Kerman.

تأثیر کتیرا روی برخی خصوصیات مورفوفیزیولوژیک و مرتبط با عملکرد دانه گیاه سیاهدانه (Nigella sativa L.) تحت شرایط خشکی

Introduction In fact, drought is stress that restricts the plant photosynthesis and causing changes in the chlorophyll content and damage to photosynthetic structures. One of the important reasons that environmental stresses such as drought reduce the growth and photosynthesis ability of the plant is a disturbance in the balance between production and removal of free oxygen radicals. Transpiration is a necessary process for photosynthesis and growth of plants but depending on the conditions may be harmful in some cases, so that the use of anti-transpirant can be one of the most effective methods for reducing the amount of water lost through transpiration and effective way to reduce the effects of drought stress on plants and adjustment the reduction of the yield due to water deficiency in arid and semi-arid regions. Climate change created in the world and the intensification of stresses caused by it, especially drought stress in arid and semi-arid regions such as Iran, make it difficult to achieve this goal. Therefore, finding strategies that can reduce the effects of water shortages on plant growth and yield and improve growth and yield can be very important. The aim of the present study was to investigate the effect of irrigation regimes and application of different concentrations of tragacanth (naturally dried exudate from some Astragalus species) on black cumin plant. Materials and Methods This research was carried out in a factorial experiment based on completely randomized design with three replications in a greenhouse of the Agriculture College of Kurdistan University in 2018. The experimental factors were including irrigation at three levels of 100% (full irrigation), 70% (mild drought stress), and 40% (severe drought stress) of field capacity of soil and spraying with tragacanth extract at six concentrations of 0, 1.25, 2.5, 5, 7.5, and 10 g/L. Spraying of this material was done using a back sprayer (Shark model) with a constant pressure of 2.4 bar and a volume of 250 liters of water per hectare. Before the data were analyzed, their normality test was performed using the Mini Tab software. After ensuring the normality of data, analysis of variance was performed using SAS ver. 9.3. LSD (Least significant difference) was used to compare the mean of treatments. The graphs are drawn using Excel software. Results and Discussion The results showed that increased drought stress intensity (irrigation reduction) led to the reduced leaf relative water content, Total chlorophyll content, efficiency of photosystem II, plant hight, number of capsules per plant, mean number of seeds per plant, biological yield and grain yield. The positive effects of tragacanth consumption on reducing and modifying the effects of drought stress on different levels of irrigation and different concentrations of tragacanth were different. In the present study, under full irrigation conditions, lower concentrations of tragacanth were useful, while in drought stress conditions, higher concentrations of tragacanth (except 10 g/L) were useful. In full irrigation, the concentration of 1.25 g/L was positive for all studied traits. In mild drought stress, the use of higher concentrations of tragacanth up to 5 g/L had the best effect and more concentrations resulted in a reverse effect on studied traits. In severe drought stress, the use of more concentrations of tragacanth extract was beneficial and improved the studied traits up to 7.5 g/L, but 10 g/L had a negative effect on these traits. Considering the effect of proper concentration of this material on the improvement of measured traits and increasing the grain yield compared to non-application of tragacanth under severe and moderate drought stress conditions by 11.6% and 28.2%, respectively. Conclusion The results of this study indicated the different effects of various concentrations of tragacanth material in different levels of irrigation on studied traits of black cumin. Therefore, it can be concluded that the application of different concentrations of tragacanth gum was completely dependent on the plant's water status. So that, using higher concentrations of tragacanth gum in drought stress conditions had a more positive effect on the plant, and vice versa, using a lower concentration of this material was useful in full irrigation. The effect of tragacanth gum on reducing and modifying the effects of drought stress in different plants requires further studies and extensive research. Tragacanth gum can be introduced as a new anti-transpirant agent with natural origin and its application can be useful and recommended in areas exposed to drought stress.

The singular and combined effects of drought and copper stresses on the morphological traits, photosynthetic pigments, essential oils yield and copper concentration of Fumaria parviflora Lam.

High concentrations of copper (Cu) can be extremely toxic for plant growth. Drought stress is also considered as a major environmental tension, as it reduces vegetative growth in medicinal plants. This study evaluated the singular and combined effects of several Cu concentrations (0, 50, 150, 300, and 400 mg kg−1) and various drought stresses (non-stress, moderate, and severe) on the different vegetative traits, photosynthetic pigments, essential oils (EOs) yield, and Cu accumulation (in roots, shoots, and distilled plant material) of Fumaria parviflora Lam. under field conditions. The seeds were collected from four zones (Z1, Z2, Z3, and Z4) located in two mineral regions (Askari and Rabor) of Kerman, Iran. Drought and Cu, both independently and combined, suppressed plant growth by decreasing different vegetative growth parameters. The Cu concentration of 50 mg kg−1 yielded the highest values in all morphological traits and photosynthetic pigments. These included the dry weight and length of both shoot and root, chlorophyll content under non-drought stress, and carotenoid content under moderate drought stress. The growth parameters and photosynthetic pigments of F. parviflora declined sharply at Cu concentrations of 300 and 400 mg kg −1. The highest EOs yield (0.56% v/w) was obtained by applying 150 mg kg−1 Cu under moderate drought stress conditions in zones Z3 and Z4. In the distilled plant material, Cu concentration was almost similar to its concentration in shoots before the distillation process. Under moderate drought and up to a Cu concentration of 150 mg kg−1, the shoot growth parameters and photosynthetic pigments were slightly less than the control. Moreover, the EOs yield was at its highest, and Cu was mainly accumulated in the roots and only slightly transferred to the shoot. Therefore, to use the shoot and EOs of F.parviflora for medicinal purposes, it is recommended that this plant be cultivated under moderate drought in stressed soils at a maximum copper concentration of 150 mg kg−1.

Silicon mitigates the effects of moderate drought stress in cover crops

AbstractCover crops are important components of sustainable agricultural systems under no‐till conditions. However, in the Brazilian Cerrado region, plant growth and straw production on the soil surface have been hampered by insufficient soil water availability during off‐season. A pot experiment was conducted to investigate the effect of silicon fertilization on the morphological and physiological characteristics of cover crops under drought stress conditions. We hypothesized that silicon could mitigate the adverse effects of drought stress because of its role in improving the photosynthetic process and antioxidant defence mechanisms of plants. Thus, two silicon fertilizer levels (0 and 180 mg/kg of Silicon), three grass cover crops (Urochloa brizantha cv. BRS Piatã, U. brizantha cv. Marandu and Pennisetum glaucum cv. ADR 300) and three drought stress levels (100% pot capacity (PC): well‐watered conditions, 50% PC: moderate water stress and 25% PC: severe water stress) were laid out as a randomized block design in a factorial arrangement and replicated four times. Morphophysiological characteristics were recorded after 22 days of exposure to drought stress. Drought stress decreased the growth rate, leaf area (LA), net CO2 assimilation rate and stomatal conductance of the three cover crops. However, with the application of silicon fertilizer, a portion of the negative effects caused by water restriction could be mitigated, even though there were differences in the responses to silicon fertilization and water stress levels among the cover crop species. Silicon application potentiated the tillering and plant growth rate and increased the photosynthetic rate and water use efficiency of U. brizantha (cv. Marandu and cv. BRS Piatã) plants grown under moderate drought stress conditions.

UAV-Based LiDAR for High-Throughput Determination of Plant Height and Above-Ground Biomass of the Bioenergy Grass Arundo donax

Replacing fossil fuels with cellulosic biofuels is a valuable component of reducing the drivers of climate change. This leads to a requirement to develop more productive bioenergy crops, such as Arundo donax with the aim of increasing above-ground biomass (AGB). However, direct measurement of AGB is time consuming, destructive, and labor-intensive. Phenotyping of plant height and biomass production is a bottleneck in genomics- and phenomics-assisted breeding. Here, an unmanned aerial vehicle (UAV) for remote sensing equipped with light detection and ranging (LiDAR) was tested for remote plant height and biomass determination in A. donax. Experiments were conducted on three A. donax ecotypes grown in well-watered and moderate drought stress conditions. A novel UAV-LiDAR data collection and processing workflow produced a dense three-dimensional (3D) point cloud for crop height estimation through a normalized digital surface model (DSM) that acts as a crop height model (CHM). Manual measurements of crop height and biomass were taken in parallel and compared to LiDAR CHM estimates. Stepwise multiple regression was used to estimate biomass. Analysis of variance (ANOVA) tests and pairwise comparisons were used to determine differences between ecotypes and drought stress treatments. We found a significant relationship between the sensor readings and manually measured crop height and biomass, with determination coefficients of 0.73 and 0.71 for height and biomass, respectively. Differences in crop heights were detected more precisely from LiDAR estimates than from manual measurement. Crop biomass differences were also more evident in LiDAR estimates, suggesting differences in ecotypes’ productivity and tolerance to drought. Based on these results, application of the presented UAV-LiDAR workflow will provide new opportunities in assessing bioenergy crop morpho-physiological traits and in delivering improved genotypes for biorefining.

Nitroxin and arbuscular mycorrhizal fungi alleviate negative effects of drought stress on Sorghum bicolor yield through improving physiological and biochemical characteristics

ABSTRACT Soil microorganisms play an important role in enhancing soil fertility and plant health. Nitroxin is a bio-fertilizer that is a combination of Azospirilium and Azotobacter rhizobacteria. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria can enhance biotic and abiotic stress tolerance in plants, whereas little is known regarding their roles in sorghum (Sorghum bicolor L.) growth under drought stress conditions. Therefore, this experiment was conducted to investigate the inoculation of grain sorghum with the bio-fertilizers of Nitroxin and Glomus mosseae effects on some physiological and biochemical traits and yield of grain sorghum under drought stress conditions in the region of Saravan, Iran, in 2017 and 2018. The results of this experiment showed that severe and moderate drought stress conditions decreased the amounts of grain protein percentage, auxin (IAA) content, root colonization, grain yield, and protein yield of grain, whereas grain starch percentage, the activity of catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) enzymes and content of total carotenoid, total anthocyanin, total flavonoid, electrolyte leakage, and malondialdehyde (MDA) were increased. Inoculation of sorghum plants with bio-fertilizers improved these traits (except starch content, electrolyte leakage, and MDA) under drought stress conditions as well as non-stress conditions. As a result, grain yield and protein yield of sorghum decreased by 43.77 and 43.99%, respectively, under severe drought stress conditions but co-inoculation with Nitroxin and AMF under severe drought stress conditions increased grain yield and protein yield of sorghum by 27 and 19.63%, respectively, compared to non-application of these bio-fertilizers. Thus, Nitroxin and AMF can be recommended for profitable sorghum production under drought stress conditions.

Genome-Wide Identification of SNAC1-Targeted Genes Involved in Drought Response in Rice

Drought stress can cause huge crop production losses. Drought resistance consists of complex traits, and is regulated by arrays of unclear networks at the molecular level. A stress-responsive NAC transcription factor gene SNAC1 has been reported for its function in the positive regulation of drought resistance in rice, and several downstream SNAC1 targets have been identified. However, a complete regulatory network mediated by SNAC1 in drought response remains unknown. In this study, we performed Chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA-Seq of SNAC1-overexpression transgenic rice (SNAC1-OE) lines and wild-type under normal and moderate drought stress conditions, to identify all SNAC1 target genes at a genome-wide scale by RNA-Seq analyses. We detected 980 differentially expressed genes (DEGs) in the SNAC1-OE lines compared to the wild-type control under drought stress conditions. By ChIP-Seq analyses, we identified 4,339 SNAC1-binding genes under drought stress conditions (SNAC1BGDs). By combining the DEGs and SNAC1BGDs, we identified 93 SNAC1-targeted genes involved in drought responses (SNAC1TGDs). Most SNAC1TGDs are involved in transcriptional regulation, response to water loss, and other processes related to stress responses. Moreover, the major motifs in the SNAC1BGDs promoters include a NAC recognition sequence (NACRS) and an ABA responsive element (ABRE). SNAC1-OE lines are more sensitive to ABA than wild-type. SNAC1 can bind to the OsbZIP23 promoter, an important ABA signaling regulator, and positively regulate the expression of several ABA signaling genes.

Action of Imazethapyr and Lactofen on the Nodulation of Conventional and Transgenic Soybean under Drought Stress Conditions

ABSTRACT: This research aimed at studying the action of the herbicides imazethapyr and lactofen on the root system and rhizobium/plant interaction, when they are sprayed at two phenological development stages of soybean cultivars under different soil water management. The soybean cultivars MG/BR 46 Conquista (conventional) and BRS Valiosa (RR) were submitted to three minimum soil water potential (Ψs): -0.03; -0.07 and -0.5 MPa at the V2 and V4 phenological stages. The herbicides imazethapyr at the rate (100 g a.i. ha-1) and lactofen at the rate (180 g a.i. ha-1) were sprayed 10 days after the start of water restrictions. Twenty-one days after the application of the herbicides, root dry matter and root nodulation were evaluated. The BRS Valiosa (RR) soybean cultivar presented better nodule formation and a more efficient and more adapted root system to support moderate drought stress conditions (-0.07 MPa). The MG/BR 46 Conquista (conventional) soybean cultivar presented lower the root system growth when submitted to the spraying of imazethapyr and lactofen. The activity of N2-fixating bacteria was affected by the spraying of the herbicides imazethapyr and lactofen.

Effects of drought stress on the photosynthetic physiological parameters of Populus × euramericana “Neva”

Populus × euramericana “Neva” is the main poplar species in China, where drought stress is becoming extremely urgent. We carried out this research to study the effects of drought stress on the photosynthesis of Populus × euramericana “Neva”. Drought stress was induced by 58–62% (light), 48–52% (moderate), and 38–42% (severe) relative soil moisture content (RSMC). The effects of drought stress on photosynthetic rate, chlorophyll fluorescence parameters, and other related physiological parameters were investigated during treatment. Net photosynthetic rate (PN), and stomatal conductance decreased significantly and intercellular CO2 concentration initially increased and then declined, whereas the stomatal limitation factors showed opposite trends in the light under moderate drought stress. Photosystem II (PSII) maximum photochemical efficiency, actual photochemical efficiency, and photochemical quenching decreased gradually under drought stress, whereas nonphotochemical quenching initially increased and then declined. Superoxide dismutase, peroxidase, and catalase activities initially increased and then decreased as RSMC was reduced, whereas malondialdehyde (MDA) content and relative electric conductivity (REC) increased gradually. These results suggest that stomatal factors accounted for the decline in PN under light and moderate drought stress, whereas leaf PN decreased mainly due to non-stomatal factors under severe drought stress. PSII was damaged; thus, photosynthetic electron transfer was restricted, indicating that heat dissipation is important for the light protection mechanism of plants. Antioxidant enzymes increased at the beginning of treatment, and the increased MDA and REC led to cell membrane damage. These results suggest that poplar seedlings stabilized their photosynthetic apparatus by reducing the light trapping ability under light and moderate drought stress conditions. This helped dissipate heat and enhance antioxidant enzyme activity. Stomatal factors accounted for the decline in PN, whereas damage to PSII and antioxidant enzymes under severe drought stress suggested that the decline in PN was caused by non-stomatal restrictive factors.

Co-overexpression of the Constitutively Active Form of OsbZIP46 and ABA-Activated Protein Kinase SAPK6 Improves Drought and Temperature Stress Resistance in Rice.

Drought is one of the major abiotic stresses threatening rice (Oryza sativa) production worldwide. Drought resistance is controlled by multiple genes, and therefore, a multi-gene genetic engineering strategy is theoretically useful for improving drought resistance. However, the experimental evidence for such a strategy is still lacking. In this study, a few drought-responsive genes from rice were assembled by a multiple-round site-specific assembly system, and the constructs were introduced into the rice cultivar KY131 via Agrobacterium-mediated transformation. The transgenic lines of the multi-gene and corresponding single-gene constructs were pre-evaluated for drought resistance. We found that the co-overexpression of two genes, encoding a constitutively active form of a bZIP transcription factor (OsbZIP46CA1) and a protein kinase (SAPK6) involved in the abscisic acid signaling pathway, showed significantly enhanced drought resistance compared with the single-gene transgenic lines and the negative transgenic plants. Single-copy lines of this bi-gene combination (named XL22) and the corresponding single-gene lines were further evaluated for drought resistance in the field using agronomical traits. The results showed that XL22 exhibited greater yield, biomass, spikelet number, and grain number under moderate drought stress conditions. The seedling survival rate of XL22 and the single-gene overexpressors after drought stress treatment also supported the drought resistance results. Furthermore, expression profiling by RNA-Seq revealed that many genes involved in the stress response were specifically up-regulated in the drought-treated XL22 lines and some of the stress-related genes activated in CA1-OE and SAPK6-OE were distinct, which could partially explain the different performances of these lines with respect to drought resistance. In addition, the XL22 seedlings showed improved tolerance to heat and cold stresses. Our results demonstrate that the multi-gene assembly in an appropriate combination may be a promising approach in the genetic improvement of drought resistance.

Evaluation of proline, chlorophyll, soluble sugar content and uptake of nutrients in the German chamomile (Matricaria chamomilla L.) under drought stress and organic fertilizer treatments

ObjectiveTo investigate the effect of drought stress and organic fertilizer on German chamomile (Matricaria chamomilla) nutrient uptake, leaf chlorophyll content and osmotic adjustment under field conditions. MethodsThis experiment was carried out through a randomized complete block design with a split factorial arrangement of treatments in three replications. The main plots were subjected to the following irrigation treatments: irrigation after 60, 90, 120, 150 and 180 mm evaporation from Class A pan. The sub-plots were treated with three vermicompost doses (0, 5 and 10 t/ha). ResultsAlthough drought stress reduced the nutrient percentages in the shoots, application of vermicompost enhanced the nutrient percentages, particularly when the plants were subjected to moderate to severe drought stress conditions. Moreover, the results of this study showed that the interaction between irrigation treatments and vermicompost rates on leaf chlorophyll content was significant. Comparison between the combined treatments indicated that under normal irrigation and moderate drought stress conditions chamomile plants received 5 and 10 t/ha vermicompost showed significantly higher leaf chlorophyll content comparing to the control treatment. ConclusionsTotally, organic fertilization by vermicompost could partly alleviate the effect of drought stress on chamomile by increasing N, P and K uptake and leaf soluble sugar, especially in stressed treatments.

Salicylic acid supplementation improves photosynthesis and growth in mustard through changes in proline accumulation and ethylene formation under drought stress

Drought stress is becoming a major threat to plant productivity loss in agricultural system. The present study was carried out to evaluate the physiological and biochemical alterations induced by salicylic acid (SA) in mustard plant under moderate drought stress conditions. Therefore, a pot culture experiment was conducted to test whether SA application at concentration of 0.5mM through foliar spray could protect the mustard (Brassica juncea L.) cultivar Pusa Jai Kisan subjected to drought stress on the basis of growth and photosynthesis. The treatments were as follows: (i) 100% FC+0mM SA, (ii) 50% FC+0mM SA, (iii) 100% FC+0.5mM SA and (iv) 50% FC+0.5mM SA. The control treatment received 100% field capacity (FC) irrigation, whereas moderate drought stress corresponded to 50% field capacity. Plants subjected to drought stress caused significant reduction in growth and photosynthetic parameters, activity of ribulose 1,5-bisphosphate carboxylase (Rubisco), nitrate reductase (NR), ATP-sulfurylase (ATPS) which accounted for decreased nitrogen (N) and sulfur (S) assimilation. Whereas, a pronounced increase was observed in proline metabolism. Exogenously applied 0.5mM SA alleviated the stress by increasing the proline production through the increase in γ-glutamyl kinase (GK) and decrease in proline oxidase (PROX) activity. In addition SA application restricted the ethylene formation by inhibiting the 1-aminocyclopropane carboxylic acid synthase (ACS) activity more conspicuously under moderate drought stress than no stress. These findings reflect that SA application alleviates the drought-induced decrease in growth and photosynthesis through increased proline content. Higher proline content was a result of increased N and S assimilation and increased synthesis of proline synthesizing enzyme which lowers the oxidative stress in mustard.

Evaluation of Drought Tolerance Indices for Selection of Confectionery Sunflower (<i>Helianthus anuus</i> L.) Landraces under Various Environmental Conditions

In order to study the response of 56 landraces of confectionery sunflower to drought stress, an experiment was conducted in the experimental field of Agricultural Research Center of West-Azerbaijan in 2012-2013 cropping seasons. The genotypes were evaluated in three separated rectangular 7 x 8 lattice design with two replications in three irrigation treatments including optimum irrigation, moderate stress and severe stress where irrigation was done after depletion of 50%, 70% and 90% of available water, respectively. Nine drought tolerance indices including mean productivity (MP), stress tolerance index (STI), geometric mean productivity (GMP), harmonic mean (HARM), stress non-stress production index (SNPI), yield index (YI), drought resistance index (DI), modified stress tolerance index in optimum irrigation (MPSTI), and modified stress tolerance index in moderate and severe stress (MsSTI) were calculated based on grain yield under well-watered (YP), moderate drought stress (YS-mild) and severe drought stress (YS-severe) conditions. Grain yield in well-watered (YP), mild and severe stress conditions was significantly and positively correlated with MP, STI, GMP, HARM, SNPI, YI, DI, MPSTI and MSSTI. Results of this study showed that in moderate drought stress conditions the indices MP, STI, GMP and HARM could be used as the most suitable indicators for screening drought tolerant genotypes. Based on cluster analysis, the studied genotypes were grouped in 3 clusters in each one of the water treatment conditions. To select drought tolerant genotypes in severe drought stress conditions, it is suggested to use indices MP, STI, GMP, HARM, SNPI and MSSTI because these indices support stable and high yield in both non-stress and stress conditions.

A QTL for high grain yield under lowland drought in the background of popular rice variety Sabitri from Nepal

Drought is the major cause of the yield reduction in rainfed rice areas. High GXE interaction in multi-location trials is a major challenge for breeders in developing breeding lines with a stable performance over diverse environments. In a BC1-derived mapping population developed from the cross IR77298-5-6-18/2*Sabitri, a large-effect QTL, qDTY3.2, was identified on the short arm of chromosome 3 near RM231. This QTL explained 23.4% of the phenotypic variance for grain yield under severe lowland drought and had a consistent effect across varying water stress severities in the Philippines and Nepal in DS2011, WS2011 and WS2012. Although this QTL co-localizes with the HD9 locus related to flowering time, an effect of this QTL was seen on the grain yield of QTL-positive lines under severe and moderate drought stress conditions regardless of the flowering time in this population. The gene content analysis of this locus showed the presence of a wide range of genes related to stress tolerance along with those related to flowering time. The study used bulk segregant analysis (BSA) coupled with screening at more than one location to simultaneously identify and test the effect of qDTY3.2 in the target environment. These results indicate that managed dry-season screening coupled with phenotyping of mapping populations at the target site and genotyping approaches such as BSA allow the identification and validation of the effect of QTLs on grain yield under drought that will lead to the rapid development of drought-tolerant versions of popular varieties through marker-assisted breeding of the identified QTLs.

Different interaction among Glomus and Rhizobium species on Phaseolus vulgaris and Zea mays plant growth, physiology and symbiotic development under moderate drought stress conditions

Even though the positive interactions between arbuscular mycorrhizal (AM) fungi and rhizobial bacteria in legume plants are well documented, their interactions under drought conditions could be negative in some species. In the present study, we examined six different strains of Rhizobiun in combination with two AM fungi (Glomus mosseae and Glomus intraradices) on the responses of Phaseolus vulgaris plants to moderate drought conditions. Moreover, to discriminate between direct competition for carbon resources from direct inhibition processes, a non-legume plant (Zea mays) was also used. Although all inoculants (single or double) increased P. vulgaris growth, only one double combination further increased total or pod dry weights. On the other hand, three double combinations decreased pod dry weight compared to plants inoculated with a single AM fungus. In Z. mays plants, one double inoculation treatment further increased shoot dry weight, but another double inoculation treatment decreased root dry weight in plants inoculated with G. mosseae. In addition, in both plant species, a higher percentage of decrease in AM root colonization by some rhizobial strains was observed. This was most likely caused by a direct inhibition of AM fungal growth by the rhizobial strains and also depended on the host plant involved. Further research is needed to elucidate on the mechanisms behind this inhibition.

Molecular tailoring of farnesylation for plant drought tolerance and yield protection

Protecting crop yield under drought stress is a major challenge for modern agriculture. One biotechnological target for improving plant drought tolerance is the genetic manipulation of the stress response to the hormone abscisic acid (ABA). Previous genetic studies have implicated the involvement of the beta-subunit of Arabidopsis farnesyltransferase (ERA1) in the regulation of ABA sensing and drought tolerance. Here we show that molecular manipulation of protein farnesylation in Arabidopsis, through downregulation of either the alpha- or beta-subunit of farnesyltransferase enhances the plant's response to ABA and drought tolerance. To test the effectiveness of tailoring farnesylation in a crop plant, transgenic Brassica napus carrying an ERA1 antisense construct driven by a drought-inducible rd29A promoter was examined. In comparison with the non-transgenic control, transgenic canola showed enhanced ABA sensitivity, as well as significant reduction in stomatal conductance and water transpiration under drought stress conditions. The antisense downregulation of canola farnesyltransferase for drought tolerance is a conditional and reversible process, which depends on the amount of available water in the soil. Furthermore, transgenic plants were more resistant to water deficit-induced seed abortion during flowering. Results from three consecutive years of field trial studies suggest that with adequate water, transgenic canola plants produced the same amount of seed as the parental control. However, under moderate drought stress conditions at flowering, the seed yields of transgenic canola were significantly higher than the control. Using protein farnesyltransferase as an effective target, these results represent a successful demonstration of engineered drought tolerance and yield protection in a crop plant under laboratory and field conditions.

The interaction between soil water regime and potassium availability on the growth of tea

Tea (Camellia sinensis L.) grown in China often suffers from severe seasonal drought in the summer causing drastic effects on productivity. In a field trial, the effect of potassium (K) fertilization on summer tea yields during 1992–1994 was studied and related to the weather conditions of the respective years. Summer tea yields of 1994 (dry year) increased significantly at K2 (300 kg K2O‐ha‐1) compared to the Kl treatment (150 kg K2O ha‐1). In contrast, only marginal effects were observed by increasing K application from Kl to K2 in the years with adequate water availability (1992 and 1993). During the latter maximum tea yields were already achieved with Kl. In addition, a pot experiment was conducted in order to investigate the interaction between the soil water regime and K availability in the soil on tea biomass production. Soil moisture was maintained at 45, 55, 65, 75, and 85% of the field capacity (FC) and K levels were 0 and 500 mg K2Okg‐1. No tea plant survived at the 45% FC level whereas all tea plants survived at or above 75% FC. The survival rate increased substantially in the K treated tea plants under moderate drought stress conditions (55% and 65% FC). The dry matter production was significantly larger with increasing soil moisture and at the high K status in the soil. This observation was most pronounced under water stress conditions. The study indicates that under moisture stress, increased survival, improved dry matter production and yields of tea plants were due to improved K bioavailability following K application. Furthermore, larger amounts of K are required under moisture stress conditions compared to normal water supply.