Well-watered Regime Research Articles

Use of Biofertilizers as an Effective Management Strategy to Improve the Photosynthetic Apparatus, Yield, and Tolerance to Drought Stress of Drip-Irrigated Wheat in Semi-Arid Environments

Irrigation scheduling, coupled with the use of biofertilizers, constitutes an effective management strategy to overcome soil drought. This study aimed to assess the individual and combined effects of three selected biofertilizers—(R) Bacillus sp. and Bacillus subtilis, (M) native arbuscular mycorrhizal fungi, and (C) compost—on Triticum durum L. The agro-physiological and biochemical traits, along with the soil properties, were evaluated under two different water regimes, 100% crop evapotranspiration (ETc) for the well-watered regime and 30% ETc for the drought-stressed regime under field conditions, using a drip irrigation system. Drought stress (DS) led to significant reductions in the biomass, physiological parameters, and biochemical markers. Furthermore, the application of CM and MR significantly boosted the shoot and root dry weight by 137% and 72%, respectively, under DS compared to the control. Moreover, CM and R resulted in a notable increase of 167% and 130% in the grain and straw yield, respectively, under the same conditions. The normalized difference vegetation index showed improved values in the plants inoculated with MR and CMR, respectively, under DS conditions. Additionally, the soil quality was positively influenced by the application of M and/or R and/or C biofertilizers. These findings provide valuable insights into the intricate soil–plant interactions and the beneficial effects of combined biofertilizers in enhancing wheat’s resilience to drought stress.

Nitrogen and water addition regulate fungal community and microbial co-occurrence network complexity in the rhizosphere of Alhagi sparsifolia seedlings

Rhizosphere microbes are key regulators of phreatophyte establishment in extremely arid environments. Although it is known that increased nitrogen (N) deposition alters microbial communities in arid lands, the effect of N enrichment in soil on phreatophyte rhizospheric microbes remain poorly understood. In a mesocosms experiment, we characterized the diversity, composition of rhizospheric bacterial and fungal communities of Alhagi sparsifolia seedlings by high-throughput sequencing in four-level N additions under drought and well-watered regimes. The relationships between microbial communities and soil properties and plant traits were also quantified. N interacted with water explained the 42.1% variation on fungal community composition, and significantly altered their alpha-diversity which positively correlated with proline accumulation in leaves, while the rhizobacterial community exhibited stability to N and water inputs. The Mantel test showed that microbial community composition at the OTU level was interrelated to soil properties and plant traits. Co-occurrence network analyses suggested that low N input (0–3 g m−2 year−1) and drought stress caused more complex associations along with vulnerability to environmental interference. Our results proposed that rhizosphere bacterial and fungal communities of phreatophyte respond differently to N enrichment under divergent water regimes. Climate change could potentially affect desert plant-microbe interactions. These findings can contribute to predicting and managing ecological and evolutionary responses of the desert ecosystem under global changing scenarios.

Endogenous ABA level modulates the effects of CO2 elevation and soil water deficit on growth, water and nitrogen use efficiencies in barley and tomato plants

Atmospheric CO2 elevation (e[CO2]) could alleviate the impact of soil water deficit, yet the underlying mechanisms remains largely elusive. This study aimed to investigate whether different endogenous abscisic acid (ABA) level modulates the response of barley and tomato plants to soil water deficit combined with e[CO2]. Wild type (WT) genotypes (Steptoe barley and AC tomato) and their corresponding ABA-deficient mutants (Az34 barley and AC-flacca) were grown in pots separately in greenhouse cells with ambient (a[CO2], 400 ppm) and e[CO2] (800 ppm) and were either well-watered or exposed to soil water deficit. The results showed that, compared to well-watered regime, soil water deficit decreased aboveground dry matter (ADM), leaf area (LA) and specific leaf area (SLA) while enhanced water use efficiency (WUE) in all genotypes. e[CO2] increased ADM and LA in tomato genotypes. Moreover, it reduced SLA, leaf N concentration while improved WUE and nitrogen use efficiency (NUE) in WT plants, not in ABA-deficient mutants. These results indicate that endogenous ABA level played an important role in modulating the response of WUE and NUE of barley and tomato to e[CO2] environment, which advances our knowledge on the physiological mechanisms of crop plants adapt to future climate changed scenarios.

Involvement of soluble proteins in growth and metabolic adjustments of drought-stressed Calligonum mongolicum seedlings under nitrogen addition.

The planting of seedlings is the most effective measure for vegetation restoration. However, this practice is challenging in desert ecosystems where water and nutrients are scarce. Calligonum mongolicum is a sand-fixing pioneer shrub species, and its adaptive strategy for nitrogen (N) deposition and drought is poorly understood. Thus, in a pot experiment, we studied the impacts of four N levels (0, 3, 6, 9gN·m-2 ·year-1 ) under drought or a well-watered regime on multiple eco-physiological responses of 1-year-old C. mongolicum seedlings. Compared to well-watered conditions, drought considerably influenced seedling growth by impairing photosynthesis, osmolyte accumulation and activity of superoxidedismutase and enzymes related to N metabolism. Nitrogen addition improved the productivity of drought-stressed seedlings, as revealed by increased water use efficiency, enhanced superoxidedismutase and nitrite reductase activity and elevated N and phosphorus (P) levels in seedlings. Nevertheless, the addition of moderate to high levels of N (6-9gN·m-2 ·year-1 ) impaired net photosynthesis, osmolyte accumulation and nitrate reductase activity. N addition and water regimes did not markedly change the N:P ratios of aboveground parts; while more biomass and nutrients were allocated to fine roots to assimilate the insufficient resources. Soluble protein in assimilating shoots might play a vital role in adaptation to the desert environment. The response of C. mongolicum seedlings to N addtion and drought involved an interdependency between soluble protein and morphological, physiological and biochemical processes. These findings provide an important reference for vegetation restoration in arid lands under global change.

Effects of HMW-GSs on quality related traits in wheat (Triticum aestivumL.) under different water regimes.

Alleles at the Glu-1 loci play important roles in the functional properties of wheat flour. The effects of various high-molecular-weight glutenin subunit (HMW-GS) compositions on quality traits and bread-making properties were evaluated using 235 doubled haploid lines (DHs). The experiment was conducted in a split plot design with two water regimes as the main plot treatment, and DH lines as the subplot treatments. Results showed that the presence of subunit pair 5+10 at the Glu-D1 locus, either alone or in combination with others, appears to provide an improvement in quality and bread-making properties. At the Glu-A1 locus, subunit 1 produced a higher Zeleny sedimentation value (Zel) and stretch area (SA) than subunit 2* when subunits 14+15 and 5+10 were expressed at the Glu-B1 and Glu-D1 loci, and 2* had a positive effect on the maximum dough resistance (Rmax) when subunits 14+15 and 5'+12 were expressed at the Glu-B1 and Glu-D1 loci, respectively. Given subunit 1 at the Glu-A1 locus and 5'+12 at the Glu-D1 locus, the effects of Glu-B1 subunits 14+15 on the tractility (Tra), dough stability time (ST), and dough development time (DT) under the well-watered regime were significantly higher than those of Glu-B1 subunits 13+16. However, 13+16 had a positive effect on SA under the rain-fed regime when subunits 2* and 5+10 were expressed at the Glu-A1 and Glu-D1 loci, respectively. Multiple comparisons analysis revealed that the Zel and Rmax of the six subunits and eight HMW-GS compositions were stable under different water regimes. Overall, subunit compositions 1, 13+16 and 5+10 and 1, 14+15 and 5+10 had higher values for quality traits and bread-baking properties under the two water regimes. These results could play a positive guiding role in selecting and popularizing varieties suitable for production and cultivation in local areas.

The dual-purpose use of orange-fleshed sweet potato (Ipomoea batatas var. Bophelo) for improved nutritional food security

Orange-fleshed sweet potato (OFSP) leaves can be utilised as a fresh green leafy vegetable, in addition to the traditional use of storage root; therefore, OFSP can be seen as a “dual-purpose’’ crop. We hypothesized that no vine harvesting combined with fertiliser application and irrigation will improve the storage root yield and selected plant parameters (water productivity, leaf and storage root nutrient concentrations, nutritional yield, and nutritional water productivity). The objectives of the study were to (i) evaluate the effect of vine harvesting on the selected plant parameters, and, (ii) assess the effect of irrigation regimes and soil fertilisation on these selected parameters. Field experiments were conducted at ARC-VOP, Pretoria, South Africa, during the 2013/14 and 2014/15 seasons. Treatments included irrigation regimes [well-watered (W1) and supplemental irrigation (W2)], soil fertilisation [well-fertilised (F1) and no fertiliser application (F2)], and vine harvesting [no vine harvesting (H1) and vine harvesting (H2)]. For the 2014/15 season, the well-watered regime improved total storage root yield (W1 = 13.0 t DM ha−1; W2 = 7.5 t DM ha−1). Under the practice of vine harvesting, soil fertility treatments did not affect (total dry storage root yield and dry marketable storage root yield) storage root production. Our results further revealed that vine harvesting reduced storage root nutrient concentrations (23% for iron; 14% for zinc; 12% for β-carotene). Nevertheless, total nutritional yields increased; the highest total nutritional yields for iron, zinc, and β-carotene were found under the water and nutrient input regime (W1F1). Assessments showed that boiled orange-fleshed sweet potato aboveground edible biomass could potentially contribute to the daily-recommended nutritional requirement of iron and vitamin A for a family of six people. More water was needed to meet the daily-recommended nutrient intake (iron, zinc, and vitamin A) with OFSP grown as a storage root crop only than when grown as a dual-purpose crop. Our results indicated that there is an opportunity to utilise OFSP as a dual-purpose crop for rural resource-poor households because total nutritional yields (iron, zinc, and β-carotene) and total nutritional water productivities (iron, zinc, and β-carotene) were improved. More research is needed to assess the effect of vine harvesting on a range of OFSP varieties and should be conducted on the farm. Rural resource-poor households are encouraged to produce OFSP for their own consumption and the surplus could be sold at the local market.

Biomass Production and Water Economy of Sugarcane and Energy Cane Genotypes Grown in Water-Deficient and Well-Watered Regimes

Biomass Production and Water Economy of Sugarcane and Energy Cane Genotypes Grown in Water-Deficient and Well-Watered Regimes

Effect of water regime on seed germination and vigor of five sorghum (Sorghum bicolor (L.) Moench) genotypes growing in the field

Received: 2016-04-05 | Accepted: 2016-05-29 | Available online: 2017-09-30 http://dx.doi.org/10.15414/afz.2017.20.03.45-48 This study was designed to examine the effect of water regime on seed quality of five sorghum genotypes. Two laboratory experiments were conducted in two successive seasons (2014 2015-2015 2016) at the Regional Seed Center Laboratory, Agriculture Research Station (ARC), Elobied. The laboratory treatments were conducted as factorial experiments in a Randomized Complete Block Design (DCBD) with four replications. The estimated quality included seed germination test. The results showed that water regimes had significant effects on germination (%). The highest seedling length was recorded by well-watered plant. The highest seedling growth rate was recorded by plants under well-watered regime. Also the results revealed that genotypes were differing in germination percent, seedling length and seedling growth rate. The results indicated that Taggat genotypes scored the highest values of most seeds quality trials were measured in this study and it might be suitable for high quality and production under rain-fed condition. Keywords: germination, seed vigor, sorghum, Sorghum bicolor (L.) Moench, water regime References ABDALLA, H.M. and GAMAR, Y.A. (2011) Climate change: Selection of sorghum genotype with wide adaptation, AG-17, for rain-fed areas of Sudan. In International Journal of Agri. Science , vol. 1, no. 3, pp. 144–555. ACHAKZAI, A.K.K. (2009) Effect of water stress on imbibitions, germination and seedling growth of maize cultivars. In Sarhad J. Agric. , vol. 25, no. 2, pp. 165-172. ACHAKZAI, A.K.K. and BAZAI, Z.A. (2007) Effect of water stress on seedling growth of maize cultivars: In mannitol plus culture solution. In Int. J. Biol. & Biotech . vol. 4, n. 1, pp. 37–42. AGHAALIKHANI, M., ETEMADI, F. and AJIRLO, A.F. (2012) Physiology basis of yield difference in grain sorghum ( Sorghum bicolor L. Moench) in a semi-arid environment. In Journal of Agricultural and Biological Science , vol. 7, no. 7, pp. 18-24. AHMED, E.E. and ALAMAM, S.H. (2010) Sorghum ( Sorghum bicolor (L.) Moench.). Seed Quality as Affected by Type and Duration of Storage. In Sudan. Agric. Biol. J. N. Am ., vol. 1, no. 1, pp. 1–8. DELOUCHE, J.C. (1969) Planting seed quality. Beitwide cotton production . New Orleans: USDA. FOUGEREUX, J. et al. (1997). Water stress during reproductive stages affects seed quality and yield of pea ( Pisum sativum ). In J. Crop Sci , vol. 37, pp.1247–1252. HAMID, B.H. (2001) Overview of sorghum and millet in Sudan. Khartoum: Ministry of Science and Technology, ARC, Sudan. HARRINGTON, J.F. (1971) The necessity for high quality vegetables. In J. Hortscience , vol. 6, pp. 550–551. KENGA, R. et al. (2006) Genetic and phenotypic association between yield components in hybrid sorghum (S orghum bicolor (L.) Moench) populations . Zaria: Institute of Agricultural Research for Development (IRAD), Ahamadu Bello University, Department of Plant Science/IAR. MOOSAVI, S.G. et al. (2011) Effect of Irrigation Intervals and Planting Patterns on Yield and Qualitative Traits of Forage Sorghum. In Advances in Environmental Biology , vol. 5, no. 10, pp. 3363–3368. SAMARAH, H. and ALQUDAH, A. (2009) Effects of late-terminal drought stress on seed germination and vigor of barley ( Hordeum vulgare L.). In Archives of Agronomy and Soil Science , in press. YOUNESI, O. and MORADI, A. (2009) The effect of water limitation in the field on sorghum seed germination and vigor. In Australian Journal of Basic and Applied Sciences , vol. 3, no. 2, pp. 1156– 1159.

How water supply during leaf development drives water stress response in Corylus avellana saplings

Corylus avellana L. (hazelnut) is one of the world’s major nut crops, and is considered a sensitive species to water stress having a low capacity for stomatal regulation. Knowledge of hazelnut response to water stress is important from an economical point of view since water stress affects fruit quality and production. In this context, the effects of three different water regimes imposed during leaf development of hazelnut saplings were analyzed. The results suggested that saplings which formed leaves under moderate and severe-water stress regimes (MS and SS saplings, respectively) displayed several anatomical, morphological and physiological acclimations compared to those developed under a well-watered regime (WW saplings), giving them a greater capacity to cope with water stress. For instance, at a morphological level, MS and SS saplings had a higher leaf mass per unit of leaf area (LMA) and leaf tissue density (LTD) (by 15% and 36%, mean value, respectively) compared to WW saplings. At a physiological level, stressed SS and MS saplings show higher dark respiration rates (RD), an improved photo-protection mechanism and a higher capacity to dissipate the excess of excitation energy (i.e. a higher carotenoid to chlorophyll ratio; a lower ΦPSII) in respect to stressed WW saplings. During the imposed water stress, the 18% increase of the intrinsic water use efficiency (iWUE) in all three treatments attests to the stomatal control in the net assimilation rate (AN) decrease. Taking into account that in the Mediterranean area supplemental irrigation in hazelnut orchards is required and that ground water supplies are declining while energy costs of irrigation are increasing, these results may provide important findings from an agricultural point of view concerning irrigation decisions about the water supply to hazelnut saplings.

Response of water deficit regime and soil amelioration on evapotranspiration loss and water use efficiency of maize (Zea mays l.) in subtropical northeastern Himalayas.

Rainfed maize production in the hilly ecosystem of Northeastern Himalayas often suffers from moisture and soil acidity induced abiotic stresses. The present study measured evapotranspiration loss (ETc) of maize crop under controlled condition (pot experiment) of water deficit (W25-25% and W50-50% of field capacity soil moistures) and well watered (W100=100% of field capacity (FC)) regimes in strong acid soils (pH=4.3) of the Northeastern Himalayan Region of India. The response of soil ameliorants (lime) and phosphorus (P) nutrition under differential water regimes on ETc losses and water use efficiency was also studied. The measured seasonal ETc loss varied from 124.3 to 270.9mm across treatment combinations. Imposition of water deficit stress resulted in significant (p<0.05) reduction (by 33-50%) of seasonal ETc losses but was at the cost of delay in tasseling to silking, 47-65% reduction in dry matter accumulation (DMA), 12-22days shortening of grain formation period, and complete kernel abortion. Liming @ 4tha-1 significantly (p<0.05) increased ETc losses and DMA across water regimes but the magnitude of increase was higher in severely water deficit (W25) regime. Unlike lime, P nutrition improved DMA only in well-watered regimes (W100) while seasonal ETc loss was unaffected. Vegetative stage (tillering to tasseling) contributed the maximum ETc losses while weekly crop ETc loss was estimated highest during 11th-14th week after sowing (coincided with blistering stage) and then declined. Water use efficiency estimated from dry matter produced per unit ETc losses and irrigation water used varied from 4.33 to 9.43gdry matterkg-1water and 4.21 to 8.56gdry matterkg-1, respectively. Among the input factors (water, P, and lime), water regime most strongly influenced the ETc loss, growth duration, grain formation, and water use efficiency of maize.

Drought-induced acclimatization of a fast-growing plant decreases insect performance in leaf-chewing and sap-sucking guilds

An initial destabilization of functions triggered by drought stress in plants is followed by acclimatization and acquisition of tolerance; however, knowledge remains limited on drought-mediated changes in plant quality for herbivores. We tested whether a water-stressed fast-growing plant negatively affects host-specialist insects in both sap-sucking and leaf-chewing feeding guilds. Collards (Brassica oleracea var. acephala) were grown in well-watered, slightly water-stressed and severely water-stressed conditions. Decreasing soil moisture adversely affected plant development, assessed as a reduction in leaf number and size, stomatal size and relative water content. Severely stressed plants had less fiber and glucosinolates; however, they showed more total nitrogen and lipids. Larval survival, pupal weight, reproductive rate (Ro) and rate of population growth (r) were lower when the leaf-chewing Plutella xylostella was reared with severely stressed collards. In multiple-choice tests, moths laid fewer eggs on leaf discs of collard that were exposed to drought. The fecundity of the sap-sucking Brevicoryne brassicae was higher and the development of alates was lower when insects were fed on plants kept in well-watered regime as compared to slight-stress and severe-stress. Despite higher nitrogen content and fewer glucosinolates, a higher level of leaf surface wax in severely stressed collards possibly decreased food quality for both herbivores. Thus, host-specific herbivores of different guilds showed similar responses to drought-stressed, fast-growing plants. Water-stressed crops could discourage the attack of specialist insects, but the intensity of the stress that is required to achieve this effect will greatly reduce crop production, in terms of plant growth or foliage increment.

Genetic control of growth, biomass allocation, and survival under drought stress in Pinus radiata D. Don seedlings

Drought is one of the critical factors limiting plant growth, and knowledge about genetic adaptation to drought is necessary to develop strategies for successful reforestation on drought-prone sites. In this study, genetic variation was investigated in 98 full- and half-sib radiata pine (Pinus radiata D. Don) families, representing Chilean coastal and interior populations, subjected to two water regimes: well-watered and drought-stressed. Assessed traits, in 5-month-old seedlings, included height (H), diameter (D), height-to-diameter ratio (HDR), dry biomass of needles (NDW), stem (SDW), roots (RDW), and total (TDW), root-to-shoot ratio (RSR), and survival (SUR). After 115 days of treatment, growth, biomass, and survival were nearly two times higher under the well-watered regime than under the stressed one. Families differed significantly in most traits, with individual tree heritabilities ranging from 0.14 for SUR to 0.63 for D in the well-watered treatment. Families from the interior showed the highest heritability for D, SDW, RDW, and TDW when grown in the water-stress treatment. The genetic correlations between treatments were moderately strong, which suggests the presence of a genotype by watering regime interaction. Most traits were strongly correlated (genetic correlations often exceeded 0.40). Compared to the first generation families from coastal sites, the third generation families from the interior sites showed an increase in SUR and RSR. Thus, potential exists to screen families at the seedling stage for drought hardiness and to identify parents from the interior sites with potential to produce a more drought-resistant breed with satisfactory growth rates and yields in dry environments.

Molecular mapping across three populations reveals a QTL hotspot region on chromosome 3 for secondary traits associated with drought tolerance in tropical maize

Identifying quantitative trait loci (QTL) of sizeable effects that are expressed in diverse genetic backgrounds across contrasting water regimes particularly for secondary traits can significantly complement the conventional drought tolerance breeding efforts. We evaluated three tropical maize biparental populations under water-stressed and well-watered regimes for drought-related morpho-physiological traits, such as anthesis-silking interval (ASI), ears per plant (EPP), stay-green (SG) and plant-to-ear height ratio (PEH). In general, drought stress reduced the genetic variance of grain yield (GY), while that of morpho-physiological traits remained stable or even increased under drought conditions. We detected consistent genomic regions across different genetic backgrounds that could be target regions for marker-assisted introgression for drought tolerance in maize. A total of 203 QTL for ASI, EPP, SG and PEH were identified under both the water regimes. Meta-QTL analysis across the three populations identified six constitutive genomic regions with a minimum of two overlapping traits. Clusters of QTL were observed on chromosomes 1.06, 3.06, 4.09, 5.05, 7.03 and 10.04/06. Interestingly, a ~8-Mb region delimited in 3.06 harboured QTL for most of the morpho-physiological traits considered in the current study. This region contained two important candidate genes viz., zmm16 (MADS-domain transcription factor) and psbs1 (photosystem II unit) that are responsible for reproductive organ development and photosynthate accumulation, respectively. The genomic regions identified in this study partially explained the association of secondary traits with GY. Flanking single nucleotide polymorphism markers reported herein may be useful in marker-assisted introgression of drought tolerance in tropical maize.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-014-0068-5) contains supplementary material, which is available to authorized users.

Genetic parameters for early growth and biomass traits of Pinus radiata D. Don under different water regimes

AbstractIn Chile, genetic improvement of Radiata pine has been directed towards characters such as volume, form and wood density. Estimation of genetic parameters for growth and biomass traits in young seedlings, as a tool for early indirect selection in the P. radiata breeding program, has not been explored yet. We aimed to estimate genetic parameters for growth and biomass traits. Five-month-old P. radiata seedlings grown under wellwatered (WW) and water stress (WS) regimes were evaluated. Root collar diameter, height, shoot dry weight, root dry weight, total dry weight, height/diameter ratio and root/shoot ratio were analyzed in both treatments. Trait with the highest heritability was root/shoot ratio in WW and WS regime (h2= 0.80 and 0.63 respectively). The highest genetic correlation was between height and shoot dry weight (rg= 0.90), under WW regime. In contrast, there were negative genetic correlations between root collar diameter and height/diameter ratio under WS regime. To breed for drought tolerance, traits such as height and root collar diameter would be effective targets for indirect selection since estimated heritabilities are high, there is sizable genetic variation, they are easily assessed, they can be measured non-destructively and they have a high genetic correlation with root/shoot ratio, a trait related to drought tolerance. The measurement of dry weights for early selection purposes is not recommended.

Evaluation of Some Wheat Landraces for Drought Tolerance based on Physiological Traits

Drought is a seriously wide-spread problem influencing wheat (Triticum aestivum) production and quality. Developing of abiotic tolerant cultivars is hampered by the lack of wheat genetic resources.The main objective of this research was to evaluate drought tolerance of some wheat landraces that were naturally acclimatized to stress environmental conditions in Egypt.Eight wheat landracescollected from diverse areas of Egypt as well as two wheat cultivars, i.e.YecoraKojo (exotic drought tolerant cultivar) and Gemmeiza 9 (Egyptian high yielding cultivar) were evaluated under four different water regimes, i.e., 75%, 50% and 25% of well-watered regime (100%) after planting irrigationduring 2010/2011 and 2011/2012 seasons. Field work carried out at Gemmeiza Agricultural Research Station. Measurements included leaf gas exchange rate and some agronomic traits. The results showed significant differencesamong genotypes in gas exchange rate, i.e. Net photosynthesis (PN), transpiration rate (E) and stomatal conductance (gs), yield and its components and drought tolerance indices,i.e. water use efficiency (WUE),drought susceptibility index (DSI)and grain yield response index (GYRI),indicating the presence of wide genetic variability among them. The reduction in soil water contents led to reduction of the gas exchange rate, yield and its components. Landraces 1and 8 had higher gas exchange rate, yield and its components under different irrigation regimes as compared to Gemmeiza 9.Also drought tolerance indices indicated that both landraces 1 and 8 are promising as drought tolerantand high yielding genotypes.

Mapping QTLs for seedling root traits in a doubled haploid wheat population under different water regimes

A deep and thick root system has a positive effect on wheat yield, particularly in drought environments. A doubled haploid (DH) population of 150 lines derived from the cross Hanxuan 10 × Lumai 14 was used to map QTLs for seedling root characteristics. The DH lines were cultivated in an agarose gel-chamber under well-watered (WW) and water-stressed (WS) regimes. Water stress was simulated by adding mannitol to the agarose gel. The seminal root traits, including maximum root length (MRL), seminal root number, total root length, project root area, root surface area, and seminal root angle were measured after 6 days of seedling development. Grain yields (GY) were measured in a field experiment. A total of 29 QTLs were identified for seedlings cultured under WW regimes, and 23 QTLs under WS regimes. Individual QTL accounted for phenotypic variations ranging from 4.98 to 24.31 %. The QTLs were distributed on 17 chromosomes, except 1D, 4D, 6B and 6D. Seven consistently expressed QTLs were detected for all the traits tested except MRL under both water regimes. The QTLs for root traits were unevenly distributed among chromosomes, and clustered in eight loci on seven chromosomes, showing pleiotropic effects on target traits. One region in the interval Xgwm644.2–P6901.2 on chromosome 3B contained 9 QTLs affecting most root traits. The present data provide an insight into the genetic basis of seedling root development under different water regimes and may benefit breeding programs using marker-assisted selection (MAS) for root traits.

Root traits and δ13C and δ18O of durum wheat under different water regimes.

Plant growth, root characteristics and the stable carbon (δ13C) and oxygen (δ18O) composition were studied in durum wheat. Four recombinant inbred lines with good agronomic adaptation were grown under well watered (WW) and water stress (WS) conditions until mid-grain filling in lysimeters. Gas exchange was measured in the flag leaf just before harvest and then the aerial dry matter (Aerial DM), root weight density (RWD) and root length density (RLD) and the specific root length (SRL) were evaluated and the δ13C and δ18O of the roots, the flag leaf blade and the spike were analysed. Water stress decreased stomatal conductance, plant accumulated transpiration and Aerial DM, whereas δ13C and δ18O increased. Genotypic differences were found for all gas-exchange and root traits and isotope signatures. Aerial DM was positively correlated with RLD, regardless of the water regime, whereas it was negatively correlated with δ13C and δ18O, but only under WW conditions. Moreover, RWD and RLD were negatively related to both δ13C and δ18O under the WW regime, but no clear pattern existed under WS. Our study supports the use of δ13C and δ18O as proxies for selecting root traits associated with higher growth in the absence of water stress.

The effect of different vigour olive clones on growth, dry matter partitioning and gas exchange under water deficit

In the last decade, high-density olive planting systems have been developed to facilitate less costly mechanical harvesting and pruning by using straddle harvesters. High-density orchards allow faster production since the first crop of fruit starts a few years after planting. In high-density orchards the control of tree size is essential. It is possible to control the vigour and size of the tree by selecting suitable cultivars, by choosing rootstocks capable of controlling scion vigour and, finally, by applying deficit irrigation to reduce plant vegetative growth. Knowledge of tree water requirements is needed for precise irrigation scheduling. In this study, the dwarfing capacity of two Leccino clones, Leccino Dwarf (LD) showing low vigour, and Leccino Minerva (LM) highly vigorous, was investigated under two water regimens, well-watered ( T 100) and water deficit ( T 50). We analysed growth rates, dry matter production, gas exchanges and water relations of one-year-old plants of Leccino Dwarf (LD) and Leccino Minerva (LM), grown in pots in open fields. The two genotypes showed significant differences in vigour, demonstrated by measuring the trunk diameter, shoot length and leaf area; values were significantly lower in clone LD. Stem water potential, photosynthesis and stomatal conductance were similar in both genotypes under a well-watered regime; they decreased when subjected to water deficit with values significantly lower in LM clone during the summer months, indicating physiological differences among clones and that LD adapts better to water deficit.

Identification of Functional Genetic Variations Underlying Drought Tolerance in Maize Using SNP Markers

Single nucleotide polymorphism (SNP) is a common form of genetic variation and popularly exists in maize genome. An Illumina GoldenGate assay with 1 536 SNP markers was used to genotype maize inbred lines and identified the functional genetic variations underlying drought tolerance by association analysis. Across 80 lines, 1 006 polymorphic SNPs (65.5% of the total) in the assay with good call quality were used to estimate the pattern of genetic diversity, population structure, and familial relatedness. The analysis showed the best number of fixed subgroups was six, which was consistent with their original sources and results using only simple sequence repeat markers. Pairwise linkage disequilibrium (LD) and association mapping with phenotypic traits investigated under water-stressed and well-watered regimes showed rapid LD decline within 100-500 kb along the physical distance of each chromosome, and that 29 SNPs were associated with at least two phenotypic traits in one or more environments, which were related to drought-tolerant or drought-responsive genes. These drought-tolerant SNPs could be converted into functional markers and then used for maize improvement by marker-assisted selection.

SHOOT DIEBACK IN CLIPPED YOUNG GOLDEN LEYLAND (CUPRESSOCYPARIS LEYLANDII) TREES—A PHYSIOLOGICAL MECHANISM?

Shoot dieback is a problem in frequently trimmed Leyland hedges and is increasingly affecting gardeners' choice of hedge trees, having a negative effect on a conifer nursery industry. Some damage can be attributed to the feeding by aphids, but it is unclear if there are also underlying physiological causes. In this study, we tested the hypothesis that shoot-clipping of conifer trees during adverse growing conditions (i.e. high air temperature and low soil moisture) could be leading to shoot ‘dieback’. Three-year-old Golden Leyland Cypress (x Cupressocyparis leylandii ‘Excalibur Gold’) plants were subjected to either a well-watered or droughted irrigation regime and placed in either a ‘hot’ (average day temperature = 40°C) or a ‘cool’ (average day temperature = 27°C) glasshouse compartment. Half of the plants from each glasshouse were clipped on Day 14 and again on Day 50. Measurements of soil moisture content (SMC), net CO2, assimilation rate (A), stomatal conductance (g s ), branchlet xylem water potential (XWP), plant height and foliage colour were made. Within the clipped and unclipped treatments of both glasshouse compartments, plants from the droughted regime had significantly lower values for A, g s and XWP than those from the well-watered regime. However, there was no difference in these parameters between the hot and cool glasshouse compartments. The trends seen for A, g s and XWP of all treatments generally mirrored changes in SMC indicating a direct effect of water supply on these parameters. By the end of the experiment the overall foliage colour of plants from the hot glasshouse was darker than that of plants from the cool glasshouse and the overall foliage colour was also darker following shoot clipping. In general, shoot clipping led to increases in A, g s XWP and SMC. This may be due to the reduction in total leaf area leading to a greater supply of water for the remaining leaves. No shoot ‘dieback’ was observed in any treatment in response to drought stress or shoot-clipping.